Both diseases are transmitted and carried by bulls that have no obvious signs of infection. Infected cows generally abort early in pregnancy and while the abortion may not be seen, the farmer may notice cows returning to service. An infertility problem, rather than obvious abortions, is a sign of both campylobacteriosis and trichomoniasis. After infection and early abortion, cows usually recover, but carrier animals and cows with chronically-infected wombs may stir be in the herd. These cows may pass the disease back to a bull.
Bulls are immune if vaccinated against campylobacteriosis.
Organisms of both venereal diseases are usually spread during mating. However, bulls mounting each other at stud or at artificial insemination centres, and the use of contaminated grooming equipment or veterinary instruments, have all been incriminated in the spread of the infection. Campylobacteriosis and trichomoniasis cause inflammation of the vagina, cervix, uterus and fallopian tubes in the cow. This inflammation usually prevents successful implantation of the embryo in the uterus and leads to early abortion. The result is seen as cows returning to heat and poor pregnancy test results.