The highly pathogenic avian influenza (HPAI) A (H5N1) virus remains a significant threat to the public health. Since the first outbreak in Hong Kong, 1997 (Chen et al., 2006), the H5N1 subtype of influenza virus has spread out to a great majority of Asian countries, Eastern Europe, northern Africa and recently to the North America (Grose and Chokephaibulkit, 2004, Keawcharoen et al., 2004, Rimmelzwaan et al., 2006 and Songserm et al., 2006). Current circulating of the H5 subtype AIVs in China is of international concern since it is easy for the viruses to be transmitted across geopolitical boundaries via wild BLZ945 and legal or illegal poultry trade (Keawcharoen et al., 2004, Kuiken et al., 2004 and Rimmelzwaan et al., 2006). Moreover, the H5N1 virus can cross species barriers and adapt to new hosts (Kuiken et al., 2004). Natural H5N1 AIV infections in several cat species have been reported in Southeast Asia (Kuiken et al., 2004, Rimmelzwaan et al., 2006 and Songserm et al., 2006). Contact exposure experiments of influenza virus (H5N1)-infected dogs with uninfected cats did not result in interspecies transmission. The different outcome of infection with the same dose of influenza virus (H5N1) suggested that cats were more susceptible than dogs to disease (Giese et al., 2008). Although cats had been considered resistant to disease from influenza virus infection, domestic cats and large felids are now known to be naturally and experimentally susceptible to infection with highly pathogenic avian influenza virus H5N1 (HPAIV-H5N1). The virus causes systemic infection, lung and liver are the mainly affected organs. Infected cats show fever, depression, dyspnoea, and neurological signs, but subclinical infections have also occurred. First, during H5N1 virus outbreaks, domestic cats are at risk of disease or death from H5N1 virus infection, either because of feeding on infected poultry or wild birds or because of contact with infected cats. Second, the role of cats in the spread of H5N1 virus between poultry farms, and from poultry to humans needs to be reassessed. Third, cats may offer an opportunity for this avian virus adapting to mammals, which increasing the risk of a human influenza pandemic (Marschall and Hartmann, 2008). Direct contact with sick or diseased poultry has been implicated as a major risk factor for feline infection with H5N1 AIV (Kuiken et al., 2004, Su et al., 2014 and Yu et al., 2014). Three clades of H5N1, 2.3.4, 2.3.2, and 7.2, have been co-circulating in domestic poultry mainland China in recent years. The clade 2.3.2 has circulated widely, causing a new wave of cross-continental spreading of H5N1 AIV from Asia to Europe since 2009. Clade 2.3.2 viruses have now been detected in 9 countries since 2007, which is highly pathogenic in chickens (100% mortality). Clade 2.3.2, clade 2.3.4 and clade 7 viruses are the main isolates in China, but the clade 2.3.2 viruses are the dominant prevalence strains, especially in southern China including Guangdong Province (Group, 2012, Guan et al., 2000, Jiang et al., 2010 and Li et al., 2010). Besides closely contact with domestic poultry, the special climatic and lifestyle environment in southern China provides more chances for cats to contact with other animals, such as wild aquatic birds, dogs, and humans. Thereby, it creates opportunities for interspecies transmission of the virus to cats. Meanwhile, cats exposed to the virus may act as repository for the influenza viruses due to frequent cohabitation and interactions with other animals and humans. Hence, cats carrying AIV can pose a threat to human health. Epidemiologic studies have identified poultry exposure as an important risk factor for human infections with H5N1 and H7N9, especially associated with live poultry markets (LPMs) (Kuiken et al., 2004, Wan et al., 2011, Wang et al., 2006 and Yu et al., 2014). As humans exposed to LPMs and poultry farms seems to be at increased risk of H5N1 and other AIVs infection, and dogs in China have been shown to be infected with AIVs, we sought to investigate if stray cats living in close-proximity to LPMs and H5N1-affected farms might have been infected with the H5N1 virus or other influenza viruses.
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