The World Health Organization revealed on Tuesday that China has detected an evolution in the H7N9 avian flu virus that makes the bird flu strain capable of causing severe disease in poultry, which needs close monitoring.

Bird Flu Virus H7N9 Mutations

Analysis of virus samples from Taiwan and China suggested that H7N9 has gone through mutations that include resistance to antiviral class of drugs called neuraminidase inhibitors. Researchers also learned that the virus has become more pathogenic in birds after virus samples collected from two infected humans were injected into birds in laboratory.

Limited Person-To-Person Transmission

The U.S. Centers for Disease Control and Prevention has earlier said that "limited" person-to-person spread of the H7N9 could not be ruled out. "Limited" means that a virus from an animal host is able to infect a person and then spread to that person's close contact but not much further.

"Based on what we know about human infections with other bird flu viruses, it's possible and even likely that there will be some limited person-to-person spread with this virus. The important factor will be to determine whether this virus gains the ability to spread easily from one person to another. Sustainable human to human spread is needed for a pandemic to start," CDC said.

WHO spokesman Christian Lindmeier said that there is no evidence that shows the changes in the virus affect the pathogen's ability to spread between humans.

"Although small clusters of human cases with avian influenza A(H7N9) virus have been reported including those involving healthcare workers, current epidemiological and virological evidence suggests that this virus has not acquired the ability of sustained transmission among humans. Therefore the likelihood of further community level spread is considered low," WHO said in a statement.

Although the mutation does not currently make the virus more infectious to humans, it allows the virus to replicate much faster in birds. The sick birds will shed more of the virus, which could mean more cases in people and possibly other mammals such as pigs. This would provide an opportunity for the virus to adapt to mammals through which it could learn to spread from person to person.

In its last update, WHO said that there were 304 new laboratory-confirmed cases of human infection and 36 deaths in mainland China from Jan. 19 to Feb. 14. Since October 2016, 425 human cases have already been reported in China, which include 73 deaths.

Infection Rates Higher Than Previously Believed

Animal experts said that bird flu infection rates could actually be higher in poultry farms in China than previously believed since the strain of the virus in humans is hard to detect in geese and chicken.

The evolution of the virus though could mean that the disease will be more easier to detect in some flocks once birds start to die off. The spread of H7N9 is often only discovered when people get sick.Those who become ill are often the ones who are most exposed to the virus in live poultry markets.

Bird Flu Vaccine

Virologists said that the only real defense against bird flu is vaccine. WHO has already given its approval to eight vaccine strains of H7N9. China has also launched clinical trials of four strains by a vaccine company owned by the state.

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