Transmission[edit] Live poultry market in Xining, China. In April, 2013, the World Health Organization (WHO) said H7N9 was unlikely to become a pandemic[66] and that there was no evidence of human-to-human transmission.[67] [35][67] In late July, 2013, however, Chinese scientists found evidence that person-to-person transmission was possible, but would not transmit easily.[68] In April, a WHO representative stated that of the hundreds of contacts monitored, there were only a very few cases in which contacts became ill.[69] It was also reported that up until that time, the virus was found only in chickens, ducks, and pigeons at live poultry markets and that no migratory birds had tested positive for the virus, easing concerns about that route of transmission.[6] At an April 26 news conference the WHO assistant director-general for health stated, This is an unusually dangerous virus for humans. We think this virus is more easily transmitted from poultry to humans than H5N1.[6] Furthermore, there is great concern because unlike the H5N1 viral form, H7N9 does not cause visible disease in poultry, which makes surveillance, prevention and control of the virus in poultry extremely difficult.[12] On April 30, it was announced that the Ministry of Agriculture of the Peoples Republic of China had asked the Director General of the World Organisation for Animal Health (OIE) to send OIE experts to assess the situation and provide advice. According to the information and data collected it was confirmed that many of the human cases of H7N9 appeared to have a link with live bird markets, but to that date no human cases or animal infections of H7N9 had been detected on poultry farms. The OIE experts made the hypothesis that people could be infected through exposure to infected birds in markets or to a contaminated environment such as live poultry markets where the virus is present. They believe that live bird markets may play a key role in human and animal infections with H7N9 and that, even if the overall level of infection is relatively low (having not been detected yet in poultry farms), live bird markets provide an environment for amplification and maintenance of the H7N9 virus.[12] The OIE mission also confirmed that currently infection with H7N9 does not cause visible disease in poultry and therefore veterinary services must be especially involved in preventing its further spread. According to the April 30 report, there is no evidence to suggest that the consumption of poultry or eggs could transmit the virus to humans. More assessment is needed to know whether poultry vaccination could be considered as a control option for H7N9. It will also be important to verify whether the H7N9 virus is transmissible from humans to animals because if established, it could be a potential channel for the global spread of the virus.[12] The number of cases detected after April fell abruptly. The decrease in the number of new human H7N9 cases may have resulted from containment measures taken by Chinese authorities, including closing live bird markets, or from a change in seasons, or a possibly a combination of both factors. Studies indicate that avian influenza viruses have a seasonal pattern, much like human seasonal influenza viruses. If this is the case, H7N9 infections – in birds and people – may pick up again when the weather turns cooler in China. Limited person-to-person spread of bird flu is thought to have occurred rarely in the past, most notably with avian influenza A (H5N1). According to the US CDC, based on previous experience, some limited human-to-human spread of this H7N9 virus would not be surprising if the virus reemerges in the fall.[17] Furthermore, according to the WHO, since migratory birds were first implicated in H7N9 transmission, the possibility that the virus may spread into other regions or countries with colder weather cannot be excluded, given the widespread bird migratory patterns.[70]
Posted on: Wed, 04 Dec 2013 12:27:56 +0000
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