Louse-borne diseases such as typhus and trench fever devastated Napoleon's army during his ill-fated invasion of Russia in 1812, killing nearly a third of his army, according to a study by French researchers.

Napoleon invaded Russia with half a million men that summer but escaped with only a few thousand. Twenty-five thousand French soldiers escaped to Vilnius, Lithuania, during the retreat, but only 3,000 survived to continue the retreat. The rest were buried in mass graves.

Historians have long stressed the role of disease in the deaths, but now Dr. Didier Raoult and his colleagues at the Universite de la Mediterranee in Marseille have provided the first firm evidence confirming this supposition. The team worked with remains found during construction at a former Soviet army barracks in the northern suburbs of Vilnius.

Napoleon's soldiers were known to be plagued with body lice, Raoult said.

The team found body segments of five lice among clothing remnants from the soldiers. Three of the five lice contained DNA from \o7Bartonella quintana\f7, which causes trench fever, they reported this week in the online version of the Journal of Infectious Diseases.

They also studied dental pulp from the unerupted teeth of 35 soldiers.