Foot-and-mouth disease virus (FMDV) RNA was measured using quantitative reverse transcription-PCR (qRT-PCR) assays in oral swab and probang samples collected from cattle and pigs during experimental infections with serotype O FMDV. During acute infection, FMDV RNA was measurable in oral swabs as well as in probang samples from both species. FMDV RNA could be detected in oral swabs and probang samples 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 oral swabs 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 oral swabs harvested beyond 10 days post infection (dpi), despite the presence of FMDV RNA in probang samples 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 probang samples 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 oral swabs 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.
Bibliographical noteFunding Information:
This work was partially financed through a PhD-scholarship to CS, from the Technical University of Denmark. Soren Alexandersen, NCFAD, Winnipeg is thanked for having supplied the original virus stock that was used for the experiments. The animal care-takers at DTU-Vet, Lindholm, are thanked for assistance during animal experiments, and Jani Christiansen, Jane Borch and Tina Frederiksen are thanked for assisting in processing of samples.
- FMDV persistence
- Foot-and-mouth disease