Reliable figures about the vole population in Finland this spring will only be available once the snow melts, but health authorities are warning residents of central and western areas in particular to take precautions against contracting vole fever this spring.
Vole fever is an illness caused by a strain of the hanta virus known as the Puumala virus, after a small village in Finland. Only the bank vole (Myodes glareolus) carries it. Found throughout the Nordics, the infection is known as myyräkuume in Finnish, sorkfeber in Swedish, and musepest in Norwegian.
Experts say that numbers of vole, also known as field mice, are actually down in Finland this year, with negligible amounts expected to survive the winter in the south and east. Populations of the virus-carrying voles surge every few years, with peak seasons followed by a plummet because many of the rodents end up dying from the virus they carry.
"They are not exceptionally abundant right now," says Finland's Natural Resources Centre researcher Otso Huitu.
He nevertheless advises spring cleaners of summer cottages and storage buildings to take care when cleaning up after the winter season, as up to two-thirds of the vole population could be carrying the Puumala virus. Droppings can spread the virus for up to two months in cold buildings like wood storage sheds, for example.
"Even just one vole can create a considerable amount of waste," Huitu says.
Symptoms include fever, headaches and abdominal pain
Humans contract the virus by inhaling the vole's excrement particles or nest dust. After an incubation period of between one and three weeks, what is known in medical circles as nephropathia epidemica sets in. Symptoms include fever, abdominal pain, headache, back pain and gastrointestinal symptoms. Internal haemorrhaging can occur in severe cases, but most people who are infected exhibit only mild symptoms. The disease does not spread from human to human.
There is no medication to treat the illness, which eventually passes on its own.
Take precautions to avoid infection
The best way to avoid infection is to set up traps and plug any holes to avoid the rodents altogether. Wearing a dust mask, plastic gloves and overalls while cleaning will bring added protection.
If you suspect there may be mouse droppings on the floor, for example, spray some water on the area to eliminate any dust being spread in the air before you begin to remove or wash it. Vacuuming is safer than using a broom. Try to clean things as quickly as possible and take off the dust mask last, after you have washed your hands with soap and water.