February 24, 2023

expert reaction to the H5N1 situation following the death of a girl in Cambodia

It has been reported that an 11-year-old girl in Cambodia has died after being infected with H5N1 avian influenza virus.

Prof Massimo Palmarini, Professor of Virology and Director of Centre for Virus Research, University of Glasgow, said:

“Human cases of H5N1 are mainly acquired from infected birds and have limited potential to spread from human-to-human.”

“The first cases of H5N1 in humans were identified in Hong Kong in 1997. Since then, viruses of the H5 serotype have been spreading globally and caused several hundred cases with about 50% mortality rate. Hence, it is likely that over the years there will be unfortunately additional human cases caused by H5N1.”

“Wild aquatic birds are the natural reservoirs of influenza viruses (known as Influenza A viruses, IAV). IAV from wild bird reservoirs can infect domestic terrestrial birds like chickens. The population density of chickens and the close contact with humans can offer opportunities for IAV to “spillover” into humans. These spillover events are normally limited to chicken-to-human transmission. There is the theoretical possibility that as avian IAV are transmitted to humans, these further mutate and adapt to replicate in their new environment. This is why it is important to detect human cases of avian influenza as quickly as possible and make sure that we give as little opportunity as possible to the virus to be transmitted further and mutate.

“The human Spanish flu pandemic of 1918 is believed to be derived from a successful transmission of an avian IAV to humans. The initial strain then adapted and became endemic in the human population giving rise to the seasonal flu viruses.”

Professor Ian H Brown, Director of Scientific Services, Animal and Plant Health Agency (APHA), said:

“There have been over 850 cases of H5 Highly Pathogenic Avian Influenza A (HPAI) cases in humans since 1996 with a high case fatality rate. Potential clusters require prompt investigation to establish if the virus has moved human to human or persons have all been infected from a common bird source. Almost all cases to date have not resulted in human-to-human (H2H) transmission but vigilance is required.”

Prof James Wood, Head of Department of Veterinary Medicine, University of Cambridge, said:

“There has been massive global challenge of wild and domestic birds with the current H5N1 avian influenza virus over the last few months and years, which will have exposed many humans; despite this, what is remarkable is how few people have been infected. There has been at least one in the UK who had close contact with affected ducks. Tragic though this case in Cambodia is, we expect there to be some cases of clinical disease with such a widespread infection. Clearly the virus needs careful monitoring and surveillance to check that it has not mutated or recombined, but the limited numbers of cases of human disease have not increased markedly and this one case in itself does not signal the global situation has suddenly changed.”

Prof Jonathan Ball, Professor of Molecular Virology, University of Nottingham, said:

“This is a very sad outcome for the young girl infected with a particularly aggressive form of avian influenza or ‘bird flu’. There is always a risk of human infection, particularly in people in close contact with poultry or wild birds, and this risk increases during times where circulation of avian influenza is particularly high, as it is now.

“Thankfully, human infections are still rare, and the likelihood of onward human to human transmission very low. But this virus keeps cropping up in various mammals and this could potentially increase the possibility of further human infections. The risk to humans is still very low, but it’s important that we continue to monitor circulation of flu in both bird and mammal populations and do everything we can to reduce the number of infections seen.

“It also highlights why efforts to develop next generation cross-reactive vaccines are so important.”

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