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How is New Bird Flu Virus Transmitted?

18 April 2013

ANALYSIS - The outbreak of a new strain of avian influenza A(H7N9) in China has seen the number of people infected rise to 82 with a further 19 cases confirmed on Wednesday, writes Chris Harris.

The World Health Organisation report that confirmed the nine cases from Zhejiang Province, seven from Shanghai Municipality and three from Jiangsu Province also confirmed a further three deaths, bringing the total number who have died from the virus to 17.

More than 1,000 close contacts of the confirmed cases are being closely monitored.

Investigations into the possible sources of infection and reservoirs of the virus are on-going.

The WHO said: “Until the source of infection has been identified, it is expected that there will be further cases of human infection with the virus in China. So far, there is no evidence of on-going human-to-human transmission.”

However, while the official line in China is also that there is no evidence of human-to-human transmission, a survey carried out in China reported that of the then 77 cases known, 40 per cent had had no contact with poultry.

And in other reports the WHO spokesman Gregory Hartl confirmed that there are people who have no history of contact with poultry.

The official line in China is still that there is no evidence of human-to-human transmission of the disease.

Feng Zijian, the director of the Health Emergency Centre at the Chinese Centre for Disease Control and Prevention said that even looking at family clusters, where the disease had been contracted by more than one member of the family, they could not say that the virus could be transmitted from human-to-human.

He said that they had found that it was “contagious from birds to people and found no evidence of human-to-human transmission”.

He said that studies are being made of families where the disease has affected more than one member to discover whether the transmission was bird-to-human, human-to-human or simply exposure to contaminated objects or the environment.

Feng Zijian added that looking at other outbreaks of avian influenza in humans half the patients knew they had been in contact with poultry and the other half could not remember.

He said: “We infer the infection is from birds to people, who are exposed to a polluted environment around poultry or who have had direct contact with poultry. This is the most important cause of infection.”

Feng Zijian attributed the blame for the outbreak firmly on the live poultry markets.

“One of our very important understandings is that the city’s live poultry markets, where they sell freshly slaughter birds are a risk factor for the disease.”

He added that the markets have old equipment and the processes they undergo in slaughter can easily form an aerosol effect and if there is a virus it makes it easy to inhale it from the environment.

As part of the measures to control the disease, thousands of birds from the Chinese live markets have been slaughtered.

However, the risk of infection from eating poultry or eggs has been dismissed.

“There is no evidence that the processing and consumption of chicken, whole chicken or eggs lead to infection,” Feng Zijian said.

“If you cook the chicken well and have good hygiene then cooked chicken and eggs are safe.

“In general, there is very limited survival for micro-organisms such as viruses in the bodies of dead animals.”

The Chinese medical authorities have at the moment ruled out a national screening for the disease and the World Health Organisation has not issued any warnings about screening and travel.

“WHO does not advise special screening at points of entry with regard to this event, nor does it recommend that any travel or trade restrictions be applied,” the WHO said.

Chris Harris

Chris Harris

Top image via Shutterstock

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