The dreaded H5N1 bird flu virus — whose outbreak has been confirmed in West Bengal — is more infectious than previously thought, according to World Health Organisation experts.
The virus can travel by sticking to surfaces, get kicked up in dust and feed to infect people and contaminate ponds and lakes, the experts said in a report published in The New England Journal of Medicine. This is a cause of worry for India, as ponds and catchments are sources of water in several villages.
In India, the WHO sounded another alert, saying the Bengal outbreak was more serious than the previous outbreaks in Maharashtra and Manipur. “More serious risk factors are associated with this current outbreak than previously encountered, including that the affected areas are more widespread and because of proximity to extended border areas,” said a WHO expert in India.
For the journal, the WHO team reviewed all known human cases of bird flu, which has infected 350 people in 14 countries and killed 217 since 2003. It found that 25 per cent of cases had no explanation. Most are passed directly from bird to people, and rarely one person can infect another — always via intimate physical contact.
“For some patients, the only identified risk factor was visiting a live-poultry market. In one quarter or more of patients with influenza A (H5N1) virus infection, the source of exposure is unclear, and environment-to-human transmission remains possible,” wrote study leader Dr Frederick Hayden.
"Eating well-cooked chicken cannot infect people, but ingestion of virus-contaminated products or swimming or bathing in virus-contaminated water might pose a risk," he wrote.
Although birds in over 60 countries have been infected with the H5N1 strain, people have rarely got infected. "After exposure to infected poultry, the incubation period generally appears to be 7 days or less, and in many cases this period is 2 to 5 days," the report said.
H5N1 infection usually causes severe pneumonia. On the symptoms, the experts wrote, "It is unknown whether influenza A (H5N1) virus infection can begin in the human gastrointestinal tract." "In several patients, diarrheal disease preceded respiratory symptoms, and virus has been detected in feces," they wrote.
The experts feared that H5N1 might mutate or combine with seasonal influenza virus and spark a pandemic that could kill millions of people.
The virus kills within 9 to 10 days and has killed 61 per cent of infected people since 2003.
Since the viruses do not commonly infect people, there is little or no immune protection against them in the human population.
Quick use of antiviral drugs can save lives, with oseltamivir (brandname Tamiflu) being the drug of choice.