Sleeping sickness. View of two teenage girls with African sleeping sickness (trypanosomiasis) waiting for a local health worker. A painful nodule (lower right) on the leg of one of the girls shows the initial site of 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.