Overview of Bovine Genital Campylobacteriosis
Bovine genital campylobacteriosis is a venereal disease of cattle characterized primarily by early embryonic death, infertility, a protracted calving season, and occasionally abortion. Distribution is probably worldwide.
The cause is the motile, gram-negative, curved or spiral, polar flagellated, microaerophilic bacteria Campylobacter fetus venerealis or C fetus fetus. For many years, it was thought that C fetus fetus was generally an intestinal organism, only occasionally caused abortion in cattle, and was not a cause of infertility. However, C fetus fetus can also be a significant cause of the classic infertility syndrome usually attributed to C fetus venerealis. There are several strains of C fetus fetus, and the only way to determine whether a strain is a cause of infertility is to test that possibility in a group of heifers. Campylobacter spp are very labile and are destroyed quickly by heating, drying, and exposure to the atmosphere. Unless cultured quickly after collection from the animal and grown under microaerophilic or anaerobic conditions, Campylobacter spp will not grow.
C fetus is transmitted venereally and also by contaminated instruments, bedding, or by artificial insemination using contaminated semen. Individual bulls vary in their susceptibility to infection; some become permanent carriers, while others appear to be resistant to infection. The primary factor associated with this variability seems to be the age-related depth of the preputial and penile epithelial crypts. In young bulls (<3–4 yr old), in which the crypts have not yet developed, infection tends to be transient, with transmission apparently relying on sexual contact with a noninfected cow within a matter of minutes to days after the initial breeding of an infected cow. Spontaneous clearance in these younger bulls does not seem to be related to any immune response, so reinfection can readily occur. In bulls >3–4 yr old, the deeper crypts may provide the proper microaerophilic environment required for chronic infections to establish.
In cows, the duration of the carrier state is also variable; some clear the infection rapidly, whereas others can carry C fetus for ≥2 yr. IgA antibodies are shed in cervical mucus in significant amounts in ~50% of cows for several months after infection and are useful diagnostically. Although most of the genital tract may be free of infection when a cow eventually conceives, the vagina may remain chronically infected through pregnancy.
Cows are systemically normal, but there is a variable degree of mucopurulent endometritis that causes early embryonic death, prolonged luteal phases, irregular estrous cycles, repeat breeding, and, as a result, protracted calving periods, assuming the breeding season is long enough to allow for complete clearance and a successful rebreeding. Observed abortions are not common. In herds not managed intensively, disease may be noticed only when pregnancy examinations reveal low or marginally low pregnancy rates but, more importantly, great variations in gestation lengths, especially when the disease has recently been introduced to the herd. In subsequent years, infertility is usually confined to replacement heifers and a few susceptible cows. Bulls are asymptomatic and produce normal semen.
Campylobacteriosis and trichomoniasis (see Trichomoniasis) are similar syndromes, and investigations should be directed at both diseases. Systemic antibody responses are not helpful, because they are often due to nonpathogenic Campylobacter spp. A vaginal mucus agglutination test (VMAT) is useful, but because of variability in individual responses, at least 10% of the herd or at least 10 cows should be sampled. An ELISA test has been developed for use on vaginal mucus and is said to be more sensitive and able to detect a wider range of antibody responses than the VMAT. Vaginal culture immediately after abortion or infection can be used for diagnosis, but the number of organisms may be low; in addition, because C fetus is labile and requires special techniques for isolation, success is limited.
An accurate diagnostic method is to test-breed heifers and then examine them for infection, but this is seldom practical. More often, the preputial cavity and fornix are either scraped and aspirated with an infusion pipette or infused with buffered sterile saline, and the prepuce is massaged vigorously in the area of the fornix. The aspirate or sheath washing is then examined using a fluorescent antibody test and culture. C fetus will survive for only 6–8 hr after collection, but inoculation into Clark’s or similar media will allow survival for >48 hr. For maximum accuracy, bulls should be sampled twice, ~1 wk apart.
Caution should be exercised when Campylobacter spp are isolated from the placenta because of the possibility of contamination by nonpathogenic fecal Campylobacter spp. Conversely, failure to successfully isolate C fetus from an infected aborted fetus or placenta often results from overgrowth of the colonies by contaminating organisms or the lethal effects of atmospheric oxygen.
Vaccination should start as soon as genital campylobacteriosis is diagnosed. Infected cows and cows at risk should be vaccinated. Vaccination of infected cows hastens the elimination of C fetus and, although cows may remain carriers, fertility is greatly improved. In routine use, the vaccine should be given once, ~4 wk before breeding starts; because antibody responses are short-lived, cows should be revaccinated halfway through the breeding season. Bulls are vaccinated for the same reason as cows (ie, for treatment as well as for prophylaxis) but are given twice the dose used for cows, 3 wk apart. The infection can also be eliminated in bulls by 1–2 treatments with streptomycin at 20 mg/kg, SC, together with 5 g of streptomycin in an oil-based suspension applied to the penis for 3 consecutive days.
For practical reasons, cows are not usually treated for genital campylobacteriosis. When practical, artificial insemination is an excellent way to prevent or control genital campylobacteriosis. Because C fetus has been isolated from cows for >6 mo after the end of pregnancy, it has been suggested that artificial insemination should continue until all the cows in a herd have been through at least two pregnancies.