Toxoplasma gondii Efrat Rorman , Chen Stein Zamir , Irena Rilkis

Transcription

Reproductive Toxicology 21 (2006) 458–472
Review
Congenital toxoplasmosis—prenatal aspects of Toxoplasma gondii infection
Efrat Rorman a,∗ , Chen Stein Zamir b , Irena Rilkis a,c , Hilla Ben-David a
a
National Public Health Laboratory, Ministry of Health, P.O. Box 8255, Tel Aviv 61082, Israel
b District Health Ofﬁce, Ministry of Health, Jerusalem, Israel
c National Toxoplasmosis Reference Center, Ministry of Health, Israel
Received 26 August 2004; received in revised form 11 October 2005; accepted 24 October 2005
Available online 28 November 2005
Abstract
Toxoplasma gondii (T. gondii) is the cause of toxoplasmosis. Primary infection in an immunocompetent person is usually asymptomatic.
Serological surveys demonstrate that world-wide exposure to T. gondii is high (30% in US and 50–80% in Europe). Vertical transmission from a
recently infected pregnant woman to her fetus may lead to congenital toxoplasmosis. The risk of such transmission increases as primary maternal
infection occurs later in pregnancy. However, consequences for the fetus are more severe with transmission closer to conception. The timing of
maternal primary infection is, therefore, critically linked to the clinical manifestations of the infection. Fetal infection may result in natural abortion.
Often, no apparent symptoms are observed at birth and complications develop only later in life. The laboratory methods of assessing fetal risk of
T. gondii infection are serology and direct tests.
Screening programs for women at childbearing age or of the newborn, as well as education of the public regarding infection prevention, proved
to be cost-effective and reduce the rate of infection.
The impact of antiparasytic therapy on vertical transmission from mother to fetus is still controversial. However, specific therapy is recommended
to be initiated as soon as infection is diagnosed.
© 2005 Elsevier Inc. All rights reserved.
Keywords: Toxoplasmosis; Toxoplasma gondii; Congenital infection; Diagnosis; Treatment; Epidemiology
Contents
1.
2.
3.
4.
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Case report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
The parasite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.1. Life cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2. Mechanism of infection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.3. Virulence of T. gondii strains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Epidemiology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Congenital toxoplasmosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.1. Incidence and prevalence in pregnant women and infants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.2. Diagnostic evaluation, manifestation and consequences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.3. Prenatal laboratory diagnosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.3.1. Sabin Feldman dye test (SFDT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.3.2. Enzyme immunoassays (EIA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.3.3. Immunosorbent agglutination assay test (IAAT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.3.4. Indirect fluorescent assay (IFA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.3.5. Avidity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.3.6. Animal and cell culture inoculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Corresponding author. Tel.: +972 50 6242904; fax: +972 3 6826996.
E-mail address: [email protected] (E. Rorman).
0890-6238/$ – see front matter © 2005 Elsevier Inc. All rights reserved.
doi:10.1016/j.reprotox.2005.10.006
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E. Rorman et al. / Reproductive Toxicology 21 (2006) 458–472
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4.3.7. Molecular diagnosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Laboratory diagnosis of infants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4.4.1. Western blots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Treatment of congenital toxoplasmosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Prevention . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.1. Primary prevention . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.1.1. Vaccine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.2. Secondary prevention – screening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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4.4.
5.
6.
1. Case report
A 26-year-old woman from a rural village in northern Israel
presented with cervical lymphadenopathy during the 13th week
of her first pregnancy. The woman was otherwise healthy and
without any symptoms. She was followed up by her primary
care physician and as the lymphadenopathy did not resolve,
was sent for surgical consultation during the 26th week of
pregnancy. The surgeon referred her to laboratory tests for Toxoplasma gondii-specific antibodies and for various other infections. The results obtained from testing a serum sample from
the 26th week of gestation, performed at the Israel National
Toxoplasmosis Reference Center were: positive for total T.
gondii-specific immunoglobulins (Ig) (250 IU/ml by Sabin Feldman Dye Test) and for T. gondii-specific IgM antibodies (by
ELFA, Enzyme-Linked Fluorescent immuno-Assay) with low
IgG avidity (0.027). These results were reported and an additional serum sample, as well as an earlier sample (whether
available) were requested. Blood samples were subsequently
delivered to our laboratory; from the 12th (sample drawn as part
of the routine pregnancy follow-up) and from the 34th weeks
of pregnancy. The results of the earlier sample were negative
for both total Ig and IgM antibodies. The results from the 34th
week were positive for total T. gondii-specific immunoglobulins (250 IU/ml by Sabin Feldman Dye Test) and negative for
T. gondii-specific IgM antibodies (by ELFA, Enzyme-Linked
Fluorescent immuno-Assay) with low IgG avidity (0.055).
The sum interpretation of the three above tests results of
the 12th, 26th and 34th week of pregnancy was consistent
with definite recent T. gondii infection (seroconversion, constant
high T. gondii-specific immunoglobulins, emergence and disappearance of IgM, low avidity and cervical lymphadenopathy).
Amniocentesis was performed during the 35th week of pregnancy and PCR result for T. gondii DNA in the amniotic fluid
was positive.
The woman was referred for follow-up at a high risk pregnancy clinic in a tertiary medical center. Anti-T. gondii therapy
including Pyrimethamine, Sulfadiazine and folinic acid was
started and continued until birth. The pregnancy course was
otherwise uneventful and fetal growth assessment through ultrasound follow-up did not reveal any abnormality. During the
38th week of pregnancy a female infant was born by spontaneous delivery. Birth weight was 2830 g and head circumference was 33 cm. Physical examination was normal. Laboratory
tests including complete blood count, glucose, electrolytes, liver
function tests and cerebro-spinal fluid (CSF) tests were all
normal. Cranial ultrasonography, brain stem evoked response
(BERA), audiometry and eye examination were all normal. Tests
for T. gondii in the infant included: PCR of CSF—negative,
immuno-sorbent agglutination assays (IgM-ISAGA)—negative
and Sabin Feldman Dye Test (SFDT)—positive (250 IU/ml),
probably reflecting maternal antibodies transfer. Despite the
serological indicators of maternal infection (most probably
towards the end of the first trimester) and positive PCR of the
amniotic fluid, there was no evidence of congenital toxoplasmosis in the neonate. The infant was treated with the same therapeutic protocol as the mother planned to be continued until the
age of 1 year. Medical evaluation, auditory and ophthalmic tests
at the age of 4 and 8 months revealed normal physical growth
and development and intensive follow-up continues (at the age
of 6 months laboratory analysis was reported to be normal).
