Improvement of a liquid phase blocking ELISA for enhanced detection and measurement of antibodies against the SAT3 serotype of FMDV

Abstract

Foot-and-mouth disease virus (FMDV) is the causative agent of one of the most serious infections of cloven-hoofed animals. An outbreak of FMD not only severely decreases livestock productivity, but also impacts on both the local and export trade of susceptible animals and their products. The Southern African Territories (SAT) types 1-3 are endemic to sub-Saharan Africa and display greater intratypic genomic and antigenic variation than the traditional Euro-Asian types. Southern Africa has an abundant wildlife, especially in National Parks and game reserves. Wildlife, particularly African buffalo (Syncerus caffer), is involved in virus maintenance and epidemiology of the disease. In communities within the proximity of National Parks and game reserves, the wildlife-livestock interface presents a challenge and poses difficulty to livestock disease eradication and control in Africa. In this study, the influence of modifications to the reagents has on the specificity, sensitivity and repeatability of a LPBE, used for the detection of antibodies against FMD, was determined. The sensitivity of the LPBE is dependent on the antigen used in the test and the ability of the sera to cross-react with the antigen. The purified and non-purified virus used as antigen and the capture and detector antibodies were prepared and standardized for this purpose. An attempt was made to reduce the subtype-specificity of the LBPE by including antigens from all the relevant SAT3 strains. A total of 515 sera from FMDV exposed cattle in Mpumalanga during 2011-2012; 1398 sera from unexposed cattle obtained during an FMD survey conducted in the Northern Cape, and 286 sera from FMDV vaccinated cattle next to the Kruger National Park (KNP) were tested with the improved ELISA. A statistical analysis was conducted to compare the results obtained with the newly developed ELISA and the current in house ELISA. The new assay has higher sensitivity for detecting antibodies in vaccinated animals compared to the standard LPBE. The test is specific and suitable for detection of antibodies, and plays a key role toward the control of FMD, specific and suitable for identification and typing of all SAT3 serotype across the range of the genetic variations in the SAT3 serotype of FMDV.