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Equine Nodular Dermatitis Associated with Alternaria tenuis Infection

1978; SAGE Publishing; Volume: 15; Issue: 6 Linguagem: Inglês

10.1177/030098587801500611

1544-2217

Bernadette Coles, Danielle R. Stevens, Robert L. Hunter,

Plant Pathogens and Fungal Diseases

Alternaria tenuis is a commo nly isolated saprophytic fungus wh ich occasiona lly has been found as an op po rtunis tic inva der in compromised hos ts [1, 2]. A. tenuis was isolated fro m skin nodules on a horse and the histologic evidence implicated this fung us as the ca usa tive age nt. The horse was a 7-yea r-old grey qu art erhor se cross which was first presented with dermatitis clin icall y diagnosed as de rmatophilosis. This con dition responded to top ical treatment. T hree months later th e hor se had randoml y distri buted skin nod ules on the head, ches t and legs. T he nodules were from 0.5 to 2 centime ters in diameter and up to I centimeter in depth (fig . I). The horse was clinically healthy and un affected by the condition . One nodule was biop sied . The fresh tissue was culture d on Sabouraud's dextrose agar and inc ubated at 25° C and 37° C. There was no growth at 37° C but fungal colonies identified as A lternaria were isola ted on plates incubat ed at 25° C. Skin sectio ns stai ned with hem at oxylin and eosin (HE) contained a I-cent imeter discrete, nonencap sulat ed , ova l, hypercellular area in the dermis. Adnexal un its were irregularly separated an d distorted an d th e epithel ium was focally convex and ulcerated. T he hypercellu lar area was compose d of a conflue nt array of micronodules that typically contained three d istinct zones: a centra l pool of neutro phils, a middle zone of epi the lioid cells, and a periphera l zone of lymphocytes (fig. 2). T he neutrophil-rich cen ter also contained nu merou s 6to 12-m icrom eter ovoi d no n-sta ining structures th at often contained an eccentrically placed 4to 8microm eter eos ino philic bod y. These structures were interpreted as fungal hyph ae. A few multinucleat ed giant cells and plasma cells were evident in the inflammatory nodules. T he granulomas were part iall y separated by existing collagenous bund les foca lly, but fib ropl asia, hem orrhage and necrosis were not pre sent. Grocott's methenamine silver-stai ned sections showe d myriad s of hyphae an d chlamydospores. The branching hyph ae were septate at irregul ar intervals, had non -p ar allel wa lls, an d were 6 to 12 micrometers in diam eter. To confirm th at Alternaria was the fungus in the histological sections, ano ther nodule was excised . Ha lf was fixed in formalin for histologic examination and half unfixed for microbiology. T he fresh tissue was cu ltu. ~ rl on Sabouraud's dextrose agar and incubated at 25° C. Alternaria was aga in isolar:' .ia d the culture was sent to the National Animal Disease Lab oratory, Ames, low , .or confirma tion an d speciation. It was identified as A lternaria tenuis. Histologic find ings were the same as for the first sections. A du al infection with Dermatophilus congolensis and A. alternata has been rep orted in a whiteta iled deer [3]. T he gross lesions were characteristic of dermatophilosis but bot h organisms were isolat ed on culture and both were demonstrated histologically. It was concluded that the Alternaria in fection was secondary to the Dermatophilus. It is possible th at A. tenuis was int roduced during th e time our horse had the dermatophilosis-like lesions an d became established in th e dermi s. No atte mpt was made to isolate the causative agent associat ed with the initial derma titis so it is possib le the condition was not caused by D. congolensis. W ha teve r the cau se of the primary dermatitis, the nodular dermatitis that followed thi s condition was caused by an infection by A. tenuis.