Brucellosis surveillance and control in Zimbabwe: bacteriological and serological investigation in dairy herds

Abstract

Brucellosis in dairy cattle is endemic in Zimbabwe. The prevalence continues to be monitored intensively. Only milk and serum samples are routinely screened. Attempts to culture Brucella spp. from clinical specimens are seldom made. Consequently, incidence of various Brucella spp. within Zimbabwe is virtually unknown, despite the high serepositivity reported. This information is paramount in understanding the transmission cycle and is also significant to public health; particularly as B. melitensis infects humans more often than do the other brucellae. This paper describes the results of bacteriological and serological investigations of brucellosis in a dairy farm near Bulawayo. The said farm was selected for the present pilot study because of the high incidence of reported abortion. The milk ring test was employed to test the bulk pooled milk samples once a month for 14 months. The test was recorded highly positive on all 14 occasions. To locate reactors, milk samples from 36 individual cows were similarly tested. Of these, 21 (almost 59 %) were found to be reacting positively. One hundred and seventy-seven animals were marked for serotesting. Of these, 40 (approximately 25 %) showed quite high serum titres (> 1 :360) in both the STT and the Rosebengal test. The farmer was advised to have all abortions fully investigated. However, all the clinical material from cases of abortion, except one, were received in an advanced state of putrefaction. From this, Brucella was isolated on culture from stomach contents and cotyledons. The isolates from both the sites were characterized in detail, employing dye inhibition, phagetyping; the oxidative metabolic test and agglutination with monospecific sera. Both the isolates belonged to B. abortus biovar I, which was confirmed by the Central Veterinary Research Laboratory, Weybridge. The significance of isolation and the need to intensify similar studies have been discussed.