Soren Froberg  /  AP file
Carriers of serious diseases, ticks are thriving and spreading in Sweden's changing climate and milder winters.
updated 7/6/2007 7:30:33 PM ET 2007-07-06T23:30:33

A bloodthirsty parasite is popping up in parts of Sweden where deep winter chills used to make survival difficult, if not impossible.

Ticks are spreading north along the Scandinavian country's shorelines, pestering pets and spreading infectious diseases to humans.

"It probably has to do with the greenhouse effect," said Thomas Jaenson, professor in medical entomology at Uppsala University. "The fact that we’ve seen ticks in January indicates that there has been a major change."

Swedish studies have shown that ticks have multiplied countrywide in recent decades, spreading north from traditional breeding grounds in the Stockholm archipelago. The pinhead-sized arachnids have even turned up near the Arctic Circle.

"There are more of them now. And they show up earlier in the year," said Marja Lodin, 69, who has a summer house near the northern city of Umea. Two years ago she was infected with Lyme disease, which causes fever, headache, fatigue and skin rash, from a tick lodged in her navel.

Sweden's disease control agency doesn't keep records on Lyme disease, but said the potentially deadly tick-borne encephalitis virus, known as TBE, is on the rise. Reported annual cases more than doubled from 60 in the late 1990s to 131 in the 2001-2005 period. In 2006, there were 155 cases, two of which turned fatal.

"It is possible that these people would be alive if we had had a more stable climate," Jaenson said.

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