a chicken. Illustrated | Getty Images
The 2022-2023 bird flu epidemic is officially the worst on record. Since last winter, an estimated 208 million birds have died or been culled by H5N1 worldwide, driving up the prices of eggs and chicken around the world. In recent days, scientists have expressed growing concern that a mutation could cause a “spillover” event, in which H5N1 is transmitted more efficiently from person to person.
Why are scientists concerned?
Revelations about the spread of avian flu in a Spanish mink farm in October sounded the alarm. The minks were infected with an H5N1 variant called 2.3.4.4b, which was discovered in 2020 and has since been seen around the world. Although it is not uncommon for mammals to contract avian flu after direct contact with infected birds, mink farming has shown evidence of transmission between minks themselves, “unprecedented in mammals”. wrote Zeynep Tufekci, a professor at Columbia University. The New York Times.
Samples taken from the mink showed a mutation that allowed the virus to take hold more easily in mammals, and this appears to be the first case of such transmission outside laboratory settings. What the virus can do to mink, it can do to us. That says virologist Tom Peacock of Imperial College London Science this “is a clear mechanism for the onset of an H5 pandemic”. Dutch virologist Marion Koopmans said on Twitter that “we are playing with fire”. The more animal species infected with H5N1, the more likely the virus is to enter humans via an intermediate host. The incident at a mink farm is one of 119 outbreaks in animals since October 2021, according to the BBC. During this period, there have been five confirmed human cases and one death.
How deadly is H5N1 to humans?
Data from the World Health Organization shows that over the past 20 years, 868 documented human H5N1 infections contracted the virus through direct contact with the saliva, mucus and feces of infected birds. Of those cases, 457 resulted in deaths, giving H5N1 a known case fatality rate (CFR) of over 53%. Although the infection fatality rate (IFR), an estimate that takes into account asymptomatic or mild cases that go unreported, may not be as high, there is no doubt that if the virus could spread easily between people, it would provoke a serious crisis of public opinion. health. In 2008, a group of Canadian researchers estimated that the human CFR of a mutant bird flu pandemic would be between 14% and 33%, making the COVID-19 crisis miniscule in comparison. Other researchers are more optimistic, believing that the mortality rate of the existing strain, which infects humans through direct contact with birds, is much lower than WHO estimates due to missed cases.
Why was this epidemic so serious?
The disaster of 2022-2023 is ongoing and approaching a year, and scientists have no clear answer as to why this epidemic is much worse than those of the past.
Bird flu kills nearly every bird it infects and can burn entire flocks within days. At least 80 bird species have been infected in this outbreak, which has affected countries around the world. Health authorities have taken different approaches to combat the outbreak. China vaccinates commercial birds, while French and British authorities have encouraged farmers to bring their flocks indoors to avoid infection from passing wild birds. U.S. farmers are being encouraged to implement a range of biosecurity measures, including limiting the number of people entering and exiting farm facilities and placing “disinfectant footbaths” at stall entrances. Other producers have effectively locked themselves in to limit their own reach.
Other countries, including France and the Netherlands, are experimenting with new vaccines in what has until now been a last resort. Vaccinated birds and their eggs are difficult to export commercially – paradoxically because vaccination is taken as proof that bird flu is occurring in the exporting country and because vaccinated birds may show no symptoms if infected. But the most common approach, and the one used in the United States, is to cull domestic herds, which can be excruciating and financially ruinous for farmers.
How concerned should we be?
Experts have been warning about the outbreak of pandemic-capable bird flu in humans for years. No mutations that would facilitate human-to-human transmission have been found in humans infected with the virus, and the risk to humans not in direct contact with infected birds is negligible. In the past, there have been cases where people have been found to be infected with versions of H5N1 that carry mutations of concern, but have not yet resulted in a pandemic. “But it seems foolish to rely on it,” Tufekci wrote. After all, “deadly influenza pandemics have occurred regularly throughout human history.”
Efforts to develop human vaccines are ongoing. Vaccines already exist that would likely be useful, but production would have to be increased dramatically and adaptations would have to be made to adapt to the new strain of flu. Eyal Leshem, director of the Center for Travel Medicine and Tropical Diseases at Sheba Medical Center in Israel, said last year: “I don’t think anyone should panic about this because bird flu has been around for a long time in various places. and a highly pathogenic pandemic influenza did not yet exist.
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