Flea allergic dermatitis

Transcription

Saunders Solutions in Veterinary Practice – Small Animal Dermatology by Anita Patel and Peter Forsythe © 2008 Elsevier Ltd. All rights reserved.
5
Flea allergic dermatitis
INITIAL PRESENTATION
Pruritus with papules, erythema, scaling and hyperpigmentation in a Jack Russell terrier.
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INTRODUCTION
In some parts of the world, flea allergic dermatitis (FAD)
is the most common allergic disease and a major cause
of pruritus in dogs and cats. In other parts it is a significant problem only at certain times of the year. Although
allergic dermatitis is the main condition associated with
fleas, a distinction between pruritus resulting from severe
flea infestation and a hypersensitivity response should be
made. In very young puppies and kittens, severe flea
infestations provoke varying degree of pruritus, but
more often patients exhibit signs of weakness, lethargy
and anaemia. Fleas are also vectors of infectious organisms such as Bartonella, Rickettsia felis and Haemoplasma
spp.
CASE PRESENTING SIGNS
A 6-year-old female Jack Russell terrier was
presented with severe erythema, pruritus, papules,
alopecia and hyperpigmentation affecting the
dorsum, feet, periocular skin, ears and muzzle.
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Long-standing history of non-seasonal pruritus involving face, feet and ventrum, and more recently the
dorsal trunk had also become involved.
The pruritus has been managed with intermittent
methylprednisolone acetate injections, but these had
become ineffective with severe deterioration in the
dog’s clinical condition.
The dog was mainly fed on a commercial pet food
and more recently an 8-week diet trial with a prescription hydrolysed hypoallergenic diet had failed to
resolve the pruritus or the clinical lesions.
The indoor environment was fully carpeted and the
dog normally slept under the owner’s bed.
Outdoor access was to the garden only.
Previous flea control had been intermittent, using
fipronil and most recently selamectin.
The three in-contact cats were unaffected and were
intermittently treated for fleas with a pet shop product.
The owner had seen fleas on one of the cats some
weeks back and had treated it with proprietary flea
product from the supermarket.
CLINICAL EXAMINATION
CASE HISTORY
This varies between individuals but most pruritic dogs
are presented with a history of pruritus and varying
lesions affecting the lumbo-sacral region. As the flea
life cycle is affected by environmental factors such as
temperature and humidity, seasonal exacerbations may
occur. Often flea control is only intermittently used
and in-contact animals, especially cats, are inadequately
treated. The history in this particular case was long and
complex. The most relevant parts were:
A whole range of clinical signs, from primary lesions such
as papules and pustules, to severe secondary hyperpigmentation, lichenification and fibropruritic nodules are
seen, depending on the chronicity of the disease. Selfinduced alopecia due to over-grooming and secondary
bacterial infection is often seen in affected dogs. Atopic
dogs are predisposed to flea bite hypersensitivity, even
those that have been well managed. Some dogs will
present with pyotraumatic dermatitis on the rump, or at
other sites.
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5 Flea allergic dermatitis
29
Figure 5.1 Erythema, papules and self-induced alopecia
on the dorsum.
Figure 5.4 Periocular dermatitis.
Figure 5.2 Lateral aspect on the trunk.
Figure 5.5 Erythema and self-induced alopecia extending
to the distal aspect of the leg.
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Figure 5.3 Papular dermatitis in inguinal regions.
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The clinical findings in this case were:
Severe generalized erythema with papules, follicular
papules and crusted patches on the trunk (Figs 5.1
and 5.2).
Erythema, alopecia and papular rash on the ventrum
and inguinal region (Fig. 5.3).
The periocular skin was hyperpigmented, lichenified
and erythematous, with evidence of excoriations
(Fig. 5.4).
Both the pinnae and vertical ear canals were
erythematous.
Erythema, self-induced alopecia, crusting and hyperpigmentation involving all four feet (Fig. 5.5).
The skin was malodorous and greasy to the touch.