This case demonstrates the complexity of establishing clinical diagnosis and interpretation of laboratory results in regard
to T. gondii infection in pregnancy. The favourable outcome
despite the timing of infection may be attributed to providing anti
parasitic therapy, although the specific role of therapy or other
unknown variables is unclear. Since many T. gondii infections
are sub-clinical or present with non-specific signs, physicians
should be able to integrate clinical and laboratory data in order
to make diagnostic and therapeutic decisions.
2. The parasite
T. gondii is a member of the phylum Apicomplexa, order Coccidia, which are all obligate intracellular protozoan parasites.
Other members of this phylum include known human pathogens
such as Plasmodium (malaria) and Cryptosporidium.
2.1. Life cycle
The life cycle of T. gondii consists of two stages—asexual and
sexual: the asexual stage takes place in the intermediate hosts,
which are mammals or birds. During this phase rapid intracellular growth of the parasite as tachyzoite takes place (generation
time in vitro is 6–8 h). The oval or crescent-shaped tachyzoites
can infect and multiply in almost any nucleated mammalian or
avian cell [1]. Following accumulation (64–128), tachyzoites are
secreted into the blood stream [2] and spread in the body, leading
to development of an acute disease (parasitemia). The normal
immune response and transformation of the tachyzoite into cystforming bradyzoites limit the acute stage and establish a chronic
infection. Bradyzoites differ from tachyzoites mainly in their
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extremely slow multiplication rate (their name reflects this slow
process) and in the distinct set of proteins they express [1,3–5].
The cysts are formed mainly in neural and muscular tissues,
especially brain, skeletal and cardiac muscles, and can persist,
inactivated, in the body for a very long time. In the immunocompromised patient the release of bradyzoites from the cyst may
cause acute encephalitis.
The sexual stage takes place in the intestine of the definitive
host. Known definitive hosts are members of the feline family, predominantly domestic cats. When bradyzoites or oocytes
are ingested by a feline, formation of oocytes proceeds in the
epithelium of the small intestine. Several million unsporulated
oocytes may be released in the feces of a single cat over a period
3–18 days, depending on the stage of T. gondii ingested [1].
Under mild environmental conditions oocytes may sporulate
within a 3-week period [6], then infecting humans and other
intermediate hosts. Oocysts can spread in the environment and
contaminate water, soil, fruits, vegetables and herbivores following consumption of infected plant material. Investigation of
outbreaks of toxoplasmosis has led to recovery of oocytes from
soil [7] but not from water [8–10]. Oocytes have been found to
be very stable, especially in warm and humid environments, and
resistant to many disinfecting agents [11], but survive poorly in
arid, cold climates [12].
2.2. Mechanism of infection
T. gondii has been shown to migrate over long distances in the
host’s body; crossing biological barriers, actively enter the blood
stream, invade cells and cross substrates and non-permissive
biological sites such as the blood-brain-barrier, the placenta and
the intestinal wall. At the same time, the parasite minimizes
exposure to the host’s immune response, by rapidly entering and
exiting cells. These two functions share common mechanisms
which depend on Ca2+ regulation [13].
Unlike many bacteria and viruses, T. gondii actively enters
the cell, in a mechanism which is mediated by the parasites’ cytoskeleton and regulated by a parasite-specific calciumdepended secretion pathway [2,14]. The first step of cell invasion
by T. gondii is recognition of an attachment point. The two
special organelles involved in this invasion process, rhoptries
and micronemes, each discharging proteins during the process
[5,15]. Following the rapid cellular invasion the parasite resides
within a vacuole, derived primarily from the host cell’s plasma
membrane [2,16]. The active motion of T. gondii, called “gliding”, occurs with no major changes in cell shape. It is fast (about
10 times faster than the “crawling” rate of amoeboid cells), and
consists of both circular gliding in a counter-clockwise direction
and clockwise helical gliding [17–21]. As an obligatory parasite,
it’s invasive capabilities play an important role in virulence and
pathogenicity, since it can only survive intracellularly where it
gets nutrients and escapes from the host’s immune response [22].
The most virulent T. gondii strain has been shown to exhibit superior migratory capacity [23] and a subpopulation of this strain
displays a special, long distance migration phenotype [14]. The
ability to cross biological barriers is associated with acute virulence and is linked to genes on chromosome VII [24,25]. The
genome of T. gondii, consisting of 14 chromosomes, is currently
being investigated and sequenced [26] (http://ToxoDB.org).
2.3. Virulence of T. gondii strains
Clinical manifestations and severity of illness following
infection are affected by features of the interaction between the
parasite and the host and include strain virulence, inoculum size,
route of infection, competence of the host’s immune response
(both cellular and humoral), integrity of the host’s mucosal and
epithelial barriers, host’s age and genetic background [27]. Various strains of T. gondii have long been known to differ in
virulence and pathogenicity [28,29]. These strains can be classified by immunologic assays, isoenzyme analysis and molecular
analysis [30–33]. There are three T. gondii clonal lineages, of
them one carries conserved genetic loci, suspected of coding
for the virulence trait [24]. Grigg et al. [34] demonstrated that a
sexual recombination, performed in vitro, between the two relatively avirulent strains can give rise to the virulent strain. This is
in accordance with polymorphism analysis of the three T. gondii
strains, which indicated that they emerged within the last 10,000
years, following a single genetic cross [34,35]. Acquisition of
an efficient mechanism to spread by direct oral transmission,
bypassing a sexual phase, leads to successful clonal expansion
of this virulent lineage [35,36].
Genetic background plays a significant role in increased susceptibility to T. gondi in humans; HLA-DQ3 appears to be
a genetic marker associated with susceptibility to developing
toxoplasma-dependent encephalitis [37,38].
3. Epidemiology
T. gondii infection is most frequently caused by ingestion
of row or undercooked meat, which carries tissue cysts, by
consuming infected water or food or by accidental intake of
contaminated soil. Toxoplasmosis is also an occupational hazard for laboratory workers. A total of 47 laboratory-acquired
cases have been reported, 81% of them were symptomatic cases
[39].
Tender et al. [40] collected data of nation-wide T. gondii seroprevalence in women at child-bearing age (1990–2000). The
rates of positive sero-prevalence, were 58% in Central European countries, 51–72% in several Latin-American countries
and 54–77% in West African countries. Low seroprevalence,
4–39%, was reported in southwest Asia, China and Korea as
well as in cold climate areas such as Scandinavian countries
(11–28%). In the US 15% of females at childbearing age were
found to be seropositive [41]. It should be noted that seropositive
prevalence in the same country may differ among populations
or geographical regions and world-wide prevalence is higher in
older populations.
