Rabbit treponematosis, commonly called rabbit syphilis or vent disease, is a contagious bacterial infection caused by Treponema paraluiscuniculi that produces crusty, ulcerative lesions around the genitals, nose, and lips. It spreads through direct contact — especially during mating — but does not infect humans. With antibiotic treatment it is fully curable.
Last reviewed: June 2026
What Is Rabbit Treponematosis (Vent Disease)?
Rabbit treponematosis is a sexually transmitted and contact-transmitted bacterial infection specific to rabbits, caused by the spirochete Treponema paraluiscuniculi — a close relative of the human syphilis bacterium but entirely rabbit-specific and not a zoonosis. The condition is also called rabbit syphilis or vent disease because the vent (perineal) area is the most commonly affected site, as described in Quesenberry & Carpenter's Ferrets, Rabbits, and Rodents: Clinical Medicine and Surgery.
The infection is more common than many owners realize, particularly in rabbits from breeders or unknown contact histories. Does can transmit it to kits during birth, which is why facial lesions can appear in young rabbits before they are sexually active.
Recognizing the Signs of Vent Disease
The hallmark sign is crusted, ulcerative, or erythematous (red, inflamed) lesions that appear around one or more of these sites:
- Perineum and genitalia — redness, swelling, scaling, and ulceration around the vulva, prepuce, or anus
- Nose and nostrils — crusty accumulations that are often mistaken for a respiratory infection
- Lips and perioral area — scabbing or ulcers at the lip margins
- Eyelids — less common, but possible in kits infected perinatally
The lesions are rarely painful enough to make rabbits systemically ill; most affected rabbits eat, drink, and behave normally despite visible skin changes. This quiet presentation means vent disease can go unnoticed for months. In breeding colonies, subclinical carriers can silently spread infection to many animals before lesions become obvious.
Diagnosis is confirmed by serology (rabbit-specific treponemal antibody tests) or by dark-field microscopy of lesion scrapings. Spirochetes are not visible on routine skin scraping culture. If your rabbit has crusty perineal or nasal lesions, mention the possibility of treponematosis to your vet so the right diagnostics are ordered (AEMV Pet Care Guides, 2024).
Treatment and Prognosis
Rabbit treponematosis responds extremely well to penicillin injections. A typical protocol is three injections of long-acting penicillin G benzathine/procaine (Penicillin G) given one week apart, as detailed in Carpenter's Exotic Animal Formulary. Lesions usually begin resolving within 1–2 weeks of the first injection and are fully healed after the course.
Oral penicillin is contraindicated in rabbits because it disrupts gut flora and can cause fatal enterotoxemia — only injectable forms should be used, and only under veterinary supervision. All in-contact rabbits should be tested and treated, including any apparent symptom-free animals that may be subclinical carriers.
After successful treatment, the rabbit is cured and lesions do not recur unless re-exposed. Treated rabbits can be safely reintroduced to healthy animals. The disease does not cause long-term organ damage when diagnosed and treated promptly.
When to See a Vet
Call your vet today if:
- You notice crusty, red, or ulcerated skin around the genitals, anus, or nose
- A new rabbit has scabby lesions anywhere on the face or perineum
- A rabbit has recently mated with an animal of unknown health status
- Kits in a litter develop facial or nasal crusting shortly after birth
- Lesions are worsening or spreading to new sites
Go to the ER immediately if:
- Your rabbit has stopped eating and has active skin lesions (combined signs suggest secondary illness)
- The rabbit is lethargic, hunched, or showing signs of pain alongside skin changes
- Lesions are spreading rapidly or appear severely ulcerated and bleeding
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Frequently Asked Questions
Can rabbit vent disease spread to humans or other pets? No. Treponema paraluiscuniculi is species-specific to rabbits and does not infect humans, dogs, cats, or other household animals. It is not a zoonotic disease. You can safely handle your rabbit during treatment; basic hygiene is still sensible but the infection poses no human health risk whatsoever.
How much does treating rabbit treponematosis cost? An exotic-vet exam typically runs $75–150. Serological testing adds $50–120. The three-injection penicillin course costs approximately $50–150 in drug and administration fees, depending on the practice and rabbit size. Total treatment for a single rabbit usually falls in the $200–400 range — quite manageable given the full cure rate.
What does vent disease look like on a rabbit? Look for crusty, reddened, or ulcerated patches around the genitals, anus, nose, or lips. Lesions may appear moist and weepy early on, then develop dry crusts. They are often mistaken for ringworm, mites, or a respiratory infection (when nasal). The rabbit typically acts normal despite the skin changes.
Can rabbit treponematosis be cured completely? Yes. With a full three-injection penicillin course, the infection is completely eradicated and lesions resolve without scarring in most cases. The prognosis is excellent as long as re-exposure does not occur. All in-contact rabbits must be treated simultaneously to prevent ping-pong reinfection.
How does rabbit syphilis spread in a colony? The primary routes are sexual contact between adults, and mother-to-kit transmission during birth. Direct skin-to-skin contact with active lesions can also transmit the spirochete. The organism does not survive long in the environment, so fomite transmission (via water bowls or bedding) is uncommon but theoretically possible with very fresh contamination.
Still Not Sure if Your Rabbit Needs a Vet?
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