JPC SYSTEMIC PATHOLOGY
Signalment (JPC# 2155783): Female rabbit (Oryctolagus cuniculus)
HISTORY: Genital lesion
HISTOPATHOLOGIC DESCRIPTION: Mucocutaneous junction, vulva (2 sections): Diffusely the epidermis is hyperplastic, thickened up to 3 times normal, characterized by acanthosis, anastomosing rete ridges, intercellular clear spaces with prominent intercellular bridging (spongiosis), and intracellular edema. There are multifocal erosions and ulcerations with replacement by a serocellular crust composed of necrotic cellular and karyorrhectic debris admixed with serum, numerous degenerate heterophils, lymphocytes, and variably sized colonies of 2 um diameter basophilic cocci. Within the adjacent epithelium there is ortho- and rare parakeratotic hyperkeratosis. The superficial dermis is infiltrated by moderate numbers of macrophages, heterophils, and fewer lymphocytes and plasma cells that surround adnexa and blood vessels, transmigrate the epidermis and follicular epithelium (exocytosis), and infiltrate follicular lumens (folliculitis). Hair follicles are multifocally dilated and filled with lamellations of keratin. Multifocally within the superficial dermis there is hemorrhage, fibrin, and increased clear spaces and ectatic lymphatics (edema). The inflammation extends into the deep dermis and panniculus carnosus muscle, surrounding, separating, and individualizing skeletal myocytes which are often shrunken and hypereosinophilic (atrophy).
MORPHOLOGIC DIAGNOSIS: Mucocutaneous junction (vulva): Dermatitis and folliculitis, suppurative and lymphoplasmacytic, diffuse, moderate, with epidermal hyperplasia, orthokeratosis, ulceration, and superficial mixed population of bacteria, breed not specified, lagomorph.
ETIOLOGIC DIAGNOSIS: Cutaneous treponemiasis
CAUSE: Treponema paraluiscuniculi (formerly T. cuniculi)
CONDITION: Rabbit syphilis
SYNONYMS: Venereal spirochetosis, vent disease, treponematosis
· Rabbit syphilis is an uncommon, self-limiting disease that results in perineal (see R-B09) and facial lesions
· Gram-negative, filamentous, microaerophilic, spirochete, 0.1-0.2 um wide by 6-15 um long with tapered ends
· Genus Treponema includes both pathogenic species and nonpathogenic species; nonpathogens are part of normal flora in the oral cavity
· Prevalence is less than 10% in enzootically infected colonies
· Effect on fertility rates has not been determined
· Spread by direct or venereal contact
· Horizontal transmission during breeding is the primary route of exposure
· Transmission via extragenital contact and vertical transmission during birth and nursing are possible, but infrequent
· There is no evidence of intra-uterine transmission
· The organism proliferates locally after penetrating damaged or intact epithelium
· There is a long 3-6 week incubation period; takes 8-12 weeks for seroconversion
· Susceptibility increases with age; young rabbits are relatively resistant
· Prevalence increases with parity and length of time in breeding program
· Bucks are often asymptomatic carriers and can spread disease to multiple does
· Asymptomatic carriers occur, with recrudescence when under stress
· Infection may increase susceptibility to other infections
TYPICAL CLINICAL FINDINGS:
· Lesions can be painful, resulting in decreased breeding activity
· Colony epidemics can result in metritis, retained placentas, neonatal deaths, and decreased conception rates
TYPICAL GROSS FINDINGS:
· Initial lesions are on the perineum and genitalia: Edema, erythema, and papules at mucocutaneous junctions (vulva, prepuce, and anal region)
· Lesions progress to ulcerations and crusting
· Autoinfection results in similar lesions on the chin, lips, nostrils, eyelids, muzzles, and periorbital region
· Bucks can have small star-shaped scars on their scrotum
TYPICAL LIGHT MICROSCOPIC FINDINGS:
· Epidermal hyperplasia, necrosis, acanthosis, erosions, and ulcerations, with infiltration by plasma cells, macrophages, and heterophils
· Infection is usually confined to the epithelium
· Prominent periadnexal infiltration with lymphocytes, macrophages, heterophils, and plasma cells
· Regional lymph node hyperplasia
· No visceral involvement
· Gram-negative, filamentous, microaerophilic, spirochete, 0.1-0.2 um wide by 6-15 um long with tapered ends best demonstrated by Warthin-Starry and Steiner’s silver stain
ADDITIONAL DIAGNOSTIC TESTS:
· Definitive diagnosis is by demonstration of spirochetes in typical lesions
· The most reliable diagnostic test is using skin scrapings to make wet mounts and dark field examination; the spirochetes have a characteristic "corkscrew" movement in wet mounts
· Scrapings stained with Giemsa stain can be used
· Warthin-Starry and Steiner’s silver stains sometimes demonstrate organisms
· Microhemagglutination assay
· Plasma reagent antibody test
· Fluorescent treponemal antigen test
· The organism shares antigenic cross-reactivity with T. pallidum (human syphilis), so screening tests developed for human syphilis will detect rabbit syphilis
· Dermatitis: Pasteurella multocida: Snuffles, conjunctivitis, and genital tract infections
· Dermatophytosis: Trichophyton mentagrophytes most commonly; head and ears
· Acariasis: Psoroptes cuniculi (ear mites); Notoedres cati, and Sarcoptes scabiei (dermatitis of the face, nose, lips, and external genitalia)
· Myxomatosis: Leporipoxvirus; mucopurulent conjunctivitis
· Traumatic lesions
· NOT zoonotic
· Very similar to Treponema pallidum (human syphilis)
· Treponema pallidum associated with genital ulceration in wild baboons
· Sheep: Contagious ovine digital dermatitis (CODD) is a cause of severe lameness resulting in with extensive solar ulceration with or without exophytic papilliform hyperkeratosis grossly and chronic lymphoplasmacytic, suppurative and ulcerative pododermatitis histologically
· CODD-associated Treponema phylogroups: Treponema medium/Treponema vincentii-like, Treponema phagedenis-like and Treponema pedis spirochaetes
· Ddx for foot lesions: Dichelobacter nodosus and Fusobacterium necrophorum
· Bovine ischemic teat necrosis, pressure sores, and hoof necrosis: Identified treponemes are similar or identical to those isolated from classical foot lesions in sheep
· Detection of Treponema phagedenis–like antibodies in serum and bulk milk from cows with and without digital dermatitis (Frossling, JVDI 2018)
· Treponeme-Associated Hoof Disease of Free-Ranging Elk (Cervus elaphus) in Southwestern Washington State, USA (Hans, Vet Pathol 2019)
· Debilitating and progressive condition, shares similarities to bovine digital dermatitis and contagious ovine digital dermatitis
· Goat: Severe foot lesions in dairy goats associated with digital dermatitis treponemes
· Main macroscopic foot lesion - extensive solar ulceration w/ or w/o exophytic papilliform hyperkeratosis
· Pigs: Ear necrosis (“necrotic ear syndrome”, “ulcerative spirochetosis of the ear”), affecting the lower to entire ear margin of 6-9 week old piglets, is thought to be caused by a Treponema sp. bacterium
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