JPC SYSTEMIC PATHOLOGY
INTEGUMENTARY SYSTEM
AUGUST 2022
I-B01

 

Signalment (JPC# 1313232):  Less than 1 month old, female, white tailed deer fawn

 

HISTORY:  This young fawn was found weak and emaciated in the summer on a farm in Connecticut.  Due to concerns about appearance of skin, animal was euthanized. 

 

HISTOPATHOLOGIC DESCRIPTION:  Haired skin:  Diffusely, the epidermis is covered by a 1.2 mm thick, laminated serocellular crust. The serocellular crust is composed of abundant alternating orthokeratotic and parakeratotic hyperkeratosis, serum, entrapped hair shafts, and linear bands of necrotic neutrophils and eosinophilic cellular and karyorrhectic debris (intracorneal pustules).  Multifocally, within the serocellular crust and infiltrating follicular epithelium and lumina are innumerable 1-2 um, paired bacterial cocci (zoospores) haphazardly arranged in rows and forming long branching filaments.  Diffusely, the epidermis is markedly hyperplastic, characterized by acanthosis and elongate broad rete ridges.  Keratinocytes, predominantly in the stratum spinosum, are often swollen with increased clear space (intracellular edema).  Throughout the less affected epidermis there are few transmigrating neutrophils, lymphocytes and histiocytes.  The epidermis is occasionally lost (ulceration), replaced by cellular and karyorrhectic debris with subjacent fibroblasts and small caliber blood vessels (granulation tissue). Within the superficial dermis subjacent to the serocellular crust, follicles are distended and occasionally effaced by many viable and necrotic neutrophils admixed with eosinophilic cellular debris, necrotic follicular epithelium, and fragmented hair shafts (folliculitis and furunculosis).  Multifocally, the follicular epithelium has one of the following changes: is necrotic, attenuated, or lost.  Multifocally, the superficial dermis is infiltrated by perifollicular and periadnexal aggregates of macrophages, lymphocytes and plasma cells with fewer neutrophils. Superficial dermal blood vessels are congested.

 

 

MORPHOLOGIC DIAGNOSIS:  Haired skin:  Epidermitis, dermatitis, folliculitis, and furunculosis, suppurative, diffuse, severe, with marked epithelial hyperplasia, parakeratotic hyperkeratosis, intracorneal pustules, ulceration and coccoid zoospores with branching filaments, etiology consistent with Dermatophilus congolensis, white tail deer (Odocoileus virginianus), cervid.

 

ETIOLOGIC DIAGNOSIS:  Cutaneous dermatophilosis

 

CAUSE:  Dermatophilus congolensis

 

SYNONYMS:  Cutaneous streptothricosis, rain scald; rain rot; lumpy wool; strawberry foot rot; cutaneous actinomycosis; Kirchi; Gasin-Gishu; Senkobo disease; Drodo-Boka; Savi; Ambarr-Madow; (“mycotic dermatitis” is a misnomer)

 

GENERAL DISCUSSION:

• Gram-positive, filamentous, branching, facultative anaerobic bacteria (order Actinomycetales) that cause an acute, subacute, or chronic superficial exudative dermatitis
• Unusual life cycle where coccoid bodies germinate to produce branching filaments (may be > 5 um wide) à undergo transverse and longitudinal septation to produce parallel rows or columns of coccoid bodies (“train track” or “stacked coin” appearance); coccoid bodies are dormant until wet conditions, then become motile zoospores
• Most common in cattle, goats, sheep, and horses; rare in pigs and small animals
• Most common in hot humid areas with heavy prolonged rainfall
• Usually a secondary invader; can co-infect poxviral lesions; damage to the hide may predispose to myiasis and secondary bacterial infections
• Zoospores survive in crusts for approximately 42 months

 

PATHOGENESIS:

• Multiple factors involved in pathogenesis, which is poorly understood (not able to be reproduced experimentally)
• Two critical factors:
  • Trauma to skin (ectoparasites, shearing, thorny pastures, etc.) – zoospores cannot penetrate hair, stratum corneum, etc.; require breaks in the skin
  • Prolonged moisture – needed for the activation, proliferation, and spread of the zoospores
• Other implicated factors include genetics, skin color (light-skinned areas more susceptible), concurrent diseases, and infection with the Amblyomma variegatum or Boophilus decoloratus tick
• Once in the epidermis: Zoospores germinate to filaments -> invade viable epidermis and outer root sheaths -> keratinocytes at sites of invasion cornify -> neutrophils accumulate below and migrate into epidermis -> separates epidermis from dermis -> neutrophils inhibit further invasion -> new epidermis formed -> new epidermis invaded -> cycle begins again, forming laminar and parakeratotic crusts

 

TYPICAL CLINICAL FINDINGS:

• Acute lesions are painful but rarely pruritic
• Begin as patches of erythema progressing to papules/pustules and then coalescing large, oval, domed scabs
• Incubation period averages 2 weeks, but can range from 1 day to a month

 

TYPICAL GROSS FINDINGS: 

• Proliferative, exudative dermatitis producing raised, alopecic, erythemic, and sometimes papillomatous lesions covered by a thick, yellow-brown, keratinized crust / scab on any area of the body
• Early lesions are erythemic patches, followed by papules and pustules
• Coalescing exudative pustules that mat large groups of hairs together (“paintbrush” lesions)
• Underneath the removed scales there is little or no pus, and the epidermis is often moist and erythematous
• In cattle: Lesions begin on the dorsal midline and extend laterally to flanks, thoracic wall, shoulders, neck, axilla, and inguinal areas
• Subcutaneous and lymph node granulomas can occur; oral lesions rarely develop

