Sleeping sickness. View of a painful nodule on a teenage girl's leg showing the initial site of African sleeping sickness (trypanosomiasis) infection. The disease is caused by Trypanosoma sp., a parasitic protozoan. The protozoa are passed onto humans by blood-sucking tsetse flies, Glossina sp., when they feed. The leg sore marks this feeding site. The protozoa infect the blood, lymph nodes, heart and brain causing a fever. Nervous system damage leads to lethargy and tremors. Without treatment, fatal damage to the heart or brain results. Photographed in Uganda.