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Warmer Sweden linked with tick-born encephalitis
( 2001-07-06 13:49 ) (7 )

Milder weather in Sweden in recent years, possibly linked to global warming, has led to a sharp rise in the number of cases of tick-borne encephalitis, or inflammation of the brain, scientists said on Friday.

The research at Stockholm University in Sweden showed that the rise in average temperatures during the last 40 years had provided fertile breeding conditions for the parasites.

Tick-borne encephalitis (TBE) is caused by a virus carried by tick parasites that causes brain inflammation in humans, which can be fatal, though only in rare cases.

"The findings indicate that the increase in TBE incidence since the mid-1980s is related to the trend towards milder winters and the early arrival of spring," said Elisabet Lindgren, one of the researchers.

She said in a report published in the Lancet science journal that there were other, non-climate factors that could help explain the jump in TBE cases. They included more people owning summer cottages, where the risk of infection was higher.

The report did not give exact figures for the number of TBE cases, but graphics showed there were between five and 30 cases per million people in the study area from 1960 to 1980. The range rose to between 20 and 45 cases from 1981 to the mid-1990s.

The peak in TBE infections came in 1994, when three times as many people suffered than the annual average. In Stockholm County 1994 was preceded by five mild winters and the early arrival of the spring season for seven consecutive years.

"Such conditions are favourable for the tick vector, and host and reservoir animals," Lancet said.

The mosquito-carried West Nile virus, which in rare cases can go on to cause encephalitis and even death in humans, was discovered in New York two years ago.