In a limited case–control study that included six large European centers it was shown that the consumption of undercooked
meat was the major risk factor for toxoplasmosis infection [42].
Another study aimed to determine the prevalence of T. gondii
in edible meat tested 71 meat samples from commercial sources
in the UK for the parasite—positive results were found in 27
samples. Twenty-one of these contaminated meat samples carried the virulent T. gondii type I [43]. Although cats play a
definite role in the epidemiology of toxoplasmosis, no significant correlation between human toxoplasmosis infection and
cat ownership could be proven [44]. Furthermore, the oocytes
are not found on cat fur but rather are buried in the soil as they
are shed with cat faeces [45–47].
Data regarding seroprevalence of specific T. gondii antibodies in the Israeli population are based on several regional
surveys performed in collaboration with the Israeli National
Toxoplasmosis Reference Center. The prevalence in certain subpopulations of pregnant women in northern Israel had been
reported to be 21% on average and the incidence rate of infection
acquired during pregnancy estimated as 1.4% [48].
Human contact with infected oocyst from contaminated soil
[7,49,50] and water [8–10] were associated with several reported
epidemics caused by T. gondii. Only in one case were T.
gondii oocysts recovered from the soil—the suspected source
of infection [7]. There are ongoing efforts to develop sensitive detection techniques for environmental samples [11,51,52].
Unfortunately, isolation of oocytes from such samples is difficult, since infectious doses are small while large volume of
sample is required for isolation of the organism. In addition,
there is a lag period between the time of infection and the time
that the contaminated source is tested, further reducing the likelihood of recovery of oocytes from the suspected environment
during epidemiological investigation.
T. gondii was reported to cause 0.8% of the total food-borne
illnesses attributed to a known pathogen, and 20.7% of the total
food-borne mortality caused by a known pathogen, in the United
States in 1996–1997. Many of these cases involved HIV-infected
patients [53].
The largest reported toxoplasmosis outbreak resulting from
contaminated water occurred in British Columbia and caused
acute infection in 100 people; 19 with retinitis and 51 with lymphadenopathy. The likely source was a municipal water system
that used unfiltered, chloraminated surface water [10]. There was
also a seasonal correlation to rainfall and turbidity in this water
reservoir. In another small outbreak North of Rio de Janeiro,
Brazil, the source of the parasite was traced to an unfiltered water
source. It was also linked to high prevalence of seropositivity in
this region of low socio-economic background [8].
4. Congenital toxoplasmosis
Most cases of acquired toxoplasma infection are asymptomatic and self-limited; hence many cases remain undiagnosed.
The incubation period of acquired infection is estimated to be
within a range of 4–21days (7 days on average) [10]. When
symptomatic infection does occur the only clinical findings may
be focal lymphadenopathy, most often involving a single site
around the head and neck. Less commonly, acute infection is
accompanied by a mononucleosis-like syndrome characterized
by fever, malaise, sore throat, headache and an atypical lymphocytosis on peripheral blood smear [54]. In immunocompromised
patients, most commonly HIV infected and organ transplant
recipients, T. gondii may cause a severe central nervous system
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disease, resulting in brain lesions or diffuse encephalitis. Other
organs, such as the heart, lung, liver, and retina may also be
involved. Most of these cases result from reactivation of latent
infection [54] although re-infection with a different T. gondii
strain in the transplanted organs may also occur.
4.1. Incidence and prevalence in pregnant women and
infants
The disease is caused by vertical transmission of T. gondii
from a seronegative pregnant woman, who is acutely infected
with T. gondii to her fetus.
The prevalence of T. gondii and its incidence of human infection vary widely amongst various countries. Worldwide, 3–8
infants per 1000 live births are infected in utero [55]. Multiple
factors are associated with the occurrence of congenital toxoplasmosis infection, including route of transmission, climate,
cultural behaviour, eating habits and hygienic standards. This
combination leads to marked differences even among developed
nations. For example, the incidence of congenital infection in
Belgium and France is 2–3 cases per 1000 live births—markedly
higher than the US incidence, which is between 1 in 10,000 to
1 in 1000 live births [47,56].
In a research conducted in Goiania, Brazil, a region with
a relatively high seroconversion rate, pregnant women were
found to have a 2.2 times higher risk for seroconversion than
non-pregnant women of equivalent characteristics. In addition,
amongst pregnant women, adolescents were shown to have the
highest risk for seroconversion [57]. The authors hypothesized
that higher vulnerability to T. gondii infection during pregnancy
may be due to a combination of pregnancy associated immunosuppression as well as hormonal changes.
Only a few cases of congenital toxoplasmosis transmitted
by mothers who were infected prior to conception have actually been reported [58–60]. One such case published recently
involved a woman who had ocular toxoplasmosis 20 years prior
to giving birth to a newborn, who suffered from congenital toxoplasmosis. The mother had a “toxoplasmic scar” in the retina
and was tested positive for specific toxoplasma IgG antibodies.
The newborn was found to be positive for both IgG and IgM
antibodies and had a macular scar on the retina, typical to toxoplasmosis, as well as a calcified brain granuloma. [59]. Such
a case could be attributed to re-infection with a different, more
virulent strain or by reactivation of a chronic disease[58].
Chronically infected women, who are immunodeficienct,
may also transmit the infection to their fetus; the risk of this
occurrence is difficult to quantify, but it is probably low. Latent
T. gondii infection may be reactivated in immunodeficient individuals (such as HIV-infected women) and result in congenital
transmission of the parasite [61].
4.2. Diagnostic evaluation, manifestation and
consequences
The diagnostic evaluation of T. gondii is part of routine pregnancy follow-up and differential diagnosis of intrauterine infection. Intrauterine ultrasonographic findings of T. gondii infection
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are usually non-specific and in most cases no pathological evidences are revealed. In certain cases the ultrasonographic findings may include: intracranial calcifications, echogenic streaks,
microcephalus, ventricular dilatation and hydrocephalus [62].
Gay-Andrieu et al. [63] described two cases of intrauterine
infection in which the diagnosis was based upon hydrocephalus
in fetal ultrasound, even though PCR of amniotic fluid was
negative in both cases. The authors emphasized that hydrocephalus is the most frequent lesion detected by fetal ultrasound, reflecting the pathological process taking place within
several months post-infection in cases of intrauterine infection
of T. gondii. Additional ultrasonographic findings may include
hepatomegaly, splenomegaly, ascitic fluid, cardiomegaly and
placental abnormalities [55,64]. Safadi et al. [65] followed 43
children with congenital toxoplasmosis for a period of at least
5 years. Most of them (88%) had sub-clinical presentation
at birth. The most common neurological manifestation was a
delay in neuro-psychomotor development. Half of the children
developed neurological manifestations, 7 children had neuroradiologic alterations in skull radiography, and 33 children in
tomography. Notably, cerebral calcifications were not associated
with an increased incidence of neurological sequelae. Chorioretinitis was the main ocular sequelae, found in almost all children
and noted years after birth, despite specific therapy in the first
year of life.
