Mexico has managed to contain avian flu, a type of flu that especially affects birds and poses a major risk for the fifth largest producer of chickens and eggs. Its biggest danger is that it begins to adapt to more and more species, as it already happens 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 contain the outbreak of Highly Pathogenic Avian Influenza AH5N1, responsible for causing a historic epidemic in Europe.
According to the authorities, the country started the new year without active sources of this highly infectious strain that is present in Europe, America, Africa and Asia, and which arrived in the territory for the first time in October, expanding very quickly through several states in the south and From north .
With Mexico, there are now 10 countries on 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 the migration of birds,” explains José Campillo, a virologist at the National Autonomous University of Mexico (UNAM). .
HPAI H5N1 severely affects domestic poultry such as chickens and turkeys. “The birds of prey and scavengers were also very affected by the virus in this last season. What is worrying is that there are many cases of transmission of the virus to a wide variety of species”, says Elisa Pérez Ramírez, a veterinarian at the Center for Research in Animal Health (CISA), in Spain.
“In Europe it has been detected mainly in foxes and seals, but also in canids, felines and mustelids”, points out the expert, highlighting a study Published in China in 2021, which demonstrated how mink are highly susceptible to avian and human influenza virus infection.
A few days ago, researcherscabinets alerted to an outbreak of highly pathogenic avian influenza detected last autumn in these intensively reared animals in Europe, after minks with symptoms of hemorrhagic pneumonia began to die on a Galician farm. “And we are seeing more and more cases of passing the virus from birds to humans, although the risk remains low,” adds Pérez.
As the zootechnical veterinarian at UNAM, Rafael Ojeda, 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 cases that have occurred so far in humans have occurred. The last one, a nine-year-old girl in Ecuador.
Stop avian flu, intensive poultry farms are a breeding ground for the virus
In Mexico, the infectious agent has so far only affected birds, being detected for the first time in a falcon in the municipality of Metepec, in the center of the country, “in an area where several migratory routes of ducks and geese from the United States and Canada”, says Ojeda As the specialist explains, “the anseriformes are an order of birds that act as natural reservoirs for most variants of the influenza virus. And, in addition, they are propagation agents”.
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 pockets of the population. Mexico is the fifth largest producer of eggs and chickenyouon a global scale. 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 huge densities of birds are perfect fertile ground for the transformation of a low pathogenic virus —of the hundreds that circulate in wild birds— into a highly pathogenic one”, agrees the Spanish virologist.
Once a highly pathogenic virus manages to infiltrate a farm, it begins to produce very high mortality. “This obliges us to take radical control and prevention measures that usually involve the slaughter of all animals on the farm,” adds Pérez.
For this reason, as soon as the first case was reported, the Mexican authorities of the National Service of Health, Safety and Agro-Food Quality (Senasica) launched the protocols to contain the outbreaks. Quarantine measures included prohibiting the mobilization of products that did not have permission from the federal health authority and the massive immunization of animals. The region of Los Altos de Jalisco, the most important poultry area in the country, was the first to start vaccinating domestic birds to prevent the AH5N1 avian flu.
Mexico, which has several national vaccines that it sells abroad, “has stopped exporting biologicals abroad to guarantee distribution on a national scale. But, the problem is that when they are made with the viruses that circulated in the past seasons, the vaccines stop being efficient very soon”, explains Ojeda.
“Vaccination is very complex in the case of avian flu, there are still many limitations for its use. As with human flu, a vaccine can be effective against a certain subtype, but completely ineffective against another that circulates in the following year. In addition, there is a certain reluctance because vaccines can facilitate the silent circulation of the virus on a farm and end up favoring its spread”, points out Pérez.
“For coronaviruses, it is easier to reformulate immunization because their evolution is slow. In contrast, the flu mutation rate is very high. That’s why you need to get vaccinated every year”, qualifies Campillo.
The high mutability of influenza viruses
Precisely this ability of influenza viruses to modify and generate different lineages is one of the biggest concerns of scientists. “These pathogens are incredible, they mutate very quickly, and the more specimens they infect, the more likely they are to adapt better to different regions of the world, which is what is currently happening,” explains Ojeda.
Until the emergence of the highly pathogenic strain of H5N1 in Guangdong, China, in the late 1990s, experts believed that avian flu hardly affected domestic birds. “From then on, we began to observe that the virus was capable of making sick and causing the death of several wild species, mainly those related to aquatic environments, where it persists more”, explains Pérez.
“Subsequently, 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, swine and human origin”, qualifies the veterinarian, exposing epidemiologists’ greatest fear: that the current AH5N1 strain will reformulate into some form of human influenza. “If that happens, the new virus could infect humans directly. And, taking into account its virulent nature, it can cause a catastrophe”, warns Campillo.
As the UNAM virologist recalls, of the 868 people infected by the virus, more than 450 of those affected lost their lives from 2003 to 2022. “This represents a mortality rate of 52%. Taking into account that covid was 2-3% globally, such a zoonosis would cause a much worse pandemic.”
At present, the current strain of Highly Pathogenic Avian Influenza AH5N1 is unable to directly infect and transmit between humans. “Therefore, the risk is very low for the general population and medium for those who have continuous contact with birds. Calculating the number of birds it has affected in recent months, there are very few cases in people. However, this virus obliges us not to let our guard down and to carry out a very intense surveillance of both domestic and wild birds”, says Pérez.
A virus that is already endemic in Europe
The migration of ducks and geese is one of the most important routes for the spread of avian influenza viruses. And, until this last season, there were cyclical or periodic epidemics associated with the arrival of migratory birds. In Spain, for example, it was very unlikely to detect cases between March and September, as outbreaks occurred with the arrival of wintering birds in autumn and winter. However, this pattern has changed radically since 2021, when the virus became endemic in wild birds in Europe”, says the CISA expert.
Something that can also happen in Latin America, where the agent is expanding. “In Mexico, we detected and studied many low-pathogenic viruses introduced in the United States. They have become endemic and most circulate among domestic and wild birds”, says Ojeda, who is responsible for denouncing these types of cases to the local authorities and who is concerned “by the risk posed by backyard systems for producers with little or no biosecurity”.
“We cannot forget other dispersal routes that people are involved in, such as the movement of sick birds and their products, or contaminated vehicles between farms. Once the virus manages to remain in the environment throughout the year and become endemic, as it happened this last season, migratory birds no longer play the fundamental role that they had until now”, warns Pérez.
“As we have seen with other zoonoses, as a society we have an increasing responsibility in matters of biosecurity and control of infectious agents”, concludes Campillo.