M. Lizhong
The Qinghai General Station of Veterinary and Animal Husbandry, Xining 810001, Qinghai, P.R. China
Following extended S2 vaccine inoculation in yak, a diagnosis study including serum agglutination test (SAT) for brucellosis and indirect haemagglutination (IHA) for Chlamydia infection was conducted using 526 serum samples from un-inoculated yak calves over 8 months old in the area covered by the vaccination programme. There was only one positive serum sample in SAT but 15 positive serum samples in IHA. The results showed that brucellosis had been successfully controlled, but that Chlamydia infection was still prevalent and, hence was responsible for the prevailing cases of abortion in yak in the area. Attention is needed for the control of these Chlamydia-caused abortions.
Keywords: Brucellosis, Chlamydia, diagnosis, yak
In historic records the serum positive rate of brucellosis in yak from the Xinghai County of Hainan Prefecture of Qinghai Province, where both brucellosis and Chlamydia infection were prevalent, was 31.19%. Since 1982, a yak vaccination project was conducted by S2 vaccine and a total of 200 thousand doses of vaccines were administrated on the same number of animals. This study was conducted in 1996 to evaluate the effectiveness of the programme and examine the epidemiology of Chlamydia infection in yak.
Five hundred and twenty six samples for test were collected from un-inoculated yak calves over 8 months old in the area where the S2 vaccination programme had been implemented.
The antigen, positive and negative control serums for brucellosis were provided by the Chendu Biological Manufacture, P.R. China. Diluting solution used in SAT was 0.9% NaCl. Antigen, positive and negative control serums, and their diluting solution were produced by the Lanzhou Veterinary Institute of the Chinese Academy of Agricultural Sciences.
For brucellosis in SAT, the index used was following the requirement in the regulation promulgated by the Ministry of Agriculture (1979). For Chlamydia infection in IHA, the index was as described by the manufacture. 96-V holes micro-plates were chosen for IHA. When 2 crosses (++) were shown in 1:16 titre (50% or up of the red cells was evenly distributed at the low part of the holes), this was considered as positive. When 2 crosses (++) or less were shown in 1:4 titration, this was treated as negative. For both the SAT and IHA, there were positive and negative duplication controls, respectively.
From Table 1, it can be seen that the positive rate of brucellosis is 0.19%, which is much lower than the 31.19% recorded in 1981 before the vaccination programme was implemented (300/982, P<0.01). These results show that the S2 vaccine inoculation project was quite successful and resulted in the control of brucellosis in yak in the study area. However, the proportion of positive cases of Chlamydia infection is up to 2.85%, which indicate that it should continue to receive attention because both brucellosis and Chlamydia infection are important pathogens responsible for abortion in yak in the study area. Yak is an important animal in this area, and abortions represent an important production constraint, which needs to be addressed. Current attention should be focused on abortions resulting from the Chlamydia infections.
Table 1. Diagnosis results of brucellosis (SAT) and Chlamydia (IHA).
Method |
Samples |
Positive |
Percentage |
SAT |
526 |
1 |
0.19 |
IHA |
526 |
15 |
2.85 |
