How bird flu could spread to humans, scientists reveal
What's the story
Indian researchers have simulated a possible outbreak of avian flu, or bird flu, in humans and its potential containment strategies. The study was led by Philip Cherian and Gautam Menon from Ashoka University, and published in the BMC Public Health journal. It used BharatSim, an open-source simulation platform originally designed for COVID-19 modeling but adaptable for other diseases.
Risk assessment
The threat of pandemic in humans
The researchers noted that a bird flu pandemic would start with a single infected bird transmitting the virus to a human, likely a farmer or market worker. The real danger lies in sustained human-to-human transmission. The study highlights how quickly an outbreak can spiral out of control if not contained early enough, with cases rising from two to 10 being the tipping point for wider spread beyond primary and secondary contacts.
Containment strategies
Quarantine could contain outbreak if done early
The paper emphasizes that if households of primary contacts are quarantined when just two cases are detected, the outbreak can be contained. However, by the time 10 cases are identified, it's highly likely that the infection has already spread into the wider population. The researchers modeled a synthetic community in Namakkal district of Tamil Nadu, India's poultry hub with over 1,600 farms and around 70 million chickens.
Infection spread
Simulation reveals key transmission metrics
The simulation showed the virus starting from a workplace and spreading to primary contacts, who then spread it to secondary contacts through homes, schools, and other workplaces. By tracking these infections, the researchers estimated key transmission metrics such as the basic reproductive number (R0). They then tested different interventions like culling birds, quarantining close contacts, and targeted vaccination to see their effectiveness in controlling an outbreak.
Intervention impact
Culling birds effective if done early
The study found that culling birds is effective but only if done before the virus infects a human. If a spillover does occur, isolating infected people and quarantining households can stop the virus at the secondary stage. However, once tertiary infections appear, the outbreak slips out of control unless authorities impose tougher measures like lockdowns. Targeted vaccination helps by raising the threshold at which the virus can sustain itself.
Caveats acknowledged
Simulation model's limitations and future implications
The researchers acknowledged some limitations of their simulation model, such as fixed household sizes and daily movement patterns. It doesn't account for simultaneous outbreaks from migratory birds or poultry networks, nor behavioral changes like mask-wearing when people learn about bird flu deaths. Seema Lakdawala, a virologist at Emory University in Atlanta, cautioned that the model assumes "very efficient transmission of influenza viruses," which may not be true for all strains.