Spectre of Avian Flu looms
Dr. Jamal Anwar
The World Health Organisation has issued a dramatic warning that bird flu will trigger an international pandemic that could kill up to seven million people. A likely instance of human-to-human transmission of bird flu has been discovered. Health experts warn that the bird flu virus will be the most likely cause of millions of deaths. Early last month confirmed cases of bird flu were found in Croatia and Britain.
All those infected in the Far East outbreak caught the disease directly from birds but experts warned that if the virus mutates and acquires the capacity for human-to-human transmission, the impact could be devastating.
According to experts, water birds carry all 15 kinds of influenza type A. This means that ducks and geese carry the viruses. They don't always get sick, so the basic seeds for the 15 kinds of flu are always out there.
Sometimes these flu strains mutate into more dangerous forms known as highly pathogenic avian influenza (HPAI). HPAI is extremely lethal to chickens. And it can be very dangerous to humans who catch the disease from domestic poultry. Contact with bird droppings is the most likely way people catch bird flu. People do not catch the virus from eating cooked chicken or eggs.
Bird flu tends to be an intestinal disease spread through feces. Human flu tends to be a respiratory disease spread by droplets (coughing, sneezing). The only way a bird flu virus can spread easily from one human to another is if the bird flu strain changes by picking up some genes from a human flu virus, a possibility that the WHO has cautioned against. Humans who have caught this year's bird flu from chickens start out with normal flu-like symptoms. This worsens to become a severe respiratory disease that has been fatal in a high percentage of cases.
The bad news is that the H5N1 strain that the current attack of bird flu is suspected to be carrying is immune to most flu drugs. However, the drug is responsive to the newer flu drugs like Tamiflu and Relenza.
Experts from the World Health Organisation and the United Nations warned that the bird flu outbreak plaguing Asia has the potential to be more deadly than SARS, and that Vietnam the country worst hit so far is ill-prepared to cope. If the H5N1 virus attaches itself to the common human flu virus and if it is then effectively transmitted, it has the potential to cause widespread damage," said Peter Cordingley, a spokesperson for WHO.
According to Cordingley this mortality rate is far higher than that of the SARS virus. The common human flu virus is far more infectious than the SARS virus and can be spread by aerosol and not just through droplets as in the case of the SARS virus. "Bird flu could be potentially more dangerous than SARS if it attaches itself to the common flu virus, and if this new virus is then effectively transmitted like the common flu virus, we have the potential for widespread damage," he added.
The virus is normally transferred from birds to human beings but scientists are worried it could now be passing from person to person-- with potentially devastating consequences. Five years ago, the world was put on high alert when six people in Hong Kong were killed by bird flu. Nearly a million chickens were slaughtered in an attempt to stop the spread of the virus. If the Hong Kong strain were to spread it would be the fourth major flu outbreak in the province in the past five years. Each one has led to massive bird culls. Governments battling the disease are: China, Thailand, Vietnam, Indonesia, Cambodia, Japan, South Korea, Laos, Taiwan and Pakistan. However, the strain of bird flu striking Taiwan and Pakistan is different from the one hitting the other countries and is not considered a serious threat to humans. The World Health Organisation urged China to take swifter action Saturday (January 31, 2004) as the world's most populous country reported two new suspected outbreaks.
How flu viruses mutate and grow
One of humankind's greatest medical mysteries about how flu viruses mutate and grow, periodically circling the globe in deadly pandemics is now the challenge.
- First jumped "species barrier" from bird to human in 1997 in humans, similar symptoms include fever, sore throat, and cough. Types known to infect humans are influenza A subtypes H5N1 and H9N2
- Fever, body ache and headache just like with other types of flu
- Will quickly turn into a severe respiratory disease
- May feature convulsion-like shivering
- Respiratory failure has lead to death in a high percentage of diagnosed cases
- People who work in poultry farms and/or handle poultry dropping are at the greatest risk, along with their families
- No risk from eating cooked chicken meat
- Human-to-human transmission not yet found
The two viruses could combine to produce a hybrid that was both highly pathogenic and transmissible between humans. Such viruses are thought to have caused pandemics in the past.
- Livestock handling should be done wearing face masks
- Any suspected flu in birds should be taken seriously; if proven, the livestock should be buried or burnt immediately
- Persons handling poultry stock developing flu-like symptoms should seek immediate medical support
It is not known whether the virus is being carried around by wild birds, which are monitored for flu in Europe and North America but not so far in Asia. Normally flu viruses form a reservoir in ducks but this strain of H5N1 virus kills ducks, a shift in virulence that has unsettled virologists. However, Thompson (WHO, Switzerland) notes that the avian virus is not transmitted very efficiently to humans: "There could be a million birds or more in Vietnam that have the disease or have had the disease, and yet we have just a handful of [human] cases."
Public health measures are an important pandemic-fighting tool
In a 2004 National Academy of Sciences report, The Threat of Pandemic Influenza: Are We Ready?, experts estimated that if a pandemic were to strike today, it would take six to eight months to identify the viral strain and release initial doses of vaccine, using standard methods.
"Given existing manufacturing capacity," the report says, "vaccine availability would fall far short of projected demand, especially in countries with out vaccine manufacturing facilities."
The threat of a global pandemic from the H5N1 bird flu virus is prompting scientists to move away from the 50-year old influenza vaccine production methods in use today and turn to techniques perfected in the current age of biotechnology.
Bangladesh Unable to Identify Bird-flue Virus
Ten Asian countries hit by the rapid spread of bird flu that has killed at least eight people and threatens to develop into an epidemic worse than SARS Experts have pointed out that Bangladesh is not prepared to face a quick spread of the disease. We can test whether a suspect is bird flu-positive or-negative, but we have no way of detecting the virus. The international agencies working in this area, especially the World Health Organisation have made it known that development of a vaccine to combat the disease may take a long time. So the task of coping with it has to be accomplished by the national governments at this stage. The country does not import chicks, but that alone hardly guarantees our safety since the infected broilers may enter the country through different points. So strict surveillance is needed to keep things under control. In this case, we are not getting much help from the international organisations, except the warning that Bangladesh is among the vulnerable countries.
(R) thedailystar.net 2005