Scientists are worried about a sudden flurry of human bird flu cases in Indonesia, warning that a failure to control the situation may raise the chances of a virus mutation and lead to a pandemic.

However, local experts say all six of the recent infections in humans were probably linked to diseased birds: investigations found that in three cases, the victims fell sick a few days after chickens died in their villages. Three of the six died.

“To me, the most likely cause is H5N1 from animals,” said I Nyoman Kandun, director-general of communicable disease control.

Indeed, apart from an 18-year-old and his 10-year-old sister, the four other cases were isolated infections and the victims lived far apart from one another.

For an 18-year-old man from Surabaya in east Java, his work - sorting feathers in a factory churning out shuttlecocks - brought him close to possible sources of infection.

And in the case of a 39-year-old man from Jakarta in west Java, he had cleared pigeon feces blocking the roof gutters on his house before falling sick. Pigeons are among the dozens of bird species known to have been infected with H5N1.

Nevertheless, the cases have drawn concern in the scientific community because Indonesia is one of the few places in the world where there has been a steady rise in the number of H5N1 human infections, which is still essentially a disease among birds.

“Of course I am worried, the problem has not improved at all in Indonesia, it’s not a good situation. The government and the WHO has to monitor it very closely,” said Leo Poon, a microbiologist and H5N1 expert with the University of Hong Kong.

“Surveillance is obviously no good and for such a big country, maybe there should be more education to teach people how to prevent it,” he said.

VACCINATIONS MASK VIRUS

Experts say the more entrenched the virus is in people, the greater the chance that it will mutate and learn how to spread efficiently among humans: a necessary precursor to any pandemic.

Soon after the first H5N1 outbreak in chickens in Indonesia in late 2003, the government launched a program to vaccinate chickens with the aim of getting rid of the virus in poultry.

This should logically remove the single biggest, potential source of H5N1 infection for its citizens as many Indonesians live very close to chickens. But that has not happened.

Although the number of chicken deaths from H5N1 has fallen sharply since vaccination began, experts say the virus is now endemic in nearly all of the country’s 33 provinces.

Forty-nine people have been infected with the disease and 36 of them have died. Thirty-three of the infections were in 2006.

Bayu Krisnamurthi of the National Committee on Avian Influenza Control and Pandemic Influenza Preparedness said vaccination has helped protect chickens from dying, but not from infection - and possibly spreading the virus - a development that is more commonly known as “masking”.

“If you vaccinate the chicken, it will survive but the virus is still in the chicken,” he said. “Even if you see a healthy chicken, the virus is there.”

Such a problem has also been observed in small numbers of chickens in southern China. It is a serious problem because, in the absence of any signs of disease, people are unlikely to take precautions and could therefore be susceptible to infection.

Indonesia’s battle with the H5N1 is also made harder because of its massive 1.2 billion to 1.3 billion chicken population.

Chickens roam freely, from the countryside to the heart of its capital, Jakarta, and “backyard chickens” are commonly reared by locals for food and for their livelihood.