An important step in the diagnosis of congenital toxoplasmosis and evaluation of time of infection is achieved by laboratory
techniques, monitoring the immune response: titer and affinity of specific antibodies (Fig. 1). Other laboratory tools focus
on direct detection of the parasite by animal or tissue inoculation or more commonly, by molecular techniques. Carvalheiro et
al. studied the incidence of congenital toxoplasmosis in Brazil,
based on persistence of anti-Toxoplasma IgG antibodies beyond
the age of 1year. Disease incidence was estimated to be 3.3 per
10,000. A definitive diagnosis was confirmed in five infants with
both serum IgM and/or IgA antibodies, and clinical abnormali-
Fig. 1. Laboratory diagnosis of congenital toxoplasmosis.
ties. They concluded that positive screening results must be carefully confirmed [66]. Laboratory methods and their implications
in supporting evidence-based diagnoses are discussed below.
The risk of fetal infection is multifactorial, depending on the
time of maternal infection, immunological competence of the
mother during parasitemia, parasite load and strain’s virulence
[40]. The probability of fetal infection is only 1% when primary maternal infection occurs during the preconception period
but increases as pregnancy progresses; infection acquired during the first trimester by women not treated with anti-T. gondii
drugs results in congenital infection in 10 to 25% of cases.
For infections occurring during the second and third trimesters,
the incidence of fetal infection ranges between 30–54% and
60–65%, respectively [54].
The consequences are more severe when fetal infection
occurs in early stages of pregnancy, when it can cause miscarriage (natural abortion or death occurs in 10% of pregnancies
infected with T. gondii [67]), severe disease, intra-uterine growth
retardation or premature birth. A multi-centre prospective cohort
study evaluated the association between congenital toxoplasmosis and preterm birth, low birth weight, and small size for
gestational age [68]. Freeman et al. reported that infected babies
were born earlier than uninfected babies and that congenital
infection was associated with an increased risk of preterm delivery when seroconversion occurred before 20 weeks of gestation.
Congenital infection was not associated with low birth weight
or small size for gestational age. The cause for shorter gestation
is not yet known. The highest frequency of severe abnormalities
at birth is seen in children whose mothers acquired a primary
infection between the 10th and 24th week of gestation [67]. The
likelihood of clinical symptoms in the newborn is reduced when
infection occurs later.
Clinical manifestations in newborns with congenital toxoplasmosis vary and can develop at different times before and
after birth. Most newborns infected with T. gondii are asymptomatic at birth (70–90%) [61]. When clinical manifestations are
present they are mainly non-specific and may include: a maculopapular rash, generalized lymphadenopathy, hepatomegaly,
splenomegaly, hyperbilirubinemia, anemia and thrombocytopenia [69]. The classic triad of chorioretinitis, intracranial calcifications and hydrocephalus is found in fewer than 10% of infected
infants [47]. Hydrocephalus and/or microcephaly may develop
when intra-uterine infection results in meningo-encepahlitis
[69]. All these signs and symptoms are included in the general
work-up of suspected congenital TORCH infections: toxoplasmosis, other (syphilis, varicella-zoster, parvovirus B19), rubella,
cytomegalovirus (CMV) and herpes infections. Cerebral calcifications can be demonstrated by cranial radiography, ultrasonography or computerized tomography. Neurologic impairment may initially present as seizures, necessitating specific
evaluation and treatment.
The most prevalent consequence of congenital toxoplasmosis
is chorioretinitis.
Chorioretinitis is diagnosed based on characteristic retinal
infiltrates. Vutova et al. [70] investigated eye manifestations of
congenital toxoplasmosis in 38 infants and children. The most
frequent finding was chorioretinitis (92%), together with other
ocular lesions in 71% of cases, and the second most common
finding was microphthalmia with strabismus. Lesions of the
anterior segment of the eye included iridocyclitis, cataracts and
glaucoma. Other uncommon findings were diminished visual
acuity and neurological sequelae such as hydrocephalus, calcification in the brain, paresis, and epilepsy.
Wallon et al. [71] reported the clinical evolution of ocular
lesions and final visual function, in a prospective cohort of 327
congenitally infected children in France. The children were identified by maternal prenatal screening and monitored for up to
14 years. After 6 years, 79 (24%) children had at least one
retinochoroidal lesion. In 23 of them a new lesion was diagnosed within10 years, mainly in a previously healthy location.
Normal vision was found in about two thirds of children with
lesions in one eye, half the children with lesions in both eyes
and none had bilateral visual impairment. Most of the mothers
(84%) had been treated. A combination of pyrimethamine and
sulfadiazine had been prescribed in all the children (38% before
and 72% after birth). Late-onset retinal lesions and relapse can
occur many years after birth, but the overall ocular prognosis of
congenital toxoplasmosis seems satisfactory, when infection is
identified early and appropriately treated. Early diagnosis and
treatment are believed to reduce the risk of visual impairment.
Relevant laboratory tests include complete blood count
(CBC), liver function tests and specific T. gondii diagnostic tests
as described in details below. If T. gondii infection is suspected
at the time of birth, diagnostic work-up includes ophthalmic,
auditory and neurological examinations, lumbar puncture and
cranial imaging [69].
In a large percentage of children the disease sequelae may
become apparent and present with visual impairment, mental and
cognitive abnormalities of variable severity, seizures or learning
disabilities only after several months or years [55].
Infants born to women infected simultaneously with HIV
and T. gondii should be evaluated for congenital toxoplasmosis,
considering the increased risk of reactivation of parasitemia and
disease in these mothers.
In a case–control study in Israel, Potasman et al. tested 95
children with variable neurological disorders: cerebral palsy,
epilepsy and nerve deafness compared with a control group of
109 healthy children, for the presence of T. gondii-specific antibodies in the serum. They found that children with any of the
neurological disorders were significantly more likely to have
T. gondii specific IgG antibodies, especially those with nerve
deafness (relative risk 2.5 and 7.1, respectively) [72].
A definite diagnosis cannot be made in the following situations: (1) the infant is older than one year of age and was not
tested for toxoplasmosis previously, (2) either the child or the
mother is seronegative, or (3) the mother was known to be seropositive prior to conception.
