2006-05-03-Pandemic Possible From at Least Four Bird Flu StrainsUnderstanding Avian Influenza
2006-05-03-Pandemic Possible From at Least Four Bird Flu Strains
At least four strains of bird flu are capable of sparking the next pandemic, including the H5N1 virus that's killed more than half the 205 people it's known to have infected since 2003, virologist Robert Webster said.
Avian influenza strains identified as H2, H9 and H7 subtypes also may change into forms that can be passed easily from human to human, said Webster, the Rosemary Thomas professor at St. Jude Children's Research Hospital in Memphis, Tennessee.
When the next flu pandemic may occur and whether it will be as lethal as the one in 1918, which killed as many as 50 million people worldwide, is impossible to predict, Webster said yesterday in an interview in Singapore, where he is addressing an avian flu forum sponsored by the Lancet medical journal.
``I have been studying this thing for 40 years and there is no way that you can predict,'' Webster, 73, said. ``I don't rule out H5N1 at the moment.''
Concern over the H5N1 virus, which has killed at least 113 of 205 people infected since late 2003, has made governments worldwide aware that eventually an avian flu strain will cause a major outbreak, Webster said. H5N1 now presents the greatest pandemic threat, he said.
``It is the worst influenza virus that I have ever seen,'' Webster said. ``When you put it in a ferret, it causes hind leg paralysis and goes to the brain. Don't take it lightly, because it could wipe the hell out of us.''
A pandemic occurs when a new influenza virus emerges and starts spreading as easily as seasonal flu, through coughing and sneezing, according to the World Health Organization. Flu pandemics can only be caused by type A viruses. The natural host of A-type flu viruses, which includes H5N1, is the migratory duck, Hiroshi Kida, professor of disease control at Japan's Hokkaido University in Sapporo, told the forum.
Humans have no natural immunity to the H5N1 virus, making it likely that people who contract any pandemic flu strain based on H5N1 will become more seriously ill than when infected by seasonal flu, the WHO said. The United Nations agency is tracking the spread of the virus in the event it becomes pandemic in humans.
Seasonal flu usually kills between 250,000 and 500,000 people worldwide, according to the agency. Most deaths from seasonal flu in developed countries occur in people over 65.
So far this year, 60 H5N1 cases and 37 fatalities have been reported worldwide, compared with 95 cases and 41 fatalities in the whole of 2005.
The tally excludes a suspected infection in a 27-year-old woman from Egypt's el-Sharabiya district. The North African country's 13th case was reported by Egyptian health authorities yesterday, Xinhua said, citing a report by Egypt's official MENA news agency.
The woman, who had been in contact with infected fowl, was admitted to a Cairo hospital on May 1 with fever and respiratory illness, the report said.
The H5N1 virus is reported to have infected birds in 34 countries across three continents this year. In Asia, almost 200 million domestic fowl have died or been culled to contain the spread of H5N1, costing countries more than $10 billion, the World Bank said in January.
``H5N1 is in the picture because it's so widespread in birds and because it does occasionally jump over to humans and to other mammals,'' Thijs Kuiken, a veterinary pathologist at the Erasmus University in Rotterdam, said in an interview today. ``There is always the chance that it will mutate in such a way that it can transmit easily among humans. For the other viruses, we don't really know that.''
H2 avian-flu subtypes have been circulating since at least as early as the 1890s and are capable of infecting poultry and wild birds. One variant, H2N2, was responsible for a flu pandemic in 1957 that killed an estimated 2 million people.
``H2 is out there and could equally well come back,'' Webster said. ``The other one that really bothers me is H9,'' which has been found in parts of Europe and Asia and may share genetic similarities with H5, he said.
A subtype of the H7 virus, H7N7, infected poultry in the Netherlands in 2003, resulting in the slaughter of 30.7 million fowl. The outbreak sickened 89 poultry and animal health workers, killing one of them.
In almost all human H5N1 cases, infection was caused by close contact with sick or dead birds, such as children playing with them, or adults butchering them or taking off the feathers, according to the Geneva-based WHO.
``Every country is in danger, and every country must prepare,'' Richard Horton, the Lancet's editor, told the two-day forum attended by representatives from 53 countries. ``Any pandemic will be sudden with no advanced warning. Infection control practices could be severely constrained and civilian order may be hard to'' ensure, he said.