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Open Access Research

Experimental infection with a Thai reassortant swine influenza virus of pandemic H1N1 origin induced disease

Nataya Charoenvisal1, Juthatip Keawcharoen2, Donruethai Sreta3, Siriporn Tantawet4, Suphattra Jittimanee1, Jirapat Arunorat1, Alongkorn Amonsin56 and Roongroje Thanawongnuwech16*

Author Affiliations

1 Department of Pathology, Faculty of Veterinary Science, Chulalongkorn University, Henri-Dunant Rd, Bangkok 10330, Thailand

2 Department of Veterinary Microbiology, Faculty of Veterinary Science, Chulalongkorn University, Henri-Dunant Rd, Bangkok 10330, Thailand

3 Faculty of Veterinary Medicine, Rajamangala University of Technology Tawan-ok, Bangpra, Chonburi 20110, Thailand

4 Department of Clinical Science and Public Health, Faculty of Veterinary Science, Mahidol University, Salaya, Nakhon Pathom 73170, Thailand

5 Department of Veterinary Public Health, Faculty of Veterinary Science, Chulalongkorn University, Henri-Dunant Rd, Bangkok 10330, Thailand

6 Emerging and re-emerging infectious diseases in animals, Research unit, Faculty of Veterinary Science, Chulalongkorn University, Henri-Dunant Rd, Bangkok 10330, Thailand

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Virology Journal 2013, 10:88  doi:10.1186/1743-422X-10-88

Published: 16 March 2013

Abstract

Background

Following the emergence of the pandemic H1N1 influenza A virus in 2009 in humans, this novel virus spread into the swine population. Pigs represent a potential host for this virus and can serve as a mixing vessel for genetic mutations of the influenza virus. Reassortant viruses eventually emerged from the 2009 pandemic and were reported in swine populations worldwide including Thailand. As a result of the discovery of this emergent disease, pathogenesis studies of this novel virus were conducted in order that future disease protection and control measures in swine and human populations could be enacted.

Methods

The pandemic H1N1 2009 virus (pH1N1) and its reassortant virus (rH1N1) isolated from pigs in Thailand were inoculated into 2 separate cohorts of 9, 3-week-old pigs. Cohorts were consisted of one group experimentally infected with pH1N1 and one group with rH1N1. A negative control group consisting of 3 pigs was also included. Clinical signs, viral shedding and pathological lesions were investigated and compared. Later, 3 pigs from viral inoculated groups and 1 pig from the control group were necropsied at 2, 4, and 12 days post inoculation (DPI).

Results

The results indicated that pigs infected with both viruses demonstrated typical flu-like clinical signs and histopathological lesions of varying severity. Influenza infected-pigs of both groups had mild to moderate pulmonary signs on 1-4 DPI. Interestingly, pigs in both groups demonstrated viral RNA detection in the nasal swabs until the end of the experiment (12 DPI).

Conclusion

The present study demonstrated that both the pH1N1 and rH1N1 influenza viruses, isolated from naturally infected pigs, induced acute respiratory disease in experimentally inoculated nursery pigs. Although animals in the rH1N1-infected cohort demonstrated more severe clinical signs, had higher numbers of pigs shedding the virus, were noted to have increased histopathological severity of lung lesions and increased viral antigen in lung tissue, the findings were not statistically significant in comparison with the pH1N1-infected group. Interestingly, viral genetic material of both viruses could be detected from the nasal swabs until the end of the experiment. Similar to other swine influenza viruses, the clinical signs and pathological lesions in both rH1N1 and pH1N1 were limited to the respiratory tract.

Keywords:
Influenza; Pandemic H1N1 2009; Pathogenesis; Reassortant; Swine; Thailand