Dr. Murai Éva szerk.: Parasitologia Hungarica 20. (Budapest, 1987)

the blood test. However, when killed on PI day 147, when she was suckling again, she proved to be negative for trypanosomes. Presumably the stress constituted by repeated pregnancies, deliveries and reconceptions etc. may have broken this animal's resistance. In some cases the trypanosomes colonised the voles' central nervous system and middle ear, too. On PI day 15 a female of 36 gramm body weight exhibited unsteady gait, then on day 16, immediately before killed, she was rotating around the longitudinal axis of her body.Necropsy revealed 4-fold enlargement of the spleen and acute serous-purulent inflammation in the right tympanic cavity with diffuse hyperaemia of the mucous membrane. Microscopic examination of the inflammatory exudate revealed vigorously moving trypanosomes. Spleen of mice Spleen of voles Before Mice dying on infection PI days 4-5 Before Voles killed on infection PI days 4-5 PI day 14 Fig. 1. Comparison of the spleen sizes of mice and voles infected with Trypanosoma equiperdum 7 Large infective doses (3 x 10 trypanosomes) produce fatal disease in a certain proportion of male and non-pregnant female voles. Five to 25% of the voles in the 8 groups with overt signs of disease died on PI days 4-7, whereas the control mice already on PI day 2. To permit a more accurate evaluation of splenic enlargement caused by trypanosomes, six litters (A to F) of voles, each comprising 4-8 voles of nearly identical body weight, were inoculated experimentally. Two to three uninfected litter mates served as control. Three control (no. 1, 2, 3) and two heavily infected (no. 4 and 5) voles of litter A were killed on PI day 5 and their spleens were weighed. In the infected voles there was a 10-fold enlargement of the spleen (Table 2) and a considerable decline in body weight. A vole of litter D, killed in death agony, had an 18-fold enlargement of the spleen and its body weight was much less than that of the litter-mate control killed at the same time (voles no. 6 and 7 in Table 2). HISTOLOGICAL EXAMINATIONS In voles dying of the infection and in those killed on PI days 4 or 5, hyperplasia of the spleen was the most characteristic finding (Figs 2 and 3). By Giemsa staining, in the blood and spleen of voles dying of acute trypanosomosis there were numerous trypanosomes, not infre-