Insect Hypersensitivity Flashcards
Eutrombicula (Trombicula) alfreddugesi (North American chigger) and Neotrombicula (Trombicula) autumnalis
Adult is scavenger living on decaying vegetable material, orange red and size of pin head. Life expectancy 10 months producing likely 1 generation per year. Eggs layer in moist ground and hatch to six-legged red larvae that are parasitic and feed on animals. They drop to the ground and become nymphs and then adults, completing the life cycle in 50-70 days but adult female mites may life >1yr.
Eutrombicula (Trombicula) alfreddugesi (North American chigger) and Neotrombicula (Trombicula) autumnalis
Diagnosis and Treatment
Affect points of contact: legs, feet, head, ears, centrum. Severe irritation and intense pruritic papulocrustous eruption but also non-pruritic papules, pustules, and crusts. Secondary scaling and alopecia. Mites may be found in and around cats’ ears but easily distinguished from Otodectes by intense orange-red color and tight adherence to the skin, 500um. Remove and place immediately in mineral oil to prevent their escape.
Seasonal in late summer/fall. History of contact in woods and fields.
Histopath: varying degrees of superficial perivascular dermatitis (spongiotic or hyperplastic) with numerous eosinophils
Tx: topical spot-on parasiticides (1-2 applications), parsiticidal dips, or topical otic with parasiticide (Tresaderm). Systemic corticosteroids for 2-3 days for itch if present. Reinfestation expected if allowed to roam same environment. 0.25% fipronil spray blocked reinfestation in 15 of 18 dogs in one study, 3 treated cats reinvested within 7-10 days.
Walchia Americana
Mite of squirrels and small rodents in SW and E United States and reported in the cat.
Larvae live on surface of skin, salivary secretions allow them to feed on tissue liquids of host. A walled-off channel is formed on the skin surface as a host reaction that attempts to isolate the parasite. Larvae detach and enter decaying wood for a quiet period. Active nymphs emerge and forage, pass through imagochrysalis quiet stage, and emerge as adults.
Feed on the Collembola insect (spring tail). Adults lay many eggs which hatch to parasitic larvae.
Prefers ventrum but also found on ears and back.
Walchia Americana Diagnosis and Treatment
Lowenstine et al. Reported in cat: lesions on ventral trunk, medial legs, interdigital spaces, palpable lesions but hair had to be parted carefully to see them easily.
Nodular thickened skin, surface cracked and scaly, with moist serous yellow exudate. Paws swollen and claws cracked (cat shook its feet as if it had stepped in something noxious). Close inspection had non pruritic papules (0.1-0.3cm) with a few wheals and flares.
Skin scrape revealed few mites but a skin biopsy contained many mites.
Histopath: varying degrees of intraepidermal pustular to vesicular dermatitis, marked hyperkeratosis, mite segments within epidermis, numerous eosinophils and mast cells
Tx: insecticidal products for mites and abx for secondary infection has good response in 10 days
Straelensia cynotis
Chigger in Spain, Portugal, and France. Most common in outdoor dogs in late summer through early autumn. Higher incidence in female dogs in 1 study.
Popular to nodular dermatitis most commonly of head and dorsum but may be generalized, lesions typically not pruritic but may be tender.
Skin scraping negative
S. Cynotis lodges itself in the follicular Ostia where it injects its saliva damaging the hair follicle, larval mite found in follicle on biopsy
Histo: pseudoepitheliomatous follicular hyperplasia and perifollicular dermal mucinosis
Tx: treatment is not seeded b/c parasite does not complete life scale on the dog but self-cure slow between 2-12 months, treatment with ivermectin and fipronil will reduce mite numbers but may not be curative
