Investigations into the carrier-state of Theileria sp. (buffalo) in cattle

Abstract

The Theileria are apicomplexan parasites transmitted by ticks to vertebrate hosts. Most Theileria species exhibit some form of host or vector specificity, since under endemic conditions only a limited number of tick species act as vectors and not all vertebrate hosts are able to maintain a persistent carrier state. Data for Theileria sp. (buffalo) suggest host specificity for African buffalo (Syncerus caffer). However, T. sp. (buffalo) infections in cattle co-grazing with African buffalo have been reported in Kenya and schizonts were cultured from these infected cattle, raising questions regarding host specificity. A Corridor disease outbreak in 2013 on a ranch in South Africa where cattle co-grazed with Theileria parva and T. sp. (buffalo) infected buffalo presented the opportunity to investigate the possible carrier-state of T. sp. (buffalo) in cattle using real-time PCR analysis. Almost all buffalo (n = 19, 95%) were infected with T. sp. (buffalo) and showed CP values (22-20) indicative of high parasitemia similar to that observed for buffalo in endemic areas. Conversely, only ~14-27% cattle (n = 69, 100, 96) were positive with CP values (31-40) suggesting low parasitemia and a carrier state epidemiology different from African buffalo. Long term monitoring of T. sp. (buffalo) positive cattle showed that most cattle lost their parasitemia or presented fluctuating parasitemia around the PCR assay detection limit. A single splenectomized animal showed a persistent carrier state. The general trends and epidemiology observed in cattle infected with T. sp. (buffalo) are similar to that seen for buffalo-adapted T. parva, for which a defined carrier state in cattle has not yet been proven. The study suggests that cattle may be infected by T. sp. (buffalo) but are not definitive hosts that play an important part in the epidemiology of this parasite.