4.3. Prenatal laboratory diagnosis
The principle method used to diagnose and evaluate timing of congenital infection relies on indirect evidence, and is
based on detection of specific antibodies, by monitoring the
immune response. Direct evidence is obtained by animal or tis-
463
sue inoculation or more commonly, by molecular techniques. It
is important to combine all available clinical and laboratory data
during the evaluation of toxoplasmosis diagnosis and providing
treatment recommendations.
Infection during gestation may cause serious damage to
the fetus and hence, a major objective of the diagnosis is to
estimate the time of maternal infection. IgG antibodies usually appear within two weeks of infection, peak within 6–8
weeks and persist in the body indefinitely [67]. IgM antibodies are considered the indicators of recent infection and can
be detected by enzyme immunoassay (EIA) or immunosorbent agglutination assay test (IAAT) relatively early—within
2 weeks of infection. Uncertainty may arise as IgM may persist for years following primary infection [73]. IgA antibodies
may also persist for more than a year [67] and their detection
is informative mainly for the diagnosis of congenital toxoplasmosis. The level of specific IgE antibodies increases rapidly
and remains detectable for less than 4 months after infection,
which leaves a very short time to be used for diagnostic purposes [74]. However, IgE serology is not useful in samples from
newborns.
When serology alone is insufficient direct evidence for
toxoplasma infection should be sought. Both the laboratory
performing the tests and the referring physician should be
aware of the limitations and select the best combination of
tests available to timely evaluate the stage of toxoplasma
infection [75]. Laboratory tests available are summarized in
Table 1.
4.3.1. Sabin Feldman dye test (SFDT)
This is the first test developed for the laboratory diagnosis of
T. gondii infection [76], it is still considered the “gold standard”.
SFDT detects the presence of anti-T. gondii specific antibodies (total Ig) and is performed only in reference centers. The
change in antibody titer as determined in SFDT in consecutive serum samples taken at least 3 weeks apart is important
for the evaluation of infection during pregnancy. A “significant”
change is considered to be at least a four-fold difference. The
absolute antibody titer is also important—values over 250 IU/ml
are considered “high” suggestive of recent infection. The tested
sera are serially diluted and incubated with live tachyzoites
(carrying toxoplasma-specific antigens) in the presence of separated human plasma from “sero-negative” donors (providing
complement components). The antigen–antibody–complement
complexes formed are subsequently lysed in the presence of
the dye methylene blue. End-point titer is established by counting the numbers of dead (unstained) and live (stained) parasites. The reported titer is that producing lysis of 50% of the
organisms. End-point titer can be converted to international
units (IU): additional standardization is achieved by preparation of a standardised control serum (consisting of a pool of
sera), tested by numerous reference centers, and adjusted so
that the SFDT value of this control serum is set at 1000 IU/ml
[77]. Recently, the WHO recognized the first international standard for human anti-toxoplasma IgG, with an assigned potency
of 20 IU per ampoule of total anti-toxoplasma antibodies
[78].
464
Table 1
Laboratory diagnostic tests for congenital toxoplasmosis
Test
Matrix
Results
Interpretation
Time
Degree of
expertise
equired
Other remarks
Suggested use
Sabin Feldman Dye
Test (SFDT)
Serum
Titer in international
units (IU) of total
specific Ig
Quantitative data:
detection of high
(≥250 IU) antibodies
titers and significant
changes (≥×4) in
titer in consecutive
samples – important
for evaluation of
recent infection
Routine = ∼2–4
× week
High, reference
center only
Gold standard
Confirmation of
infection
“hands
on” = several
hours
Live parasites
and animal
injection → risk
to lab employee
Standardized
assay
(international
effort)
Possible false
negative very
early infection
Very
subjective and
difficult to
standardize
Partial results
(combine with
IgM detection)
Requires
further testing,
IgE – not in
newborn
Follow-up
change in titer
EIAa /total Igb
Serum
Positive/negative for
total specific Ig
Exposure to T. gondii
Several hours
Low = simple
automated test
IFAc -total Ig
Serum
Titer (in IU) of total
specific Ig
Several hours
High, reference
center only
IgG by EIA
Serum
specific IgG Abs
Several hours
Low = simple
automated test
IgM/IgA or IgE by
EIA
Serum
specific IgM, IgA or
IgE Abs
Possible recent
infection with T.
gondii
Several hours
Low = simple
automated test
IgM/IgA or IgE by
IAAT
Serum
IgE Abs
Possible recent
Infection with T.
gondii
Several hours
Relatively high
IgM/IgA or IgE by
IFA
Serum
IgE Abs
Possible recent
Infection with T.
gondii
Several hours
High, reference
center only
IgG avidity
Serum
Avidity = functional
affinity
High avidity supports
“past infection” (≥4
months)
Several hours
Relatively
simple
Mice
Body fluids/tissue
Positive/negative
Presence of parasite
3–6 weeks
High, reference
center only
Live parasites
and animal
injection → risk
to lab employee
Most sensitive
and specific
test
Very
subjective and
difficult to
standardize
Supportive
evidence
Low
sensitivity
Screening test
When SFDT is
unavailable
Screening test
IgM –
Screening
IgM/IgA –
Newborn
IgE – Earlier
IgM/IgA –
Newborn
Western blot
should be
considered if
contamination
with maternal
blood is
suspected
When ISAGA is
unavailable
When only a
single serum
sample is
available, in the
beginning of
pregnancy
Strain isolation
465
Table 1 (Continued)
Test
Matrix
Results
Interpretation
Time
Degree of
expertise
equired
Other remarks
Suggested use
Cells
Body fluids/tissue
Positive/negative
Presence of parasite
3–6 days
Low
sensitivity
When available
for a direct proof
of infection
PCR
Body fluids/tissue
Serum
Positive/negative
Presence of parasite’s
DNA
Fetal/newborn
infection
Several hours
Very high
reference center
only
Live parasites
High
High
sensitivity
Infrequent
availability
Amniotic fluid
Western blot IgG,
IgM
a
b
c
Identical/unidentical
to maternal Ig
1 day
High, reference
center
Confirmatory
test or
fetal/newborn
infection
EIA: enzyme immunoassay.
Ig: immunoglobulin.
IFA: indirect fluorescent assay.
4.3.2. Enzyme immunoassays (EIA)
The most common laboratory tests for toxoplasmosis
infection, also available as commercial kits and/or automated platforms, are EIA. These tests include: enzyme-linked
immunosorbent assay (ELISA) and enzyme linked fluorescent
immuno-assay (ELFA) which test for the presence of IgG and/or
IgM antibodies specific for the parasite in human sera. EIA are
useful as fast, low-cost screening tests and have been improved
over the years to avoid false positive results due to non-specific
detection of interfering factors such as rheumatoid factor and
antinuclear antibodies.
