Influenza viruses comprise a broad group of viruses that affect different animal species, including humans, birds, and other mammals. There are four types of influenza, A, B, C, and D. The avian influenza virus falls into type A. Influenza viruses of avian origin are classified according to the combination of two proteins found on the surface of the virus: hemagglutinin or H protein and neuraminidase or N protein. There are 16 types of H protein (1-16) and nine of the N-type (1-9).
Many combinations of H and N can be found in nature. Each combination is considered a subtype, and viruses with some variation within a subtype are referred to as a lineage. Another important characteristic of avian influenza viruses to keep in mind is their classification as "low pathogenic" or "highly pathogenic", according to certain genetic characteristics and the severity of the disease they cause in poultry. The H5N1 avian influenza virus is considered "highly pathogenic" due to the severity of the disease it causes.
The H5N1 avian influenza virus was first identified in China in a goose farm in 1996, but it was in 2021 that numerous outbreaks of avian influenza began in different regions of the world, including Mexico. These outbreaks have had a significant impact on animal health and welfare and have jeopardized the food security and livelihoods of those who depend on poultry farming.
In Mexico, the first report of H5N1 avian influenza was in October 2022, and as of early January 2023, the H5N1 virus has affected around 5.5 million birds on 23 poultry farms in the states of Yucatan, Sonora, Nuevo Leon, and Jalisco. These numbers represent 0.26 percent of the national inventory. To deal with this problem, the Ministry of Agriculture and Rural Development undertook a series of control measures and today there are no outbreaks of this virus in Mexico.
It should be remembered that this microorganism mainly affects poultry and wild birds, and can occasionally infect mammals, including humans. In this regard, in recent months an increasing number of cases of H5N1 avian influenza have been observed in terrestrial and aquatic mammals. This situation has raised concern in the international community due to the threat that this pathogen represents to the health of domestic and wild animals and, potentially, to public health.
The characteristics of the H5N1 avian influenza virus have put it in the spotlight because of the risk it poses by adapting to mammals, i.e. that it can easily replicate and be transmitted to other animals, including humans. Recently, this agent caused an outbreak in a mink farm in Europe, and the main concern was the infection of a large number of animals.
Such events can lead to the emergence of new strains that are more harmful to humans. However, we should keep in mind that this virus was first identified in 1996, so it has somehow "been around" all these years. We do not know and there is no way to predict the future of this virus. What we do know is that there are vaccines available today and tools to develop new vaccines, in case it mutates and can be effectively transmitted between people.
It is necessary to maintain epidemiological surveillance in domestic animals and wild birds to try to identify promptly some mutations in the H5N1 avian influenza virus and prevent the spread of the disease when it occurs in a poultry farm, through strict biosecurity measures, avoiding direct contact or handling sick or dead birds.
Author: Jesús Hernández and Mónica Reséndiz Sandoval, researchers of the Immunology Laboratory of CIAD.