Diversity of SAT2 foot-and-mouth disease virus in Sudan: implication for diagnosis and control.

Like other East African countries, Sudan experienced circulation of more than one topotype of SAT2 foot-and-mouth disease virus (FMDV). In Sudan, topotype XIII of SAT2 virus was recorded in 1977 and 2008 and topotype VII in 2007, 2010, 2013, 2014 and 2017. This work evaluated the impact of such diversity on diagnosis and control. After one or three doses of a vaccine derived from a Sudanese SAT2 virus of topotype VII originated in 2010, heterologous neutralizing antibody titres with Sudanese SAT2 viruses in 2008 were ≤ 1.2 log 10, not consistent with likely protection. Simultaneously, homologous titres were 1.65 (after one dose) or 1.95 and 2.55 log10 (after 3 doses). When r1 values between the vaccine virus and the SAT2 viruses isolated in 2008, whilst topotype XIII was circulating, were derived, values (≈ 0.00) suggested similarly poor antigenic relationship and unlikely cross protection. Concurrently, 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 enhanced virological surveillance with rapid genotyping and matching studies are necessary approaches. When more frequent circulation of more than one SAT2 topotype occurs, retrospective diagnosis by serological surveys could be problematic or imprecise.

Serological detection and genetic characterization of foot-and-mouth disease virus from cattle in northern sudan, 2016­2018.

Northern Sudan is an important corridor cluster between pools of foot-and-mouth disease virus (FMDV) in East and North Africa. It involves almost the whole border area with Egypt and represents a considerable part of a projected disease-free zone in Sudan. The study monitored FMD infection between 2016 and 2018 in Northern Sudan. Clinical and serological surveillance were carried out. Results largely confirmed previous reports that have described the relatively lower circulation of FMDV in the area than in other parts of the country. Clinical FMD was confirmed, once in the three years period, as serotype O of an unnamed lineage within the topotype East Africa 3 (EA3). Using serial testing (the ID ELISA and virus neutralization test), sero-prevalence estimates of serotype-specific antibodies in the two States of Northern Sudan ranged between 15.4% (serotype A) in the River Nile State to 3.4% (serotype SAT2) in the Northern State. Striking disparities between patterns of FMD in Northern Sudan and the rest of Sudan were observed. Unlike Western, Eastern, Central and Southern Sudan, no predominance of serotype O antibodies was detected in Northern Sudan. Concurrently, a serotype O isolate from Northern Sudan in 2016 was found to be of transboundary nature circulating in East and North Africa and in the Middle East (nt. id. > 99%); like serotype O that caused the last episode of disease in Northern Sudan in 2012. Molecular findings were compatible with the inferred low circulation of FMDV in Northern Sudan. Elsewhere in Sudan, endogenous serotype O viruses seemed to be circulating more unabated. It was concluded that low animal density and limited animal movement in Northern Sudan together with the high antibody levels against serotype O in immediately neighbouring States (Khartoum and Kassala) effectively decreased infiltration of endogenous O viruses.