Field and laboratory studies on Corridor disease (Theileria parva infection) in cattle population at the livestock/game interface of uPhongolo-Mkuze area, South Africa

Abstract

Corridor disease (Theileria parva infection in cattle associated with carrier buffaloes) had not been reported to cause serious outbreaks in South Africa prior to 1994. In recent years, there has been an increase in the introduction of T. parva-infected buffaloes onto private game parks in Northern KwaZulu-Natal (KZN). The objectives of this study were to investigate the number of T. parva outbreaks in cattle at the livestock/wildlife interface and to establish the possible T. parva carrier status in cattle which were diagnosed to have recovered from clinical disease.

The occurrence of outbreaks was closely monitored from 2004 to 2009 covering a total of 15 localities. The observations included the number of cattle involved in the outbreaks, clinical signs, parasitological and post-mortem examinations, as well as serological and molecular tests specific for T. parva. Sentinel cattle were introduced to monitor tick transmission and some of these recovered from clinical T. parva infection in the field and confirmed to be positive by PCR, were challenged using lethal T. parva stabilates to ascertain their immune status.

Thirty-one Corridor disease outbreaks were recorded during the study period. Of the 846 cattle tested for Corridor disease during the study period, 140 (16.5%) were found positive by the real time PCR and IFA tests. Eighty-two (9.7%) cattle were found positive by the IFA test only. The prevalence of T. parva infection was 26.2%. Adult R. appendiculatus fed as nymphs on 5 bovines which recovered from clinical T. parva infection in the field transmitted only T. taurotragi to susceptible bovines. However, 8 of the field-recovered cattle resisted lethal challenge using T. parva tick stabilate. Though the study could not demonstrate cattle-to-cattle transmission by ticks using 5 previously infected cattle in the field, it is suggested that Corridor disease should be considered a potential emerging disease, and more stringent control methods should be implemented.

Introduction

Buffalo-associated theileriosis, commonly known in South Africa as Corridor disease, is a fatal disease of cattle caused by buffalo-derived Theileria parva transmitted by Rhipicephalus appendiculatus and Rhipicephalus zambeziensis. Corridor disease outbreaks are generally encountered when there is contact between carrier African buffalo (Syncerus caffer) and susceptible cattle in a vector area or when cattle graze pastures where carrier buffaloes have been. In the face of an outbreak, the mortality rate can exceed 90% (Neitz et al., 1955, Potgieter et al., 1988).

Being one of the so-called ‘Big-Five’, buffaloes are in high demand for introduction onto private game reserves as tourist attractions. Corridor disease is endemic in buffalo populations in Provinces of Northern Mpumalanga, North Eastern Limpopo at the Kruger National Park interface and in Northern KwaZulu-Natal (KZN). Most commercial cattle farms in these areas have been converted into game farms or game-ranching enterprises. Consequently, there has been an increase in the introduction of T. parva-infected buffaloes onto private game farms in these districts as well as other areas of KZN province.

National legislation on buffalo ranching prescribes that T. parva-infected buffaloes can only be kept on registered game farms, and those farms must be within the designated endemic Corridor disease control boundary of the province. One of the requirements for registration is that T. parva-infected buffaloes must be kept on farms adequately enclosed with a game-proof fence which is electrified on the inside with a minimum voltage of 5500 V at all times (Animal Diseases Act 1984, Act No. 35). In spite of disease-control regulations, an increase in Corridor disease outbreaks was reported in Vryheid, Nongoma, and beyond the Corridor disease boundary (Annual Report, 2003, Annual Report, 2004, Latif et al., 2005, Thompson et al., 2008). The course of the disease recognized from these outbreaks seemed to be different from what was believed to occur in the epidemiology of Corridor disease in South Africa (Potgieter et al., 1988), in which case not all cattle that showed clinical signs had died, but some fully recovered, possibly through treatment interventions using antibiotics (Thompson et al., 2008, Yusufmia et al., 2010). Theilericidal drugs such as “Buparvaquone, butalex” have been used to successfully treat clinical cases of T. parva and other pathogenic Theileria species, but this treatment does not sterilize infections, and a carrier state is produced in recovered cattle (Dolan, 1986, Potgieter et al., 1988). The South African Government policy continues to be eradication rather than control of T parva infections in cattle which led to prohibition of treatment of clinical cases. Control regulations are further enforced through prohibition of translocation of T. parva carrier buffaloes into non-endemic areas and by enforcement of quarantine measures coupled with strict tick control when outbreaks occur.

The introduction of East Coast fever (ECF, caused by T. parva) into southern Africa from eastern Africa in 1902 resulted in the death of about one million cattle (Potgieter et al., 1988). The disease was eradicated in the mid 1950s through very expensive measures including the introduction of chemical tick control, quarantine measures and slaughter policies (Lawrence, 1992). Cattle-adapted T. parva which cause ECF and January disease are maintained by cattle. However, the occurrence of a carrier state in the cattle population in South Africa has not been reported (Neitz et al., 1955, Neitz, 1957, Potgieter et al., 1988). It was shown that buffalo-derived T. parva stocks after serial passage in cattle by means of a vector tick can behaviourally change and become parasitologically indistinguishable from cattle-adapted T. parva stocks (Barnett and Brocklesby, 1966, Grootenhuis et al., 1987). Using tick-cattle passages of a buffalo-derived isolate, Maritim et al. (1992) were able to change the behaviour of the isolate to that of T parva cattle-derived which produced relatively high schizont parasitosis and piroplasm parasitaemia in cattle. However, the monoclonal antibody profile showed little evidence of antigen change of the original parasites during passages. Thus, Uilenberg (1981) suggested that classical East Coast fever might re-emerge at one time wherever strains of buffalo-derived occur. It was also shown that a buffalo-derived T. parva carrier state can be achieved in splenectomized and intact cattle after chemotherapy (Neitz, 1958, Potgieter et al., 1988). Therefore, the South African veterinary authorities are strict in the policy of eradication of Corridor disease because of the threat of re-emergence of ECF.

The main aim of this study was to clarify the epidemiology of Corridor disease in cattle at the livestock/game interface in uPhongolo-Mkuze area by monitoring the numbers of outbreaks and investigations on the possible occurrence of a carrier status in cattle.