<%-- Page Title--%> Health <%-- End Page Title--%>

<%-- Volume Number --%> Vol 1 Num 143 <%-- End Volume Number --%>

February 27, 2004

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Outbreak An Approaching Nightmare

Whenever SARS first surfaced, health experts were fearfully watching whether another wave of flu nightmare was going to happen, which is due over long time. Scientists finally found another deadly virus, which visited more than 20 countries within few months, infected over 8000 people and finally ended with more than 800 lives.

The recent Bird flu outbreak is a reminder of the nightmare, during World War I. Although Bird flu usually does not infect humans but may pave the way for killer flu pandemic. The Spanish Flu (a misnomer, since it had nothing to do with Spain) would perhaps be better called the "Forgotten Plague". Despite devastating the planet in 1918, causing over 30 million deaths, this epidemic has been forgotten except by a few researchers.

Possibly, in October 1917, a benign human influenza virus jumped into a pig in USA and underwent a random mutation and turned out to be a universal killing machine within a few months .A chain reaction began, soon engulfing the world. Some people fell ill and died within a matter of hours. New York commuters boarded their trains healthy and were dead upon arrival in the city. Unusually, the virus targeted healthy young people, killing them preferentially over older individuals. Panic broke out in cities around the globe as hospitals and morgues filled with the dead and dying. In the United States, troop camps were disbanded and emergency health measures instituted. In other places the result was far worse. Half the population of some Pacific islands was wiped out in this epidemic. Untold millions died in Asia. The Spanish flu took the country by storm during another time of crisis- World War I. This factor aided the spread of the disease considerably. As soldiers travelled from port to port, they brought with them flu germs as well as their weapons. The virus stalked everyone, everywhere. There was no hiding place and there was no cure. One could only hope not to become infected. Astonishingly, the lethal killer disappeared without any trace after 18 months of rampage.

Scientists are chasing over time, following the footprint of the deadly virus. After 45 years of outbreak, they traced out the remnant of genetic material from a 1918 flu-infected dead body, exhumed from Alaska and finally decoded the genetic material of this deadly flu. From the evolutionary path it can be categorically seen that that virus comes from pig. Experts believe that the descendent of the Spanish flu still is alive in wild birds especially, duck and fowl, and will come back again with lethal power.

Mankind has experienced a couple of flu outbreaks after the Spanish flu. Outbreaks in 1957-58 and in 1968-69 caused a million deaths each time. The length of time between the last major outbreak and now is what's making observers nervous.

There are three types of influenza virus-A, B, C, all of which can infect humans.

Only Influenza type A viruses are found in many different animals, including ducks, chickens, pigs, whales, seals and horses. There are Fifteen subtypes of influenzas.

Virus A are known to infect birds (chickens and ducks included), named as Avian or Bird flu virus, which was first identified in Italy more than 100 years ago, occurs worldwide. All birds are thought to be susceptible to infection with Avian influenza virus (some migratory birds, especially wild ducks are resistant to infection and may act as carriers to ferry the germs place to place). To date, all outbreaks of the highly pathogenic form have been caused by influenza A viruses of subtypes H5 and H7 variant of bird flu virus.

Viruses are the simplest form of life. They are little more than a set of instructions, coded in DNA or RNA (genetic material), for reproducing themselves. Part of their cunning is that viruses don't carry their own reproductive machinery. When a virus floats in the air, or sits on a door handle, it is inert. When it gains access to a suitable living cell, it springs into action, hijacking the cell's machinery to replicate itself before moving on. Viruses get inside the cell using the proteins on its outer coating. They are like keys that match up with receptors on the outside of the cell to allow the virus inside. Once in, it copies itself again and again. These copies have the same urge to replicate, and so they "bud" out of the cell membrane into the host's body where they find another suitable cell and start the process again.

The flu virus is able to mutate faster than almost any other virus. Every year there is a slight drift or mutation in the virus' genetic instructions due to lack of mechanisms of proofreading or repair of errors that occur during replication, allowing it to constantly evade the immune systems of its hosts. That's why flu shots must be given every year in order to be effective. While drift is responsible for the annual outbreaks of flu, things can get really nasty when the virus undergoes a sudden genetic "shift" ? usually through recombination with another strain, perhaps from a pig or bird. Most striking feature of flu virus is that, its genetic material is segmented. Whenever two different variants of flu virus infect a single animal, the consequence would be a brand new killer virus due to drastic genetic reassortment. Only pigs can be infected with both human and bird flu viruses in addition to swine influenza viruses. Because pigs are susceptible to avian, human and swine influenza viruses, they potentially may be infected with influenza viruses from different species (e.g., ducks and humans) at the same time. If this happens, it is possible for the genes of these viruses to mix and create a new deadly virus.

Why is H5N1 of particular concern: Of the 15 Avian influenza virus subtypes, H5N1 is of particular concern for several reasons. H5N1 mutates rapidly and has a documented propensity to acquire genes from viruses infecting other animal species. Birds that survive infection excrete virus for at least 10 days, orally and in faeces, thus facilitating further spread at live poultry markets and by migratory birds. The epidemic of highly pathogenic avian influenza caused by H5N1, which began in mid-December 2003 in the Republic of Korea and is now being seen in other Asian countries, is therefore of particular public health concern. H5N1 variants demonstrated a capacity to directly infect humans in 1997, and have done so again in Viet Nam in January 2004. The spread of infection in birds increases the opportunities for direct infection of humans. So far, the good news is that viruses leave not yet learnt how to transmit human to human. If more humans become infected over time, the likelihood also increases that humans, if concurrently infected with human and avian influenza strains, could serve as the mixing vessel for the emergence of a novel subtype with sufficient human genes to be easily transmitted from person to person. Such an event would mark the start of an influenza pandemic.

What would happen if another virulent mutation struck in a world much more populous and interconnected than in 1918? It is not clear that modern medicine and health systems are any better prepared than in 1918. The world is entering a profoundly dangerous era of emerging diseases. Humanity sits on a biological time bomb. A new Hiroshima is approaching, and mankind is unprepared for this approaching apocalypse that may rewrite the future of our planet.

Mohammad Sorowar Hossain, the writer is Research Fellow Virology Lab, National University of Singapore Sorowar@tll.org.sg





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