Seroepidemiology of Bovine brucellosis

Abstract

An investigation was carried out on 1602 cattle and buffaloes of Kerala including 1535 cattle and 67 buffaloes to assess the seroprevalence of brucellosis using serological tests like Rose Bengal plate' test, Standard tube agglutination test, 2-Mercaptoethanol test and Avidin-Biotin ELISA. Sera samples were collected from bovines belonging to different farms, hospitals and households of Kerala covering eleven districts. Samples were collected randomly from animals of different sex, age, breed, gestation, lactation, reproductive performance, management practices and also from slaughter house. Out of the 1602 sera samples tested 15.29 per cent gave positive result for brucella antibodies. Of this cattle showed a seropositivity of 14.72 per cent and buffaloes showed 28.35 per cent seropositivity. Female cattle and female buffaloes showed higher seroprevalence than male cattle and male buffaloes. Bulls and cows aged more than five years showed the highest seropositivity. Among the breeds pure bred Holstein Friesian bulls and crossbred Jersey female cattle showed the highest seroprevalence. Seroprevalence of brucellosis was found higher in pregnant cattle, in late stage of gestation, in pregnant dry animals and also in cows and heifers with the history of repeat breeding. Animals maintained under unorganised farming system, animals from high altitude agroecological region showed more number of positive reactors. Northern zone of Kerala showed more number of positive reactors. Districtwise analysis revealed that animals belonging to Kozhikode district having highest seropositivity and animals from Kottayam and Malappuram districts as zero positives. RBPT, STA T and 2 MET was evaluated for the sensitivity, specificity, predictive values and accuracy using, A-B ELISA as the 'gold standard'. RBPT was found to have higher sensitivity, predictive value of a negative test and accuracy than STAT and 2 MET and all the three tests found to have 100 per cent specificity and predictive value of a positive test with that of ELISA. It was concluded that RBPT can be used as a preliminary screening test and ELISA as a confirmatory diagnostic test.