I had this crop up in my herd once from a rabbit that was given to me. Since she was in isolation it was simply a matter of treating her.
Vent disease is not a particularly good disease to have in your rabbitry and often requires all rabbits to be treated for it.
some resources to pursue in one's search for more knowledge on this disease
Vent disease is highly contagious and can be spread either by direct contact, during breeding, and passed to offsprings to kindling. Any rabbit showing signs of vent disease should be removed from your breeding program until they have been properly medicated. Quarantining the rabbit from the herd for a short time should also be practiced.
Topical application of ointments may relieve the area of its soreness but will not rid the rabbit of this disease. Vent disease can be effectively treated using Pen BP-48 which is a combination of Procaine Penicillin G and Penicillin G Benzathine. We successfully treated by giving a dosage of 20,000 IU per pound of body weight. As with any medication, care should be taken to read the label so you understand how much medication you are administering to the rabbit. The bottle of Pen BP-48 that we purchase contains 300,000 IU per mL. So a 4 pound rabbit would receive 2.5/10 of a mL. This should be administered once a week for three straight weeks. The medication is to be given subcutaneously (SQ). A 25 gauge needle should be small enough for the rabbit, yet large enough for this somewhat thicker medication.
As with any antibiotic care should be taken to watch your rabbit for any signs of diarrhea. Hay should be free fed during the treatment to aid the rabbits digestive system and prevent diarrhea. You may also consider removing pellets from the diet for the first couple of days after treatment.
This link has pictures and a variety of links to look through.
According to Ferrets, Rabbits, and Rodents: Clinical Medicine and Surgery by Katherine E Quesenberry and James W. Carpenter, my source for this article, penicillin G benzathine-penicillin G procaine (sold as Combi-Pen and commonly referred to as pen B) administered at 7-day intervals for 3 injections (42,000 to 84,0000 IU per kilogram of rabbit weight given subcutaneously) is an appropriate treatment.
My Combi-Pen has 300,000 IU per milliliter. A 4-lb. rabbit weighs 1.8 kg. The range for a 4 lb. rabbit is therefore 75,600 to 151,200 IU or 1/4 to 1/2 mililitters or cc’s. The convention many breeders use is 1/10 cc per pound. Please make your own calculations and consult your vet before administering medications.
If you use Pen G, then you must give it for 5 to 7 days straight intramuscular. I find this treatment harder on the rabbit’s GI tract, though, and harder to administer. Other breeders have found that vent disease is more likely to reoccur with the Pen G treatment.
Treponematosis, a specific venereal disease of domestic rabbits, is caused by the spirochete Treponema paraluis cuniculi . It occurs in both sexes and is transmitted by coitus and from the doe to offspring. Although closely related to the organism ( T pallidum ) that causes human syphilis, T cuniculi is not transmissible to other domestic animals or humans.