Two cases of bird flu infection have been reported among people, a father and a daughter, in a village in Pre Veng province in Cambodia. Earlier this week, an 11-year-old girl had died.
Cases reported in Cambodia for the first time since 2014 raised fears that the virus has acquired the ability to spread between people and could trigger another pandemic. But the World Health Organization said on Friday that 11 people in contact with the girl, four of whom have flu-like symptoms, had tested negative for H5N1 flu virus infection.
According to the health ministry, the 49-year-old father, who has tested positive, was not showing any symptoms. WHO is working with the Cambodian government to determine whether both father and daughter caught the virus from direct contact with infected birds – most likely – or whether they infected each other.
Experts noted that there have been hundreds of sporadic cases of H5N1 infection in people since the virus was first identified, and there is no evidence that it had adapted to humans.
“Transmission between people is very, very rare, versus a common source of infection,” said Richard Webby, a bird flu expert at St. Jude Children’s Research Hospital in Memphis and a consultant to the WHO.
But people should take precautions to avoid contact with wild birds that may be infected, Dr. Webby said.
“The risk to your average person on the street from this virus is very low right now, but it is not zero,” he said. “And that’s mainly because there are just too many infected birds around.”
Bird flu, or avian influenza, is a group of flu viruses primarily adapted to birds. The particular virus in these new cases, called H5N1, was first identified in some swans in China in 1996 and in people in Hong Kong in 1997.
Since then, nearly a thousand cases have been reported in people in 21 countries, but a vast majority have resulted from prolonged, direct contact with birds. It appears that H5N1 has not yet adapted to spread efficiently between people.
“At the end of the day, this is a continuation of the same outbreak that started back in 1996,” said Dr Malik Peiris, head of virology at the University of Hong Kong, who has helped oversee responses to several bird flu outbreaks. is of. Southeast Asia. “Actually, it never went away.”
H5N1 is commonly carried by aquatic birds, such as ducks, which can transmit the virus to domestic poultry through feces, saliva, or other secretions.
The current variant of the virus has been unusually widespread, causing the largest bird outbreak ever recorded in Europe and the United States, affecting 58 million farmed birds in the latter. According to Dr. Webby, it is now considered endemic in many countries in Asia and Europe.
The virus has also taken a toll on wild birds, causing mass mortality, and is spreading to mammals, particularly scavengers, such as foxes, which may feed on infected carcasses.
Any report of infection in people warrants investigation to confirm that H5N1 has not yet adapted itself to human-to-human transmission. Six other cases of H5N1 have been reported in people since September, with the death of an 11-year-old girl this week the first bird flu death in Cambodia since 2014, according to the WHO.
Experts have been closely monitoring H5N1, especially since an outbreak at a Spanish mink farm in October suggested the virus may be spreading efficiently among some mammals. Virus samples isolated from mink contained a genetic mutation that is known to help the flu replicate better in mammals.
No human infection was found. But a mink-adapted version of the virus may be one step closer to efficient transmission between people.
Scientists would be concerned if the variant of H5N1 identified in Cambodia was found to be closer to that seen in Spain than previous Asian outbreaks, Dr. Peiris said. “It is important to try to understand what is really going on in Cambodia”, he said.
“WHO is updating a bank of vaccine candidate viruses that are suitable for manufacture, should it be needed,” the agency said in a statement. WHO is also making available antiviral drugs from the available stock.
Genetic analysis can reveal whether H5N1 has undergone changes that help it spread among people.
“This should give us a good indication of whether or not the virus has indeed progressed a step further,” said Dr. Shayan Sharif said.
But how the two family members got infected in Cambodia will be more difficult to ascertain. That’s because the H5N1 samples from father and daughter are likely to be nearly identical, regardless of whether the virus was obtained from the same person or from the same infected birds, Dr. Webby said.
“If they were both infected with the same set of chickens, they were going to be infected with very similar viruses,” he said. It may be more informative for scientists to chart the path of the virus by examining the nature of contact between infected people.
The virus poses the greatest danger to people who are in direct contact with birds, such as poultry farmers. Safety measures on farms and in poultry processing plants, including the use of personal protective equipment by workers, can help reduce the risk of infection.
To prevent local outbreaks, infected herds are usually culled and farms placed under quarantine. But the virus is now so widespread in birds that experts are beginning to consider whether wider measures such as vaccination of poultry may be needed.
Vaccination has not traditionally been used to control avian influenza in poultry in the United States or Europe. But officials are reconsidering that stance and trials of bird flu vaccines are underway.
“I really don’t think we should panic at this point,” Dr. Sharif said. But “as we look at all these different bits and pieces of the puzzle coming together,” he said, “I do believe that we need to get really seriously prepared for an emergency.”