Variation analysis of theVP1and3ABCgenes from yellow cattle isolates persistently infected byFoot-and-mouth disease virus

The potential relationship between the establishment ofFoot-and-mouth disease virus(FMDV) persistent infection and gene variation was identified by investigating the variation ofVP1and3ABCgenes from yellow cattle persistent infection isolates. Five yellow cattle were inoculated on their tongue with 1.0×104ID50/ml of FMDV O/Akesu/58 strain. After displaying clinical or subclinical signs, they probably became asymptomatic carriers. Oesophageal–pharyngeal fluids were collected monthly from the carriers with a probang and inoculated into a baby hamster kidney cell line (BHK-21); 12 FMDV isolates were obtained. TheVP1and3ABCgenes of the 12 isolates were then amplified by reverse-transcriptase polymerase chain reaction (RT-PCR). Cloning and sequencing revealed that the homology of theVP1nucleotide and amino-acid sequence of all the isolates was above 98%, with no base deletion or insertion. When compared with the O/Akesu/58 FMDV strain, the homology of theVP1nucleotide sequence of the isolates was only 85%, and that of the deduced amino-acid sequence only 90%.There were several nucleotide mutations in theVP1gene of the isolates, including 16 consistent nucleotide mutations, with only two of them leading to a change in amino acid (I56→T, A210→E). Moreover, it was found that four nucleotide points and three amino-acid points had transversions among all isolates. The3ABCgene had only 13 nucleotide transversions and five amino-acid mutations. It was presumed that persistent FMDV infection might have little connection with variation in theVP1and3ABCgenes, and was probably related to other structural protein gene and key factors.