Update on Foot-and-Mouth Disease in North-Western Syria: Circulating Serotypes and Post-Vaccination Monitoring

Information on the circulation of foot-and-mouth disease (FMD) in Western Syria is very limited. It is known that the country is affected by a prolonged humanitarian crisis that may certainly have contributed to such lack of information and the latest available data date back to 2002. Since 2021, there has been a significant increase in reporting of FMD clinical cases in dairy cattle in the region that led to implementing a vaccination campaign, using a tetravalent vaccine and targeting 35 subdistricts in the governorates of Aleppo and Idleb. Sampling for postvaccination monitoring was carried out, on average, around 2 months from the date of vaccination. Sera from 886 animals were collected and tested through ELISA tests to detect antibodies against FMD virus nonstructural proteins (NSPs) and structural proteins (SPs). Results revealed the presence of antibodies in 22.6% of the animals, directed towards viral NSP, indicating a previous infection. This was likely due to a rather recent exposure, considering the comparable NSP antibody prevalences among different age groups. Serological analyses revealed a good antibody response to Asia1 serotype following vaccination but an insufficient antibody response to serotypes A and O. Multiple logistic regression of the serological titers obtained for the different serotypes showed a significant association between high titers detected for serotype O and positivity towards the NSP of the virus. This result suggests the recent circulation of serotype O in the area under consideration.