Diversity of SAT2 Foot-and-Mouth Disease Virus in Sudan: Implication for Diagnosis and Control

Abstract Like other East African countries, Sudan experienced circulation of several SAT2 topotypes. In Sudan, topotype XIII and VII of SAT2 virus were recorded. This work meant to evaluate the impact of such diversity on diagnosis and control. A Sudanese SAT2 foot-and-mouth disease virus (FMDV) of topotype VII originated in 2010 showed poor antigenic relationship (r1 value ≈ 0.00) with Sudanese SAT2 FMDV from 2008 when topotype XIII was circulating. After one or three doses of a vaccine derived from SAT2 virus in 2010, heterologous antibody titres with SAT2 virus in 2008 were ≤ 1.2 log 10, not consistent with likely protection, while homologous titres were 1.65 (after one dose) or 1.95 and 2.55 log10 (after 3 doses). SAT2 positive field sera from Sudan in 2016 were not unvaryingly identified by virus neutralization tests (VNT) employing SAT2 viruses from 2010 and 2008. Proportions of positive sera by SAT2 virus from 2010 were always higher than those by viruses from 2008; consistent with the more frequent and recent circulation of topotype VII prior to 2016. Proportions by SAT2 virus from 2010 were 0.68 (±0.1) in one location (n=72), 0.39 (±0.1) in another one (n=94) and 0.52 (±0.1) in the whole test group (n=166). Corresponding values by viruses of 2008 were 0.53 (±0.1), 0.27 (±0.1) and 0.38 (±0.1). In the whole test group, differences were statistically significant (p=.02339). Like post-vaccination sera, field sera (natural immunity) showed no considerable cross neutralization between topotype VII and presumably XIII; almost 45% (43/96) of SAT2 positive field sera were positive to one topotype but not to the other. Experimental and surveillance findings emphasized the implication of SAT2 diversity in Sudan. It is concluded that it is difficult to control SAT2 infection in Sudan using a monovalent vaccine. Beside a prophylactic vaccine from topotype VII, stockpiling of antigens from topotype XIII and rapid genotyping and matching studies are necessary approaches. When more frequent circulation of more than one topotype occurs, retrospective diagnosis by serological surveys could be problematic or imprecise.