Humans get infected only if they come in close contact with diseased birds. According to the World Health Organisation (WHO), the virus has the potential to improve its transmissibility among humans through two mechanisms. The first is a “reassortment” event, in which genetic material is exchanged between human and bird viruses during human co-infection. Re-assortment could form a new highly transmissible pandemic virus very quickly. The second is the more gradual process of adaptive mutation, where the capa- bility of the virus to bind to human cells in- creases during subsequent human infections.

Public health experts want to stamp out the virus before it mutates by identifying and destroying all infected birds quickly. The High Se- curity Animal Disease Laboratory (HSADL) in Bhopal — the only agency conducting tests for the H5N1 in India — screens between 4,000 and 5,000 samples each week collected from poultry and migratory birds from across the country (see interview). “Wild birds carried the H5N1 virus to India last year, so we have heightened surveil lance," says Dr HK Pradhan, director, HSADL.

The health ministry also held a meeting to take stock of the the situation. “The mild tem peratures in February and March are favourable for the spread of the H5N1 virus. The health ministry constantly reviews surveillance meas ures to ensure that India is prepared to contain an outbreak, if it happens,” says Health Minis ter Anbumani Ramadoss.

Bird flu is caused by an orthomyxovirus, which is a type of flu virus that can survive for considerable time outside of the host. The H5N1 virus can survive in bird faeces for at least 35 days at low temperature (4oC) and for six days in higher temperature (37oC). It is very infectious in poultry, killing infected flock within 48 hours. Bird flu vaccine for humans Sixteen manufacturers from 10 countries are in the process of developing prototype pandemic influenza vaccines against the H5N1 variant of the bird flu virus. Five are also developing vaccines against other virus strains (H9N2, H5N2, and H5N3).

What is worrying public health experts is that the young are more likely to die of bird flu. An analysis of reported human cases and deaths by the WHO showed that 90 per cent of the people in fected were under the age of 40, and 60 per cent of them died. The highest deaths (76 per cent) were in those aged 10-19 years.

"At present, 40 clinical trials have been com pleted or are ongoing. Most of them have focused on healthy adults, but some have initiated clini cal trials in the elderly and in children,” says An drei Muchnik, department of immunisation, vaccines and biologicals, WHO, Geneva.

Email Sanchita Sharma: sanchitasharma@hindustantimes.com