#12-095

Complete

Date Full Report Received

07/01/2013

Date Abstract Report Received

07/01/2013

Investigation

Institution:
Primary Investigator:

Since the 2009 pandemic H1N1 virus (pH1N1) was found to transmit to pigs worldwide including in the USA, subsequent reassortment events between pH1N1 and endemic swine influenza viruses (SIVs) have occurred. We have isolated and characterized 60 swine influenza isolates from diseased or dead pigs in Midwestern swine farms with outbreaks of respiratory disease that include 1 H1N1, 11 H3N2 and 15 H1N2 reassortant SIVs containing 1 to 6 genes from the pH1N1. To date little is known about these novel reassortant SIVs and whether these novel reassortant viruses will be maintained in the swine operations. In the present proposal, we investigated pathogenicity and transmissibility of these novel reassortant viruses in pigs to determine whether they can be established and become predominant viruses in pigs.

To determine pathogenicity and transmissibility of novel reassortant H3N2 SIVs, 3 reassortant H3N2 and 1 endemic H3N2 viruses, which were full-genome sequenced, were selected for in vitro and the pig study: one reassorant H3N2 virus has 5 genes (PB2, PA, NP, M and NS) from the pH1N1; another 2 reassortant H3N2 viruses both contain NP, M and NS genes from the pH1N1, but they have a genetically different NA gene; the endemic H3N2 virus is a triple reassortant virus with genes from avian- (PB2 and PA), human- (HA, NA and PB1) and swine-origin (NP, M and NS) viruses. All 3 novel reassortant H3N2 viruses grew to higher titers than the control endemic H3N2 SIV in canine, swine and human cell lines. In the pig study, all 3 novel reassortant viruses were able to replicate efficiently in lungs and transmit to sentinel animals, similar to the control endemic H3N2 virus. The novel reassortant viruses with 3 genes (NP, M and NS) from pH1N1 were more transmissible when compared to the reassortant virus with 5 genes (PA, PB2, NP, M and NS) from pH1N1. Concurrent swine surveillance for influenza viruses showed that the novel H3N2 virus with 3 genes from pH1N1 is continually isolated from swine herds in the Midwest swine farms.

To investigate pathogenicity and transmissibility of novel reassortant H1N2 SIVs, One reassortant H1N2 (2+6 rH1N2), 1 H1N2 variant isolated from swine (swH1N2v), 1 H1N2 variant isolated from human (huH1N1v) and 1 endemic H1N2 (eH1N2) viruses were selected for the pig study: the selected reassorant H1N2 (2+6 rH1N2) virus has 6 internal genes (PA, PB2, PB1, NP, M and NS) from the pH1N1 and 2 surface gene from endemic H1N2 SIVs; the H1N2 variants isolated from swine (swH1N2v) and human (huH1N1v) have M gene from the pH1N1 and remaining 7 genes from endemic H1N2 viruses. All 4 viruses replicated efficiently in pigs’ lungs and successfully transmitted to sentinel animals. However, both variant H1N2 viruses caused more severe lung lesions in infected pigs when compared to the 2+6 rH1N2 and eH1N2 viruses. Although all four viruses were detected in the lungs of contact animals, the swH1N2v shed more efficiently than the other three viruses in contact animals. Additionally, the huH1N2v displayed delayed and inefficient shedding kinetics in sentinel animals. Taken together, the H1N2 variant viruses are pathogenic and transmissible in pigs and could pose a threat to public and animal health.

All these results demonstrate that novel reassortant SIVs including H3N2 and H1N2 subtypes are pathogenic and transmissible in pigs which is in agreement with outbreaks observed in the swine farms. Concurrent swine surveillance for influenza viruses showed that both the novel H3N2 virus with 3 genes from pH1N1 and the H1N2 variant are 2 major novel reassortant viruses that are continually isolated from swine herds in the Midwest swine farms, indicating that they will be most likely maintained in swine herds and could pose a big threat to the swine industry.

Contact information: Dr. Wenjun Ma, Email: wma@vet.k-state.edu; Tel: 785-532-4337