Detection of a carrier state in Theileria parva-infected cattle by the polymerase chain reaction.

Two sets of oligonucleotide primers, one derived from a repetitive sequence and the other from the gene encoding a 67 kDa sporozoite antigen of Theileria parva, were used to amplify parasite DNA from the blood of T. parva-infected carrier cattle using the polymerase chain reaction (PCR). PCR amplification products were obtained from 15 carrier cattle infected with one of 4 different T. parva stocks. Successful amplifications were performed using DNA from 2 cattle infected with T. p. parva Pemba Mnarani, 10 cattle infected with T. p. parva Marikebuni, 2 cattle infected with T. p. bovis Boleni and 1 animal infected with T. p. lawrencei 7014. No amplification products were obtained from any of 7 cattle which had been infected with the T. p. parva Muguga stock. A synthetic oligonucleotide, which hybridized specifically to T. p. parva Marikebuni DNA among 6 T. parva stocks tested, was designed using sequence data from within the region of the T. parva genome amplified by the repetitive sequence primers. The oligonucleotide was used to probe PCR products and to increase the sensitivity and specificity of carrier animal detection. Southern blot analysis using a T. parva repetitive sequence probe demonstrated the existence of restriction fragment length polymorphisms between parasites isolated from T. p. parva Marikebuni-infected carrier cattle. The use of the PCR and other methods of carrier animal detection are discussed.