Pathology Case of the Month - Big Brown Bat

Gross Findings: On external examination, there were no significant findings.

Histopathological Findings: At the junction of the haired skin and oral mucosa, there is a focal ulceration. The bed of the ulcer is lined by low to moderate numbers of free red blood cells. Subjacent to the ulcer, a hair follicle (suspect vibrissae) is plugged with large numbers of cross sections of mites measuring up to 40 μm in diameter. Mites have a thin, eosinophilic, chitinous exoskeleton, a hemocoel, digestive and reproductive tracts, and striated muscle. Jointed appendages are also observed. Moderate numbers of lymphocytes, fewer macrophages, and scattered eosinophils are present in the wall of and surround the hair follicle.

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Morphologic Diagnoses:

1. Folliculitis and perifolliculitis, lymphohistiocytic and eosinophilic, focal, mild, subacute with intralesional mites
2. Ulcerative dermatitis, focal, mild, acute with hemorrhage

Etiology: Demodecid mite. There are currently 122 validated species of demodecid mites within the family Demodecidae with 106 in the genus Demodex. The greatest diversity of Demodecidae is described for bats with 5 genera and 27 species. While there are reports of demodecid mites in big brown bats, there are no validated Demodex spp. for this species.

Distribution: Found on all continents outside of the polar regions.

Host range: Found in most orders of mammals with high host specificity.

Life cycle: Most Demodex spp. are obligate parasites and live their entire life cycle on the host. Mites inhabit hair follicles or sebaceous glands as part of normal fauna of the host.

Transmission: Usually occurs during nursing by direct contact between dam and offspring.

Disease: Infections are typically asymptomatic even with a high parasite burden. Demodecosis (formerly demodicosis) occurs rarely and more commonly in immunosuppressed hosts. Disease can be localized or generalized.

Pathology: Gross lesions include alopecia, erythema, comedones, scales, and crusts. Microscopic lesions include hyperkeratosis, folliculitis, follicular pigmentary incontinence, and intrafollicular mites. When follicles become plugged with mites and keratin, and bacteria proliferate, the inflamed follicle can rupture resulting in granulomatous or pyogranulomatous dermatitis. In severe infections, inflammation can spread to the subcutis and result in lymphadenitis and septicemia.

Diagnosis: Microscopic detection of mites in a deep skin scraping with mineral oil from affected area; histopathology; PCR.

Public health concerns: No known human health concerns. Mites are host specific and cannot be transferred across species. Therefore, no zoonotic potential exists.

Wildlife population impacts: Most infections are incidental/asymptomatic, and it is not thought that infection with Demodex spp. has significant impacts on wildlife populations.

Management: No current management strategies for control of Demodex spp. are in place.

References:

Ginn PE, Mansell JEKL, Rakich PM. 2007. Skin and appendages. In: Jubb, Kennedy & Palmer's Pathology of Domestic Animals, Vol. 1, 5th Ed., Maxie MG, editor, Saunders Ltd., New York, New York pp. 724–727.

Hargis AM, Myers S. 2017. The integument. In: Pathologic Basis of Veterinary Disease, 6th Ed., Zachary JF, editor, Elsevier, St. Louis, Missouri pp. 1084–1086.

Izdebska JN, Rolbiecki L. 2020. The biodiversity of demodecid mites (Acariformes: Prostigmata), specific parasites of mammals with a global checklist and a new finding for Demodex sciurinus. Diversity: 12, 261:1–29.