Sept. 29 (Bloomberg) -- Bird flu may have infected a quarter of backyard fowl in some of Indonesia's most densely populated areas, the country's top veterinary official said, risking human lives and increasing the threat of a pandemic.

Random tests carried out in areas where the virus is most prevalent on the island of Java detected the H5N1 influenza strain in as much as 27 percent of fowl and caged birds, said Director of Animal Health Musny Suatmodjo. He didn't say how many birds were tested or when the survey was done.

Contact with infected birds risks spreading the disease to humans. The prevalence of H5N1 among Indonesia's 300 million poultry helps explain why the country accounts for one-in-three human deaths from the disease worldwide since 2003. The infection creates chances for H5N1 to mutate into a form that spreads easily among people, touching off a global outbreak that could kill millions.

``The backyard sector is the weakest link'' in controlling the virus, Suatmodjo said in a Sept. 27 interview in the capital, Jakarta. ``The survey of hotspots in the backyard sector showed almost every flock has been previously infected,'' though not all birds show symptoms of the disease, he said.

The past three years, H5N1 is known to have infected 251 people in 10 countries, killing 148 of them, the World Health Organization said yesterday. Almost all human cases have been linked to close contact with sick or dead birds, such as children playing with them or adults butchering them or plucking feathers, according to the United Nations agency.

50 Cases This Year

Indonesia reported the infection today in a 21-year-old woman whose brother died from the disease last week. Her case marks the nation's 50th this year.

Poultry are raised in the backyards of 80 percent of the country's 55 million households, according to the UN's Children's Fund. About 62 percent of Indonesian poultry are found on Java, where more than two-thirds of the country's human H5N1 fatalities have occurred.

Suatmodjo, who was appointed in July, is the agriculture ministry's third animal health director since 2003. Previous incumbents were replaced by the government, which cited delays in stemming poultry outbreaks.

The virus has been found in fowl in 30 out of 33 provinces in the archipelago of 18,000 islands, making it difficult for disease trackers to detect outbreaks. The latest eruption was reported this month in the eastern province of North Sulawesi.

`Great Concern'

``Wherever teams are carrying out active surveillance activities, they find the disease prevalent in poultry,'' said Christine Jost, chief technical adviser with the Food and Agriculture Organization's avian flu program in Indonesia. ``The disease is endemic in many large islands of Indonesia like Java, Bali and Sumatra, where there is high prevalence of the disease and it is a great concern.''

The H5N1 virus spread to the Southeast Asian nation in late 2003, affecting mostly commercial poultry farms. Disease control measures and vaccination programs have lowered the rate of infection among intensive poultry farms, while the virus is circulating freely in many backyard flocks.

In the first eight months of this year, 1.3 million fowl died from H5N1 or were culled to stem its spread. That compares with 1.2 million in 2005, according to the agriculture ministry. Outbreaks last year may have been under-reported, it said.

`Problem Persists'

``We can't know whether the results from a set of samples taken today indicate things are getting better or getting worse'' in Indonesia, said David Fedson, a former vaccine developer and University of Virginia professor of medicine. ``Either way, the continued occurrence of human cases of H5N1 infection indicates the problem persists,'' Fedson said in a Sept. 27 e-mail.

Suatmodjo estimates that 10 percent of backyard poultry are vaccinated to prevent the disease. The agriculture ministry plans to introduce regulations next month requiring fowl be kept in coops, rather than being allowed to roam freely.

``They are more exposed to virus if they aren't cooped,'' Suatmodjo said. ``Today they can be negative, tomorrow they can be positive because infection in fowl spreads easily.''

Vaccinating and confining backyard poultry will work to stem the virus, said the FAO's Jost. The UN agency recommends people raising backyard poultry be encouraged to build night housing for their poultry.

``It is of low cost, easy to maintain and is feasible to carry out interventions like vaccination when necessary,'' Jost said. A preventive vaccine campaign would require 1.2 billion doses of vaccines a year just for backyard chickens in Indonesia, she said.

`Limited Resources'

Given the country's ``limited resources,'' the UN agency is ``encouraging stakeholders to target resources'' at areas that would have the greatest chance of controlling the disease, she said. ``Vaccination would have the highest impact in controlling the disease.''

The agriculture ministry will need 90 million doses of avian flu vaccine next year to immunize backyard chickens, particularly in areas where the virus is most prevalent. Government funds may allow the ministry to buy as many as 60 million of doses for next year, Suatmodjo said.

To contact the reporter on this story: Karima Anjani in Jakarta at kanjani@bloomberg.net.

Last Updated: September 29, 2006 05:58 EDT