Pilot investigation of selected milk-borne pathogens in communal cattle in the uMkhanyakude district of KwaZulu-Natal, South Africa

Abstract

This study was a pilot investigation of selected milk-borne pathogens in communal cattle in the UMkhanyakude district of KwaZulu-Natal, South Africa. Fifty seven milk samples were collected from 12 bovine tuberculosis (BTB) positive cattle herds. Udder hygiene assessment was also carried out during sample collection. Convenience sampling of milk samples was done during a BTB diagnostic pilot project involving selected BTB positive herds at the Nibela diptank in the uMkhanyakude district. The milk samples were tested for the presence of the following milk borne pathogens: Mycobacterium bovis (M. bovis), Brucella abortus (B. abortus) and Staphylococcus aureus (S. aureus). In addition, the microbiological quality of milk in the study population was assessed by means of total bacterial counts, total coliforms counts and total E. coli counts. A questionnaire survey to determine the level of knowledge, milking hygiene and milk consumption behaviour of 12 households that participated in the BTB pilot study was administered. A total of 21 cattle representing 6 cattle herds, tested positive for B. abortus antibody on Brucella Milk Ring (BMRT) test. The detection of S. aureus in the milk samples was done by bacterial culture, catalase tests, oxidase tests and staphylase tests. The prevalence of S. aureus was found to be 49%. The isolation of B. abortus and M. bovis was attempted but compromised by constraints that were beyond the investigator?s control (drought related decrease in milk production and inadequate laboratory facilities). The constraints included inability to collect adequate quantities of milk as required for tests due to a sharp decrease in milk production of cows during the severe prevailing drought. Lack of adequate laboratory facilities for B. abortus and M. bovis culture in the study area and the resulting long time lag between collection of milk samples and identification of B. abortus and isolation of M. bovis at the designated bacteriology laboratory of DVTD further decreased the probability of successful culture. The seroprevalence of B. abortus in milk was determined by Brucella Milk Ring test and was found to be 38%. The presence of M. bovis was confirmed by PCR in one pooled milk sample from 5 cows. On quantification of total coliforms, 21% of the milk samples had more than 20 cfu/ml and 59% of milk samples contained E. coli. It was found that 59% of the milk samples yielded 100 cfu/ml and 26% of milk samples had results recorded as ?too numerous to count? and 15 % milk samples had total bacterial count of less than 100 CFU/ml. All 10 respondents who reported consumption of milk from their own cattle confirmed that all household members consumed milk on daily basis. With regards to treatment of milk before consumption, 10 respondents indicated that they either boil or sour the milk before consumption. Consumption of raw milk was reported by 1 respondent and only 1 respondent indicated that they sold excess milk. As treatment of milk reduces the risk of zoonotic pathogens transmission from milk to humans the fact that the majority of respondents applied his intervention before consumption can be seen as risk reduction behaviour for the transmission of zoonotic pathogens from milk to humans. Although the results on the presence of B. abortus were inconclusive, the overall findings in the study indicated that the raw milk in the study population posed a high risk of transmitting zoonotic diseases to humans. The cows? milk in this study was found to be of poor microbiological quality because of the presence of M. bovis, high prevalence of S. aureus and the counts for coliforms and E. coli that exceeded the limits set by the South African standards under the Foodstuffs, Cosmetics and Disinfectants Act, No. 54 of 1972: Regulations relating to milk and dairy products.