Flu pandemic inevitable, say experts
EVEN IF the present bird flu scare turns out to be a false alarm, epidemiologists say it is only a matter of time before the avian influenza virus takes wing and starts targeting humans.india Updated: Feb 22, 2006 00:46 IST
EVEN IF the present bird flu scare turns out to be a false alarm, epidemiologists say it is only a matter of time before the avian influenza virus takes wing and starts targeting humans.
A tracking pattern by the WHO has established that influenza pandemics generally occur every 15-20 years, roughly the time it takes for the flu virus to mutate and emerge in a new form.
The latest variant - H5N1 - emerged in Hong Kong in 1997. However, no large-scale epidemic has occurred for the last 35 years. “It is almost certain that an influenza pandemic will be witnessed very soon,” says Prof Dr Sanjay Dixit, HoD of Community Medicine at MGM College. When that happens, India will be particularly susceptible, as it hosts a large number of migratory birds, carriers of the bird flu virus, he adds.
Now for the good news. Unlike previous variants, the H5N1 strain is not transmitted to humans through pigs but appears to be jumping directly from birds to humans. “As pigs have much greater access to urban human habitation than poultry their removal from the transmission chain will greatly curtail spread of the virus,” points out Dubey.
The importance of preventing the virus from being transferred to humans cannot be over-emphasised, says the epidemiologist. “As humans have no natural immunity an outbreak of the avian flu will have disastrous consequences”. The virus will also spread much more rapidly.
“Unlike bird-to-human transmission, which requires physical contact, the virus will travel from human-to-human through the aerial route, much like the common cold”. Only with far more deadly results.
The flu virus’ ability to cause widespread havoc is well known. Dubey cites the 1918 pandemic, the so-called Spanish Flu (H1N1), which resulted in more than 20 million deaths. This was followed by the ‘Asian Flu’ (H2N2) and the Hong Kong Flu (H3N2), both of which resulted in a million deaths apiece.
“I believe that, to a certain extent, Indore may be saved this time from any serious consequences because of the rapidly escalating temperature. The virus multiplies and spreads rapidly at temperatures in the mid-20’s (Celsius) but is retarded by too cold or too hot temperature conditions,” says the epidemiologist.
THE INFLUENZA virus is divided in two subtypes - heamaglutinin (H) and neuraminidase (N) - that affect blood cells and the nervous system, respectively. There are 15 H and nine N subtypes and a particular viral strain is named after the combination. For instance the current strain H5N1 is a combination of H subtype 5 and N subtype one.
THE INFLUENZA virus mutates rapidly developing ever-newer combinations among the H and N subtypes making it difficult to develop a vaccine. Take, for instance, the H5N1 virus, which has developed two major sub-strains - H9N2 and H7N7 - which hit Hong Kong (1999) and Netherlands (2003) since it was first reported in ’88.
Although the US claims to have developed a H5N1 vaccine this has not yet been approved by the WHO, apparently because it does not take into account mutations the virus undergoes after finding a human host.