Parasites – things that make you go `Ewww`.

Parasites – things that make you go ‘Ewww’.
Doireann Dowling DipVN RVN BAHonsModEnvSci
The implications of parasitic infestations and infections on animal health are something
veterinary professionals are quite familiar with, from the widely publicised and potentially fatal
Angiostrongylus vasorum lungworm infection to the hairless dog with demodectic mange. What
is often overlooked, however, is something that we veterinary professionals tend to forget about
– HUMAN health! It is important for us to realise that we have a huge responsibility to our
clients, our colleagues, the general public and to ourselves in this regard. In this article we will
look at some zoonotic diseases (diseases that are transmissible from animals to humans) which
all pet owners and veterinary professionals need to be informed.
Table 1: Zoonotic parasites of dogs and cats of importance within ROI:
Parasite:
Fleas
Taxonomic Name:
Ctenocephalides canis, C.felis
Mites
Sarcoptes scabiei var. canis
Ticks
Roundworm
Cheyletiella
Ixodes ricinus
Toxocara canis
Toxocara felis
Hookworm
Tapeworm
Uncinaria stenocephala
Dipilidium caninum
Taenia spp.
Echinococcus granulosus
Effects on human health:
Flea bites, pruritis, secondary
infections, allergic reactions,
Dipilidiasis (flea-tapeworm infection),
Cat-Scratch disease.
Scabies, secondary infections, Crusted
scabies.
Transient, localised dermatitis
Pruritis, Lyme disease
Viceral larva migrans (VLM)
Ocular larva migrans (OLM)
Neurological larva migrans (NLM)
Covert toxocariasis
Cutaneous larva migrans
Dipilidiasis
Taeniasis
Hydatidosis
1. Fleas
Probably the most frequently observed parasite in veterinary practice is the humble flea. Only
fleas aren’t so humble – they are insects from the Order Siphonaptera who feed on the blood of
any unwilling / unwitting species of blood donor (i.e. fleas are not host specific).
If a dog or cat is diagnosed with a flea infestation, owners should be aware that only 5% of the
problem is seen as the parasitic, adult life-stage on the animal….the other 95% is in the
environment in the form of eggs, larvae and pupae. (Figure 1)
Figure 1: The flea lifecycle
Figure 2: Flea bites on a person's leg
Pupated fleas are stimulated to emerge from their cocoons as adults by factors including heat,
movement and carbon dioxide concentrations i.e. factors that would indicate that a living,
breathing, potential host was nearby. People moving into a new home may stimulate an
existing, dormant flea population to emerge if pets previously occupying the house were not
protected effectively against fleas.
Symptoms of flea bites include itchy reddened, potentially raised lesions. Sensitive individuals
may also be allergic to the saliva of the flea, with symptoms then varying according to the allergy
level.
Fleas are also responsible for the transmission of other zoonotic diseases – e.g. ‘Cat Scratch
disease’, Dipylidiasis and…oh yes, historically, the PLAGUE!!! (Yersinia pestis)
2. Ticks
The importance of tick vigilance cannot be overemphasised. Ticks act as vectors for other
zoonotic infections such as Lyme disease (Borrelia bacterium), Erlichiosis (Erlichia and Anaplasma
bacteria) and Babesiosis (Babesia burgdorferi intracellular parasite).
The HSE estimates that there are between 50-100 cases of Lyme disease in Ireland each year
(HSE, 2013). In the UK, the prevalence of Lyme disease in humans is increasing with 1,395 people
testing positive for B. burgdorferi in 2009 – an increase of 27.0% from 2008 (Defra, 2009).
Historically tick populations were considered to peak in Spring and Autumn, nowadays, possibly
due to climate changes, ticks may be seen year round in most rural areas in Ireland.
Figure 3: An Ixodes ricinis tick
3. Mites
Figure 5: A Cheyletiella mite
Figure 4: A Sarcoptes scabiei mite
Sarcoptes scabiei var. canis is a mange mite affecting dogs and foxes. ‘Scabies’ is the condition
caused in humans infested with this mite. Human infestation may occur through direct contact
(petting an infected dog) or indirect contact (touching contaminated bedding, grooming
equipment etc.) The mites burrow into the skin, particularly in warm areas such as the skin folds
between fingers, buttock creases, breast creases, under fingernails or jewellery. Spontaneous
remission usually results after 12-14 days (Grøndalen et al., 2008) however there may be
secondary infections caused from scratching. A rare complication is a condition called ‘crusted
scabies’ which may affect people with weakened immune systems.
Cheyletiella mite species are sometimes referred to ‘walking dandruff’. These surface mites can
cause a localised, red rash +/- crusting, on humans that are in repeated contact with infested
pets. These mites can also survive in the environment for up to ten days (ESSCAP, 2012). Human
infestations are fortunately usually transient.
Additionally Neotrombicula autumnalis (harvest mites) and Otodectes cynotis (ear mites) have
also been reported on humans!
