Rabbit Treponematosis Signs: Vent Disease (Rabbit Syphilis) Explained
Treponematosis — commonly called rabbit syphilis or vent disease — is a spirochete infection caused by Treponema paraluiscuniculi that produces crusty, ulcerated lesions around the genitals, lips, and nose. It's not contagious to humans, but it spreads readily between rabbits via mating and close contact. A 14 to 21 day course of penicillin G benzathine/procaine clears almost every case (Wenzlow et al., 2022, JEPM). Crusts around the genitals or lips that don't heal deserve treponematosis on the differential.
Last reviewed: June 2026
What Treponematosis Is
Treponematosis is infection with the spirochete Treponema paraluiscuniculi, which is closely related to the human syphilis organism but is host-specific for rabbits and not zoonotic. Lesions develop at sites of mucocutaneous contact — the vulva or penis, perineum, lips, nasal planum, and eyelids. The bacterium survives poorly outside the host and is transmitted by direct contact during mating, mutual grooming, or close housing. As reviewed in Quesenberry and Carpenter's Ferrets, Rabbits, and Rodents, untreated rabbits can carry latent infection for years and reactivate during stress.
How Owners First Notice It
Owners typically notice crusty, slightly raised lesions around the genitals or anus, sometimes spreading to the lips, nose, or eyelids. Lesions are usually not very painful at first but bleed easily if disturbed. Affected rabbits may shake their heads from facial lesions, paw at the face, or have decreased appetite if oral lesions develop. Pairs or bonded groups often show simultaneous outbreaks. Crusting that doesn't respond to topical antibiotics or antiseptics over 10 to 14 days is suspicious.
Why Diagnosis Is Tricky
Treponematosis looks like several other conditions: scabby mites, dermatophytosis (ringworm), pasteurellosis abscesses, and herpes-related lesions. As detailed in Mitchell and Tully's Manual of Exotic Pet Practice, dark-field microscopy of fresh exudate from a lesion shows the spirochetes, or PCR on a lesion swab confirms the organism. Many practices treat empirically when the lesion distribution is classic — genital plus oral or facial — and confirm by therapeutic response.
Treatment That Works
The gold standard is penicillin G benzathine/procaine at 42,000 to 84,000 IU/kg subcutaneously once weekly for 3 weeks. This regimen reliably clears infection in essentially all cases when given properly (Wenzlow et al., 2022, JEPM). Oral antibiotics like amoxicillin are NEVER used in rabbits — they cause fatal dysbiosis and clostridial overgrowth. Topical antiseptics provide no benefit alone. All cohoused rabbits must be treated simultaneously even if asymptomatic, because subclinical carriers reinfect treated cagemates. As described in the Carpenter Exotic Animal Formulary, lesions typically resolve fully within 10 to 21 days of starting treatment.
When to See a Vet
Call your vet today if:
- Crusty lesions around the genitals, anus, lips, or nose
- A pair of rabbits both develop similar facial or perineal scabs
- Lesions that bleed when touched and don't heal in 10 days
- A rabbit recently introduced to a new partner develops new lesions
- Decreased appetite combined with facial crusts
Go to the ER immediately if:
- A rabbit stops eating completely for more than 12 hours (GI stasis risk)
- Severe lethargy with cold ears
- Heavy bleeding from a lesion
- Sudden inability to use the back legs
- Open wounds with maggots or foul odor (flystrike risk)
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Frequently Asked Questions
Can humans catch rabbit syphilis?
No. Treponema paraluiscuniculi is host-restricted to rabbits and does not infect humans. The organism shares ancestry with human syphilis but cannot establish infection in people. Normal hand hygiene after handling lesions is sufficient.
How much does diagnosis and treatment cost?
Initial exotic vet exam typically runs $75 to $200 in the US. PCR or dark-field cytology of a lesion costs $80 to $250. A 3-week course of weekly penicillin injections for a single rabbit runs roughly $60 to $150 (most exotic vets handle the injections in clinic). If multiple rabbits in the household need treatment, total costs scale accordingly. Catching it early before secondary infection avoids expensive bandaging and follow-up.
Will my rabbit be cured for life?
Most rabbits clear infection completely with a single proper 3-week penicillin course. Reinfection occurs only with re-exposure to an untreated carrier. Single-treated rabbits in stable households do not relapse. Treating all cohoused rabbits prevents relapse from carrier transmission.
Are oral antibiotics OK in rabbits?
Most are absolutely not. Oral penicillins (amoxicillin, ampicillin), cephalosporins, lincomycin, and clindamycin cause fatal Clostridium overgrowth in the rabbit cecum. Only carefully selected oral antibiotics (trimethoprim-sulfa, enrofloxacin, metronidazole) are safe, and even these can disturb gut flora. For treponematosis specifically, injectable penicillin G is the standard.
Still Not Sure if Your Rabbit Needs a Vet?
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