Hyphae, pseudohyphae, yeasts, spherules, spores, and more: A review on the morphology and pathology of fungal and oomycete infections in the skin of domestic animals.

Fungi are among the most common infectious agents affecting the skin of animals. The skin can serve as a port of entry for fungal infections, which can eventually become disseminated. In some regions of the world, oomycetes, such as Pythium and Lagenidium, are also responsible for a significant number of severe cutaneous infections. Histologic evaluation of fungal morphology, including size, shape, septation, branching, and budding characteristics, combined with the distribution of inflammatory infiltrates within different skin layers can potentially identify etiologic agents, guiding selection of antifungals and additional diagnostics. Fungal infections of the skin surface are typically caused by Malassezia and rarely Candida, with opportunistic fungi also capable of colonizing the skin surface, especially when the barrier is broken. Folliculocentric infections, caused by dermatophytes, result in mild to severe inflammation and can occasionally penetrate deep into the skin. A wide range of fungi, including agents of hyalohyphomycosis, phaeohyphomycosis, and dimorphic fungal infections, as well as oomycetes, result in nodular cutaneous and subcutaneous lesions. With the occasional exception of dimorphic fungi, fungal speciation often requires cultures performed on fresh tissues. However, molecular techniques such as pan-fungal polymerase chain reaction on paraffin blocks is becoming an increasingly useful tool to distinguish between cutaneous fungal pathogens. This review focuses on describing the clinical and histologic features of the most common fungal and oomycete infections affecting the skin of animals, divided according to distribution patterns of lesions and fungal or oomycete morphology.

Histology, prevalence, and environmental sources for pulmonary silicates depositions in domestic and wild animals.

The source and significance of pulmonary silicate crystals in animals and people are poorly understood. To estimate the prevalence and characterize the pulmonary crystalline material in animals from St. Kitts, tissue samples from dogs, horses, cattle, sheep, goats, pigs, chickens, mongooses, and monkeys were examined by light microscopy, scanning electron microscopy with energy-dispersive x-ray analysis (SEM/EDXA), and x-ray diffraction. Crystalline material was seen in 201 of 259 (77.6%) lung samples as perivascular and interstitial accumulations of heterogeneous crystalline particulate material, free or within macrophages (silicate-laden macrophages [SLMs]), mostly lacking evidence of chronic inflammation or fibrosis. The crystalline material was birefringent, basophilic on acid-fast, and composed of silicas on SEM/EDXA. Mongooses (100%) and monkeys (98%) had the highest prevalence of SLM, followed by cattle and chickens. Lesions were graded on a 3-point scale based on the histologic location and extent of silicates and SLM and were significantly more severe in mongooses (median = 3) than in monkeys (median = 2), dogs (median = 2), and chickens (median = 1). On EDXA, the crystalline material from lungs, air, and topsoil was composed of silicon, oxygen, aluminum, and iron, with a particulate matter size between 2.5 and 10 µm. We hypothesize Saharan dust, volcanic ash, topsoil, and rock quarry dust are potential sources of siliceous dust inhalation and SLM accumulations lacking chronic inflammation (silicosis); dust generation may be potentiated by road vehicle or wind suspension. Future investigations are warranted on the role of silicate inhalation and respiratory comorbidities in people, with monkeys, mongooses, or chickens serving as possible sentinels for exposure.