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Explained: What is H5N1 avian influenza, its symptoms, and how fatal can it be?

The most common route of virus transmission is direct contact — when a person comes in close contact with infected birds, either dead or alive.

On July 21, an 11-year-old boy died of H5N1 avian influenza in Delhi. This is the first recorded death due to the bird flu in India this year. In January, bird flu was confirmed in several states with thousands of birds, including migratory species, being found dead.

What is bird flu?

Bird flu or avian influenza is a disease caused by avian influenza Type A viruses found naturally in wild birds worldwide. The virus can infect domestic poultry including chickens, ducks, turkeys and there have been reports of H5N1 infection among pigs, cats, and even tigers in Thailand zoos.

Avian Influenza type A viruses are classified based on two proteins on their surfaces – Hemagglutinin(HA) and Neuraminidase(NA). There are about 18 HA subtypes and 11 NA subtypes. Several combinations of these two proteins are possible e.g., H5N1, H7N2, H9N6, H17N10, etc.

Infection in humans

There have been reports of avian and swine influenza infections in humans including A(H1N1), A(H1N2), A(H5N1), A(H7N9), etc. The first report of human H5N1 infection was in 1997 and currently, over 700 human cases of Asian Highly Pathogenic Asian Avian Influenza A (HPAI) H5N1 virus have been reported to the World Health Organisation from 16 countries. The infection is deadly as it has a high mortality rate of about 60%.

The most common route of virus transmission is direct contact — when a person comes in close contact with infected birds, either dead or alive.

Humans can also be affected if they come in contact with contaminated surfaces or air near the infected poultry. There is no sufficient evidence suggesting the spread of the virus through properly cooked meat.

Symptoms of avian influenza

According to US CDC, the reported signs and symptoms of avian influenza A virus infections in humans have ranged from mild to severe influenza-like illness.
– Fever, cough, sore throat, muscle aches, nausea, abdominal pain, diarrhea, vomiting
– Severe respiratory illness (e.g., shortness of breath, difficulty breathing, pneumonia, acute respiratory distress, viral pneumonia, respiratory failure)
– Neurologic changes (altered mental status, seizures)

Risk groups

Children and adults below 40 were seen to be the most affected and mortality was high in 10-19 years olds.

Human-to-human transmission

AIIMS chief Dr. Randeep Guleria told PTI that human-to-human transmission of the H5N1 virus was very rare and there was no need to panic. “The transmission of the virus from birds to humans is rare and sustained human-to-human transmission of the H5N1 virus has not yet been established and therefore there is no need to panic. But then people working closely with poultry must take precautionary measures and maintain proper personal hygiene.”

A paper published in 2005 in The New England Journal of Medicine, investigated possible person-to-person transmission in a family cluster in Thailand and wrote that the “disease in the mother and aunt probably resulted from person-to-person transmission of this lethal avian influenza virus during unprotected exposure to the critically ill index patient.”

Dr Neeraj Nischal, an associate professor in the Department of Medicine at AIIMS, told PTI that Avian influenza or bird flu is predominantly a zoonosis, and there is no evidence of sustained human-to-human transmission so far.

“Although a few isolated family clusters have been reported, transmission in these clusters may have occurred through common exposure and in rare situations a very close physical contact; there is no evidence of human-to-human transmission via small-particle aerosols,” he added.

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