The Swedish University of Agricultural Sciences and Umeå University have studied why the number of cases of swine fever varies greatly between winters in Sweden. One explanation for the increased cases is the number of forest vultures, but this is not the only explanation.
– We saw that the more rainfall during the November months, the higher the degree of infestation in forest mice, says Saana Sipari, a postdoctoral fellow in the Department of Game, Fish and Environment at SLU in Umeå.
Heavy rains in mid-winter (December-March) had no effect on the degree of infestation in mice. The period leading up to a protective snow cover, often November, appears most sensitive to the spread of infection.
“Crowded in small spaces”
But there are many aspects that cause the virus to spread among mice, including so-called rain-on-snow events with ice bark formation as a result that may lead to woodland mice crowding into small tracts of land and that the virus thrives best in such an environment.
Several studies predict an increased risk of animal disease outbreaks in the future and a warmer climate, especially in northern regions. However, our study shows that this has already happened, says Frauk Eike, senior lecturer at SLU in Umeå.