Use of Confocal Immunofluorescence Microscopy To Localize Viral Nonstructural Proteins and Potential Sites of Replication in Pigs Experimentally Infected with Foot-and-Mouth Disease Virus

Replication of foot-and-mouth disease virus in infected pig epithelium has been studied by immunofluorescence labeling of the viral nonstructural protein 3ABC and confocal microscopy. The results were correlated with viral RNA copy numbers in tissue samples from adjacent sites determined by reverse transcription-PCR (RT-PCR). Lesion formation was seen in the tongues and coronary band epithelia of infected pigs 2 days after infection. Viral replication was observed in cells of the epithelium of the tongue and coronary band but not in the associated stromal cells. Infected epithelial cells were present in the stratum spinosum, away from the lesion, with small lesions formed above the basement membrane. Viral replication was markedly reduced in tongue epithelium by day 3 postinfection but remained apparent in the coronary band tissue up to 5 days postinfection. These results were confirmed by the RNA copy number determined by RT-PCR.