Background and aim: The pandemic (H1N1) 2009 influenza (H1N1pdm09) virus has affected both human and animal populations worldwide. The transmission of the H1N1pdm09 virus from humans to animals is increasingly more evident. Captive animals, particularly zoo animals, are at risk of H1N1pdm09 virus infection through close contact with humans. Evidence of exposure to the H1N1pdm09 virus has been reported in several species of animals in captivity. However, there is limited information on the H1N1pdm09 virus infection and circulation in captive animals. To extend the body of knowledge on exposure to the H1N1pdm09 virus among captive animals in Thailand, our study investigated the presence of antibodies against the H1N1pdm09 virus in two captive animals: Camelids and Eld´s deer.

Materials and methods: We investigated H1N1pdm09 virus infection among four domestic camelid species and wild Eld´s deer that were kept in different zoos in Thailand. In total, 72 archival serum samples from camelid species and Eld´s deer collected between 2013 and 2014 in seven provinces in Thailand were analyzed for influenza antibodies using hemagglutination inhibition (HI), microneutralization, and western blotting (WB) assays.

Results: The presence of antibodies against the H1N1pdm09 virus was detected in 2.4% (1/42) of dromedary camel serum samples and 15.4% (2/13) of Eld´s deer serum samples. No antibodies were detected in the rest of the serum samples derived from other investigated camelids, including Bactrian camels (0/3), alpacas (0/5), and llamas (0/9). The three positive serum samples showed HI antibody titers of 80, whereas the neutralization titers were in the range of 320-640. Antibodies specific to HA and NP proteins in the H1N1pdm09 virus were detected in positive camel serum samples using WB. Conversely, the presence of the specific antibodies in the positive Eld´s deer serum samples could not be determined using WB due to the lack of commercially labeled secondary antibodies.

Conclusion: The present study provided evidence of H1N1pdm09 virus infection in the captive dromedary camel and Eld´s deer in Thailand. Our findings highlight the need for continuous surveillance for influenza A virus in the population of dromedary camels and Eld´s deer. The susceptible animal populations in close contact with humans should be closely monitored. Further study is warranted to determine whether Eld´s deer are indeed a competent reservoir for human influenza virus.