In January, a four-year-old girl from West Bengal’s Malda district, who was recovering from a respiratory infection, fell ill.

Her parents took her to a local paediatrician in Kaliachak on January 26.

On February 1, she was admitted in the paediatric intensive care unit in a Malda hospital after she developed respiratory distress, high-grade fever and intense stomach cramps.

A day later, she tested positive for the influenza B virus and adenovirus. It took her the whole month to recover and get discharged.

But within days, the symptoms reemerged. She was then referred to Kolkata’s Nil Ratan Sircar Medical College and Hospital for respiratory distress.

This time, her nasal swab tested positive for influenza A virus and rhinovirus. The sample was referred to Pune’s National Institute of Virology, which detected the avian flu virus – the H9N2 subtype of influenza A virus – in her.

Avian influenza generally infects poultry and birds. Some cases of avian influenza have been reported in humans, though it is a rare occurrence.

This is the second such case from India. The first was reported in 2019, when a 17-month-old boy tested positive in Melghat, a tribal hamlet in Maharashtra’s Amravati district.

The two cases have not led to any human-to-human infection.

But is there a potential risk of an outbreak? Experts Scroll spoke to said the risk of infection due to avian flu remains low in India as long as human-to-human transmission has not been established.

‘Source of infection unknown’

Since 2006, over 99 cases of the H9N2 virus in humans have been reported to the World Health Organisation from China, Vietnam, Bangladesh, Hong Kong, Oman, Senegal, Pakistan and Cambodia. This includes at least two deaths.

While a press release from the World Health Organisation on June 11 stated that the child was infected by poultry near her house, officials in Bengal told Scroll there is no poultry farm in the surrounding neighbourhood.

“The source of infection remains unknown,” said Dr Dipankar Majhi, state surveillance officer in West Bengal, who visited Malda to monitor the situation. “There is no history of migration of birds in that period either.”

The child remained in the Kolkata medical college for over two months. She was finally discharged on May 1, but continues to require oxygen support at home.

Avian influenza in humans is known to cause mild illness. In the four-year-old’s case, however, the respiratory distress continued for four months.

“That is because she already had a past history of lung infection before she caught this infection. Her health was already weak,” said Majhi.

The child remained in the Kolkata medical college for over two months. She was finally discharged on May 1, but continues to require oxygen support at home.

Contact tracing

Dr Siddhartha Niyogi, director of health services in West Bengal, said no new cases of human infection have been found in the area in the last five months.

Majhi said they began tracing close contacts of the girl, including her family, neighbours and the medical staff that treated her. “We tested symptomatic cases and did not find any positive avian flu case,” Majhi told Scroll. Asymptomatic contacts were not tested.

The animal husbandry department also began to screen poultry, wild birds and animals in the neighbourhood.

Between April and June, it tested 1,728 samples – all of them tested negative for the virus subtype.

The state health department, however, conducted no sewage water testing. Checking for the presence of the H9N2 virus in wastewater could highlight the extent of its spread in a locality.

Low risk of outbreak

Both the WHO and the state health department have labelled the risk of a possible outbreak as low.

The previous case of Melghat from 2019, where a 17-month-old boy was diagnosed with the virus after developing fever, cough, and breathlessness, was the only other confirmed case in the country. While the infant was not exposed to contaminated poultry, his parents had traveled for a religious gathering a week before he developed symptoms.

His father, too, had similar symptoms when he returned but was never tested. No other case in the neighbourhood was diagnosed.

“It is hard to make much out of purely isolated cases,” said Dr Anurag Agrawal, former director of the Institute of Genomics and Integrative Biology and now dean of bio-sciences and health research, Ashoka University.

“Human-to-human transmission is what you worry about. It has not been established that this subtype can transmit from one human to another,” Agrawal added.

For that to happen, he said, the virus will need further mutation and a high viral load in the upper respiratory tract of humans.

While the risk posed by H9N2 is low, other subtypes of avian influenza have been swiftly adapting and mutating.

The subtype H5N1, for instance, has jumped to mammals such as foxes, ferrets, seals, cats, bears and skunks. Recently, the USA reported 47 cases of H5N1 infection in mice, which brings them closer to infecting human beings.

“The more animals the virus infects, the more likely it is to acquire mutations which we don’t want,” Agrawal said.

The fact that H5N1 subtype is able to infect mice makes the risk for humans greater. “But influenza is not a new virus and right now there is nothing to suggest alarm of any kind,” Agrawal said. The latest series of cases is only proof that the virus lives amongst us, he added.

Gautam Menon, head of the Centre for Climate Change and Sustainability in Ashoka University, however, warned that “the presence of this virus in household animals suggests the need for caution, given the larger possibility of exposure.”

Menon added that one worry that remains in the scientific world is of “reassortment”. “If a pig were infected with a human influenza A virus and an avian influenza A virus at the same time, then reassortment of different parts of these viruses could produce a new influenza virus that might then be able to infect humans and spread easily from person to person,” he explained.

If such a virus is able to spread, it can pose a risk of an outbreak or pandemic. “Surveillance is important, including sequencing of viruses from humans and animals infected with avian influenza A viruses, to identify such a possibility,” Menon said.

Dr Chitra Pattabiraman, genomic epidemiology and infectious diseases researcher pointed out that there is an ongoing outbreak of avian influenza in North and South America, with an increased number of mammals getting infected. Within India, however, such cases are yet to be reported.

“Currently human infections with avian influenza are very rare,” she said. “Many states in India, including Andhra Pradesh, Maharashtra, Kerala and Jharkhand, have reported recent outbreaks of bird flu but no associated human cases have been reported. That means there are no red flags for now,” she said.

This reporting was supported by a grant from the Thakur Family Foundation. Thakur Family Foundation has not exercised any editorial control over the contents of this article.