In recent months, the world has recorded several cases of H5N1 avian influenza in birds. The pathogen responsible for the infection has been spread by migratory birds and has already affected some farms. In 2022, in the United States alone, 58 million birds were infected and died.
In poultry, H5N1 is quite dangerous — the mortality rate in chickens and chickens is 90% to 100%, and there is a practice of euthanizing animals exposed to the virus to prevent its spread.
According to the Deutsche Welle news agency, the virus is probably already in Central and South America, since 240 pelicans were found dead in Honduras in the last week and there are cases of the disease registered in Peru, Venezuela, Ecuador and Colombia.
H5N1 was first identified in 1996 in China and primarily infects chickens and other types of poultry. The virus has been circulating since then, but it has been drawing the attention of the scientific community today not only because of the number of animals infected, but because it managed to infect small mammals, such as minks.
A study published in the scientific journal Eurosurveillance, in January 2023, warns that the virus has already undergone eight mutations, including one in the PB2 gene, which can make the pathogen more transmissible in mammals. A mutation in this same gene was identified in H1N1, the swine flu virus that caused a pandemic in 2009. The research adds that H5N1 infected minks and the small mammals were able to transmit the virus to each other.
In humans, for now, transmission is complicated. Close contact with infected animals is required, and there are no reports of contamination between people. In January 2023, the World Health Organization (WHO) was alerted to the case of a young Ecuadorian woman infected, but none of her relatives had the disease. The girl recovers well.
For the director general of the WHO, Tedros Adhanom Ghebreyesus, the risk of a pandemic caused by H5N1 is low, but it is important that the international community is attentive to the possibility of infection of mammals. “It is a virus that has been running for 25 years, but the jump to mammals needs to be accompanied. We have not seen sustained transmission between humans to date, but we need to warn the population not to touch or collect sick or dead animals ”, he warned, at a press conference this Wednesday (8/2).
Sylvie Brian, director of preparedness for pandemics and epidemics at the WHO, explained at the press conference that, for now, the virus remains zoonotic, that is, it only circulates among animals.
“It is a virus that is well adapted for animals. Between humans, transmission is rare, except by very close contact. But, due to the nature of the virus, we need to be vigilant and ensure that H5N1 is controlled, without giving it the possibility of evolving and becoming transmissible in humans,” said the director.
She also says that, as with other zoonotic viruses, when H5N1 infects humans, it usually causes a lot of damage to the lungs and triggers a serious condition. The mortality rate among those infected is 30% to 50%.
known virus
University of Brasilia (UnB) professor Bergmann Ribeiro, a virus specialist, explains that influenza viruses are named H and N according to the type of two proteins, hemagglutinin and neuraminidase. Substances remain on the surface of the pathogen, as with the spike in the coronavirus, for example.
There are several types of hemagglutinins and neuraminidases, which is why viruses are given names such as H5N1, H1N1, H3N2, etc. “Another important point regarding this family is that its genome is divided into eight pieces, which can be exchanged with other types of influenza. This recombination can cause different mutations that increase the probability of the virus starting to infect humans”, says the professor.
An animal infected with two types of influenza, for example, may represent the ideal situation for the viruses to exchange information that favors their future survival. This is a possible explanation for the adaptation of the virus in mink infected in Europe.
Ribeiro says that there is indeed the possibility that H5N1 might cause a new global public health emergency, especially considering that influenza has already been responsible for four pandemics throughout history. However, for now, it is a zoonotic virus, which primarily affects animals and can have a great impact on agriculture, but not on public health.
He also points out that, for regarding 70 years, 150 countries (including Brazil) have been monitoring the types of influenza virus in circulation. If H5N1 starts to infect a large number of people, it will be detected early on.
And, even if the virus mutates enough to guarantee human-to-human transmission, the UnB professor claims that it is possible to produce a vaccine quickly. “We are prepared in case the influenza virus becomes pandemic once more. In 1918, in the Spanish flu, 50 million people died. But in the following pandemics, we considerably reduced the number of deaths and, in 2009, there were 300,000 deaths. It is a virus that, even with the modifications, has been circulating for many years and we even have some antibodies to fight it”, explains Ribeiro.
Still, WHO says it is working with international animal health bodies to try to resolve the bird-to-bird outbreak before H5N1 has adapted enough to be transmitted between humans.
“No need to worry, authorities are doing what they can to prevent this virus from becoming a bigger problem,” said WHO director of emergencies Michael Ryan.
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