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Last Tuesday (see CHP: Notification of confirmed human case of H7N9 in Guangdong Province) we learned of a 3-year-old boy in the city of Dongguan, Guangdong Province, who was hospitalized with the H7N9 virus. While the route of infection was unknown, the assumption is that most people contract this virus through contact with infected poultry.
Yesterday we learned that attempts by Dr. Ko Wing-man – SFH of Hong Kong – to prevent importation of poultry from farms close to Dongguan City were blocked (see Hong Kong: No Deal On Poultry Import Restrictions From Areas With Human H7N9 Cases) as the virus had not yet been detected in poultry there – only in humans.
One of the the many mysteries surrounding this avian virus is that despite roughly 140 human cases scattered across China since last February, the virus has only rarely been detected in poultry. This has led to speculation that there might be another – intermediate – host involved in its transmission to humans.
But thus far, despite a good deal of investigation and testing, no other likely host has been identified.
Today we’ve a report from Yangcheng Evening News (published in Guangzhou City, Guangdong, China) indicating that out of 175 recent samples tested by their agricultural department, no positive results were found in Dongguan City poultry. The (machine translated) version is linked below:
Poultry samples found no H7N9 virus
Yangcheng Evening News reporter Qin Xiaohui reports: the evening of 8, Dongguan City Bureau of Agriculture informed that, recently, Dongguan City Bureau of Agriculture animal disease prevention and control center for the major poultry markets Changping sample testing of 175 samples were collected from poultry, the City level veterinary laboratory testing found no H7N9 bird flu positive.
The evening of 8, Dongguan City, Guangdong Dongguan Bureau of Agriculture released a children (living in Dongguan Changping) confirmed H7N9 avian influenza infection in the latest issue of the Bulletin. Informed that since April this year detected H7N9 bird markets Dongcheng three positive samples after Dongguan City Bureau of Agriculture animal H7N9 avian influenza projects into the routine monitoring of the project, in accordance with provincial deployment requirements to carry out sampling and monitoring, has been operating in the city of poultry, aquaculture sectors cumulative sampled more than 20,000 copies, of which 1550 were from Changping samples were not detected H7N9 bird flu positive.
Dongguan City Bureau of Agriculture said it would closely monitor the progress of events, and strictly implement work measures. First, continue to proactively with the provincial and municipal departments communication and collaboration, mutual exchange reported; second is to continue to step up inspections to monitor and increase focus on the area of the frequency of workplace inspections; third is to continue to strengthen quarantine supervision, requiring all three birds wholesale market in Field quarantine quarantine personnel strictly control market; fourth is to continue to strengthen publicity and urge employees to do personal protection.
Given the likelihood that poultry are the vector, one has to wonder if the sensitivity (or perhaps the sample collection method) of these tests being used to detect this virus in poultry is somehow lacking.
Genetic analysis clearly shows that the H7N9 virus has an avian origin.
In May, the CDC posted the following graphic that shows the evolutionary (reassortant) steps they believe led to the creation of the new H7N9 virus in China.
The eight genes of the H7N9 virus are closely related to avian influenza viruses found in domestic ducks, wild birds and domestic poultry in Asia. The virus likely emerged from “reassortment,” a process in which two or more influenza viruses co-infect a single host and exchange genes.
This can result in the creation of a new influenza virus. Experts think multiple reassortment events led to the creation of the H7N9 virus. These events may have occurred in habitats shared by wild and domestic birds and/or in live bird/poultry markets, where different species of birds are bought and sold for food.
As the above diagram shows, the H7N9 virus likely obtained its HA (hemagglutinin) gene from domestic ducks, its NA (neuraminidase) gene from wild birds, and its six remaining genes from multiple related H9N2 influenza viruses in domestic poultry.
While infected poultry remain the most likely culprit, the definitive answer to exactly how the H7N9 virus is spreading in China, and occasionally manages to infect humans, remains frustratingly elusive.