 

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Palisading crust of thick, laminar, alternating layers of orthokeratotic-parakeratotic hyperkeratosis, serous fluid, degenerate inflammatory cells, and necrotic debris with varying degrees of perifolliculitis-folliculitis, intraepidermal pustular dermatitis, or hyperplastic superficial perivascular dermatitis
• Narrow, branching filaments with transverse and longitudinal septation that form parallel rows of cocci in superficial layers of the skin, within crusts, and within hair follicles

 

ADDITIONAL DIAGNOSTIC TESTS:

• Histopathology is characteristic
• Culture is difficult
• Cytologic exam of direct smears reveals parallel chains of cocci in “railroad track” configurations
• RT-qPCR assays have recently been validated for the detection of congolensis

 

DIFFERENTIAL DIAGNOSIS:

Proliferative/Hyperkeratotic Skin Lesions in Cattle:

• Dermatophytosis (Trichophyton, Microsporum spp.): Chained or disassociated arthrospores and hyphae can be located in the stratum corneum, hair follicles, and hair shafts; "domino effect"- serially damaged hair follicles damaged by necrotizing and pyogranulomatous folliculitis suggests dermatophytosis
• Ectoparasitism: Demodex, Psoroptes spp.- Elongate mites, measuring 40 x 250-300 um (shorter and longer forms exist), and keratinous debris plugging follicles; variable numbers of mites
• Pustular dermatitis (impetigo; subcorneal pustular dermatosis; pemphigus foliaceus): Pustules present with varying inflammatory cells, zoospores not present
• Viral dermatitis: Contagious pustular dermatitis (parapoxvirus); lumpy skin disease (capripoxvirus): intracytoplasmic, eosinophilic inclusion bodies, located within epithelial cells
• Photosensitization: Parakeratotic hyperkeratosis, acanthosis, apoptotic cells scattered through the dermis, with dermal hyperemia, edema, and perivascular mononuclear cellular infiltrate
• Zinc-responsive dermatosis: Parakeratotic hyperkeratosis extending into hyperplastic follicular infundibula is characteristic

 

COMPARATIVE PATHOLOGY:

• Sheep: Variable location; scale crusts in woolly skin are often pyramidal because the lesion spreads laterally as the crust is formed and may be up to 3 cm thick (“lumpy wool disease”);  on the extremities known as “strawberry foot rot”; concurrent infection with contagious ecthyma and pox may occur
• Horses: Lesions are located on the dorsal aspect of the body and look as if large drops of liquid have scalded the skin (“rain scald”); uncommonly associated with pastern dermatitis
• Calves and foals: Muzzle, head, neck, poll, and ears
• Cats: All reported lesions have been subcutaneous or extracutaneous infections and consisted of draining nodules involving the area of the popliteal lymph node, subcutaneous tissue of  the paw, and serosal surface of the bladder
• Goats: Head, dorsal midline, legs (grease heel), and ventral abdomen, often seen in conjunction with parapoxvirus (contagious ecthyma)
• Camels: affects rump, neck, flanks, and lower abdomen (legs are generally spared). Hyalomma spp. tick may play an important role in the pathogenesis in camelids
• Dogs; pigs: Rare
• Tortoises, turtles: chelona (now named Austwickia chelonae)
• Crocodile: Dermatophilus spp.
• Captive bearded dragons: Is associated with ranavirus infection
• Deer: Face, ears and distal limbs
• Cases have been reported in camels, mules, donkeys, zebras, giraffes, Thompson’s gazelles, woodchucks, striped skunks, South American sea lions, raccoons, hedgehogs, gerbils, foxes, ground squirrels, beluga whales, seals, owl monkeys, captive polar bears, chamois, tortoises and Australian bearded lizards

 

References:

1. AuFox EE, Frank LA, et al. The prevalence of Dermatophilus congolensis in horses with pastern dermatitis usuing PCR to diagnose infection in a population of horses in Southern USA. Vet Dermatol. 2018; 29(5):435.
2. Conley KJ, Shilton CM. Crocodilia. In: Terio K, McAloose D, Leger J, eds. Pathology of Wildlife and Zoo Animals, San Diego, CA: Elsevier 2018: 860-861.
3. Howerth EW, Nemeth NM, Ryser-Begiorgis MP. Cervidae. In: Terio K, McAloose D, Leger J, eds. Pathology of Wildlife and Zoo Animals, San Diego, CA: Elsevier 2018: 165.
4. Mauldin EA, Peters-Kennedy J. Integumentary System. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. 6th ed. Vol. 1. Louis, MO: Elsevier; 2016: 632-634.
5. Nemeth NM, Ruder MG, Gerhold RW, Brown JD, 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.
6. Origgi FC. Lacertilia. In: Terio K, McAloose D, Leger J, eds. Pathology of Wildlife and Zoo Animals, San Diego, CA: Elsevier 2018: 884-885
7. Rodriguez CE, Duque AMH, Steinberg J, Woodburn DB. Chelonia. In: Terio K, McAloose D, Leger J, eds. Pathology of Wildlife and Zoo Animals, San Diego, CA: Elsevier 2018: 845.
8. Welle MM, Linder KE. The Integument. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022: 1167-1168.

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