4. Roundworms
Figure 6: Toxocara canis adult worms
Figure 7: OLM
Toxocara canis and T. felis are zoonotic roundworms that reproduce within dogs and cats
respectively. Toxocariasis (sometimes referred to as Toxocarosis) is the human infection of the larvae of
Toxocara species which can migrate through various areas of the human body. There are four recognised
forms of toxocariasis: Visceral Larva Migrans (VLM), Ocular larva migrans (OLM), Neurological larva
migrans (NLM) and Covert toxocariasis. In cases of VLM, the liver and lungs are usually affected; in cases
of OLM, the eyes; and in cases with NLM, the nervous system.
For most people who become infected with Toxocara larvae, the symptoms are minor (cough, headache,
abdominal pain, headaches, behavioural or sleep disturbances) or the infection may indeed be
asymptomatic. Generally in these cases, the worm larvae will die automatically within several months.
This form of toxocariasis is known as ‘Covert toxocariasis’.
OLM can result in granuloma formation and retinal damage to the eye which in turn may cause unilateral
or bilateral blindness. An Irish study in 2004 reported 9.7 cases of OLM per 100,000 school children
(Good et al, 2004). Children between the ages of 1-4 are particularly at risk but OLM can affect people of
all ages.
Toxocariasis is not notifiable in Ireland and thus there is no clear indication as to the total number of
cases there are. The Health Protection Agency (HPA) in the UK reported only 30 cases between 20002010 and we could potentially assume that toxocariasis is similarly as rare in Ireland as it is in the UK.
Saying that, I can’t imagine anyone who reads the story of Millie Knight from the UK (Bates, 2012) would
be happy to risk Toxocara larvae infecting themselves or their children.
Figure 8: Granuloma formation in the eye resulting from OLM
Figure 9: Typical roundworm lifecycle
5. Hookworms
Approximately 92% of Irish foxes are infected with the zoonotic hookworm, Uncinaria
stenocephala (Wolfe et al, 2001). The fox population is a source of infection of dogs, who are
also final hosts for this parasite. Hookworm infections generally occur through ingestion of
larvae, however transcutaneous infection may also occur. In people, infection with this
hookworm causes a condition known as Cutaneous Larva Migrans.
Figure 10: Cutaneous larva migrans
6. Tapeworms
Figure 11: Echinococcus granulosus - A 3-5mm tapeworm
Figure 12: Hydatid cysts in the lungs
A tapeworm called Echinococcus granulosus is responsible for a zoonotic disease known as
hydatid disease. Hydatid disease in humans involves the slow development of fluid filled larval
cysts. These cysts are extremely slow developing and thus symptoms of disease may not appear
for years. The liver is the most common organ to be affected, 50-70%, followed by the lungs, 2030% (Weese & Fulford, 2010) and the symptoms of hydatid disease are thus dependent on the
location of the cyst e.g. jaundice and abdominal pain from liver cysts or coughing and chest pain
in cases with lung cysts. Rupture of these cysts can result in serious anaphylactic reactions.
Echinococcus granulosus affects sheep and other livestock (intermediate hosts) and uses both
dogs and foxes as its final hosts. Thus a higher prevalence of this disease is seen in rural, sheepfarming regions of endemic areas.
The incidence and prevalence of hydatid disease in Ireland is unknown. Geographical hotspots
have been identified in rural areas of Wales (19 cases of hydatid disease between 2000-2013)
and Scotland.
Note that under the Pet Travel scheme, dogs travelling to Ireland must be treated for
Echinococcus species of tapeworms, 24-120 hours before their scheduled arrival. (DAFF, 2013)
Two relatively minor zoonoses associated with tapeworms are dipylidiasis and taeniasis. These
diseases are caused by ‘flea tapeworm’ Dipylidium caninum and some species of Taenia
tapeworms respectively. Dipylidiasis is contracted by ingesting a flea infected with Dipylidium
larva and Taeniasis is contracted through ingestion of uncooked, infected meat
Thankfully infections are rare in Ireland.
Important preventive measures to prevent zoonotic infections:
 Treat all pets prophylactically against infestations and infections
o Veterinary nurses should perform individualised parasite risk assessments for all
patients. A perfect opportunity to do this and to advise clients appropriately is at puppy
parties or annual health check visits.
 Otherwise treat pets monthly for fleas and quarterly for worms. Note that dogs
require monthly treatments of Advocate®(Bayer Animal Health) for prophylactic
protection against potentially fatal infections of A. vasorum.
o Veterinary practitioners should prescribe or advise clients to use only reputable
products to protect pets against parasites.
o Supply tick tweezers to clients in rural areas and demonstrate their correct use.
o Veterinary professionals should perform tests such as skin scrapes, microscopy or
serology to ensure that accurate diagnoses are achieved.
