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This article was published in 1993
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Bovine Venereal Campylobacteriosis: Incidence of the Disease and Evaluation of the IGA Vaginal Mucus Elisa
HUM S. QUINN C. and KENNEDY D.
Bovine venereal campylobacteriosis (BVC) is caused by Campylobacter fetus subsp. venerealis, an obligate parasite of the mucosa of the male and female genital organs. The disease is characterised by temporary infertility of female cattle as a result of subacute diffuse mucopurulent cervicitis, endometritis and salpingitis. Abortion occurs in a small percentage of infected cows. Infected bulls show no clinical signs but become carriers and infect females at service.
Diagnosis of BVC is difficult, because of the low survival rate of the organism with conventional sampling procedures and the absence of reliable sero-diagnostic methods. For this reason the prevalence of BVC is underestimated. To estimate the disease incidence and to evaluate the new vaginal mucus IgA ELISA a field study was undertaken.
From 1988 to 1991, 2311 cattle from 241 beef and dairy herds in New South Wales with fertility problems were subjected to the vaginal mucus IgA ELISA. The test was offered as a herd test and usually 10 problem animals were sampled by veterinarians.
Collection of Standard Vaginal Mucus
The sampling protocol was as follows: after cleaning the perineum, vaginal mucus was collected using a standard (15cm long) sterile cotton swab by pressing and turning the swab a few times against the cervico-vaginal area to ensure saturation. The cotton head of the swab was cut off and placed in 4.5ml phosphate buffered saline containing 0.05% Tween 20 (PBST).
Vaginal Mucus IgA ELISA
The vaginal mucus IgA ELISA results are summarised in Table 1.
TABLE 1 . The result of the vaginal mucus IgA ELISA
| YEAR | NUMBER OF FARMS | NUMBER OF ANIMALS TESTED | FARMS WITH REACTORS | FARMS WITH NO REACTORS | |
|---|---|---|---|---|---|
| ONE REACTOR | TWO OR MORE REACTORS | ||||
| 1989 | 32 | 273 | 4 | 10 | 18 |
| 1990 | 67 | 647 | 7 | 21 | 39 |
| 1991 | 142 | 1391 | 16 | 53 | 73 |
| TOTAL | 241 | 2311 | 27 | 84 | 130 |
Out of the 241 farms tested one or more positives were detected on 111 farms (46%). Eighty four (75.6%) reported infertility, 10 (9%) multiple abortions and on 17 farms (15.4%) infertility as well as abortions were observed. Infertility in most instances was identified by low pregnancy rates revealed at pregnancy testing, usually 2-3 months after the end of joining. Pregnancy rates varied from a low of 30% to a suboptimal of 90% but on most farms pregnancy rates were around 60%. Heifers were usually the most severely affected. Other findings occasionally reported included prolonged oestrus, vaginal discharge, a high return to service rate, irregular cycling and a spread out calving in the previous breeding season. Abortion in most cases occurred in the 3rd trimester, but it was not always reported and in 2 cases it was only suspected because cows did not calve after their positive pregnancy test at 3 months post-joining. The cause of infertility was not ascertained on 130 farms where no reactor was found.
Evidence of BVC was convincing on 84 farms (35%) where 2 or more positives were found. However interpretation of the results was difficult on the 27 farms (11.2%) where only one reactor was found. It is possible that these farms were infected but the distribution of the disease within the herd was very limited, or that by chance only one infected animal was selected for sampling. Fluctuations of antibodies found in convalescent animals may also be involved. This phenomenon which can be responsible for false negative reactions is probably due to the antigenic variation of the infecting strain, the variation of the amount of vaginal mucus collected or perhaps the changing antibody concentration in the vaginal mucus during oestrus or dioestrus. If these farms were re-tested, possibly more than one animal would have been found to react. Alternatively it may have been a false positive reaction as a result of previous sensitisation by C. fetus subsp. fetus. As demonstrated by testing of disease free animals the specificity was 98.5%, so false positives should be expected occasionally.
From this study the prevalence of BVC cannot be estimated because only herds with infertility were tested. It is apparent, however, that the disease is a significant cause of infertility and abortions in New South Wales, and further research is in progress to evaluate the economic impact of the disease.
From these results it appears that at present the vaginal mucus IgA ELISA is the test of choice for the diagnosis of BVC. Sampling is simple, practical and the ELISA is ideal for high volume testing. Because of the possibility of false negative reaction caused by antibody fluctuations in individual cattle, for infertility investigations the ELISA is best used as a herd test where a representative number of animals are sampled. Every effort should be made to sample groups or individuals most likely to be infected. Since high level of antibodies were observed in cattle aborting as a result of BVC, it may be used to diagnose abortion. Vaccination against BVC will not interfere with the IgA ELISA since only IgG is present in the vaginal mucus of vaccinates. The IgA ELISA can also be used to predict infertility. If reactors are found around the end of joining a less than optimal pregnancy rate can be anticipated and appropriate management decisions can be made.
Eradication of the disease in infected herds is best attempted by vaccination of all breeding animals in the herd with an additional antibiotic treatment of bulls at the time of the second vaccination. This procedure is recommended since vaccination does not always cure an infected bull. The next year bulls and replacement heifers are vaccinated and from the third year bulls are vaccinated annually.
Preventative vaccination of bulls remains the most practical and economic measure to control BVC, because immunised bulls are highly resistant to infection. Vaccination of bulls as a preventative measure therefore should be promoted.