Foot-and-mouth disease sero-surveillance in Africa and vaccine matching

Abstract

Foot-and-mouth disease virus (FMDV) was the first animal pathogen to be identified as a virus, and today, more than a century later, it remains at the forefront of major animal diseases. It is a very contagious disease and affects cloven-hoofed domestic and wild animals, mostly cattle, swine, sheep, goats and buffaloes. To be able to advice on the best control measures in Africa, information on transmission of FMDV, circulating FMDV topotypes and strains in Africa and how to match vaccines to circulating outbreak virus strains is essential. In this thesis these issues are addressed. The research work described in this thesis has been performed for three important aspects. The first was to get an overview of the role that animal husbandry, trade and wildlife have on the transmission of FMD virus and to provide a scientific basis for different FMD control measures in Africa. On the same track, two surveillance studies on FMD were carried out to know the level of sero-prevalence and identify the serotypes in cattle in Eritrea. The second was to determine which serological test method is best to be used to test cross-reactions in serology and addresses the inherent variability of the relationship coefficient (r1-value). To this end we analysed the cross-reactions in serology using serum samples from cattle vaccinated with 10 different FMDV serotype A strain vaccines using three serological test methods (virus neutralization test, neutralization index test and the liquid phase blocking ELISA). The third was to investigate whether the formulation of using different adjuvants, antigen composition, antigen payload and administration route of an FMD vaccine had any influence on the breadth of the antibody response in cattle. The review of reported outbreaks shows that substantial diversity of the circulating FMDV serotypes and topotypes is linked to the complexity of the livestock husbandry system, the marketing structure, and livestock-wildlife interface reflecting the significant influence on the risk of transmission of the virus. The sero-surveillance studies show that serology can give indications of virus circulation not detected by agent surveillance. The comparisons of tests used for antigenic matching shows that the LPB-ELISA is the best test for detecting antigenic differences between FMDV strains. Our study on vaccine formulation and application shows that breadth of the antibody response depends mainly on the vaccine strain; we therefore propose that, for vaccine preparation, only FMD virus strains are selected that, among other important characteristics, will induce a wide antibody response to different field strains. For Africa control of FMDV by vaccination seems the best option, as control of animal movement will be difficult. Use of broadly cross-protective vaccines for FMD is recommended as variant viruses could be introduced from neighbouring countries/regions. A vaccination strategy has still a number of challenges, among others vaccine quality control and quality control of the vaccination campaign. We believe that despite the enormous investments needed in the long run, FMDV control in Africa would improve national and regional economies and food security and protect livelihoods.