Press information

August 01, 2006

The Ljungan virus may cause mysterious mass death among rodents

The Swedish research company Apodemus AB has unexpectedly discovered that small rodents carrying the Ljungan virus develop diabetes and heart disease, not only in laboratory studies, but also in nature. This discovery could explain why the number of rodents sometimes plunges substantially. The results are now published in the scientific journal Oecologia. The Ljungan virus has been identified in Europe and America.

“Laboratory experiments have shown that voles and mice infected with the Ljungan virus and exposed to stress develop diabetes and myocarditis. We now see that the same thing happens to small rodents in the wild as well”, says Professor Bo Niklasson, research director of Apodemus AB.

This new study was conducted in cooperation with scientists at Umeå University in northern Sweden. A large fraction of the wild animals tested were found to carry the Ljungan virus, and had also very high glucose levels. The results indicate that animals in the wild may carry the virus for a long time without symptoms, and that they – like the animals in the laboratory environment – develop disease only when subjected to stress.

Up until now the rapid reduction of rodents that always follows a lemming or vole year has been attributed to an increase in the number of predators. It now seems however that the lethal combination of the Ljungan virus and stress plays a vital role in rodent population crashes.

“The periodic fluctuation in the number of voles and lemmings is one of Scandinavian nature’s most enigmatic phenomena. The Apodemus report is without a doubt one of the most important contributions in a long time in efforts to establish the causes”, says Staffan Ulfstrand, professor emeritus of zoology at Uppsala University.

Apodemus has previously shown that the number of voles found in nature covaries with the number of new cases of diabetes among humans in the same area. Apodemus has subsequently discovered the Ljungan virus in voles and other small rodents, both in Europe and America. Apodemus’ hypothesis is that the Ljungan virus is transferred from animals to humans and that this may be an underlying cause of diabetes and other chronic illnesses.

For further information please contact:

Bo Niklasson, research director, Apodemus AB
Telephone: +46 708-23 23 23

Staffan Ulfstrand, professor emeritus of zoology, Uppsala University
Telephone: +46 18-105 737

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The research company Apodemus AB hypothesise that several chronic diseases may be caused by a virus, the Ljungan virus, which is transmitted from animals to humans. The Ljungan virus is carried by bank voles, the most common mammal in Scandinavia.