Mbizenia SN, Potgieter FT et al. Field and laboratory studies on Corridor disease (Theileria parva infection) in cattle population at the livestock/game interface of uPhongolo-Mkuze area, South Africa, Tick and tick-borne Diseases 4 2013; 227-234
Why they did it
Corridor disease, caused by buffalo associated Theileria parva, had not been reported to cause major disease outbreaks prior to 1994 however with the strengthening game ranching market has come a closer cattle/wildlife interface with resultant Corridor disease outbreaks in Vryheid, Nongoma which falls outside of the Corridor disease boundary. The course of the disease also seemed different to what was believed to be epidemiologically true for Corridor. Cattle associated T. Parva causes the highly infectious East Coast Fever (ECF) in cattle. It was introduced into South Africa in 1902 and was eradicated after causing the death of over 1 million cattle at considerable cost to the farmer and government. Due to the high similarity of the two strains and the possibility of re-emergence of ECF if Corridor disease is allowed to seep into the cattle population, it is a strictly state controlled disease. As a result of concerns about the movement of Corridor disease out of large wildlife parks and into the surrounding cattle population this epidemiological study was conducted.
What they did
The occurrence of Corridor disease outbreaks within cattle populations in the uPhongolo-Mkuze are in the Zululand district of KZN were monitored from 2004 to 2009. At sites where disease outbreaks occurred, sentinel cattle were introduced which were tested negative to T.parva exposure prior to introduction, R.appendiculatus were collected from infected animals and of all infected animals there were 8 positive animals who had survived initial infection. These were challenged again with a virulent buffalo-derived T. parva stabilite.
What they found
31 outbreaks of Corridor disease were recorded from 2004 to 2009. Both commercial farmers and communal grazers were affected with 3 of the commercial farms experiencing outbreaks every year whereas others had only a single outbreak during the entire study period. From 15 localities where cattle were bordering along the wildlife zone 846 cattle were tested and T.parva prevalence within these animals was 26.2%. It was found that there was a strong seasonal peak in clinical outbreaks with 88% occurring between March and May which corresponded to the adult stage of the tick. Of the sentinel cattle introduced onto the infected farms there was a 36% (10/28) infection rate with a 29% (8/28) mortality rate with all deaths of the sentinel cattle corresponding to natural outbreaks in the resident cattle. Of the 8 animals that had survived a previous outbreak that were exposed again to T. parva, only one developed a mild clinical reaction, the rest showed no clinical signs despite displaying a parasitaemia.
Take home message
Corridor disease is increasing in prevalence at the cattle/wildlife interface within Northern KZN with two of the affected farms being well away from the known Corridor disease barrier and bordering onto Ithala Game Reserve. Of the animals infected 6.5% of cattle remained seropositive and parasitaemic for between 30 – 50 days. These animals could act as potential T. parva carriers although it is yet to be seen if they in turn can infect R. appendiculatus and therefore infect susceptible cattle.