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United States Department of Agriculture

Agricultural Research Service


Location: Animal Parasitic Diseases

Title: Evolution and homologous recombination of the hemagglutinin-esterase gene sequences from porcine torovirus

item Cong, Y -
item Zarlenga, Dante
item Richt, J -
item Wang, X -
item Wang, Y -
item Wang, J -
item Ren, Y -
item Li, G -
item Ren, X -

Submitted to: Virus Genes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 24, 2013
Publication Date: N/A

Interpretive Summary: Toroviruses are enveloped, positive-stranded RNA viruses that cause severe enteric diseases in animals and humans. Toroviruses identified thus far have been grouped on the basis of host tropism namely, porcine (PToV), bovine, equine and human toroviruses. Epidemiological information on PToV derived from studies in different countries indicates that these toroviruses are circulating in pig populations worldwide with a high prevalence. Research on toroviruses has been limited because they are very difficult to propagate in cell culture. Few studies have investigated recombination among toroviruses because of the ability of these viruses to rapidly mutate. Therefore, the objective of the present study was to gain new insights into the evolution, homologous recombination and selection pressures imposed on the PToV by examining on all currently available sequence data for the hemagglutinin-esterase (HE) gene of PToV. Results showed that all PToV HE sequences partitioned into two distinct groups where the most recent common ancestor in this study is estimated to have emerged 62 years ago. No geographical barriers were seen because both groups contained isolates from Spain, Italy and South Korea. At least one recombination event was observed between isolates from geographically distinct South Korean farms suggesting that these viruses evolve rapidly and are capable of interchanging genetic information. The information in this study is important to other scientists and those investigating coronaviruses in general because it provides important insights into the rapid dissemination of the viruses worldwide and to their ability to mutate and remain viable in nature.

Technical Abstract: The objective of the present study was to gain new insights into the evolution, homologous recombination and selection pressures imposed on the porcine torovirus (PToV), by examining changes in the hemagglutinin-esterase (HE) gene. The most recent common ancestor of PToV was estimated to have emerged 62 years ago based upon HE gene sequence data obtained from PToV isolates originating from Spain, South Korea, Netherlands, Hungary and Italy and using the HE gene of Bovine torovirus isolates Niigata1 (AB661456) and Niigata3 (AB661458) as outgroups. The HE gene sequence data segregated all PToV isolates into two well-supported monophyletic groups; however, various isolates from Spain, Italy and South Korea did not segregate geographically suggesting very recent translocation of the viruses to these localities. Evidence of recombination was observed between 2 South Korean isolates that partitioned into 2 distinct subclades. Data further suggest that most nucleotides in the HE gene are under negative selection; however, changes within codon 237 showed evidence of positive selection.

Last Modified: 4/24/2014
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