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SMALL ANIMAL DERMATOLOGY
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The peripheral lymph nodes were not enlarged and
the other physical parameters were within normal
limits.
DIFFERENTIAL DIAGNOSES
In this case, given the clinical signs and the
distribution of the lesions, there was evidence for
more than one type of hypersensitivity. The facial,
pedal and ventral distribution suggested atopic
dermatitis, and that affecting the dorsal aspect,
flea allergy dermatitis. A concurrent adverse food
reaction could also have been contributing to the
pruritus. The other differentials included:
● Staphylococcal pyoderma
● Malasseziosis
● Sarcoptic mange
● Demodicosis
● Otodectes hypersensitivity
● Dermatophytosis
● Adverse drug reaction.
CASE WORK-UP
A number of the differential diagnoses were ruled out
with simple in-house tests:
● Skin scrapes were performed to rule out demodicosis
and to look for sarcoptic mange. Negative skin scrapes
do not definitively rule out sarcoptic mange and
therefore a Sarcoptes IgG ELISA test was performed,
which was also negative.
● There was no fungal growth after 3 weeks of culturing of a sample obtained by the MacKenzie toothbrush technique.
● Tape-strip samples, obtained from crusted lesions,
revealed clumps of coccoid bacteria, neutrophils and
keratinocytes.
● Staphylococcus intermedius was isolated from a swab
submitted for bacterial culture, which was sensitive
to amoxicillin/clavulanate, cefalexin, enrofloxacin,
marbofloxacin, clindamycin and trimethoprim/
sulphonamide. It was resistant to amoxicillin, penicillin and tetracycline.
● Coat brushings failed to demonstrate any fleas or flea
faeces.
In addition to atopic dermatitis, the history, clinical signs
and distribution of lesions were suggestive of flea allergic
dermatitis. The diagnosis of flea allergy dermatitis is supported with additional tests and with response to aggressive flea control. The simplest test is the demonstration of
fleas or flea faeces using a flea comb; however, about a
third of animals fail to show any evidence of fleas, for
various reasons:
● Self-grooming removes the fleas and flea faeces
● Owners often groom or bath the animals before
coming into the practice
● Intermittent flea control reduces the numbers, making
it difficult to find them
● Exposure to the flea source may be intermittent.
In these cases further diagnostic tests may be of
value; however, it is important to remember their limitations and ultimately a positive response to aggressive
flea control is needed to confirm the diagnosis.
In vitro testing: In this case an in vitro Allercept IgE
ELISA test using recombinant flea saliva revealed a markedly elevated flea allergen specific IgE concentration,
which was consistent with flea allergy dermatitis and
suggested current flea exposure. However, the specificity and the sensitivity of the testing are variable, and the
test does not recognize those animals with cell-mediated
hypersensitivity immune responses. It is useful as a diagnostic aid but a negative test should not necessarily rule
out FAD. It is estimated that about 15–30% of individuals may show just cell-mediated immune responses. In
addition, a serum IgE test for other allergens was performed (see Chapter 3) to assess the role of environmental allergens. This revealed high levels of IgE to house
dust and storage mite allergens.
Intradermal testing: Intradermal testing with wholebody flea antigen or flea saliva may also support the
diagnosis. This test produces immediate reactions
(15–30 minutes), or late-phase reactions (4–6 hours) or
delayed reactions (24–48 hours) to specific antigens
injected intradermally. The test site should be examined
at the appropriate times. Late-phase and delayed-type
reactions are recognized either by an erythematous ring
at the site of injection and/or a raised wheal. In this case
this test was not deemed to be suitable for either flea
antigen or other environmental allergens, because the
last injection of methylprednisolone acetate had been
given only 2 months prior to the initial examination by
the dermatologist. The duration of action of this drug is
anything between 4 and 6 weeks, and varies between
individuals. Ideally, intradermal testing should be carried
31
out not less than 12 weeks after the injection of a
reposital glucocorticoid.
flea bite and accounts for 15–30% of the flea allergic
cases.
