Investigation and analysis of abortion in sheep after immunization against brucellosis in a Gansu sheep farm
Massive abortion and infertility still occurred after the application of the vaccine to immunize the sheep.In order to find out the causes of abortion and infertility in those sheep,a total of 54 vaginal swab samples,including 31 samples of aborted and 23 samples of infertile sheep,and their corresponding sera were collected from this sheep farm for testing.Sera were subjected to competitive enzyme-linked immunosorbent assay(cELISA),Brucella antibody IgG detection test and tube agglutination test(SAT).Fifty-four swabs were subjected to fluorescent probe PCR for detection of miscarriage-associated pathogens such as Brucella,Coxiella burnetii,and Chlamydia.Identification of Brucella species were carried out on Brucella-positive samples by using AMOS-PCR.Rifampicin-resistant(rpoB)gene was am-plified and sequenced.After the sequencing results were compared with its standard reference strains,an evolutionary tree was constructed.The results showed that 22 samples were anti-Brucella positive from 54 sera tested by cELISA,with a positive rate of 40.7％,and SAT confirmed 16 samples of these to be anti-Brucella positive,of which 6 samples were positive in aborted sheep,with a positive rate of 19.4％,and 10 samples were positive in infertile sheep,with a positive rate of 43.5％,and an overall positive rate of 29.6％.Nineteen samples were tested for infection by Brucella antibody IgG.Six aborted sheep were positive,with a positive rate of 19.4％,and 13 infertile sheep were positive,with a positive rate of 56.5％and an overall positive rate of 35.2％.There were 10 swab samples positive for Brucella with a positive rate of 18.5％,12 positive samples for C.burnetii with a positive rate of 22.2％,and 0 positive for Chlamydia,as detected by fluorescent PCR.After identification by AMOS-PCR,a band of 731 bp was ampl ified,and analysis of the rpoB gene revealed that all the amino acid sequences showed that no rifampicin-resistant mutation was detected.AMOS-PCR and the rpoB gene phylogenetic tree analysis showed that sheep were infected with B.melitensis.In conclusion,the occurrence of herd abortion in the farm could be caused by pathogenic infection after Brucella immunization failure,accompanied by mixed infection with C.burnetii and other pathogens.
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