Indian scientists predict how bird flu could spread to humans

By Admin

19 Dec, 2025

Understanding the growing concern around H5N1
For years, scientists have warned that bird flu, scientifically known as H5N1, could one day make the dangerous jump from birds to humans and trigger a global health emergency. Avian flu, a type of influenza virus, has remained entrenched across South and South-East Asia since emerging in China in the late 1990s. While human infections have been rare, their severity has kept global health agencies on alert.

According to the World Health Organization, from 2003 to August 2025, there have been 990 confirmed human cases of H5N1 across 25 countries, resulting in 475 deaths a fatality rate of nearly 48%. Recent outbreaks have also raised alarm beyond Asia. In the United States, the virus has affected over 180 million birds, spread to more than 1,000 dairy herds across 18 states, and infected at least 70 people, mostly farmworkers. India has also witnessed spillover impacts, including the deaths of three tigers and a leopard at a wildlife rescue centre in Nagpur earlier this year.

How bird flu affects humans
When humans do get infected, symptoms often resemble severe influenza. These include high fever, cough, sore throat, muscle aches, and sometimes conjunctivitis. Some infected individuals show no symptoms at all. Although the current risk to the general public remains low, health authorities worldwide are closely monitoring the virus for any mutation that could allow easier human-to-human transmission.

This concern has driven Indian scientists to explore a critical question: if H5N1 adapts to humans, how fast could it spread, and can early action stop it?

Inside the Indian modelling study
A new peer-reviewed study by Philip Cherian and Gautam Menon from Ashoka University, published in the journal BMC Public Health, attempts to answer this question using advanced computer simulations. The researchers used BharatSim, an open-source modelling platform originally developed to study Covid-19, to simulate how an H5N1 outbreak might unfold among humans.

The model uses real-world demographic data to recreate realistic outbreak scenarios, helping scientists test how different interventions might change the course of an epidemic. Professor Gautam Menon explained that while the threat of an H5N1 pandemic is real, improved surveillance and faster public health responses could still prevent disaster.

How an outbreak could begin and spread
The simulations suggest that a bird flu pandemic would likely begin quietly, with a single infected bird transmitting the virus to a human most likely someone working closely with poultry, such as a farmer or market worker. The true danger does not lie in that first infection, but in whether the virus can sustain human-to-human transmission.

To make the model realistic, the researchers focused on a single village in Namakkal district, Tamil Nadu, one of India’s largest poultry hubs. The district hosts over 1,600 poultry farms and around 70 million chickens, producing more than 60 million eggs daily. A synthetic village of 9,667 residents was created, complete with households, workplaces, schools, and markets.

In the simulation, the virus begins at a workplace such as a poultry farm or wet market, spreads to primary contacts who work there, and then moves outward to secondary contacts through homes, schools, and other workplaces. Using this network, researchers tracked how infections progressed and estimated key metrics such as the basic reproductive number, or R0.

The narrow window for containment
One of the study’s most striking findings is how small the window for effective intervention could be. The researchers found that once detected cases rise beyond roughly two to ten people, the virus is likely to spread beyond primary and secondary contacts into the wider community.

If households of primary contacts are quarantined when just two cases are identified, the outbreak can almost certainly be contained. However, by the time ten cases are confirmed, it is overwhelmingly likely that the virus has already escaped early containment, making its spread nearly indistinguishable from a scenario with no intervention at all.

The effectiveness and limits of interventions
The simulations tested several control measures, including culling infected birds, quarantining close contacts, and targeted vaccination. The results were clear. Culling birds is highly effective, but only if done before the virus infects a human. Once spillover occurs, speed becomes critical.

Isolating infected individuals and quarantining households can stop the virus at the secondary transmission stage. However, once tertiary infections appear   meaning contacts of contacts   the outbreak becomes extremely difficult to control without drastic measures such as lockdowns.

Targeted vaccination helps by raising the threshold at which the virus can sustain itself in the population, though it does little to reduce immediate household transmission. The study also highlighted a difficult trade-off: quarantining too early can increase household spread, while quarantining too late has little impact on overall transmission.

Expert views and remaining uncertainties
External experts caution that modelling has limitations. Seema Lakdawala, a virologist at Emory University in the US, notes that transmission efficiency varies widely between influenza strains. Emerging research also shows that not all infected individuals spread the virus equally, a phenomenon similar to Covid-19 super-spreaders, though less well understood for flu.

If H5N1 does become established in humans, Dr Lakdawala believes its impact may resemble the 2009 swine flu pandemic rather than Covid-19, as the world is better prepared for influenza outbreaks. Antivirals are available, and candidate vaccines already exist. However, she warns against complacency, as the virus could mix with existing flu strains, potentially reshaping seasonal influenza patterns in unpredictable ways.

Why this research matters
The Indian researchers emphasise that their simulation framework can be run in real time and updated as new data emerge. With further refinements   including accounting for reporting delays and asymptomatic cases such models could provide public health authorities with crucial guidance during the earliest hours of an outbreak.

In a world where pandemics can escalate rapidly, the study underscores one central lesson: when it comes to bird flu, early detection and swift, targeted action may be the difference between containment and crisis.