Dermatitis associated with microfilariae of a nematode of the superfamily F
ilarioidea was diagnosed in 10 dogs from the western United States. Clinica
lly, lesions were single or multiple papules and plaques with alopecia, sca
rring, erythema, ulceration, or crusting. Eight dogs had lesional pruritus.
Microscopically, there was perivascular, periglandular, to interstitial in
flammation, with many eosinophils and/or plasma cells, and scarring affecti
ng the dermis and subcutis. Microgranulomas containing microfilaria were se
en in six dogs. Microfilariae were noted in microgranulomas or free in the
dermis or subcutis, but not in vessels. In one case, an adult female nemato
de emerged from a biopsy sample that was placed in physiologic saline. Stud
y of this nematode revealed that it was a filarioid of the family Onchocerc
idae; it was identified as Acanthacheilonema sp. (syn: Dipetalonema). Antig
en tests of five dogs were negative for Dirofilaria immitis. The Knott test
s and/or filter tests of nine dogs were negative for microfilariae. An indi
rect fluorescence antibody test of one dog was also negative for D. immitis
. One dog was not evaluated for microfilariae.