A former Soviet biological weapons scientist , Kenneth Alibek , has said that an outbreak of Tularemia among German soldiers shortly before the siege of Stalingrad was due to intentional release of F. tularensis by Soviet forces , but this claim is rejected by others who have studied the outbreak . A former Soviet biological weapons scientist , Kenneth Alibek , has alleged that an outbreak of Tularemia among German soldiers shortly before the siege of Stalingrad was due to the release of F. tularensis by Soviet forces , but this claim is rejected by others who have studied the outbreak .