Avian flu, alert in the USA and Europe: risk of large-scale spread if the virus mutates

In 1918 the Spanish flu taught us this: the avian virus, transmitted by an animal, can adapt so well to humans that it becomes, in fact, “human”. Now, that danger could return, say the European Center for Disease Prevention and Control (ECDC) and the European Food Safety Authority (EFSA).

The alert comes from a joint report published on April 4: due to the intense spread of the virus and its continuous evolution – it is underlined – “new strains carrying potential mutations for adaptation in mammals could be selected”. A situation that, according to the virologist Fabrizio Pregliascomedical director of the Galeazzi Hospital in Milan, “must be kept under observation”.

“The risk of a repeat of what happened with the Spanish flu potentially exists, that is, that the avian virus adapts by passing from man to man – explains Pregliasco -. Therefore, maximum compliance with hygiene rules in intensive animal farming is essential , this is because the risk of contagion increases if there is no biocontainment action.”

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Man infected in the USA, signs of adaptation to mammals in the virus

The thesis put forward by the two European agencies is also supported by the fact that, in recent days, on a cattle farm in the USA, a man was infected with the A/H5N1 avian virus. And now that case, analyzed by experts, is worrying. Because that virus has a mutation that indicates adaptation to mammals.

The American Centers for Disease Control and Prevention made the discovery known, adding, however, that for now “it does not change the assessment of the level of risk, which remains low”. The sequencing of the genome of the pathogen detected in the patient, completely similar to that detected in dairy cattle in Texas, confirmed that the cause of the infection is highly pathogenic avian influenza type A/H5N1 (clade 2.3.4.4b ), but presents a mutation “associated with mammalian adaptation”, because it improves “the efficiency of replication in the cells of the same mammals”, explains the CDC report.

Twelve farms affected in five states

This mutation (PB2 E627K) is not new, however: it has been identified previously both in other people and in mammals infected with avian flu. Furthermore, it does not appear to affect the virus’s ability to transmit from human to human, nor does it confer resistance to available antivirals. In all likelihood – explain the CDC – “the mutation could have been acquired in the patient during the development of conjunctivitis”.

The level of attention on A/H5N1 influenza is therefore raised. After three years of the pathogen circulating at a particularly high rate among wild and farmed birds, also infecting mammals and expanding its area of ​​diffusion, for just over a week all eyes have been focused on the United States, where infections in dairy cow herds. At the moment, a dozen farms located in five states (Texas, Kansas, Michigan, New Mexico, Idaho) are affected.

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Europe on alert

Returning to Europe, the ECDC and EFSA agencies state that “to date the A/H5N1 virus of clade 2.3.4.4b, currently circulating, has caused only a few cases of human infection”. But they point out that “the high number of infections and transmission events between different animal species increases the probability of viral reassortment and/or the acquisition of mutations that could improve the ability of new emerging influenza viruses to infect, replicate and transmit efficient to and among mammals”. Then they go into detail, recalling that the pathogen has already “demonstrated the ability to take some evolutionary steps towards adaptation to mammals”.

How the virus works

In practice, A/H5N1 has learned to multiply more effectively in mammalian cells, combined with the ability to mislead certain components of the immune response. Furthermore, it seems particularly capable of combining with other circulating viruses, a peculiarity that could give it further advantageous characteristics for spreading in mammals. This strategy allowed him to infect a wide range of wild animals and cause small epidemics even in companion animals, such as cats. This is the state of the art, and there is currently no evidence of mammal-to-mammal transmission. Nor are there any indicators to suspect that the virus has acquired a greater ability to infect humans. If this transformation occurred, the agencies point out, “man would be particularly vulnerable to infections from the A/H5N1 virus”.

Rare antibodies

In this regard, ECDC and EFSA maintain that “neutralizing antibodies against A/H5 viruses are rare in the human population, since H5 has never circulated in humans”, and that “this means that any A/H5 virus Transmissible H5, with a basic reproduction number (R0) greater than 1, will spread.”

According to the report, at the moment, the risk of infection with the A/H5N1 virus for the general population is low, despite the high number of infections in birds and transmission in several mammalian species. It is instead “low to moderate for those who are exposed professionally or otherwise to animals infected with Avian influenza”.

But the situation could change and – the agencies warn – “future sporadic transmissions from animals to humans and related serious diseases in individuals cannot be ruled out”. Therefore they invite us to raise our guard: “On farms, biosecurity should be strengthened”, they suggest. Furthermore – they conclude – it is necessary to “limit the exposure of mammals, including humans”, to intensify “surveillance on animals and humans”, “together with genomic analysis and sharing of sequence data”.

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Pregliasco: “The risk of contagion is higher where there is animal density”

“The first episode of human-to-human transmissibility of the A/H5N1 avian virus dates back to 1995, in Hong Kong: some cases had been recorded, but the outbreak had been stopped – recalls Pregliasco -. And other episodes were registered in the Netherlands, even though in that circumstance the virus had not passed from human to human. This tells us that the possibility exists, and not now. It also tells us that since then the virus has not acquired this ability to independent passage”.

Where is it most likely that Avian Flu could mutate into a human epidemic? “The place doesn’t matter, what matters is the density of the animal population, in addition to the proximity between man and animal, as happens in Asian countries, which is also a matter of style – continues Pregliasco -. Let’s keep in mind that the risk exists in Italy too , given the presence of many intensive farms”.

What to do? “The physical division between avian farms and those of other mammals is important, because a transversal spread of the virus is probable – concludes the expert -. Therefore we must continue to monitor the apparently indistinguishable cases of influenza, and control the birds: both those in captivity and migratory birds. This is to prevent a repeat of what happened with the Spanish flu, to prevent the avian virus from adapting so well to humans that it does not leave it easily.”