Cases of human-bird flu investigated in Cambodia

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Cambodian officials placed placards in the village of Prey Veng to warn of the dangers of bird flu.Credit…Cambodia Ministry of Health, via Associated Press

Cambodia has reported two human cases of bird flu infection, a father and a daughter, in a village in Prey Veng province. The 11-year-old girl died earlier this week.

The cases, which were reported in Cambodia for the first time since 2014, raised fears that the virus had gained the ability to spread among humans and could trigger another pandemic. But the World Health Organization said Friday that 11 contacts of the girl, four of whom have flu-like symptoms, tested negative for infection with the H5N1 flu virus.

Cambodian authorities said on Saturday the father was infected with a virus variant endemic to the country and unrelated to outbreaks in birds in the United States and Europe. According to the Ministry of Health, the 49-year-old showed no symptoms.

WHO is working closely with the Cambodian government to determine whether the father and daughter both contracted the virus through direct contact with infected birds — the most likely possibility — or if they infected each other.

Experts noted that there have been hundreds of sporadic cases of H5N1 infection in humans since the virus was first identified, and that there was no evidence it had adapted to humans.

Human-to-human transmission is “very, very rare compared to a common source of infection,” said Richard Webby, avian flu expert at St. Jude Children’s Research Hospital in Memphis and adviser to the WHO

But people should be careful to avoid contact with potentially infected wild birds, said Dr. Webby.

“The risk of this virus for an average person on the street right now is very low, but not zero,” he said. “And that’s largely because there are so many more infected birds right now.”

show moreSnow geese in the Middle Creek Wildlife Management Area near Kleinfeltersville, PA. The virus has taken a heavy toll on wild birds.Credit…Jim Lo Scalzo/EPA, via Shutterstock

Avian influenza, or bird flu, is a group of influenza viruses that are mostly adapted to birds. The particular virus in these new cases, called H5N1, was first identified in geese in China in 1996 and in humans in Hong Kong in 1997.

Since then, there have been almost a thousand human cases in 21 countries, but the vast majority have resulted from prolonged, direct contact with birds. H5N1 does not appear to have adapted to spread efficiently among humans.

“Ultimately, this is a continuum of the same outbreak that started in 1996,” said Dr. Malik Peiris, chief of virology at the University of Hong Kong who has helped oversee responses to several Hong Kong avian flu outbreaks in Southeast Asia. “Really, it never went away.”

H5N1 is typically transmitted by waterfowl, such as ducks, which can transmit the virus to domestic fowl through feces, saliva, or other secretions.

The current version of the virus was unusually widespread, causing the largest-ever bird outbreaks in Europe and the United States, affecting 58 million farmed birds in the latter. according to dr Webby is now considered endemic in several countries in Asia and Europe.

The virus has also taken a heavy toll on wild birds, causing mass deaths and has spread to mammals, particularly scavengers such as foxes, which may feed on infected carcasses.

Experts have been watching H5N1 closely since an outbreak at a mink farm in Spain last October suggested it could be spreading efficiently among some mammals.Credit…Mads Claus Rasmussen/Agence France-Presse — Getty Images

All reports of human infection warrant investigation to confirm that H5N1 has not yet adapted to human-to-human transmission. Six more human cases of H5N1 have been reported since September, according to the WHO. The 11-year-old girl’s death this week is Cambodia’s first bird flu death since 2014.

Experts have been watching H5N1 closely, particularly since an outbreak at a Spanish mink farm in October suggested the virus could be spreading efficiently among some mammals. Samples of the virus isolated from the mink carried a genetic mutation known to help the flu replicate better in mammals.

No infections have been identified in humans. But a mink-adapted version of the virus could be one step closer to efficient transmission between humans.

The WHO is “updating a bank of vaccine candidate viruses suitable for manufacturing should the need arise,” the agency said in a statement. WHO also provides antiviral drugs from an available supply.

Peruvian officials examined a dead sea lion they feared had died of bird flu.Credit…/EPA, via Shutterstock

Genetic analysis can reveal whether H5N1 has acquired mutations that help it spread among humans.

“That should give us a good indication of whether or not the virus has really jumped a step further,” said Dr. Shayan Sharif, an avian immunologist at the University of Guelph’s Ontario Veterinary College in Canada.

However, it is more difficult to determine how the two family members got infected in Cambodia. That’s because H5N1 samples from father and daughter are likely to be nearly identical, regardless of whether the virus came from a person or from the same infected birds, said Dr. Webby.

“If both were infected by the same chickens, they will 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.

Caged chickens on a farm in Buenos Aires.Credit…Mariana Nedelcu/Reuters

The virus poses the greatest risk to people who are in direct contact with birds, such as poultry farmers. Safety measures on farms and poultry processing plants, including the use of personal protective equipment by workers, can help reduce the risk of infection.

In order to contain local outbreaks, infected herds are usually culled and farms quarantined. But the virus is now so widespread in birds that experts are beginning to consider whether broader measures, such as vaccinating poultry, might 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 avian flu vaccines are underway.

“I don’t really think we should panic right now,” said Dr. Sharif. But “as we see all of these different pieces of the puzzle coming together,” he said, “I think we need to be really serious about preparing for an emergency.”