The comparative utility of oral swabs and probang samples for detection of foot-and-mouth disease virus infection in cattle and pigs

Foot-and-mouth disease virus (FMDV) RNA was measured using quantitative reverse transcription-PCR (qRT-PCR) assays in oralswab and probangsamples collected from cattle and pigs during experimental infections with serotype O FMDV. During acute infection, FMDV RNA was measurable in oralswabs as well as in probangsamples from both species. FMDV RNA could be detected in oralswabs and probangsamples from a time point corresponding to the onset of viremia in directly inoculated animals, whereas animals which were infected through contact exposure had low levels of FMDV RNA in oralswabs before viral RNA could be measured in serum. Analysis of samples collected from cattle persistently infected with FMDV showed that it was not possible to detect FMDV RNA in oralswabs harvested beyond 10 days post infection (dpi), despite the presence of FMDV RNA in probangsamples that had been collected as late as 35 dpi. An interesting feature of the persistent infection in the cattle was the apparent decline in the level of FMDV RNA in probangsamples after the acute phase of infection, which was followed by a marked rise again (in all the carrier animals) by 28 dpi.

Results from this study indicate that qRT-PCR analysis of oralswabs is a useful approach in order to achieve a time efficient and reliable initial diagnosis of acute FMD in cattle and pigs, whereas probang sampling is essential for the detection of cattle that are persistently infected “carriers” of FMDV.