Is H5N1 a threat to humans? | Explanation

the story So Far: The highly pathogenic avian influenza (HPAI) H5N1 strain is affecting cattle in several states in the US, and for the first time, three cases of human infection have also been reported in dairy farm workers, raising apprehensions about the risk of widespread transmission of the virus from cattle to humans. Kerala's Alappuzha, Kottayam and Pathanamthitta districts, where water bodies, migratory birds, poultry and integrated farms are part of the ecosystem, have reported H5N1 outbreaks at 19 locations since April. However, the death of a large number of crows in Alappuzha and subsequent confirmation of the H5N1 virus in their carcasses has raised concerns that the virus may spread far and wide.

How dangerous is it?

Since H5N1 emerged in 1996, it has caused the mass slaughter of billions of wild birds and poultry. The virus has spread to about 26 mammalian species, especially cattle, and there is now evidence that it can also infect humans, raising the risk that H5N1 could cause the next global pandemic. Of particular concern is that herd-to-herd transmission of H5N1 is now occurring in the US, involving about 12 states, and the virus has been found in raw milk and milking machines.

According to scientists, the virus does not have changes that would make it better suited to transmit between people and, therefore, the risk to human health remains low. However, the ability of influenza viruses to evolve rapidly and the wide geographic spread of H5N1 indicate that more human infections should be expected.

What is the risk level for humans?

The virus appears to spread from birds/animals to humans, who come in close contact with them without adequate personal protection.

According to the WHO, nearly 900 human infections with H5N1 have been reported from 23 countries between 2003 and April 1, 2024, more than half of which were fatal. Although the risk of human infection from H5N1 is still considered low, this may change rapidly as the virus spreads to more animals, especially cows or domestic rats, which have closer contact with humans. In districts like Alappuzha where water birds, poultry, dairy cows and humans share the same environment, the chances of human infection should be considered high.

What are the symptoms of H5N1?

The general symptoms of H5N1 are similar to those of influenza-A illnesses, including difficulty breathing, fever, cough, sore throat, and pneumonia, all of which can potentially worsen, especially in people who are immunocompromised or who already have an illness. In the US, conjunctivitis or pink eye was the only symptom reported in one of the infected farm workers.

Also in April, the Centers for Disease Control and Prevention (CDC) issued a health advisory that physicians should consider the possibility of H5N1 infection in people with respiratory illness or conjunctivitis if they have been exposed to livestock or dead birds. Early detection and prevention of infection is critical to prevent widespread spread of the virus.

In Kerala so far, since only poultry has been found to be affected in all outbreaks, the strategy adopted for containment has been mass culling of birds within a certain radius of the reported infection. However, the incident of mass death of crows has now changed the equation, as it is possible that the infection may have been carried by crows beyond the existing surveillance area. Continuous surveillance by testing environmental samples – water, bird faeces – as well as human samples with influenza-like illness will be necessary in the designated surveillance areas. People who have cattle and birds at home are being advised to wear masks, and wherever H5N1 positive cases are found, people are being prescribed the antiviral Tamiflu as prophylaxis.

What are the necessary precautions?

People should avoid contact with infected birds or animals or their contaminated environment. If a person has been exposed to an H5N1-contaminated environment, he or she should monitor themselves for symptoms of new respiratory illness, including conjunctivitis, for 10 days and seek appropriate medical advice. It is better to ensure that people use only pasteurised milk and poultry meat and eggs are thoroughly cooked to prevent any possible food-borne transmission of H5N1.

In a recent editorial, the Lancetspoke about the need for a strong and coordinated response to H5N1. It pointed out that the concept of 'One Health', though often acknowledged, is rarely prioritised and implemented.

Kerala, however, has taken ‘One Health’ beyond a conceptual framework and the project is currently being implemented in four districts – Alappuzha, Pathanamthitta, Kottayam and Idukki – as part of the World Bank-assisted ‘Rebuild Kerala’ project. It has set up a community-based disease surveillance network in these districts with 2.5 lakh volunteers trained in the ‘One Health’ concept who will report any unusual occurrence or death of animals/birds in an area so that early warning and early preventive or control measures can be taken.