This type of influenza, which especially affects poultry, poses a great risk to the fifth largest producer of chickens and eggs. Its greatest danger is that it begins to adapt to more and more species, as it is already doing in other parts of the world. The researchers warn that if the infectious agent manages to adapt to humans, the health crisis would be greater than that caused by covid-19.

After suffering the loss of more than 5.5 million birds, Mexico seems to have managed to stop the outbreak of Highly Pathogenic Avian Influenza AH5N1 , responsible for having caused a historic epidemic in Europe.

According to the authorities, the country began the new year without active sources of this highly infectious strain with a presence in Europe, America, Africa and Asia, and which first arrived in the territory in October, expanding very rapidly throughout various southern and northern states.
With Mexico, there are already 10 countries in the American continent where this pathogen has arrived, which has already caused a serious epidemic in other parts of the world. “The first cases in the region occurred in the United States in 2014, but in recent months it has spread to many Latin American countries due to bird migration,” explains José Campillo, a virologist at the National Autonomous University of Mexico (UNAM).

A few days ago, Spanish researchers warned about an outbreak of highly pathogenic avian influenza detected last autumn in these intensively reared animals in Europe, after mink with symptoms of haemorrhagic pneumonia began to die on a Galician farm. “And we are seeing more and more cases of the virus jumping from birds to humans, although the risk remains low,” adds Pérez.

As UNAM zootechnical veterinarian Rafael Ojeda , a specialist in disease ecology, explains: “For a person to become infected, there must be close contact with the sick or dead specimen.” This is how all the cases that have occurred so far in humans occurred. The last one, a nine-year-old girl in Ecuador .

Intensive poultry farms: breeding ground for the virus

Ducks that arrived from the north of the continent would have been responsible for spreading the virus to the many Mexican commercial farms that had to slaughter millions of birds, “causing enormous economic losses, making the product more expensive and affecting the pocket of the population. Mexico is the fifth largest chicken and egg producing country in the world. As it is a low-income country, they are its main sources of protein, a factor behind its intense production systems”, warns the veterinarian.

“ Intensive poultry farming is a risk factor for the emergence and persistence of viruses such as H5N1. Farms with enormous densities of birds are a perfect breeding ground for the transformation of a low-pathogenic virus —of the hundreds that circulate in wild birds— into a high-pathogenic one”, agrees the Spanish virologist.

Once a highly pathogenic virus manages to sneak onto a farm it begins to produce sky-high mortality rates. “This forces us to take radical control and prevention measures that usually entail the slaughter of all the animals on the farm,” adds Pérez.

For this reason, as soon as the first case was reported, the Mexican authorities of the National Agri-Food Health, Safety and Quality Service (Senasica) launched the protocols to stop the outbreaks. The quarantine measures included the prohibition of the mobilization of products that did not have the permission of the federal health authority and the massive immunization of the animals. The Los Altos de Jalisco region, the most important poultry area in the country, was the first to start vaccinating backyard birds to prevent AH5N1 avian influenza.

Mexico, which has different national vaccines that it markets abroad, “stopped exporting biologicals abroad to ensure distribution on a national scale. But, the problem is that when they are made with the viruses that circulated in past seasons, the vaccines stop being efficient very soon”, explains Ojeda.

“Vaccination is very complex in the case of bird flu, there are still many limitations to its use. As with  human influenza , a vaccine can be effective against a particular subtype but completely ineffective against another that circulates the following year. In addition, there is some reluctance because vaccines can make it easier for the virus to circulate silently on a farm and end up favoring its spread”, Pérez points out.

“For coronaviruses it is easier to reformulate the immunization because its evolution is slow. In contrast, the mutation rate of influenza is very high . That is why you have to get vaccinated every year ”, Campillo qualifies.

The high mutation capacity of influenza viruses

Precisely this ability of influenza viruses to modify and generate different lineages is one of the greatest concerns of scientists. “These pathogens are incredible, they mutate very quickly, and the more specimens they infect, the more likely they are to better adapt to different regions of the world, which is what is currently happening,” Ojeda explains.

Until the appearance of the highly pathogenic H5N1 strain in Guangdong, China, in the late 1990s, experts believed that bird flu hardly affected domestic birds. “Then it began to be observed that the virus was capable of making sick and causing the death of various wild species, especially those related to aquatic environments, which is where it persists the most,” Pérez explains.

“Later, it was found that they could recombine with those that affect different species, as happened in Mexico in 2009 with the H1N1 strain, which resulted from a triple mutant recombination of avian, porcine, and human origin,” the veterinarian qualifies, exposing the Epidemiologists’ greatest fear: that the current AH5N1 strain will reformulate with some type of human influenza . “If this happens, the new virus could directly infect humans. And, taking into account its virulent nature, it could cause a catastrophe”, warns Campillo.

At the moment, the current strain of Highly Pathogenic Avian Influenza AH5N1 does not have the capacity to directly infect and transmit between humans. “So the risk is very low for the general population and medium for those who have continuous contact with birds. Calculating the number of birds that it has affected in recent months, there are very few cases in people. However, this virus forces us not to let our guard down and to carry out very intense surveillance of both domestic and wild birds,” says Pérez.