Exactly one year after bird flu was confirmed in Maharashtra on February 18, 2006, India is once again on high bird flu alert. The highly-infectious H5N1 variant of the bird flu (avian influenza) virus has been confirmed in poultry and wild birds in neighbouring Pakistan, all within flying distance of India.
The deadly H5N1 strain has killed millions of birds worldwide, but the chances of people getting infected remain low. Since bird flu was first confirmed in humans in December 2003 in Vietnam and China — it killed its first four victims — H5N1 has infected 273 people in 11 countries and killed 166.
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 "re-assortment" 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 capability of the virus to bind to human cells increases 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 Security 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 surveillance," says Dr HK Pradhan, director, HSADL.
The health ministry also held a meeting to take stock of the the situation. "The mild temperatures in February and March are favourable for the spread of the H5N1 virus. The health ministry constantly reviews surveillance measures to ensure that India is prepared to contain an outbreak, if it happens," says Health Minister 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 infected 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 completed or are ongoing. Most of them have focused on healthy adults, but some have initiated clinical trials in the elderly and in children," says Andrei Muchnik, department of immunisation, vaccines and biologicals, WHO, Geneva.