Signalment:  

<1 month-old, female white-tailed deer fawn, Odocoileus virginianus. This young fawn was found weak and emaciated in the summer on a farm in Connecticut. Due to concerns about the appearance of its skin, it was shot and submitted for necropsy.

Gross Description:  

The fawn was in poor body condition with absence of subcutaneous and visceral fat stores. There were extensive areas of alopecia and multiple red dermal abrasions on all four legs. Innumerable, firm, 1-2 mm thick, brown crusts that entrapped hair across multiple follicles were disseminated on the skin surface of the entire body, particularly on the dorsum and dorsolateral aspects of the trunk and on the face. 

Histopathologic Description:

Haired skin: Covering an epidermis that is frequently ulcerated are thick crusts spanning multiple hair follicles and composed of layers of keratin with retained nuclei (parakeratosis), abundant hyaline eosinophilic (proteinaceous) material, accumulations of degenerate neutrophils (intracorneal pustules) and necrotic debris, entrapped hairs and small areas of hemorrhage. Throughout the crusts and extending into inflamed and frequently ruptured hair follicles (furunculosis) are innumerable tangled, branching, 1-2 μm wide filamentous structures composed of parallel rows of coccoid bodies. More amorphous colonies of coccoid bacteria are also present. In the remaining epidermis there is mild diffuse acanthosis and areas of spongiosis that also involve the follicular epithelium. Large numbers of neutrophils fill follicular lumina, disrupt follicular epithelium and extend into the surrounding dermis from areas of ulceration and furunculosis. Also present in the dermis are smaller numbers of macrophages, lymphocytes and plasma cells. 

Gram Stain (not submitted): The filamentous and coccoid forms of bacteria stain gram-positive.

Morphologic Diagnosis:  

Skin: Severe, exudative, crusting and neutrophilic dermatitis and folliculitis with ulceration, furunculosis, parakeratosis, and filamentous and coccoid bacteria, consistent with Dermatophilus congolensis. 

Condition:  

Dermatophilus congolensis

Contributor Comment:  

The gross appearance and histopathologic findings in this deer fawn were typical of dermatophilosis, caused by the Gram-positive actinomycete Dermatophilus congolensis. Although D. congolensis has a worldwide distribution, disease has historically been more common in tropical and subtropical climates, especially during prolonged periods of rain.(2,5) Dermatophilosis, also termed cutaneous streptothricosis, cutaneous actinomycosis, rain scald, rain rot, lumpy wool, and strawberry foot rot, has been reported in many species. Among domestic animals, it is most commonly seen in cattle, sheep, and goats, with horses less frequently affected.(1-3) The disease is also zoonotic, and spread from white-tailed deer to humans has been described.(3)

The first reports in white-tailed deer were from the New York state region in the 1970s, along with an isolated case in a fawn from South Carolina.(3,5) A recent survey of bacterial and parasitic dermatologic diseases in white-tailed deer from 1975-2012 found a 0.7% incidence (19/2569) of dermatophilosis.(4) At 21.6% of the cases, this was second only to demodicosis in frequency of bacterial or parasitic skin disease among deer in the Southeastern United States.(4) As in initial reports in twin fawns,(5) lesions most commonly involved the head/face and limbs and consisted of exudation and crusting, alopecia, ulcers and erosions.(4) In the current case, the lesions were particularly severe on the face but were also generalized. It has been hypothesized that a predilection for the rostrum in fawns could be due to transmission from an infected dam during nursing.(5) Dermatophilosis has been found in fawns as young as 2 weeks old,(5) and the study by Nemeth et al. found significantly more juveniles affected (63%) than adults.(4) Debilitation and emaciation in the fawn in this case were attributed to the severity of the dermatophilosis, which has been reported as a cause of death in other affected fawns.(3,4)

The diagnosis of dermatophilosis in this case was based on the presence of thick lamellated crusts in association with characteristic filaments of parallel rows of Gram-positive coccoid bodies (railroad track configuration) formed from transverse and longitudinal septation.(2) A combination of skin damage and prolonged moisture are generally required for establishment and spread of infection, as the organism is minimally invasive in intact epidermis, and wet conditions are needed for activation of coccoid bodies into motile zoospores.(2) Ectoparasites can be a cause of trauma and may also act as mechanical vectors to spread the infection.(2) Although usually confined to the epidermis and outer root sheaths of hair follicles, there are rare reports of deeper skin or lymph node involvement.(1,2) Ulceration and furunculosis were prominent features in the current case, but there was no evidence of spread to lymph nodes or other tissues. 

JPC Diagnosis:  

Haired skin: Epidermitis and folliculitis, suppurative, diffuse, severe, with epithelial hyperplasia, parakeratotic hyperkeratosis, and numerous filamentous bacteria. 

Conference Comment:  

The contributor gives an exceptional overview of dermatophilosis, a distinctive disease most often observed in production animals. Buried within the pathogenesis of infection with this gram-positive, actinomycete bacterium is a glimpse of the skins effectiveness in providing a barrier to disease. The combination of hair, surface lipid, and stratum corneum equate to an insurmountable barricade for Dermatophilus in the normal state. However, with even minor disruptions of the hosts defenses combined with the moist conditions required to activate the zoospores, the bacteria incite a fulminant infection which contributes to significant meat, milk and wool production loss throughout the world.(2)

Dermatophilus produces exoenzymes and has an affinity for a low carbon dioxide environment which facilitates its colonization and tissue-specificity for the epidermis. The host responds to infection with cornification of keratinocytes and invasion of neutrophils effectively walling off the bacteria from the dermis. The progenitor cells of the follicular epithelium then propagate, forming a new layer of epidermis.(2) Subsequent invasion of this new layer followed by repetitive and unsuccessful defense responses of the host creates the thick laminar and parakeratotic crusts with entrapped hair follicles which are so characteristic to this bacterial infection and nicely exemplified in this case. 

References:

1. Byrne BA, Rand CL, McElliott VR, Samitz EM, Brault SA. Atypical Dermatophilus congolensis infection in a three-year-old pony. J Vet Diagn Invest. 2010;22:141-143.

2. Ginn PE, Mansell JEKL, Rakich PM. Skin and appendages. In: Maxie MG, ed. Jubb, Kennedy, and Palmer's Pathology of Domestic Animals. Vol. 1. 5th ed. Edinburgh, UK: Elsevier Limited; 2007:681-682.

3. Gordon MA, Salkin IF, Stone WB. Dermatophilus dermatitis enzootic in deer in New York state and vicinity. J Wildl Dis. 1977;13(2):184-190. 

4. Nemeth NM, Ruder MG, Gerhold RW, et al. Demodectic mange, dermatophilosis, and other parasitic and bacterial dermatologic diseases in free-ranging white-tailed deer (Odocoileus virginianus) in the United States from 1975 to 2012. Vet Pathol. 2014;51(3):633-640.

5. Roscoe DE, Lund RC, Gordin MA, Salkin IF. Spontaneous dermatophilosis in twin white-tailed deer fawns. J Wildl Dis. 1972;11(3):398-401.

Click the slide to view.

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2-1. Haired skin

2-2. Haired skin

2-3. Haired skin

2-4. Haired skin

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