Susceptibility of Rats and Donkeys to two stocks of Trypanosoma evansi Infection in the Sudan

Abstract

The present study was designed to investigate the susceptibility of rats and donkeys to different stocks of Trypanosoma evansi infection in the Sudan. Two geographically different stocks of T.evansi were isolated from the two selected Eastern and Western camel zones of the country. Both of these strains were found to be highly pathogenic with 100% fatality rate for both rats (10 individuals) and donkeys (4 head). However, parasitological, pathological, haematological as well as clinical differences between the two geographically different stocks were reported in this study. Based on wet preparation diagnostic technique, parasitaemia was detectable in the blood of both kinds of infected animals within 4 days post inoculation. The course of the infection was quite variable as regards to species. It was 22 to 93 days in rats and 55 to 153 days in donkeys. In addition to the statistically significant (p< 0.05) decrease in the red blood cells count (-38.1% to -69.2% or -58.7% to -75.5%), packed cell volume (-29.5% to -42.3% or - 63%) and haemoglobin concentration (-38.5% upto -42.9%) of the infected rats or donkeys, one particular mechanism of anaemia known as erythrocyte osmotic fragility was also found to be progressively increased-particularly in the donkeys infected with T.evansi (Showak stock)-compared with the control group and the preinfection values. Moreover, some visual and microscopical blood disorders-such as erythrocyte granulation, rouleau formation and Methemoglobinaemia as well as lymphocytosis and excessive accumulation of fat granules were observed in these infected animals. Fever (41ºC) was observed at the onset of the disease in the infected donkeys. However, respiratory and heart rates were the most and continuously affected, fluctuating throughout the duration of the disease. This was clearly explained by the obvious gross pathological lesions found in these vital organs at necropsy (pigmentation and white spots in lung, tracheal collapse and white spots in heart). It was concluded that both strains of T.evansi were highly pathogenic to rats and the donkeys. Thus the donkey may not only act as a reservoir when naturally infected with T.evansi in the Sudan but it may die of the infection. In addition, the eastern strain (Showak-84) was more sever and more evident in the blood stream compared with the western one (Abu-Zabad-1), which was found to be hidden in the microvascular system of the tissue organs as well as other body fluids rather than blood.