DIAGNOSIS
EPIDEMIOLOGY
The diagnosis in this case was that of bacterial pyoderma, flea allergic dermatitis and atopic dermatitis.
There is no sex predisposition and sensitization can occur
at any age, but appears to be seen mainly in older
animals. Intermittent exposure is associated with
increased sensitization, whereas continuous exposure
may result in some tolerance.
The incidence of the disease is dependent on the
presence of environmental conditions in which the fleas
are likely to thrive and perpetuate. An ambient temperature of 18–30ºC and high relative humidity of between
70% and 80% favours flea reproduction and survival;
however, the flea’s biology is such that it ensures its own
and/or its intermediate stages’ survival, even when the
conditions are unfavourable. Although the flea itself is
unable to survive cold temperatures, or high temperatures with low relative humidity, the pupal stage (Fig.
5.6) is able to endure them for up to 300 days. Then,
when appropriate environmental conditions are encountered (see below), the adult flea emerges. The flea life
cycle from egg to adulthood can therefore vary from
15 to 300 days depending on the environmental
conditions.
The cat flea, Ctenocephalides felis felis, is the main
species implicated in flea allergic dogs and cats. Ctenocephalides canis is also reported in some countries. Less
commonly, flea species that normally infest other
mammals and birds may be involved (Table 5.1). The
female adult flea is an obligate parasite and needs a
blood meal in order to produce eggs and, if the conditions on the host are ideal, it can lay up to 30–50 eggs
a day. Feeding fleas can live up to 100 days and lay as
many as 2000 eggs in their lifetime.
Fleas do not jump on and off animals, but tend to
live on the host. The eggs fall into the animals’ environ-
PROGNOSIS
The long-term prognosis was good, provided the owner
was able to maintain thorough long-term flea control on
all the animals in the house and it was possible to effectively manage the concurrent atopic dermatitis. There
may be flare-ups from time to time depending on the
allergen load.
AETIOPATHOGENESIS OF
FLEA ALLERGIC DERMATITIS
Although most cats and dogs have fleas at some point
or other, not all develop clinical signs associated with
hypersensitivity and it is probable that those that don’t
are not sensitized to the flea saliva. However, exposure,
either intermittent or continuous, to flea bites is a
predisposing factor in the development of the allergic
response, as is atopic dermatitis. Sensitization can occur
at any age and is usually lifelong.
Several allergenic proteins identified in flea saliva can
result in an individual becoming sensitized. The proteins
range from 12 to 50 kDa in molecular weight. Three
types of allergic responses – immediate, late-phase and
delayed-type responses – have been identified.
● Immediate-type hypersensitivity occurs within minutes
of the flea bite and is associated with mast cell
degranulation triggered by the chain of events following the binding of the allergen to the IgE.
● Late-phase reactions are associated with an influx of
inflammatory cells in response to the release of preformed and newly synthesized inflammatory mediators including cytokines and chemokines. Infiltration
of basophils, in particular, occurs in flea allergic dermatitis. Degranulation of basophils is associated with
basophil hypersensitivity. This occurs at 4–6 hours
after a flea bite.
● Delayed-type hypersensitivity is cell mediated; there is
an influx of lymphocytes and macrophages associated
with an interaction of several cytokines. This reaction
shows clinical signs about 24–48 hours following a
Table 5.1 Flea species and their main hosts
Flea species
Natural host
Ctenocephalides felis felis
Ctenocephalides canis
Pulex spp.
Echnidophaga galinacea
Spilopsysllus cuniculi
Archaeopyslla erinacei
Xenopsylla spp.
