Asian Bird Flu Epidemic Stops Spreading

GENEVA, Switzerland, February 20, 2004 (ENS) - The avian influenza epidemic that has killed at least 20 people and caused the deaths of some 80 million chickens across Asia has stopped spreading beyond the countries currently infected, according to the World Organization for Animal Health. The number of countries infected by the H5N1 strain of the flu virus has been stable since the beginning of February.

Another piece of encouraging news came from government labs in Australia, the Commonwealth Scientific Industrial Research Organization (CSIRO said this week. There is a drug that fights this deadly flu strain.

Drugs based on CSIRO's research into the influenza virus have been shown to be effective, in laboratory tests, against a sample of an H5N1 influenza virus currently infecting chickens in Asia.

CSIRO Health Sciences and Nutrition scientist, Dr. Jenny McKimm-Breschkin, has tested the ability of the flu drug Relenza™ to inhibit the H5N1 virus. The tests, used to monitor virus sensitivity to drugs, have shown that the drug Relenza™ is as effective, in laboratory experiments, against this bird flu as it is against other strains of flu that affect humans.

"There is a direct correlation between enzyme sensitivity as measured by these laboratory tests and the ability of the drug to prevent the virus from multiplying," said McKimm-Breschkin.

The Asian bird flu has not been shown to be passed from human to human. All people who have died from this disease have caught it directly from infected birds, international health experts say.

Live chicken markets across Asia are still at risk of avian influenza. (Photo courtesy WH)

In order to establish that Relenza™ is effective in humans infected with bird flu, clinical data from humans will be needed, she said. It should be noted that CSIRO receives a royalty income from sales of Relenza™. The test results reported here have been conducted independently of the drug manufacturers, CSIRO says.

While 10 Asian countries have been affect by the H5N1 bird flu, human deaths have occurred in just two - Thailand and Vietnam.

Since January 23, the Thai Ministry of Public Health has reported nine laboratory confirmed cases of human infection with H5N1 avian influenza. Of these, seven have died. The situation is reviewed daily by a joint team of ministry officials and staff from the World Health Organization (WHO).

The surveillance system in Thailand is on high alert. To date, 510 reports of human cases have been brought to the attention of health authorities. Of these, 354 have been excluded from consideration following thorough laboratory, epidemiological, and clinical investigation.

The most recently announced confirmed case was a four year old boy from the northeastern province of Khon Kaen. His family raised chickens, and many died shortly before the onset of his symptoms, WHO says.

To date, WHO states, "no evidence suggests that human-to-human transmission has occurred in Thailand."

In Vietnam, 31 people have come down with the H5N1 flu, and of these cases, 22 people have died, many of them young children.

The H5N1 virus has been reported in several wild birds, and in a rare clouded leopard kept in a zoo near Bangkok, which died January 27, raising concerns that many other species could be affected.

The World Health Organization said today that the agency has learned of H5N1 infection in a single household of domestic cats in Thailand. While officials are concerned, there is no need to panic, the agency said.

Feral cats in Bagkok's Lumphini Park (Photo courtesy Basilisk)

Investigations are under way and no firm conclusions can be made at present, WHO says, but "concern is great" and several specific questions are being raised about risks to humans in close contact with infected cats and the need for surveillance of disease in cat populations.

Thailand’s Ministry of Public Health is investigating the incident in cats and is monitoring the health of human contacts. The Food and Agriculture Organization (FAO) is also contributing expertise.

While WHO says conclusions are "premature pending the results of these investigations," confirmation of H5N1 infection in cats is "not considered likely to enhance the present risks to human health." Nor is it considered likely to influence the future evolution of the outbreak in humans in any significant way.

Studies have shown that a small number of mammalian species, including pigs, seals, whales, mink, and ferrets, are susceptible to natural infection with influenza viruses that are purely avian in their genetic make-up.

Of these species, only the pig has significance for human health, WHO says. Pigs can be co-infected with both avian and human influenza viruses and can thus serve as the “mixing vessel” for the mingling of genetic material, possibly resulting in the emergence of a new influenza virus subtype. Most experts agree that pigs played a role in the emergence of pandemic viruses in 1957 and 1968.

Up to now, domestic cats have not been considered susceptible to disease caused by natural infection with influenza viruses. Some older studies, from 1970, 1972, and 1981, reported experimental infection of domestic cats under laboratory conditions.

Although infection occurred - virus was recovered from the cats' respiratory tract - all of the cats remained healthy. None developed typical symptoms of influenza, including fever, nasal discharge, coughing or sneezing. "These findings are important in that they strongly suggest that, should additional cats become infected with H5N1, they would not shed large quantities of the virus," WHO said in a statement today.

By contrast, H5N1 virus replicates in the intestines as well as the respiratory tract of birds. In the present outbreak, very large quantities of virus are being excreted in the faeces of infected birds, resulting in widespread contamination of the environment. This wide presence of the H5N1 virus in the environment creates one of the most important risks for human exposure and subsequent infection.

Eliminating wild birds is not an appropriate measure to control the spread of the avian influenza virus, FAO officials said Thursday. Killing wild birds will not help to prevent future bird flu outbreaks.

Prevention must be based on a control and surveillance system to ensure that any contact between wild birds and poultry is avoided or at least monitored, the UN agency said. For example, commercial poultry owners need to ensure that poultry pens and poultry drinking water supplies cannot be contaminated by migrating birds. If this cannot be done, then making the drinking water safe by appropriately treating it is necessary.

The World Bank country office in Hanoi, this week addressed the issue of what the bird flu is doing to the Vietnamese economy. Klaus Rohland, director of the World Bank in Vietnam, said that under an "optimistic" scenario in which the bird flu epidemic does not lead to human-to-human transmission, its overall economic impact will be less than one percent of Gross Domestic Product.

But even if all the poultry of Vietnam had to be culled to contain the epidemic, cost is estimated at US$690 million, or the equivalent of 1.8 percent of the annual GDP of Vietnam.

“The gap between the costs under the optimistic and the pessimistic scenario calls for decisive actions at this stage," said Rohland. "It also appears that this epidemic could affect the poor more than SARS did. So, measures such as appropriate compensation policies for bird culling and restocking of farms are important to mitigate the social impact of the epidemic."

"It is also critical to strengthen veterinary services and improve surveillance, in order to avoid resurface of this disease and quickly control any new outbreaks in the future," Rohland said, adding that the World Bank is helping Vietnamese authorities to develop a medium term strategy.