Sathaporn Jittapalapong

Trypanosoma evansi is a blood parasite principally transmitted by mechanical vectors (tabanids and stable flies) in large animals such as livestock. However, in other types of hosts, such as carnivores and rodents, oral transmission may be more important. In this experiment, attempts were made to infect rats and mice by the peroral route using infected blood, and ticks engorged on infected rats, in order to evaluate the potential role of ticks as passive vectors of trypanosomes. A strain of Trypanosoma evansi isolated from a cow in Thailand was grown in a rat and blood was collected at the peak of parasitaemia. In the first experiment, 5 rats and 5 mice were fed respectively with 1 ml and 0.5 ml of blood containing 107 Trypanosoma evansi/ml. In the second experiment, adult ticks belonging to the species Rhipicephalus sanguineus, which had fed on parasitaemic rats, were given as food to 3 healthy rats. For both experiments, the presence of parasites in the blood of the rats and mice was checked daily for 10 days, then every 2 days for the following 20 days. Within an average of 4.5 days post blood ingestion (from 4 to 5), 80% (CI95% 29–99) of the rats exhibited parasites by direct microscopic examination of the blood. Similarly, with an average of 4.7 days post ingestion (from 4 to 6), 60% (CI95% 15–95) of the mice exhibited blood parasites. After tick ingestion, no parasites were found in the blood of the rats fed with infected engorged ticks. Consequently, in this experiment, as in others, rats and mice appeared to be receptive by the oral route, but the possible role of ticks as a passive vector could not be demonstrated. Other models could be explored, involving the cattle tick (Rhipicephalus (Boophilus) microplus), to investigate the link from large to small animals.