February 5, 2004. Copyright 2004. Graphic News. All rights reserved.

War plan on bird flu microbe

LONDON, February 5, Graphic News: The current avian flu outbreak rampaging through Asia is the fifth in the past seven years to infect humans. The rapid spread of the virus has prompted the World Health Organisation (WHO) to call for money, expertise and a stockpile of drugs to fight an all-out war against it.

The lethal H5N1 virus Òis quite clearly on the moveÓ, said Peter Cordingley, WHO spokesman for the Western Pacific region. The WHO fears the bird flu virus could mutate in a human host with an existing human flu virus and spark a devastating flu pandemic -- a worldwide epidemic such as the so-called Spanish flu of 1918 that killed more than 20 million people.

So far, there is no sign of this happening and there has been only one unconfirmed case, in Vietnam, of human-to-human transmission of the bird flu in this outbreak.

History suggests that deadly influenza pandemics have occured three times in each century over the past 300 years -- with the last in 1968 -- and experts warn that the next is due at any time.

ItÕs all up to a virus that is variable and fickle, constantly changing its genetic makeup, and the time when it hits upon a combination that lets it take off worldwide is a Òroll of the genetic dice,Ó said Dr. William Schaffner of Vanderbilt University in Nashville, Tennessee.

So the lack of a pandemic in the past 36 years basically means Òthe genetic dice havenÕt been rolled that way,Ó Schaffner said. ÒWhile weÕre grateful for that, it makes us nervous.Ó

ThereÕs plenty to be nervous about. The WHO estimates that the next pandemic is likely to kill between 280,000 to 650,000 people and send one million to 2.3 million people to hospital.

Avian flu is caused by one of three types of influenza viruses designated A, B, and C. Types A and B are responsible for epidemics of respiratory illness that occur almost every winter and are often associated with increased rates for hospitalization and death. Type C infection usually causes either a very mild respiratory illness or no symptoms at all; it does not cause epidemics.

Type A viruses undergo two kinds of changes. One is a series of mutations that occur over time and cause a gradual evolution of the virus. This is known as antigenic Òdrift.Ó The other kind of change is an abrupt change in the genetic signature, called antigenic Òshift.Ó Influenza type B viruses change only by the more gradual process of antigenic drift. Monitoring the drift and shift of the virus each year is carried out globally by a network of more than 125 laboratories under the auspices of the WHO. 

The viral subtype H5N1, responsible for the current outbreak, originates in water fowl, primarily ducks. Ducks can usually withstand the virus -- making them ideal carriers -- but chickens have little resistance. When one chicken is infected, the virus can spread to and kill an entire flock within hours.

After bird flu first spread from chickens to people in Hong Kong in 1997 the WHO began development of a vaccine, but the virus causing the latest outbreak -- though still H5N1 -- has mutated so much that development must start again. A new vaccine will take at least six months to develop and manufacture. In 1997 the strain was treated with a class of anti-viral drugs called M2 inhibitors. These include the generic medicines rimantadine and amantadine. The strain has now become resistant to these medicines.

However, two newer anti-viral drugs, called neuraminidase inhibitors, are effective against all kinds of flu, including the H5N1 strain. RocheÕs Tamiflu and GlaxoSmithKlineÕs Relenza block the action of neuraminidase in the budding process. Doctors say only one brand, Tamiflu, is practical for large-scale stockpiling, but so far no government has bought the big amounts needed for a pandemic. Relenza, which requires an inhaler, is not considered suitable for stockpiling. 

For now, worldwide supplies of Tamiflu are skimpy. Roche makes only as much as is needed for a typical flu season and does not stockpile the drug for an emergency. But in the war against the microbe the WHO intends to increase supplies of the drugs in several European countries and Roche is in Òpreliminary discussionsÓ with the U.S. Department of Health and Human Services on stockpile plans.
/ENDS

Sources: Science, World Health Organisation, Centers for Disease Control and Prevention