Isospora suis is economically one of the most important infections of young piglets and causes diarrhoea (Mundt et al., 2006a), which lasts for three till seven days (Mundt et al., 2003). Histologically, villous necrosis and villous atrophy is found in the jejunum and ileum (Mundt et al., 2006a; Taylor, 2006). Treatment with Toltrazuril can lower the prevalence of diarrhoea and the number of diarrhoea days. It also will achieve a lower oocyst excretion and a higher weight gain than in infected pigs (Mundt et al., 2006b). In this experiment there were sixteen piglets used, who were orally infected with 1000 oocysts per piglet on study day 3. On study day 5 eight of the piglets were treated with Toltrazuril and the other eight piglets remained untreated. The following parameters were determined: Counting oocysts; study day 7 – 20 Faecal consistency; study day 3 and day 7 – 20 1 = normal, 2 = pasty, 3 = semi-liquid, 4 = liquid Weighing; study day 3, 5, 7, 14, 21 and 28 Blood samples; study day 7, 14, 21 and 28 1 Hematology Erythrocytes, haemoglobin, haematocrit, MCV, MCH, MCHC, leukocytes and white blood cell differentiation 2 Indirect immunofluorescence assay The oocyst excretion of the non-treated piglets showed a biphasic pattern with a first peak on day 9 and a second peak on day 16. The treated piglets did not shed oocysts. The faecal score was significantly higher in the non-treated group. The weight was not significant different between the groups, which could be the result of the breed used for this experiment (Landrace x Duroc x Pietrain). The piglets of this breed had no bad diarrhoea and started shedding oocysts quite late in the infection. Haematology showed that the eosinophils, erythrocytes, lymphocytes, monocytes and mean cell volume (MCV) were significantly different for the parameter study day. The eosinophils, erythrocytes, lymphocytes and monocytes increased during the study period. An explanation could be that this increase is due to the normal development of the piglet immune system. The mean cell volume increased significantly during the study period by the replacement of foetal erythrocytes by normal ‘adult’ erythrocytes. Finally, the indirect immunofluorescence assay showed that there was a significant difference in antibody titer between treated and non-treated piglets for study day 21 and 28. This difference could be due to the decrease in maternal antibodies in the treated piglets and the production of own antibodies in the non-treated group. The overlap for the production of own antibodies and the decrease of maternal antibodies could lie somewhere between study day 14 and study day 21. Also, due to gut damage in non-treated piglets and therefore creating a decreased barrier against incoming pathogens, a result could be, a prolonged infection. This longer infection period could cause the sustained high antibody titer of non-treated piglets. The presence of maternal antibodies against Isospora suis in piglets was proven by an indirect immunofluorescence assay on colostrum and precolostral serum. The colostrum tested positive for the presence of maternal antibodies and the precolostral serum tested negative for these antibodies. However, the maternal antibodies do not protect against an infection with Isospora suis
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