Submitted to: Canadian Journal of Veterinary Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 6, 2000
Publication Date: N/A
Interpretive Summary: The disease transmissible gastroenteritis has been estimated to cost U.S. swine producers more than 80 million dollars a year due to deaths in young pigs, poor feed conversion in finishing animals and loss of export markets for swine breeding stock. Because commercial vaccines are ineffective in eliminating the disease and reservoirs are unknown, methods to control the disease have not been successful. Passage of the virulent virus in cell culture reduced its virulence for young piglets but not its ability to elicited protective antibodies in sows vaccinated with the virus. Analysis of the nucleotide sequence of one gene identified a stable change in its sequence that was not present in the virulent virus.
Technical Abstract: Serial passage of virulent transmissible gastroenteritis (TGE) virus through cell culture reduced its virulence for three-day-old piglets. Intramuscular inoculation of pregnant gilts with two doses of this modified- live virus elicited a level of lactogenic immunity that protected their nursing piglets against a lethal dose of virulent virus. Sequence analysis of RT- PCR fragments of the spike gene from the original and the serially passed viruses were identical except for three bases. Gel analysis revealed that the RT-PCR fragment from the virulent virus ORF-3A gene was smaller than the fragment from the serially passed ORF-3A gene. Sequence analysis of the fragment from the serially passed virus revealed that the nucleotide sequence between base 5310 and base 5434 was replaced by a 636 bp fragment from the polymerase 1A gene. This replacement resulted in the loss of the CTAAACTT leader RNA-binding site and ATG start codon for the ORF-3A gene. Analysis of the same RT-PCR fragment after 30 additional cell culture passes, confirmed the replacement fragment was still present. The identification of a change in the genomic structure of the MLV TGE virus isolate is discussed in relation to virulence.