Researchers have confirmed that the A H7N9 bird flu virus, which began in February 2013, was transmitted from chickens at a wet poultry market to humans, according to a new study published in the The Lancet.

Wet markets, which are common in Asian countries, are live animal markets.

A H7N9 avian influenza (bird flu) has already infected around 108 people and killed 22 in several different parts of China since its emergence. The first reported case of human illness was in the Shanghai region, however, since then A H7N9 has spread south to the province of Zhejiang and north to Beijing.

Following the admission to hospital of a 39 year old patient infected with the A H7N9 virus, a team of researchers, led by Professor Lanjuan Li, of Zhejiang University, Hangzhou, China, and Professor Professor Kwok-Yung Yuen of the University of Hong Kong, China, carried out retrospective testing among a total of 486 patients who reported symptoms of respiratory infection.

The tests showed that three of the patients were infected with the H7N9 virus. They carried out further tests to more clearly define the clinical symptoms of the disease.

As all of the infected patients had been exposed to poultry, they set out to determine whether the virus could have been transmitted from the poultry-to-humans. The researchers took cloacal swabs from chickens, quails, pigeons and ducks across six poultry markets where the patients had been to.

Forty percent of the pigeons as well as 20 percent of the chickens were tested positive for H7N9.

The team compared the genetic makeup of the H7N9 bird flu virus of one of the patients with an H7N9 isolate from one of the chickens – they found a number of similarities that suggest the virus was transmitted from the chickens.

For the first time since this outbreak started, researchers can now confirm that there is definite bird-to-human transmission for the H7N9 bird flu virus.

The authors concluded that the virus is currently unable to transmit between humans. After carefully monitoring 303 of the patient’s household and workplace contacts, none of them had developed the A H7N9 bird flu-like symptoms.

The scientists added that the virus does have the ability to adapt and to become human transmissible. If that were to occur, it would probably be less deadly.

Co-lead author of the study, Professor Kwok-Yung Yuen said:

“Overall, the evidence, in terms of epidemiology and virology, suggests that it is a pure poultry-to-human transmission, and that controlling [the epidemic in humans] will therefore depend on controlling the epidemic in poultry.”

The researchers noted a similarity between the symptoms of the H7N9 bird flu virus and the H5N1 bird flu virus, in which infected patients develop high fever and have difficulty breathing.

The authors concluded:

“Aggressive intervention to block further animal-to-person transmission in live poultry markets, as has previously been done in Hong Kong, should be considered. Temporary closure of live bird markets and comprehensive programmes of surveillance, culling, improved biosecurity, segregation of different poultry species, and possibly vaccination programmes to control H7N9 virus infection in poultry seem necessary to halt evolution of the virus into a pandemic agent.”

Replikins Ltd, from Boston, USA, is working on two completely synthetic vaccine candidates, one of which targets H7N9 alone.

A team of scientists from MIT wrote in the journal Cell (June 2013) that the H7N9 and H5N1 bird flu virus strains need only one or a few genetic mutations to become easily human transmissible, which would raise the likelihood of there being a flu pandemic.

Written by Joseph Nordqvist