The H7N9 virus that has plagued China since last March flu can be transmitted from person to person via the respiratory route, according to the result of several parallel studies in ferrets.
Since a new avian flu began to sicken and kill many people in China in March, one of the most pressing questions that has been raised is whether the virus type H7N9, is easily spread from human to human, potentially cause a global pandemic.
Fortunately, so far no sign of such transmission has proved, and the epidemic has led Chinese cities assigned to close poultry markets and kill many birds seem to have reached a standstill.
But three new studies on ferrets show that the virus can be spread through the air between mammals, waking concerns of human to human transmission.A team led by virologist Hualan Chen of the Veterinary Research Institute of Harbin in China, reported in an article published online in the journal Science that in experiments on ferrets, an H7N9 virus from a human being "proved highly transmissible" by respiratory droplets.
In the ferret model, widely regarded as one of the best methods to assess transmission between humans, the researchers intentionally infected animals in a cage and determined if the virus spreading to others in a cage adjacent. When Hualan Chen and colleagues inoculated ferrets in a cage three samples of the H7N9 virus from a person who had contracted the disease in the province of Anhui, three ferrets in an adjacent cage became infected, and virus consistent with those used in the test.
The researchers repeated the experiment and found the same result. Two other viral samples from different patients are transported to one of three exposed animals, as well as virus taken from a bird.
Although the method has limitations ferret, Hualan Chen and his colleagues concluded that their results announced future problems. "Currently, the implementation of mandatory control measures on the markets positive H7N9 virus in poultry prevent new human infections, but the elimination of H7N9 virus of nature is an important challenge and long term," they writing.
"The duplication of men will provide further opportunities for the virus to acquire more mutations and become more virulent and transmissible to the human population."
But a group of U.S. Centers for Disease Control and Prevention (CDC) in Atlanta who conducted a similar experiment with the same sample of Anhui Province came to a different conclusion. After inoculated into two groups of three ferrets, they discovered that it had led to the contamination of two of the six ferrets in adjacent cages. Different human sample showed the same frequency of respiratory transmission.
As CDC researchers conclude in their article published in the July 10 issue of the journal Nature, the virus "was not transmitted easily through the respiratory tract." In comparison with the Hualan Chen team, the CDC said that "the further adaptation of the virus to mammals will be necessary to achieve the highly transmissible phenotype observed by inhalation observed for influenza A virus seasonal and pandemic."
A second study published in the same journal, led by Yoshihiro Kawaoka, a virologist at the University of Wisconsin and the University of Tokyo, reported that the Anhui sample has infected one of three ferrets, the same percentage that what the CDC found. However, researchers have drawn a different conclusion from this result, writing that respiratory transmission they observed contributed to their assessment that the H7N9 viruses represent "a significant threat to public health."
Although the results of these different groups of scientists differ, virologist Ron Fouchier of Erasmus MC in Rotterdam, the Netherlands, note that they are not so different than they appear. "The H7N9 is clearly transmitted by aerosol or respiratory droplets in ferrets," said Ron Fuchier, "In general, human influenza viruses are transmitted to 100% of ferrets, avian viruses to 0% and it is located between the two. "
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