Avian influenza continues to take a heavy toll on India’s poultry sector. Thus far, the disease has spread in 11 states. Besides chickens, other species of birds, including ducks, crows and pigeons, have also been found dead. Recently, officials reported that a brown fish owl in the Delhi zoo had tested positive for the disease.
While the virus’s rate of transmission between different species of birds is in itself alarming, people are also becoming more apprehensive about the pathogen’s spread to humans, via poultry meat and eggs. This in turn is affecting the poultry industry in a big way.
Avian influenza or bird flu is caused by type A influenza viruses. There are various subtypes of the virus. Those belonging to subtype H5 are grouped under the “highly pathogenic avian influenza” category, causing up to 100% mortality in birds. So far, two subtypes – H5N1 and H5N8 – have been detected in the current outbreak.
Aquatic birds are natural hosts of avian influenza viruses. Many of them are migratory, which could explain why the virus has spilled over to so many other species of birds.
To date, scientists have not documented a single H5N8 infection in humans. However, between 2003 and 2020, officials have reported 862 human cases of H5N1 infections to the WHO. In most cases, researchers have attributed infections to contact with infected live or dead poultry.
This said, the consumption of poultry meat and eggs is not considered to be the principal source of transmission. Studies have noted that H5N1 viruses spread from poultry to humans primarily by contact with respiratory secretions, faeces, blood and the organs of infected birds.
People at increased risk for avian influenza virus exposure are farmworkers, butchers, veterinarians and others who work in proximity to infected birds. The majority of human exposure risk occurs at the farm and in the processing steps.
Though there have been instances when avian influenza viruses have crossed the species barrier and infected humans, there exists no convincing evidence for human to human transmission of the virus. Similarly, there is no data to prove that human beings can contract the virus simply by consuming infected meat. (There have been stray reports of human cases of H5N1 infection after drinking raw duck blood in Vietnam.)
It’s essential to follow certain safety practices while consuming poultry products. The avian influenza virus is sensitive to heat. So cooking at 70º C (‘piping hot’) will certainly kill the virus. If a thermometer is not available, it is advisable to cook the meat until it is no longer pink.
Avian influenza viruses can survive freezing and refrigeration. In fact, low temperatures increase the virus’s stability, so the act of freezing fresh meat alone won’t eliminate the virus.
According to the WHO, people handling raw poultry products should thoroughly wash their hands with soap and warm water, and disinfect the working space.
Eggs laid by infected birds harbour the virus inside as well as on the surface of the eggshell. The risk associated with egg consumption is naturally mitigated to a certain extent because birds infected with highly pathogenic influenza viruses tend to stop laying eggs. Nonetheless, as a precaution, it is not advisable to consume raw eggs; they have to be fully cooked, at least until the egg yolk is no longer runny. This egg pasteurisation process completely inactivates the virus.
It’s important to remember that a certain degree of risk is associated with preparing infected poultry products for eating. Chopping and cutting could generate aerosols that spray up infective materials into mucous membranes. That is, the bigger challenges vis-a-vis poultry products have to do with preparation, not consumption. Chefs and cooks need to take special care in this regard.
Speculation about chicken meat consumption was rife in the early days of the COVID-19 pandemic as well. However, the coronavirus that has been affecting chickens for decades belongs to an entirely different genus – not to the one to which the novel coronavirus belongs. Experts are also fairly certain that chickens don’t harbour the novel coronavirus. Thus, there is no possibility for transmission of coronavirus from chickens to humans.
But in the case of the bird flu, based on previous reports, we can’t yet rule out the virus’s transmission from poultry to humans. At the same time, there is no clear-cut evidence that humans could get avian influenza by consuming infected poultry products. So while it is important to be cautious while preparing poultry meat and eggs, just cooking them properly will eliminate the risk.
Niranjana Rajalakshmi is a veterinary microbiologist.