There is no standardization of these tests, which causes high
variability in results obtained with different kits and/or in different laboratories. Consequently, and also as a result of the high
incidence of false-positive results even in reference centers, the
US Food and Drug Administration (FDA) issued a health advisory to physicians on July, 1997. The FDA recommends avoiding
reliance of results obtained with any single commercial kit for
the detection of toxoplasma-specific IgM, as the sole determinant of recent toxoplasma infection in pregnant women. In
our experience at the Israeli National Toxoplasmosis Reference
Center, during the years 1997–2002, in an average of 747 samples (range: 652–816) received annually for confirmation, only
17% ± 2.6% were indeed positive for T. gondii-specific IgM. It
is therefore recommended that patient follow-up would be performed by a reference center, and that commercial kits would be
locally evaluated to achieve the highest degree of accuracy and
repeatability possible for screening tests.
In general, when toxoplasma infection is suspected based on
detection of specific IgM antibodies specimens are referred for
confirmation by a reference center where SFDT, PCR and other
advanced assays can be performed.
4.3.3. Immunosorbent agglutination assay test (IAAT)
IAAT is highly specific in detection of anti-T. gondii IgM,
IgA or IgE antibodies [79]. This assay utilizes the entire tachyzoite and is the most sensitive commercially available method
[80–82]. Unfortunately, it is expensive, requires a high degree of
expertise and is not automated. It is consequently seldom used in
reference centers, usually in neonates suspected of having con-
genital infection (where the expected levels of antibodies are
very low) [74,83].
Toxoplasma-specific IgE antibodies can be detected by EIA
or IAAT in sera of recently infected adults, congenitally infected
infants, and children with congenital toxoplasmic chorioretinitis
[84]. IgE detection is, however, ineffective in evaluating fetal or
newborn samples where IgA tests are most informative.
4.3.4. Indirect ﬂuorescent assay (IFA)
The IFA was widely used to demonstrate T. gondii-specific
antibodies: serially diluted serum samples are incubated with
live, inactivated toxoplasma fixed to a glass slide. T. gondiispecific antibodies present in the serum would bind to the inactivated parasite, and the complex is then detected using fluorescein
isothiocyanate-labeled anti-human Ig (or anti-IgG or anti-IgM).
IFA is safer to perform and more economical than the SFDT. It
appears to measure the same antibodies as the dye test, and its
titers tend to parallel dye test titers [47,85]. However, the IFA
interpretation is subjective and time consuming. False positive
results may occur with sera containing antinuclear antibodies
and rheumatoid factor [86], and false negative results of IFA for
IgM may occur due to blockage by T. gondii-specific IgG [87].
4.3.5. Avidity
IgG avidity testing was developed by Hedman et al. and is
based on the increase in functional affinity (avidity) between
T. gondii-specific IgG and the antigen over time, as the host
immune response (and specific B cell selection) evolves [88].
Dissociation of the antigen–antibody complexes reflects the
lower avidity closer to primary infection. Pregnant women with
high avidity antibodies are those who have been infected at least
3–5 months earlier, which makes the avidity test most useful and
reliable in the first trimester when high-avidity is detected [89].
In one study, 35 out of 63 patients (55%) who were classified
by toxoplasma-specific serology as having recent or borderline infection showed high avidity-antibodies and were therefore
treated as chronic patients [90]. Lappaplainen et al. [91] were
able to follow 13 women who showed high-avidity antibodies in
the first trimester and confirmed that none of the born infants was
found to be infected with T. gondii (as determined serologically
466
after birth). The avidity test is most important when only a single serum sample is available at the time when critical decisions
must be made. To the best of our knowledge, commercial IgG
avidity kits have been licensed in Europe but not in the US [92].
When avidity is low or borderline it may be misleading and
a more careful interpretation of all laboratory tests results in
conjunction with other clinical findings, should then be undertaken. Several studies have shown that this test is reliable and
valuable in diagnosis of recent infection during early pregnancy
[88,93–98].
Accurate and definitive serologic diagnosis of recently
acquired toxoplasma infection is still difficult and depends on
testing of more than one sample. Efforts to develop better
diagnostic approaches continue based on antigens specifically
expressed either during the primary phase (i.e. GRA7, GRA4)
or the latent phase (i.e. GRA1) of infection. These antigens can
be produced by recombinant DNA technologies and may lead to
a more informative serologic diagnosis, based on a single serum
sample [47,99,100].
4.3.6. Animal and cell culture inoculation
A definite laboratory confirmation of active toxoplasmosis
infection (especially in immunocompromised patients and pregnant women) can be established by inoculation of body fluids or
tissue into mice or cell culture [47].
Mice are injected intraperitoneally or subcutaneously with
10–30 ml of sediment from amniotic fluid or whole fetal blood.
The mice are bled prior and 3–6 weeks following inoculation.
Antibody detection by SFDT establishes infection and final
proof is obtained by staining to demonstrate brain cysts [101].
Cell culture inoculation with amniotic fluid or blood uses
indirect IFA to detect the parasite in monolayers within 3–6
days following inoculation [102]. When compared, inoculation
of both blood and amniotic fluid from an infected fetus resulted
in toxoplasma isolation from both cultures in 70% of cases.
However, in 40% of the cases T. gondii isolation is successful in
only one of the samples [100]. Derouin et al. [100] demonstrated
similar sensitivities comparing cell culture and mice inoculation.
Thulliez et al. [102] reported that the sensitivity of amniotic
fluid cell culture inoculation is only 53% compared with 73%
sensitivity in mice inoculation.
Currently, the principle role for these methods may be confirmation of PCR as they are complex, expensive and relatively
insensitive. [103].
4.3.7. Molecular diagnosis
Replacing fetal blood analysis, which is a high risk procedure for the fetus, with molecular evaluation of amniotic fluid
has provided a low risk diagnosis of congenital toxoplasmosis.
Polymerase chain reaction (PCR) is currently the most common
molecular technique routinely used for diagnosis of toxoplasmosis, although, it has not yet been standardized. No attempts have
been made to standardize either the sample preparation process
or the PCR amplification itself, and numerous laboratories use
multiple “in-house” methods of varying sensitivities and reliability [104,105]. Recently, a commercial PCR proficiency test
became available.
As in all diagnostic tests based on amplification of DNA,
a few technical aspects are of crucial importance in achieving
reliable results. Therefore, PCR based test should be carefully
designed to include negative, positive and internal control, target
DNA for amplification should be specific, sample preparation
techniques should be perfected to extract minute parasite DNA
[105] and to prevent cross contamination.
