JPC SYSTEMIC PATHOLOGY
Signalment (JPC #1313232): Ox
HISTORY: This ox had raised, alopecic skin lesions covered by thick crusts
HISTOPATHOLOGIC DESCRIPTION: Haired skin: Diffusely, the mildly hyperplastic and multifocally ulcerated epidermis is overlain by a 1 mm thick serocellular crust that entraps fragmented hair shafts and sebaceous glands. The crust is composed of laminations of abundant orthokeratotic and parakeratotic keratin debris (hyperkeratosis), fibrin, numerous viable and degenerate neutrophils, and eosinophilic cellular and karyorrhectic debris (intracorneal pustules). Superficially within the crust there are numerous 1-2 um, paired bacterial cocci (zoospores) haphazardly arranged in rows and forming long, branching filaments, admixed with large colonies of 2 um diameter coccal zoospores. Diffusely, the underlying epidermis is mildly hyperplastic, with acanthosis and short rete peg formation. Multifocally the epidermis is ulcerated, and the subjacent dermis contains hemorrhage and edema. Multifocally within the superficial dermis, surrounding hair follicles, there are reactive fibroblasts and low numbers of macrophages, neutrophils, lymphocytes, and plasma cells admixed with variable amounts of hemorrhage and multifocal mineralization. Multifocally, superficial dermal vessels are lined by hypertrophied endothelium and are occasionally occluded by dense fibrillar to beaded, eosinophilic material (fibrin thrombi) which rarely contain endothelial lined slit-like channels (recanalization).
MORPHOLOGIC DIAGNOSIS: Haired skin: Epidermitis, exudative and proliferative, chronic, diffuse, severe, with ulceration, fibrin thrombi, and superficial coccoid zoospores and branching filaments, etiology consistent with Dermatophilus congolensis, breed not specified, bovine.
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)
· Gram-positive, filamentous, branching , facultative anaerobic bacteria (order Actinomycetales) that causes an acute, subacute or chronic superficial exudative dermatitis
· Unusual life cycle where coccoid bodies germinate to produce branching filaments (may be > 5 um wide) > 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 rainfall
· Usually a secondary invader; can co-infect poxviral lesions; hide damage may predispose to myiasis and secondary bacterial infections
· Zoospores survive in dried exudate on animals for years
· Mechanically damaged skin (ectoparasites, shearing, thorny pastures, etc.) and prolonged moisture are the two most important factors in the initiation and development of dermatophilosis; in addition concurrent diseases or stresses may contribute to the development of dermatophilosis by compromising the host’s immune system
· A definitive association between infestation with the tick Amblyomma variegatum and dermatophilosis in cattle has been found
· Warm, wet environments activate coccoid bodies into motile zoospores that germinate, producing filaments that penetrate the epidermis and the hair follicle external root sheath (probably the initial site of infection); rarely enter the dermis or deeper tissue
· Bacterial invasion stimulates an acute inflammatory response with superficial dermal edema and large numbers of neutrophils
· Neutrophilic exocytosis forms microabscesses in the superficial epidermis and external root sheath > underlying epidermal layers cornify prematurely, forming a new keratin layer below the exudate within 36 hours
· D. congolensis cyclically invades the newly formed keratin, which results in a thick scab composed of alternating layers of dermal inflammation with neutrophilic exudate, ortho- and parakeratotic hyperkeratosis, and epidermal regeneration
TYPICAL CLINICAL FINDINGS:
· Acute lesions are painful, but rarely pruritic
· 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 and neck, axilla and inguinal areas
· Subcutaneous and lymph node granulomas can occur; oral lesions rarely
TYPICAL LIGHT MICROSCOPIC FINDINGS:
· Palisading crust of thick laminar, alternating layers of orthokeratotic-parakeratotic hyperkeratosis, 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
Proliferative/Hyperkeratotic Skin Lesions in Cattle:
· Dermatophytosis: Trichophyton spp., Microsporum spp.: Chained or disassociated arthrospores and hyphae can be located in the stratum corneum, hair follicles and hairs; "domino effect"- serially damaged hair follicles damaged by necrotizing and pyogranulomatous folliculitis suggests dermatophytosis
· Ectoparasitism: Demodex spp., 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
· 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”); distal limbs and head also
· 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)
· Dogs; pigs: Rare
· Tortoises, turtles: D. chelonae
· 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
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