Swine Influenza in Sri Lanka

The Study

Conclusions

Acknowledgments

References

Figure 1

Figure 2

Table 1

Table 2

Technical Appendix 1 [10 KB - 1 page]

Technical Appendix 2 [154 KB - 3 pages]

Suggested Citation

Harsha K. K. Perera, Geethani Wickramasinghe, Chung L. Cheung, Hiroshi Nishiura, David K. Smith, Leo L. M. Poon, Aluthgama K. C. Perera, Siu K. Ma, Narapiti P. Sunil-Chandra, Yi Guan, and Joseph S. M. Peiris

Author affiliations: Author affiliations: University of Hong Kong, Hong Kong Special Administrative Region, People’s Republic of China (H.K.K. Perera, C.L. Cheung, H. Nishiura, D.K. Smith, L.L.M. Poon, S.K. Ma, Y. Guan, J.S.M. Peiris); University of Kelaniya, Kelaniya, Sri Lanka (H.K.K. Perera, N.P. Sunil-Chandra); Medical Research Institute, Colombo, Sri Lanka (G. Wickramasinghe); Japan Science and Technology Agency, Kawaguchi, Japan (H. Nishiura); Colombo Municipal Council, Colombo (A.K.C. Perera)

Abstract

To study influenza viruses in pigs in Sri Lanka, we examined samples from pigs at slaughterhouses. Influenza (H3N2) and A(H1N1)pdm09 viruses were prevalent during 2004–2005 and 2009–2012, respectively. Genetic and epidemiologic analyses of human and swine influenza viruses indicated 2 events of A(H1N1)pdm09 virus spillover from humans to pigs.

Data on swine influenza in southern Asia are limited (1–3). Sri Lanka is an island in this region with a human population of 21 million and a swine population of ≈83,785 (4,5). Pigs are not routinely imported into Sri Lanka. Most (61%) swine farms are located in the western costal belt spanning the Puttlam, Gampaha, Colombo, and Kalutara districts. In 2010, for these 4 districts, pig population densities were 7, 15, 12, and 1 animal per km², respectively (4,5). In 2001, for these districts, the human population densities were 246, 1,539, 3,330, and 677 persons per km², respectively (6).

The Study

During 2004–2005 and 2009–2012, tracheal and nasal swab and serum samples were collected from pigs at government slaughterhouses in Sri Lanka (Table 1). Culture tubes with MDCK cells were inoculated with the swab samples, and 2 blind passages were made. Also, embryonated eggs were inoculated by the allantoic route with swab samples collected during 2004–2005. Virus isolates were subtyped by hemagglutination inhibition (HAI) testing and neuraminidase inhibition testing with reference antiserum as described (7,8), and results were confirmed by sequencing the hemagglutinin and neuraminidase gene segments.
RNA extraction, cDNA synthesis, PCR, genome sequencing (9), and one-step quantitative real-time reverse transcription (RT-PCR) for rapid genotyping of all 8 gene segments (10) of A(H1N1)pdm09 isolates were performed as described. Methods used for the phylogenetic analysis are described in Technical Appendix 1