Short communication: Evaluation of Brucella infection of cows by PCR detection of Brucella DNA in raw milk

The collection of serum samples from cows is frequently difficult to implement in large-scale surveys, and may involve a high risk of occupational infection. This study assessed the potential of using raw milk sampling as a suitable method for use in a pilot survey of Brucella abortus infection status in cattle. Raw milk samples from 816 cows were examined. Polymerase chain reaction assays of raw milk, with primers derived from the IS711 element of the Brucella genome, were used. Of the cows, 55 were Brucella positive based on serum agglutination test (SAT) results. Polymerase chain reaction amplified Brucella DNA in 25 (45%) of the 55 SAT-positive cows. All of the 689 SAT-negative cows were found to be negative in PCR assays of their milk. Brucella infection status based on PCR results was then predicted for 72 cows from private herds in which the brucellosis status was unknown. Subsequently, SAT verification of Brucella status was performed. There was no significant difference between predicted and actual SAT-positive rates in those 72 cows. This study indicates a relationship between Brucella detection levels obtained using milk-based PCR results and SAT results. The specific, rapid, and easy sampling procedure within milk-based PCR assaying for brucellosis detection makes the milk PCR method an attractive alternative for evaluation of B. abortus infection in cows, particularly if used as a routine screening and surveillance tool to reduce brucellosis outbreaks.