MANILA, Philippines – Dr. Takeshi Kasai is a lean, graying and worried flu hunter. He’s got news about his adversary, and it’s not good.

“I am personally very scared,” he said. “No, wait. I am translating that directly from the Japanese word. Let me say I am personally very concerned.”

The bird flu virus is still killing, still spreading and still mutating. In recent weeks, it’s reappeared in Korea and flared in Somalia, Cote d’Ivoire, Ukraine and Russia. The death toll among birds, both those infected and those killed to avoid the spread of the disease, exceeds half a billion. Deaths among humans are at 154, with nearly half of those occurring this year.

Yet “bird flu fatigue” has set in among the media and government health ministries, said Kasai, a Japanese disease tracker who is an adviser to the World Health Organization’s Western Pacific office in the Philippines.

There are plans drafted for containing any human-to-human outbreak. There are stockpiles of antivirals in many countries.

“What we need to do is more or less clear. But whether people are preparing is another question,” he said.

National response plans and a global plan for trying to isolate the first outbreak are written. Some have already been tested. The weakness Kasai sees is the lack of adequate preparation for a mutation of the H5N1 bird flu virus that the WHO says could spread across the world in a matter of weeks, infecting as many as 2 billion people and killing anywhere from a few million to 100 million people.

“If the disease spreads everywhere, governments are more and more limited,” he said. “In a pandemic, you will get no help from your neighbors.”

And this is a truly wicked disease. It can sear the lungs like poison gas and cause massive bleeding from the mouth, eyes and other orifices.

OK. We’ve been scared by this prospect before. Bird flu might never mutate into a form that threatens widespread human illness. And we’ve been preparing. President Bush unveiled a national response plan in May. The Dallas County Department of Health and Human Services has a plan, Southern Methodist University has a plan, and lots of other institutions and companies have plans.

Kasai wonders how many households have stocks of food and water that you would want on hand in the event of a natural disaster or major homeland security threat. And what about the hospitals?

“When SARS broke out, it was the medical facilities that were the venue for infection,” he said. “They have to be able to maintain the ability to serve the sick without spreading the disease. But if everyone crowds into the hospitals, it will be very difficult.”

It’s not just complacency that worries Kasai. The virus is changing.

This fall, the disease spread from one person to another in an Indonesian family of eight. The first member of the family sickened had contact with infected birds, but the rest caught the disease from each other.

When bird flu first started killing people, about 80 percent of those infected died. The lethality has dropped to about 60 percent. Cases reported outside of Indonesia have a better than 50 percent chance of survival.

Normally, that’s good news. But bird flu needs a living host to undergo the genetic mutations that can spread it from one person to the next. The host also needs to be well enough to circulate, coughing and sneezing and touching, to ignite a pandemic. So the less lethal the virus, paradoxically, the more dangerous it becomes.

The Spanish flu epidemic of 1918 killed just 2 percent of those infected, but that death toll was estimated at 50 million or more.

Kasai is concerned about vaccine developments as well. The strain of H5N1 virus that infected people in Turkey, Iraq and much of Asia this year has been susceptible to the experimental vaccine developed by U.S. and other scientists. But with six other subtypes, most of them appearing in Indonesia, the vaccine doesn’t seem to be effective.

There are lots more supplies of the antivirals Tamiflu and Relenza than there were at the beginning of the year, but that’s still far short of what would be needed to treat most of those who could be infected.

“It’s not realistic to think we could secure antivirals for everyone,” Kasai said. “But there are many other things we could be doing – secure medical, fire and police services, food and water stocks, company disaster plans.

“We have to continue to move forward. The bird flu situation has not changed.”