Ljungan virus, transmitted from animals to humans, has been found in 11 of 12 cases of Sudden Infant Death Syndrome or SIDS. Investigators from Sweden and the USA present these findings in the scientific journal Forensic Science in Medicine and Pathology. Animals infected with the virus suffer from a similar disease. Population cycles of wild rodents carrying Ljungan virus correlate with the frequency of SIDS cases.

Ljungan virus has recently been associated with malformations and intrauterine death in pregnant women. Investigators from Sweden and the USA have now also found this virus in the heart, lung and brain of children dying during their first year of life from so called Sudden Infant Death syndrome (SIDS). Twelve cases were investigated.

"We found the Ljungan virus in four out of five cases where no natural cause of deaths had been found. The virus was also found in seven infant deaths that showed signs of myocarditis," says author Bo Niklasson adjunct professor at Uppsala University and Research Director at Apodemus AB Stockholm, Sweden.

Laboratory mice infected with the virus during pregnancy suffer from a similar disease. Pups die before or after birth sometimes without any pathological findings.

Coauthor Petra Råsten Almqvist, MD, PhD, Department of Forensic Medicine, Stockholm, Sweden, a department investigating some 10 cases annually, notes:

"Animals carrying Ljungan virus also die without any visible signs of disease to explain the cause of death just like in cases of SIDS."

Ljungan virus is a zoonosis transmitted from animals to humans. The virus has wild rodents as its main natural reservoir. Recent studies have found that Ljungan virus is also associated with severe diseases during pregnancy such as malformation and fetal death during late pregnancy, so called intrauterine fetal death (IUFD). The scientists have shown a correlation between the number of small rodents in nature and the incidence of both IUFD and SIDS.

Ljungan virus has been found in many countries in Europe and in the USA.

"It will be important to investigate whether Ljungan virus similarly causes prenatal and postnatal death in other parts of the world," says Dr William Klitz, geneticist and co-author of the report at the Public Health Institute in Oakland and the University of California, Berkeley.