Most human cases of infection with zoonotic influenza viruses are sporadic and result from close contact with poultry, swine or their products, via activities that include occasional contacts at markets or fairs, care giving, slaughtering, butchering and preparation of meat for consumption (Table 1). Similarly, transmission of LPAIV H7N7 to humans has occurred during necropsy of infected harbour seals [42]. Such at-risk activities may lead to inhalation of infectious fomites, droplets or aerosols, or self-inoculation of the upper respiratory tract or conjunctiva [22]. Occupational exposure to poultry

or swine greatly increases the risk of zoonotic influenza virus infection [43]. In the case of HPAIV H5N1, this is further demonstrated in Egypt, where slaughtering, de-feathering, and preparation of poultry for consumption are carried out mainly by women, who were shown to present a higher risk of infection than men [44]. Nonetheless,

Gefitinib in vitro given the intensive contact between humans and their livestock worldwide, and the relatively few reported cases of zoonotic influenza virus infections, other barriers likely limit cross-species BI 2536 supplier transmission of influenza viruses from animals to humans. The route of transmission of influenza viruses from animal reservoirs to humans may represent another important animal-to-human transmission barrier. Faecal-oral transmission of LPAIV appears favoured by aquatic habitats and associated waterbird behaviour, and is

the main route of transmission of LPAIV in wild bird reservoirs [2], [15] and [16]. On the other hand, respiratory transmission of influenza viruses appears to be favoured among terrestrial birds and mammals [7] and [25]. The ability of zoonotic influenza viruses to use the respiratory route of transmission, in particular via droplet or aerosol transmission, should probably be considered an important determinant for crossing animal-to-human transmission barriers. In the case of HPAIV H5N1, transmission via the digestive tract has been suggested in mammals, given the frequent transmission of these viruses to carnivores [7] and following reports of human patients presumably infected after consumption DNA ligase of raw duck blood [45]. This is unusual as this route of transmission is generally not exploited by influenza viruses in mammals. Experimental studies demonstrated that consumption of infected carcasses led to HPAIV H5N1 infection in cats, ferrets and red foxes (Vulpes vulpes) [46], [47], [48] and [49]. Further studies demonstrated infection following entry via the intestinal tract in ferrets, mice, hamsters and cats [49], [50], [51] and [52]. The potential use of both respiratory and oral routes of transmission of HPAIV H5N1 in mammals may contribute to their unusual ability to cross the species barrier from birds to mammals and increase the risk of eventual adaptation of these viruses to humans.