Prevalence of Bovine Brucellosis and Cow Milk Contamination by Brucella in Benue State, Nigeria

Abstract

Serological and bacteriological studies were carried out to determine the prevalence of brucellosis among cattle in Benue State, Nigeria; and to determine the level of contamination of fresh bulk herd and fermented milk sold to the public for consumption; as well as detect and characterize the causative agent of bovine brucellosis in the area; and to evaluate a new diagnostic test for brucellosis, the Brucella Lateral Flow Assay (the rapid field test). Serum samples obtained from cattle (n = 1556) were initially screened using the Rose Bengal Plate Test (RBPT) and positive reactors were further subjected to the serum tube agglutination test (SAT). An overall animal-level seroprevalence of 8.42% (131/1556) was obtained. Seroprevalence among production herds 8.82% (72/816) was not significantly (χ2 = 0.36, P > 0.05) different from that of slaughtered cattle 7.97% (59/740). The herd-level Seroprevalence was 73.97% (54/73). Significantly (χ2 = 7.55, P < 0.05) higher seroprevalence was obtained among female cattle tested than males with 9.85% (99/1005) of females and 5.81% (32/551) of males testing positive. Significantly (χ2 = 8.51, P < 0.05) higher seroprevalence was obtained among N’Dama (12.28%), White Fulani (9.19%), Bororo (8.99%) breeds of cattle tested than Muturu (6.67%), Sokoto Gudali (5.43%) and Adamawa Gudali (4.59%) breeds. Seroprevalence increased with age and older animals >3 years of age had significantly (χ2 = 9.7, P < 0.05) higher prevalence than younger animals. Seroprevalence differed significantly (χ2 = 4.06, P < 0.05) among the geopolitical zones of the state with Zone B having 9.94%, Zone C 7.38% and Zone A 6.76%. Season of the year had no significant (χ2 = 2.48, P > 0.05) influence on the seroprevalence of brucella infection, though the rainy (wet) season had a slightly higher prevalence (8.96%) than the dry season (8.01%). There was no significant difference in the prevalence of brucellosis among production herds and cattle slaughtered but sex, age, breed and area were associated risk factors in bovine brucellosis. Of the 1556 cattle sampled and tested in this study, 19(1.22%) had hygroma and of the 73 production herds sampled, 18(24.66%) had incidence of hygroma, 18(33.33%) of 54 seropositive herds had animals with hygroma, 8(14.81%) of the positive herds had history of abortions while 7(12.96%) reported retained placentas on vii their farms. Four (7.41%) of the 54 positive herds tested had clinical evidence of orchitis. Hygroma were seen in Adamawa Gudali, NDama, Sokoto Gudali, and White Fulani breeds. History of abortions, retained placenta, the presence of hygroma and orchitis are good indicators of the presence of brucellosis in a farm. The comparison of the rapid field test and RBPT in the screening of trade herds (animals kept for sale and slaughter) (n = 206) indicated strong agreement (95.8%) beyond chance (kappa, 0.80; SE 0.07) with RBPT showing 13.59% (28/206) and the rapid field test 15.53% (32/206) positivity, implying that the rapid field test can be used in place of the RBPT in field-based serological surveillance. The result of the milk ring test (MRT) showed significant (χ2 = 0.51, p < 0.05) difference in the seroprevalence of Brucella antibodies between fresh bulk herd and fermented milk sold by Fulani vendors with the former showing 17.74% (11/62) and the latter 12.5% (5/40) seropositivity and an overall prevalence of 15.69% (16/102) implying potential health risk to consumers. Bacteriological examination of 83 clinical samples consisting of 32 milk, 19 hygroma and 32 vaginal swabs for the isolation and characterization of brucellae in order to obtain species and biovar thereby establishing the identity of the causative agent of bovine brucellosis in the study area. Six Brucella isolates (31.58%) from 19 hygroma specimens were characterized, biotyped and identified as Brucella abortus biovar 1. Successful isolation of Brucella was made only from hygroma fluid obtained and cultured within 48 hours. Of the six isolates, 1(16.67%) was from NDama, 3(50%) from White Fulani, 1(16.67%) from Adamawa Gudali and 1(16.67%) from Sokoto Gudali breeds. No Brucella isolates were obtained from milk or vaginal swabs. The epidemiological significance of these findings is discussed. Some observations on the zoonotic and public health implications of brucella infection of cattle are presented. A control programme involving improved management, animal movement restrictions, public health education and mass vaccination of animals is suggested. In conclusion, the results from this study have indicated that bovine brucellosis is prevalent in Benue State, Nigeria; that both fresh bulk herd milk and soured milk sold to the public in form of nono by Fulani milk maids are largely contaminated with Brucella and poses potential health hazard to consumers; that the causative agent of bovine brucellosis in the area is Brucella abortus biovar 1. The Brucella lateral flow assay or viii the rapid field test can be used in place of the RBPT for field-based surveillance or screening of herds. More work on isolation and characterization of Brucella infecting animals is recommended.