BABOONS AS RESERVOIR HOSTS OF SCHISTOSOMA MANSONI

During August and September 1966 15 of 17 visitors contracted S. mansoni after bathing in the Ndala river in Lake Manyara National Park. 12 experienced severe swimmer's itch and later suffered acute schistosomiasis. 6 of these, all children, became ill 42–45 days later and eggs were found in their faeces 45–47 days after exposure. This determines accurately the prepatent period for acute infections in children. 2 children infected on the same day were ill simultaneously 42 days later—one in England, one in Tanzania. 2 others were so ill in Rhodesia that the doctor was reluctant to give them an antimonial drug. They were given Ambilhar and were cured without side effects. It has been shown that infected snails from the river did not become infected from man, at the time of these visits or during the subsequent 18 months. Instead, the infection in the snails has been attributed to a troop of baboons (Papio anubis) which inhabit the area. 7 of 7 baboons shot harboured paired adult S. mansoni, and on examination with concentration techniques or straight slide smears 78 of 277 faecal samples from baboons were found to contain S. mansoni eggs. By infecting snails from these eggs and then mice from the cercariae emitted, the parasite has been positively identified as S. mansoni and the eggs shown to be viable. Fresh baboon faeces reach the water, and baboons have contact with the water by drinking and paddling. The baboons have maintained the parasite among themselves for at least 18 months, and the S. mansoni is infective to man. The conclusion drawn is that baboons acted as reservoir hosts for S. mansoni in this area. © 1969 Royal Society of Tropical Medicine and Hygiene.