AFIP SYSTEMIC PATHOLOGY

JPC SYSTEMIC PATHOLOGY

INTEGUMENTARY SYSTEM

August 2016

I-B07

 

Signalment (JPC 2155783):  Female rabbit (Oryctolagus cuniculus)

 

HISTORY:  Genital lesion

 

HISTOPATHOLOGIC DESCRIPTION: Mucocutaneous junction, vulva (2 sections): Diffusely the epidermis is thickened up to 3 times normal and characterized by acanthosis, anastomosing rete ridges, spongiosis, and intracellular edema.  There are multifocal erosions and ulcerations with replacement by a serocellular crust composed of necrotic debris admixed with serum, numerous degenerate heterophils, lymphocytes, and variably sized basophilic colonies of 2x4 um rods and 2 um diameter 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, exocytose the epidermis, and infiltrate follicular epithelium and lumens (folliculitis).  Hair follicles are multifocally dilated and filled with lamellations of keratin.  Multifocally within the superficial dermis, there is hemorrhage and lymphatics are ectatic (edema).

 

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

 

GENERAL DISCUSSION:

·         Rabbit syphilis is an uncommon, self-limiting disease that results in perineal and facial lesions; infection may increase susceptibility to other infections

·         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

 

PATHOGENESIS:

·         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 5-6 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

 

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 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

 

DIFFERENTIAL DIAGNOSIS:

·         DermatitisPasteurella multocida: Snuffles, conjunctivitis, and genital tract infections

·         Dermatophytosis: Trichophyton mentagrophytes most commonly; head and ears

·         Ascariasis: Psoroptes cuniculi (ear mites); Notoedres cati, and Sarcoptes scabiei (dermatitis of the face, nose, lips, and external genitalia)

·         Myxomatosis: Leporipoxvirus; mucopurulent conjunctivitis

·         Traumatic lesions

 

COMPARATIVE PATHOLOGY:

·         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\

·         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.

 

REFERENCES: 

1.     Angell J, Clegg S, Sullivan L, et al. In vitro susceptibility of contagious ovine digital dermatitis associated Treponema spp. isolates to antimicrobial agents in the UK. Vet Dermatol. 2015;26(6):484 e115. 

2.     Angell J, Crosby-Durrani H, Duncan J et al. Histopathoological characterization of the lesions of contagious ovine digital dermatitis and immunolabelling of Treponema-like organisms. J Comp Pathol. 2015;153(4):212-226.

3.     Clegg S, Crosby-Durrani H, Bell J, et al. Detection and isolation of digital dermatitis treponemes from bovine pressure sores. J Comp Pathol. 2016;154:273-282.

4.     Crosby-Durrani H, Clegg S, Singer E, et al. Severe foot lesions in dairy goats associated with digital dermatitis treponemes. J Comp Pathol. 2016;154:283-296.

5.     DeLong D, Manning P. Bacterial diseases. In: Manning PJ, Ringler DH, Newcomer CE, eds.  The Biology of the Laboratory Rabbit. 2nd ed. San Diego, CA: Academic Press; 1994:151-154.

6.     Knauf S, Batamuzi E, Mlengeya T et al. Treponema infection associated with genital ulceration in wild baboons. Vet Pathol. 2012;49:292-303.

7.     Maboni G, Frosth S, Aspan A. Ovine footrot: new insights into bacterial colonization. Vet Rec. 2016;17:pii: vetrec-2015-103610.

8.     Pare JA, Paul-Murphy. Disorders of the reproductive and urinary systems. In: Quesenberry KE, Carpenter JW, eds. Ferrets, Rabbits, and Rodents: Clinical Medicine and Surgery. St. Louis, MO: Saunders; 2004:187.

9.     Percy DH, Barthold SW. Rabbit. In: Pathology of Laboratory Rodents and Rabbits, 3rd ed., Ames, IA: Blackwell Publishing; 2007:282-283.

 

 


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