Does H5N1 pose a threat for humans? | Explained

Highly pathogenic avian influenza H5N1 outbreak in U.S. cattle raise concerns of human transmission, prompting global pandemic fears.

The story so far: The highly pathogenic avian influenza (HPAI) H5N1 strain has been affecting cattle across several States in the U.S., and for the first time, three cases of human infection in dairy farm workers were also reported, raising fears of the risks of a wider transmission of this virus from cattle to humans. The districts of Alappuzha, Kottayam and Pathanamthitta in Kerala, where water bodies, migratory birds, fowls and integrated farms form part of the ecosystem, have reported H5N1 outbreaks in 19 places since April. However, the death of crows in large numbers in Alappuzha, and subsequent confirmation of the H5N1 virus in their carcasses have given rise to concerns that the virus could spread far and wide.

Ever since it emerged in 1996, H5N1 has resulted in the mass killing of billions of wild birds as well as fowls. The virus’s jump to some 26 mammalian species, especially cattle and the now emerging proof that it can infect humans, has heightened the threat perception that H5N1 could lead to the next global pandemic. Of particular concern are the facts that herd-to-herd transmission of H5N1 is now taking place in the U.S., involving some 12 States and that the virus has been detected in raw milk and in milking machines.

According to scientists, the virus lacks changes that would make it better adapted to transmit between people and therefore, the risk to human health remains low. However, the potential for influenza viruses to rapidly evolve and the wide geographic spread of H5N1 signals that more human infections should be expected.

The virus seems to spread from birds/animals to humans who may be closely interacting with these, without adequate personal protection.

According to the WHO, between 2003 and April 1, 2024, close to 900 human infections of H5N1 have been reported from 23 countries, of which, more than half were fatal. Even though the risk of human infections from H5N1 is still perceived to be low, this can change rapidly as the virus spreads to more animals, especially cows or domestic mice, which have closer contact with humans. In districts like Alappuzha where water fowls, chicken, dairy cows and humans share the same environment, the opportunities for human infections should be perceived as high.

The common symptoms of H5N1 are similar to those of influenza-A illnesses, including respiratory difficulties, fever, cough, sore throat and pneumonia, all of which can potentially worsen, especially in those who are immunocompromised or have underlying conditions. In the U.S., conjuctivitis or pink eye was the only symptom that was reported in one of the farm workers who was infected.

In April itself, the Center for Disease Control and Prevention (CDC) had sent out a health advisory that clinicians should consider the possibility of H5N1 infection in persons who report with respiratory illness or conjunctivitis, if they have had exposure to livestock or dead birds. Early detection and containment of the infection is important to prevent the extensive spread of the virus.