Cats and dogs
Dogs and cats
Humans
Birds
Rabbits
Hedgehogs
Small mammals
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Female fleas: Produce on average
30–50 eggs per day following a blood meal
Pupae: Can remain dormant for over
a year but may hatch after 5–9 days
under ideal environmental conditions
(i.e. temperature, humidity and
presence of host)
Eggs: May hatch into larvae on the
animal, or can fall off anywhere in
the environment
Larvae: Undergo 3 moults (L1–L2–L3)
before pupating
Figure 5.6 The flea life cycle.
ment during grooming or scratching, as they are nonadherent. The eggs hatch into the first larval stage,
which burrow deep into crevices, carpet pile, etc., as
they are photophobic and geotrophic. This stage feeds
on flea faecal pellets and other organic debris in the
environment. There are three larval stages and the third
stage transforms into the pupa. This stage is a cocooned
pre-emerged flea which is protected from environmental
insults (including parasiticidal agents) and will only
emerge if conditions ensure that its survival is more or
less guaranteed by the presence of a host. These conditions include carbon dioxide, warmth and air movements, which indicate the presence of a host.
TREATMENT OPTIONS
Multiple therapies are usually required in the early stages
of treatment of flea allergy dermatitis. They include
those that limit pruritus, deal with any secondary infections and those that specifically kill the flea and its
intermediate stages, both on the animal and in the
environment.
Flea control: Both the treatment of all animals in the
house and that of the environment should go hand in
hand, at least during the initial stages. The treatment
should be tailored to suit each case, depending on the
number of animals within the household, the ability of
the owner to use the products as indicated and the
cost.
Fipronil: Fipronil belongs to the phenylpyrazole family
and its mode of action is by blocking the pre- and postsynaptic transfer of chloride ions through the cell membrane, thus acting as an insect GABA antagonist. It has
both insecticidal and acaricidal activity. It is available in
spray and spot-on formulations and kills fleas within 24
hours, and tick and other insects within 48 hours. It is
combined with s-methoprene, an insect growth regulator which inhibits the development of immature stages
by mimicking the juvenile hormone.
Nitenpyram: Nitenpyram is used as a fast-acting, orally
administered insecticide, which kills fleas on the animal
as soon as 15 minutes after administration and has an
efficacy of up to 100% kill within 24 hours. It acts by
inhibiting specific nicotinic acetylcholine receptors. It is
a useful product to achieve quick kill in cases such as
this one, but is not designed to be used on its own. It
can, however, be combined with lufenuron to provide
integrated flea control.
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Imidacloprid: Imidacloprid belongs to the group of
chloronicotinyl compounds. Its mode of action is to bind
to the nicotinergic acetylcholine receptors on the postsynaptic region of the insect nervous system, thereby
stopping the acetylcholine from binding to the receptors. This results in the paralysis and death of the insect.
Imidacloprid is effective against adult fleas as well as
larval flea stages. It is available as a spot-on formulation
and the label permits weekly use of this product.
Selamectin: Selamectin is a semi-synthetic avermectin
with a broad spectrum of activity against endoparasites
as well as ectoparasites. It is an adulticide with larvicidal
and ovicidal properties. The product is absorbed percutaneously and then redistributed back to the cutaneous
tissue via the circulation.
Metaflumizone: Metaflumizone belongs to the semicarbozone group of compounds and is available as a
spot-on treatment against fleas. It is a sodium channel
blocker which prevents the flow of sodium ions across
the nerve cell membrane. This disrupts the transmission
of nerve impulses and the eventual result is death by
paralysis. For use in dogs, it is combined with amitraz to
provide action against fleas and ticks. On its own, it is
available for use in cats.
Pyriprole: Pyriprole belongs to the phenylpyrazole
group of compounds. It is a spot-on formulation that
has both insecticidal and acaricidal activity and its mode
of action is similar to that of fipronil (see above). It is
licensed for use against fleas and ticks in dogs only.
Pyrethrins: Pyrethrins are naturally occurring flea repellents and pyrethroids synthetic ones. A combination
of permethrin, a pyrethroid and imidacloprid has a
veterinary licence for use in dogs (contraindicated in
cats).
Environmental control
Insect growth regulators: Insect growth regulators
such as fenoxycarb, methoprene and pyriproxyfen are
analogues of the juvenile hormone, which allows pupation when its concentration falls. Excessive concentrations prevent metamorphosis and thereby break the life
cycle. These products are available as environmental
aerosol sprays combined with an adulticide for effective
control and in the case of methoprene as a spot-on
treatment for the animal combined with fipronil.