In a small (5 laboratories) inter-laboratories comparative
work [106] followed by a larger study (15 laboratories) [104] significant differences in test performances were obtained, including false negatives and false positives. These results should
definitely urge optimization and standardization of the test. More
recently, three PCR protocols were optimized prior to a comparative study, using three different targets: 18S ribosomal DNA,
B1 gene and AF146527. No significant difference was observed
between the results of the three protocols [107].
Chabbert et al. [108] used two different primer sets of the B1
gene to compare PCR performance followed by Southern blot,
on various sample types (including amniotic fluid, blood and
tissues). For amniotic fluid both PCR conditions produced similar results. The fragments produced by one of the primer sets
had to be confirmed by specific hybridization, otherwise nonspecific results were obtained. The PCR product of the same
amplification procedure was sequenced by Kompalic-Cristo and
suspected of originating from human DNA, as predicted by
bioinformatics analysis [109].
Different protocols influence the sensitivity and specificity
of PCR assays. The specificity and positive predictive value of
PCR tests on amniotic fluid samples is close to 100% [110,111].
However, the sensitivity of these PCR tests varies and estimated,
based on a large number of studies, to be 70–80% [105]. One
report showed that the sensitivity of PCR from amniotic fluid is
affected by the stage of pregnancy in which maternal infection
occurs: best sensitivity was detected when maternal infection
occurred between 17 and 21 weeks of pregnancy [89,111,112].
In addition, treatment with anti-toxoplasma drugs may also
affect the sensitivity [89,112]. However, the reliability of a PCR
test performed on amniotic fluid prior to the 18th week of pregnancy requires further evaluation [110,111]. It should also be
noted, that testing amniotic fluid for T. gondii was found to be
effective about 4 weeks following infection, which is already
during the parasitemic stage in the infected mother. Therefore,
PCR test should not be performed in the absence of serologic or
other clinical/sonographic data indicative of infection.
In the last 4 years there have been reports on the use of Real
Time PCR, a sensitive and specific technique, which enables
rapid detection of amplification products as well as hybridization
of amplicon-specific probes, similar to PCR followed by Southern blot analysis. The method, which will ultimately replace
traditional PCR, enables an overall time for amplification and
detection of less than two hours. In addition, cross contamination is prevented by elimination of the need to handle amplified
amplicons. In Real Time PCR it is possible to perform a quantitative study and follow the parasite load, allowing determination
of parasite count and its correlation with clinical symptoms and
impact of treatment. The technique permits linear range over 6
logs of DNA concentrations [113,114].
The most popular target gene for PCR diagnosis of T. gondii
is the 35-fold repetitive gene B1. A variety of primers have been
used for amplification, some of which include nested primers.
The second common locus is the single copy gene P30 also
known as SAG1, which encodes for a surface antigen. Another
PCR target is the 18S ribosomal DNA. As reviewed by Bastien
[105], two other target loci have been examined but are currently
not used by most laboratories. Recently, some laboratories have
shown success in amplification of a DNA fragment, AF146527,
which is repeated 200–300 times [89,113,114].
4.4. Laboratory diagnosis of infants
Laboratory diagnosis of Toxoplasma infection in infants is
based on a combination of serologic tests, parasite isolation,
and nonspecific findings [112].
When suspected, serologic follow-up of the newborn is recommended for the first year of life [90]. Evaluation for direct
evidence as described above should be repeated as well during
this period.
Serologic tests should follow total (or IgG) T. gondii specific
antibodies titer (taking into account that closely after birth these
are maternal in origin, transferred through the placenta), IgM
and IgA titers. Though passively transferred maternal IgG has a
half life of approximately 1 month, it can still be detected in the
newborn for several months, generally disappearing completely
within one year [112]. Appearance of autonomous IgG antibodies in a congenitally infected newborn begins, in an untreated
patient, about 3 months after birth. Anti-parasitic therapy may
delay antibody production for about 6 months and, occasionally,
may completely prevent antibodies production [86].
4.4.1. Western blots
Remington et al. introduced Western blots (using T. gondiispecific labeled antigens to detect antibodies, separated by electrophoresis and transferred to a membrane) to compare newborn
versus maternal antibodies [115–117]. Western blotting could
potentially separate maternal from fetal/newborn antibodies.
The test is not widely used mainly because of its technical complexity and high price.
5. Treatment of congenital toxoplasmosis
Anti T. gondii treatment initiation generally requires confirmatory laboratory tests in a reference center, followed by
consultation with experts. Treatment is indicated in the following conditions: infection during pregnancy and congenital
infection as well as infection of an immunocompromised host
(e.g. HIV/AIDS) and in case of an invasive disease. In pregnant
women and infected neonates, both symptomatic and asymptomatic, specific treatment of T. gondii infection is indicated
immediately following established diagnosis. The combination
of pyrimethamine, (adult dosage 25–100 mg/d × 3–4 weeks),
sulfadiazine adult dosage 1–1.5 g qid × 3–4 weeks) and folinic
acid (leucovorin, 10–25 mg with each dose of pyrimethamine,
to avoid bone marrow suppression) is the basic treatment protocol recommended by the WHO [118] and CDC [119]. Other
467
drugs such as spiramycin (adult dosage 3–4 g/d × 3–4 weeks)
and sometimes clindamycin are recommended in certain circumstances. Spiramycin is used to prevent placental infection; it is
used in many European countries especially France, Asia and
South America. In the US, spiramycin is currently not approved
by the FDA but, available as an investigational drug, requiring
special approval. Treatment with pyrimethamine and sulfadiazine to prevent fetal infection is contraindicated during the first
trimester of pregnancy due to concerns regarding teratogenicity,
except when the mother’s health is seriously endangered. During
the first trimester sulfadiazine can be used alone.
As recently reviewed by Montoya and Liesenfeld [112], treatment protocols vary among different centers. The effectivity of
anti-T. gondii treatment is evaluated based on two criteria: rate
of mother to child transmission and prevalence and severity of
sequelae. The majority of the studies are retrospective or cohort
studies of various populations and case definitions. The difference in study patterns and methodologies affects the reliability
and validity of the results and thus prevents issuing further recommendations.
Wallon et al. [120] reviewed studies comparing treated and
untreated concurrent groups of pregnant women with proved
or likely acute toxoplasma infection. Outcomes data of the
offspring were reported. The results showed treatment to be
effective in five studies but ineffective in four. Gras et al. [121]
reported that the effect of prenatal pyrimethamine–sulfadiazine
combination treatment on the cerebral and ocular sequelae of
intrauterine infection with T. gondii was not beneficial in 181
children of infected mothers. Neto reported the outcome of
patients with congenital toxoplasmosis who were all treated with
pyrimethamine, sulfadiazine and folinic acid; of 195 patients 138
(71%) were asymptomatic until the age of 2 years. The authors
suggest that for six patients with sequelae because of the delay
in anti-toxoplasma treatment (6–14 months post diagnosis) the
disease was not prevented [122]. Gratzl et al. [123] reported variable concentrations of spiramycin and its metabolites in serum
and amniotic fluid of 18 pregnant women following treatment.
