A field study evaluating the humoral immune response in Mongolian sheep vaccinated against sheeppox virus

Sheeppox is a transboundary disease of small ruminants caused by infection with the capripoxvirus sheeppox virus (SPPV). Sheeppox is found in Africa, the Middle East and Asia and is characterised by fever, multifocal cutaneous raised lesions, and death. Vaccination with live attenuated capripoxvirus (CPPV) strains is an effective and widely used strategy to contol sheeppox outbreaks, however there are few reports of post-vaccination field surveillance studies. This study used a commercially available ELISA to examine quantitative and temporal features of the humoral response of sheep vaccinated with a live attenuated CPPV strain in Mongolia. 400 samples were tested using the ELISA commercial kit, and a subset of 45 samples were also tested with a virus neutralisation test (VNT). There was substantial agreement between the VNT and ELISA tests. Antibodies to CPPV were detected between 40 and 262 days post vaccination. There was no significant difference between serological status (positive / negative) and sex or age, however an inverse correlation was found between the length of time since vaccination and serological status. Animals between 90 and 180 days post-vaccination were more likely to be positive than animals greater than 180 days post vaccination. Our results show that a commercial CPPV ELISA kit is a robust and reliable assay for post CPPV vaccination surveillance in resource-restricted settings and provide temporal parameters to be considered when planning sheeppox post-vaccination monitoring programmes.