Published Date: 2011-11-19 17:58:35
Subject: PRO/AH/EDR> Influenza (68): Hong Kong swine-origin H3N2 reassortant
Archive Number: 20111119.3411
INFLUENZA (68): HONG KONG SWINE-ORIGIN H3N2 REASSORTANT
A ProMED-mail posthttp://www.promedmail.org
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International Society for Infectious Diseaseshttp://www.isid.org
Date: Thu 17 Nov 2011
Source: The Hong Kong Standard [edited]http://www.thestandard.com.hk/news_deta ... 11117&fc=4
Threat played down after new swine flu virus find
A new swine flu virus with human genes has again been found in mainland pigs at a Hong Kong slaughterhouse. But the swine flu H3N2 virus is unlikely to cause a "major" human health risk, the Centre for Food Safety said. 15 pigs were found infected with "essentially a swine influenza H3N2 virus that has picked up some genes of human swine influenza virus," the center said. They were detected out of 1000 samples taken from August to mid-October .
The same flu subtype [had been] isolated also in the last round of the surveillance programs, from May to July 2011, in 16 pigs. In both instances, the department said it had notified mainland authorities. There have been no recent reports of such H3N2-infected swine in Guangdong province, however.
Flu expert Malik Peiris said the H3N2 subtype seen in the pigs is not the same swine-originated new H3N2 that has infected 7 people in the United States since July . The US Centers for Disease Control and Prevention said earlier that while [these] infections have been mainly mild, they are being closely monitored [see: ProMED-mail archived reports below]. Dr Nancy Cox, head of the Atlanta- based agency's influenza division, said a seed strain for a vaccine that would protect against the virus has already been developed and given to manufacturers. [This statement likely refers to the USA-swine-origin H3N2 reassortant (see ProMED-mail Influenza (66): USA swine-origin H3N2 reassortant, update 20111105.3298) and not the Hong Kong swine-origin H3N2 reassortant. - Mod.CP]. The World Health Organization also said that for pandemic preparedness purposes, it has developed and made available 2 candidate vaccine viruses.
All pigs coming from the mainland are slaughtered centrally in the Sheung Shui slaughterhouse before they are taken to Hong Kong markets. A spokesman for the Food and Environmental Hygiene Department said the infected pigs were destroyed. However, abattoir workers have not been checked for the presence of the virus, the spokesman revealed. "There is no routine check of influenza antibody level in slaughterhouse staff," he said, in response to questions from The Standard. But staff are advised to wear face masks and gloves while on duty, and to observe personal hygiene.
Peiris said human flu viruses cross to pigs occasionally, and vice versa. "This one [H3N2] is a pandemic reassorted virus," he said, adding it was derived from the 2004-5 human flu, so most of the population would have [acquired] immunity from [exposure to] it, except very young children. "There is really no risk of acquiring viruses from eating pork meat."
[Byline: Mary Ann Benitez]
-- Communicated by: ProMED-mail from HealthMap alerts
[A previously characterised swine-origin H3N2 reassortant, responsible for a few isolated non-contagious benign infections in children, had acquired one of the genes -- the M gene -- of the H1N1 flu strain that caused the 2009 pandemic. The CDC reported the swine H3N2 virus probably picked up the M gene from the pandemic H1N1 virus when a pig was co-infected with swine H3N2 and the H1N1 strain. It's not clear whether the acquisition of this human-origin gene facilitated transmission of the reassortant to humans, but It did not enhance its virulence or facilitate its transmissibility among humans.
Likewise there is no evidence (yet) that the Hong Kong swine H3N2 reassortant virus described above has any increased virulence for humans or enhanced ability to infect human hosts. It is likely that sub-unit reassortment of influenza A virus genome sub-unit is a frequent occurrence, and inapparent without some specific selection pressure to reveal its occurrence. - Mod.CP]
[The most common subtypes currently found in pigs are H1N1, H1N2 and H3N2; however, the situation is complex, as 2 or more viruses of each subtype are circulating in swine populations. "Swine influenza" is not included in OIE's list of notifiable animal diseases. A recent exception was registered when an influenza H3N2 virus was found, in Denmark in 2009, as the causative agent of a new disease entity in minks, subsequently reported to the OIE as an "emerging disease."
The definition of an emerging disease is "a new infection resulting from the evolution or change of an existing pathogenic agent, a known infection spreading to a new geographic area or population, or a previously unrecognized pathogenic agent or disease diagnosed for the 1st time and which has a significant impact on animal or public health". Subscribers are referred to the archived post 20091023.3660 addressing the said event, and in particular to the following citation from the commentary by Mod.PC: "The 1968 Hong Kong influenza in humans was an H3N2, swine in Europe have been infected for decades with an H3N2, and an H3N2 swine strain became a prominent virus in the North American swine population in 1998. H3N2 has been isolated from turkeys in USA. As is the case with H1N1, it is critically important to do surveillance in both the affected animal population and people to try as best we can to establish time ordering of events and the directionality of transmission. The key to this is comprehensive, integrated outbreak investigations in geographically co-located animal and human subpopulations." - Mod.AS]
[The interactive HealthMap/ProMED map for Hong Kong is available at: http://healthmap.org/r/1s3-