Avian flu, in its different strains, has been on the radar of health authorities for some time: a mutation that facilitates the jump to humans and its spread between people could have serious consequences. The WHO reported this Wednesday the first known death in the world due to the A (H5N2) variant. It occurred in April in Mexico. Other types of bird flu had already caused human deaths in other parts of the world. This is what is known about the virus, its variants and its dangers:
What is bird flu?
It is a disease caused by viruses from the same family as those that cause human flu. There are four types: A, B, C and D. The one that spreads among birds is A. Within it, there are subtypes, five of which have been shown capable of jumping to humans: H5, H6, H7, H9 and H10. The one that has been under the spotlight for a few years is H5N1, which has frequently jumped to mammals and, for more than a year (as far as we know), it has been transmitting between them. H5N2, which has caused death in Mexico, had not been detected before in humans.
Can it be spread between humans?
In the case of H5N1, jumps of the virus to humans are not frequent, but not extraordinary either. Since its discovery in 2003, about 900 have been documented, with fatality rates of more than 50%. What has not been proven so far is any contagion from one person to another. With respect to H5N2, until Mexico, no human cases had been confirmed in the laboratory, so there is no known contagion from one person to another.
How was the first person killed by this variant infected?
It’s a mystery. He was a 59-year-old man who had no contact with birds, which is the route of transmission of avian flu to humans. He was a person who was already in the hospital with various pathologies. He had been bedridden for three weeks with fever, difficulty breathing, diarrhea, nausea and general malaise. “The role of this virus in the fatal outcome cannot be assumed to be directly responsible without further investigation. The rapid follow-up of health professionals and family members in contact with the infected patient reassures us, since this is an isolated case,” Ian Brown, head of the Avian Virology group at the Pirbright Institute, responded to the SMC agency. Ed Hutchinson, senior lecturer at the MRC-University of Glasgow Virus Research Centre, believes that it is most likely a “spillover” infection, in which a virus adapted to one host species manages to infect a member of the host. another species (in this case a human), but is not capable of continuing to transmit.
Could it spread among humans?
In its statement, the WHO assures that avian flu “can have a great impact on public health”, although it considers H5N2 represents a “low” risk for the population. “Available epidemiological and virological evidence suggests that A(H5) viruses from previous events have not acquired the capacity to maintain human-to-human transmission, so the current probability of sustained human-to-human spread is low,” the agency reports.
In the opinion of Ian Jones, professor of Virology at the University of Reading (United Kingdom), it is “impossible” to know from a single case. “However, given that the infected person had underlying medical conditions, which may have contributed to the outcome, it would be reasonable to assume that this is an isolated case of zoonotic transfer with no potential for spread. This would be consistent with previous examples of occasional bird flu infections in people. Unless or until there is evidence of strain adaptation or sustained transmission, the risk to the population is very low. The case should serve to reinforce the importance of monitoring and eradicating outbreaks in poultry as soon as they occur,” he explained to SMC.
Where does H5N2 come from?
Although it is not known how the victim became infected, there have been recent outbreaks of the H5N2 flu virus in poultry in Mexico.
How is it different from H5N1?
There are two subtypes of avian flu, but H5N1 is much more widespread throughout the world. Recently, it is spreading to cow farms in the United States, without it being clear how it is transmitted between them. Although it is not perceived as an imminent threat to humans, it is of much greater concern than H5N2 does, for several reasons: since 2021 it has proliferated more among non-aquatic birds, such as scavengers. This has produced more contact with mammals (which are the food of these species). And, for the first time, last year contacts between mammals were detected, which have been expanding to more species and specimens. The mutation to be contagious between humans is very complicated, but not impossible, which is why international health authorities maintain surveillance, as they are now doing to get to the bottom of the case of death from H5N2.
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