Seroprevalence of Rift Valley fever and lumpy skin disease in African buffalo (Syncerus caffer) in the Kruger National and Hluhluwe-iMfolozi Parks, South Africa

Abstract

Lumpy skin disease (LSD) and Rift Valley fever (RVF) are transboundary viral diseases occurring in Africa and the Middle East (e.g. Israel, Saudi Arabia and Yemen) with increasing potential for global spread. Although the role of wildlife in the epidemiology of these diseases is still not clearly understood, the African buffalo (Syncerus caffer) is thought to play a role in the epidemiology of these diseases. This study sought to expand our understanding of the role of buffalo in the maintenance of RVF and LSD by determining seroprevalence to these viral diseases in buffalo during the inter-epidemic period. Lumpy skin disease is endemic in Africa, and has spread to the Middle East (e.g. Israel); consequently there is a high risk of lumpy skin disease virus (LSDV) expanding its geographical distribution to other areas and due to its economic importance it is included in the list of Notifiable Diseases of the World Organization of Animal Health (OIE). The African buffalo is also suspected to play a role in the epidemiology of RVF. Like LSD, RVF was, until recently, only endemic in Africa. However, it spread to the Arabian Peninsula (Saudi Arabia and Yemen) in 2000 exacerbating concerns that it will extend to other regions of the world. Studies have already established that competent mosquito vectors for RVFV exist in North America and other parts of the world. A total of 248 buffalo sera was tested for antibodies to capripoxviruses and neutralising antibodies against LSDV and RVFV using an indirect enzyme-linked immunosorbent assay (I-ELISA) as well as the serum neutralisation test (SNT). The samples were obtained from the Kruger National Park (KNP) and Hluhluwe-iMfolozi Park (HiP) in South Africa. The prevalence of antibodies to LSDV and RVFV in the sera tested was 70/248 (28.2%) and 15/248 (6.1%), respectively using an I-ELISA. The LSDV I-ELISA, using a sheeppox virus as antigen, has not been validated for use in African buffalo. The high percentage of LSDV positive antibody results obtained in this study is however a concern. Results obtained is in contrast with other published results as well as results obtained with the SNT for antibodies against LSDV. The SNT is currently the gold standard for LSDV antibody testing. Using this test for LSDV in this study, 5/66 (7.6 %) samples tested positive. The results of the RVF I-ELISA, which had previously been validated for use in the African buffalo, correlated with the SNT results. From 12 SNT RVFV-positive sera, 3 (25%) had very high SNT titres of 1:640. Neutralising antibody titres of more than 1:80 were found in 80% of the positive sera tested. Eleven buffaloes (4.4% of the total samples) also showed evidence of antibodies to both LSDV and RVFV. The results obtained in this study complement other reports indicating the role of African buffalo in the epidemiology of these diseases during inter-epidemic periods.