Parasitological and immunological studies on rats experimental infected with Saudi Arabian strain of Trypanosoma evansi.

Surra, an enzootic disease caused by Trypanosona evansi, is one of the most important trypanosomiasis in Kingdom of Saudi Arabia. The state of parasitaemia in relation to the corresponding humoral response in experimentally infected Wister rats for 15 days were investigated. The prepatent period was found to be 5 days. The disease was characterized by intermittent fluctuation of parasitaemia and a significant difference in the level of parasitaemia (P > 0.05) was detected in specimens of day 7, 9, 13 & 14. There was a difference in the mean number of blood parasites in relation to sex throughout the 15 days of the study. This difference was statistically significant (P < 0.05). Using indirect haemagglutination serological test, almost all inoculated rats displayed specific antibodies of diagnostic value on day 7 after infection ranging between 1/80-1/160. Thereafter, antibody titers increased progressively to reach very high positive dilutions of > 1/2048 in all animals at the end of study on day 15. No sex difference could be observed in both serological specimens of 7 & 15 days. Also no correlation was observed between the state of parasitaemia and the serological titers in infected rats.