Insect growth inhibitors such as lufenuron inhibit the
synthesis of chitin, thus preventing successive larval
moults.
Summary of environmental treatment: Aerosol
sprays, pump sprays and foggers are available, which
generally contain permethrin plus an insect growth
inhibitor or regulator.
● Treat all the areas where the pet might visit (the
whole house, cars, baskets, under beds, etc.).
● Clear out organic debris from the outside environment, as this can be a source for re-infestation even
in the winter months.
● In cases where there is a severe infestation two treatments 2 weeks apart are necessary to eliminate newly
hatched fleas.
Delivery methods for topical treatment of pets:
● Spot-on formulations
● Spray formulations
● Shampoos
● Dips
● Flea collars
● Systemic products.
Treatment in this case
In this case the long-term treatment also included
allergen-specific immunotherapy for the management
of the atopic dermatitis.
NURSING ASPECTS
Many clients will discuss their concerns with the
nurse, or lay staff, rather than the vet. They
should be able, tactfully, to reassure them and
give them the correct advice. A good grasp of the
flea life cycle, together with knowledge of the
range of flea products on the veterinary market
and their modes of action, is the key to giving
correct advice to the client. Flea control within
an individual household should be tailored to its
needs. Many owners who are registered with the
practice will call in to buy products during the
summer months when the problem is most
apparent. It is at this point, when they recognize
the problem, that the client is most receptive to
advice on supplementing topical therapy with
environmental treatment.
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CLINICAL TIPS
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Never believe an owner when they say they use
routine flea control, unless your records show
that enough products have been bought from
the practice to regularly treat all the cats, dogs,
rabbits and ferrets in the house. Sometimes,
because of the expense, clients will only treat
obviously infested animals within the house, but
not all of them.
Never dictate to the client which product they
should use. For best compliance, involve the
client in the decision making, so that the owner
accepts the time and the cost involved.
When considering a diagnosis of FAD, failure to
find evidence of fleas does not rule out flea
allergic dermatitis.
The environment was treated twice 2 weeks apart
with a spray containing permethrin and methoprene.
The cats and the dog were treated with a spot-on solution containing fipronil and methoprene every 2 weeks
for four occasions (extra-label use), then every 3–4
weeks. At the start of the treatment, all the animals
(three in-contact cats and the dog) were given 3 days
of nitenpyram orally to ensure quick kill and reduction
in the flea population as soon as possible.
Antibiotic treatment: In this case cefalexin (15 mg/kg
b.i.d.) was prescribed for 3 weeks, without any antipruritic treatment. At the end of the course, clinical examination and tape-strip preparations did not reveal any
bacteria and antipruritic treatment was started (see
below).
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Suspect FAD as a flare factor in atopic dogs
in whom the pruritus was previously well
controlled.
During history taking, always find out about incontact animals, including visiting animals, dog
walkers, visits to grooming parlours, boarding
kennels/catteries, etc. Veterinary surgeries can
also be the source of infestation, for instance
in cats that are normally kept indoors but
occasionally visit the practice.
The concentration of the product on the skin is
reduced by swimming, shampooing and
frequent wetting of the hair.
hours of prednisolone was prescribed for 7 days, after
which it was reduced to alternate-day treatment. After
4 weeks it was reduced to 0.5 mg/kg on alternate days
and stopped once the dog reached the maintenance
phase of the allergen-specific immunotherapy.
FOLLOW-UP
Long-term flea control was maintained on all the animals
in the household. The pedal pruritus persisted even
after 1 year on allergen-specific immunotherapy and
so 0.1 mg/kg of prednisolone was administered as a
concurrent treatment. The dog has been successfully
managed on this combination at the time of writing. It
is possible that this dog has a concurrent adverse food
reaction as well, but the owner was unwilling to repeat
a diet trial.
Antipruritic treatment: Given the severe pruritus and
its effects on the animal’s welfare, 1 mg/kg every 24

Flea allergic dermatitis

Transcription

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