 Encourage client compliance:
o Recommend or prescribe a product that is convenient for each individual client to use
e.g. spot on formulation / tablet / collar
o Demonstrate correct product administration and patient restraint methods
o Provide oral AND written, illustrated instructions
o Supply clients with ‘pill poppers’ to administer oral medications to cats
o Provide an email or SMS reminder service free of charge e.g. http://www.drontal.com/reminders/
o Educate the public with regard to zoonotic risks. In particular, identify and inform at-risk
demographs including children, pregnant women and those immunocompromised.
 Good hygiene
o Keep nails cut short and use an effective hand washing technique
o Use PPE where appropriate
o Develop an awareness of your own hand-to-mouth habits and STOP THEM!
o Wash fruit and vegetables properly before consumption
o Ensure meat is thoroughly cooked before consumption
 Responsible pet ownership:
o Scoop up dog poop! It is an offence to allow dogs to foul public places under Section
22 of the Litter Pollution Act 1997 (Citizens Information, 2013)
o Vacuum regularly - the highest concentration of flea eggs and larvae are found in ‘point
sources’ – areas where an infested pet spends most of their time. Vacuuming helps
reduce concentrations of these flea lifestages.
o Use animal beds that can be machine washed at 60°C within a pet wash bag to protect
your machine from hairs!
o Clients in rural areas should:
 Check both themselves and their pets for ticks every 24 hours. (Removal of ticks
within this timeframe minimises the risk of the transfer of other tick-borne diseases.)
 Prevent dogs from roaming.
 Do not allow dogs to access to animal carcasses or viscera.
References:
Bates, C. (2012). Girl nearly goes blind after parasite in dog mess that travelled from her
stomach to her eyeball. Health. Mail Online, [online], 04/12/12, available:
http://www.dailymail.co.uk/health/article-2242751/Girl-nearly-goes-blind-inadvertently-eatingparasite-dog-mess-travelled-stomach-EYEBALL.html [Accessed 10/08/13]
Butler,M.W., Mullan, R.H., Schaffer, K.E., Crotty, T.B., Luke, D.A., Donnelly, S.C. (2003).
Pulmonary cystic hydatid disease in Ireland. Irish Journal of Medical Science, [online], 172 (4),
available: http://www.ijms.ie/Portals/_IJMS/Documents/1724204.pdf
Citizens information. (2013). Control of dogs, [online], available:
http://www.citizensinformation.ie/en/environment/animal_welfare_and_control/control_of_do
gs.html [Accessed 10.08.13]
Department for Environment, Food and Rural Affairs (2011) Zoonosis report: UK 2009, [online],
available:
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/69313/pb135
71-zoonoses2009-110125.pdf (Accessed: 10.08.10)
Department of Agriculture, Food and the Marine. (2013). Requirement for entry or re-entry of
dogs, cats and ferrets from another EU Member State and certain other European Countries and
Territories, [online], available: http://www.agriculture.gov.ie/pets/requirementforentryorreentryofdogscatsandferretsfromanothereumemberstateandcertainothereuropeancountriesandte
rritories/ [accessed 10.08.10]
Grøndalen, J., Sævik, B., Sørum, H. (2008). Companion animals as reservoir for zoonotic
diseases. European Journal of Companion Animal Practice (EJCAP) (18/3), pp. 213-221
Health Service Executive. (2013). Handwashing technique, [online], available:
http://www.hse.ie/eng/services/Publications/HealthProtection/Health_Care_Associated_Infecti
on/Handwashing_Technique.pdf [accessed 10.08.10]
Health Service Executive. (2013). Lyme disease, [online], available:
http://www.hse.ie/portal/eng/health/az/L/Lyme-disease/ [accessed 10.08.10]
National Health Service. (2013). Toxocariasis, [online], available:
http://www.nhs.uk/Conditions/Toxocariasis/Pages/Introduction.aspx. [accessed 10.08.10]
Overgaauw, P.A.M., van Knapen, F. (2008) Toxocarosis, an important zoonosis. European
Journal of Companion Animal Practice (EJCAP) (18/3) pp. 259-264
Public Health Wales (2013). Hydatid disease (Echinococcosis), [online], available :
http://www.wales.nhs.uk/sites3/page.cfm?orgId=457&pid=27729 [accessed 10.08.13]
Weese, J.S. and Fulford, M. eds. (2011). Companion Animal Zoonoses. Iowa: Wiley Blackwell.
Wolfe, A., Hogan, S., Maguire, D., Fitzpatrick, C., Mulcahy, G., Vaughan, L., Wall, D. and
Hayden, T.J. (2001). Red foxes (Vulpes vulpes) in Ireland as hosts for parasites of potential
zoonotic and veterinary significance. Veterinary Record,( 149/25), pp.759-763
Wolfe, A., Wright, I.P. (2003) Human toxocariasis and direct contact with dogs. The Veterinary
Record, 152 pp.419-427