Reassortment of avian H1N1 and swine H3N2 influenza viruses in pigs

A genetic reassortment of influenza viruses of different hosts is an important mechanism for overcome the species barrier. Therefore the aim of this study was to define the percentage of reassortants and their gene constellation after co-infection of pigs with 2 influenza virus strains of different subtype and origin.

Six pigs were intranasally inoculated with A/Swine/Gent/172/08 (H3N2) and A/Duck/Italy/1447/05 (H1N1) viruses to study the likelihood of genetic reassortment in the pig. At 2 DPI, 6 naïve pigs were introduced.

Swabbing and body temperature check were performed daily. At 4 DPI/DPC 3 infected and contact exposed pigs were euthanized and samples from the respiratory tract were tested by qRT-PCR (M gene). Blood samples for HI test and IPMA were collected at 14, 21 and 28 DPI/DPC.

All positive in the qRT-PCR samples were used for plaque purification and virus isolation. The genetic characterization of isolated viruses was executed with use of different molecular methods (RT-PCR, PCR-RFLP, sequencing).

Virus shedding was detected from 1 to 6 DPI/DPC in the infected and contact exposed pigs. From all samples positive in the qRT-PCR in total, 202 and 26 isolates from tissue and swab samples were obtained, respectively. In both cases most of them (for tissue about 65%; for swabs more than 90%) were isolate from contact exposed pigs.

A differentiation between avian and swine origin of all genes of obtained isolates was done. All viruses from tissue were H3N2, whereas from swabs 18 isolates were H3N2 and 8 isolates (3.5%) were H1N1. All H1N1 viruses were isolate from contact exposed pigs. Among the H1N1 isolates 3 strains (1.3%) were reassortants with one gene of swine origin (NP or M). All collected sera were seronegative for H1N1 and seropositive for H3N2 in HI test, whereas in IPMA all of them were seropositive for both H1N1 and H3N2 virus.

Based on the results we can state that for the reassortment to occur co-infection of pig with two or more influenza virus and their efficient replication must take place. However, the reassortment is a very complex process and different factors such as location of virus replication, its virulence and titer, a host susceptibility e.t.c, may influence on its occurrence. Under experimental conditions we manage to achieve the reassortation between H1N1 and H3N2 viruses of different origin, however the percentage of reassortants suggests low genetic compatibility of viruses used in the study.

*This work was supported by FLUPIG Project No 258084 founded by EC FP7.

Disclosure of Interest: None Declared.