All the drug concentrations were below the level reported to
inhibit parasite growth in vitro. The authors suggested that the
possible reasons being individual pharmatokinetic variability
and patients’ treatment compliance. Gilbert et al. [124] reported
the effect of prenatal treatment in 554 infected women and
their offspring. In this study comparison of early versus late
treatment and of combination treatment (pyrimethamine, sulfadiazine) with spiramycin or no-treatment, were all statistically
insignificant. The possible interpretation is that delayed treatment initiation led to failure to prevent parasite transmission.
Another European multicenter study comparing transmission
rates and clinical outcomes in 856 mother–infant pairs, found
no significant association between the outcome and the intensity
of treatment protocol in pregnancy [125]. Bessieres et al. [126]
studied the effect of treatment during pregnancy in a cohort of
165 women and found that cases could be identified during pregnancy as well as during the neonatal period. They also noted
that T. gondii was less frequently isolated in women treated
with pyrimethamine and sulfadoxine than in women treated
with spiramycin only. Foulon et al. [127] reviewed the measures
468
6.1.1. Vaccine
Development of a vaccine for toxoplasmosis can prevent
human disease by immunization of human as well as animals
(the source of infection). Both attenuated parasite and immunogenic antigens are considered as potential agents for vaccination.
Live attenuated S48 strain is in use for vaccination of sheep in
Europe and New Zealand but is unsuitable for human use due to
its expense, short shelf life and most importantly, to the ability of
the attenuated parasite to revert to a pathogenic strain [130–133].
Much of the work has been focused on SAG1, a surface antigen expressed on tachyzoites, in attempts to induce protective
immune response (mainly T-helper response) when introduced
to the host with various adjuvants [134–136]. Development of
vaccine using antigens expressed by bradyzoites and oocytes is
also under investigation[134,137].
State of Goias, Brazil as recommended by experts [127]. Screening of women should begin prior to conception with follow-up
monthly tests during pregnancy to detect seroconverion. This is
the basis for the French [138] screening program and the Austrian Toxoplasmosis Prevention Programs, both recommend routine serologic testing, in Austria three times during pregnancy:
in the first, second and third trimesters and in France six times
following the initial finding [139]. Treatment is recommended
if one of the tests suggests definite or probable primary maternal infection [140]. In Massachusetts, USA, where there is low
seroprevalence in the population, only newborns are screened
for the presence of T. gondii-specific IgM [141]. IgM detection is followed by an extensive clinical evaluation and a one
year treatment regimen combination of pyrimethamine and sulfadiazine [140]. A recent study screened 364,130 neonates in
the United States for T. gondii specific IgM and confirmed 195
cases of congenital toxoplasmosis (1 in 1867). Moreover, a 7year follow-up of the treated patients revealed no symptoms or
at least no progress of the disease. Based on these findings, the
authors suggest including toxoplasmosis in neonatal screening
programs [122].
In the United Kingdom a national committee concluded that
no prenatal or neonatal screening for T. gondii should be performed, which brought out controversy among specialists [142].
A survey conducted in Italy reported 35/1000 pregnant
women with primary T. gondii infection and recommended
maternal screening during pregnancy rather than neonatal
screening [143]. In Norway, screening of pregnant women was
recommended until 1977 when the National Institute of Public
Health discouraged it, following a large study that showed low
(0.17 %) incidence of primary infection during pregnancy [144].
Two years following this change in policy, a study by Eskild et
al. [145] showed that despite the recommendations, 81% of the
pregnant women were still routinely tested for T. gondii-specific
antibodies.
In Finland, a cost-benefit analyses of screening programs for
pregnant women as well as education programs revealed the beneficial effect of such programs in both low and high incidences
of toxoplasmosis [146].
Cost-effectiveness of optional screening programs (no
screening, pre-conception or neonates screening, frequency of
tests during pregnancy) depends on local factors: incidence of
congenital toxoplasmosis, available diagnostic and therapeutic
services, and the population compliance with screening. It is
important to promote public, as well as professional, knowledge
regarding the disease, in order to effectively prevent, diagnose
and treat congenital toxoplasmosis.
In conclusion, it is highly recommended to educate the public and professionals to minimize risk of infection. Screening
programs of women at childbearing age and upon gestation or
at least newborn screening is highly effective for early treatment
and prevention of sequelae.
6.2. Secondary prevention – screening
Acknowledgments
Routine toxoplasmosis screening programs for pregnant
women have been established in France, in Austria and in the
Dr. Irena Volovik Sub-district Health Officer, Hadera, Israel,
for providing data of the presented case.
of prevention of congenital toxoplasmosis and concluded that
treatment during pregnancy significantly reduces sequelae and
treatment of infected children has a beneficial effect when therapy is begun soon after birth.
In conclusion, the efficacy of anti-T. gondii treatment in pregnancy is still an unsettled matter. It is difficult to find the effect
of treatment when comparing the different studies because of:
different treatment regimes and timing (for small groups of
patients), the pharmacokinetics patterns of drugs (concentration in amniotic fluid and fetal CSF), patient (none) compliance
with treatment and different methodologies of follow-up in each
study.
As concluded by Peyron et al. [128] and others, further large
scale, carefully controlled studies are necessary in order to clarify this controversial issue. At present the anti-parasite treatment
recommended for toxoplasmosis as outlined above, should be
considered as the guideline for good medical practice.
6. Prevention
6.1. Primary prevention
In the United States efforts at prevention of congenital toxoplasmosis have been primarily directed towards health education, focused to avoid personal exposure to the parasite (hygienic
and culinary practice during pregnancy). In Poland, an extensive
health education campaign, increased toxoplasmosis awareness
and knowledge of preventive behaviour significantly within the
4 years of the reported study [129]. Many other countries have
introduced educational programs aimed at reducing the incidence of congenital toxoplasmosis. Such programs depend on
careful identification of unique target-populations and tailoring
appropriate approaches of education. To evaluate the success of
such programs it is important to measure incidence rate before
onset and at pre-determined intervals after introducing the campaign.
Mrs. R. Kaufman and Mrs. R. Avni for excellent laboratory
work.
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Toxoplasma gondii Efrat Rorman , Chen Stein Zamir , Irena Rilkis

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