VICTORIA, B.C. – The mystery emerged slowly, its clues maddeningly diverse.

Sally Lester, an animal pathologist at a British Columbia laboratory, slipped a slide under her microscope – a tissue from a dog on Vancouver Island. Her lens focused on a tiny cell that looked like a boiled egg. It was late 1999. She had started seeing a lot of those.

On the eastern side of the island, several dead porpoises washed ashore early the next year. Scientist Craig Stephen, who runs a research center on the island, slit one open. He found its lungs seized by pneumonia and its other organs swollen by strange, flowerlike tumors.

At work at the family trucking firm in Victoria, Esther Young, a lively 45-year-old mother, was feeling lousy in the fall of 2001. She had headaches and night sweats and was tired, her family said. The doctor told her she was premenopausal and it would pass.

All would become pieces of a medical mystery centered on a tropical disease apparently brought to North America by a warming climate. A fungus took root on Vancouver Island eight years ago and has since killed eight people and infected at least 163 others, as well as many animals.

Similar cases have been found elsewhere in British Columbia and in Washington and Oregon. Scientists say the fungus may be thriving because of a string of unusually warm summers. They say it is a sign of things to come.

“As climate change happens, new ecological niches will become available to organisms, and we will see this kind of thing happen again,” said Karen Bartlett, a scientist at the University of British Columbia who played a central role in the search for the disease’s cause.

Her investigation eventually would focus on a fungus, a member of the yeast family, called Cryptococcus gattii. The microscopic fungus is normally found in the bark of eucalyptus trees in Australia and other tropical zones.

Physicians in North America are familiar with a relative, Cryptococcus neoformans. In humans, it shows up through pneumonia when immune systems already are weak, most typically in AIDS patients. In dogs and cats, it can form abscesses below the eyes. Lester, working in her pathology lab in 1999, was used to seeing tissue specimens from six to 10 pets a year with it.

But by 2000, vets on the island were sending her 10 positive samples a month. Lester knew Cryptococcus causes a disease that affects animals and humans. She put in a call to the British Columbia Center for Disease Control.

Murray Fyfe, the head epidemiologist at the provincial CDC, Fyfe consulted Pamela Kibsey, a microbiologist at the Vancouver Island Health Authority. Kibsey said she had noticed an increase in human cases of Cryptococcus. And there was something strange about it. It was infecting healthy people, not just the sick.

Fyfe formed a group to begin combing records of veterinarians and hospitals, tracing the first cases back to 1999. He asked Bartlett, at UBC, to join the group. They sent samples of the Cryptococcus for further analysis. The results showed it wasn’t the familiar form of “crypto.”

“This was an Australian fungus,” Stephen said. “We said, ‘What’s a nice girl like you doing in a place like this?’”

More disturbing, the fungus appeared to be more virulent than in Australia.

The scientists can only guess how, or when, the fungus arrived. It could have been brought on trees imported from Australia. Or it may always have been on the island, quietly clinging to life unnoticed until the warm summers spurred it to proliferate.

“With global warming, it may have finally been able to emerge to a level (at which) it is infectious,” Fyfe said. Humans and animals living in the area, having had no exposure, had developed no immunities.

Bartlett formed a team of students to try to find gattii in the wild. Armed with new detection kits, they tramped through yards on Vancouver Island, digging up soil, taking air samples, swabbing bark on trees. They talked to survivors of the disease and to owners of infected pets.

One common site came up: Rathtrevor Beach Provincial Park. Patient Esther Young had gone to the park to kayak. Several other patients had been there.

Fyfe helped the students swab an old Douglas fir at the park. Two weeks later, Bartlett called him, excited. The swabs had come back positive, the first discovery of Cryptococcus gattii in the wild.

With the summer of 2002 approaching, Fyfe had a problem. The park had a popular campground. Fyfe knew most people could come into contact with gattii with no ill effects. Those few who did become infected could be treated successfully.

So he decided on a low-key information campaign. He posted pamphlets in the park and sent out notices to vacationers who had made Internet reservations. The reaction was prompt: The park got 750 cancellations.

Word was also getting out through the news media. Ken James heard it on TV. He had been plagued by a tickle in his chest, a nagging cough, night sweats and an intense desire every day to take a nap. When he heard the report on “this weird fungal disease,” he said, it ticked off the same symptoms.

His doctor was skeptical, but a chest X-ray showed nodules in his lung – either cancer or the fungus. To James’s relief, it was gattii, and after a year of oral medication, he is cured.

“Did I walk past a tree when the fungus was exploding? Who knows,” he said. “If I hadn’t seen that news report, things could have been very different for me.”

By the start of 2003, Bartlett’s students had found the fungus in other spots. They eventually concluded that it had infested a several-hundred-mile range on eastern Vancouver Island. Health authorities agreed that it was no longer fair to target the park alone, and warning signs came down in favor of a wider information campaign.

If doctors catch the disease early, oral doses of antifungal drugs will kill the cells. Undetected, the fungus can get into the spinal fluid, causing potentially fatal meningitis.

New cases on Vancouver Island have leveled off at about 25 a year. Eight people have died. Bartlett’s focus now is to figure out whether – and how – the fungus is moving.

Five human cases have been found on the British Columbia mainland; two people have been sickened in Washington state; and Oregon has had two fatalities from a similar but not identical strain of gattii. Health authorities in Washington and Oregon say the disease is still too rare in their areas to warrant alarm, but they are watching it. Bartlett said it is unclear whether the fungus has been tracked elsewhere.

“One possibility for what we are seeing on the mainland is the first colonization, like we had on the island in 1999,” Bartlett said. Another is that those traces will disappear.