Oocysts sporulation

Unsporulated oocysts of E. tenella have high SOD activity and contain several electrophoretically distinct forms of the enzyme, including two forms of Cu,ZnSOD, two forms of FeSOD and two forms of MnSOD. The SOD activity decreases during sporulation and oocysts sporulated for 48 h have low levels of SOD and contain only one form of the enzyme (MnSOD) (34). 

Eimeria leukarti is the intestinal coccidian of horses. Infection with . leukarti follows the ingestion of sporulated oocysts in contaminated food or water. After exposure to bile in the small intestine, the oocysts excyst and individual protozoa, the sporozoites, emerge. The sporozoites penetrate the intestinal epithelium and differentiate... 

Fig. 6.8 Life cycle of Cryptosporidium. Sporulated oocysts, containing four sporozoites, are excreted by the infected host...

Birds acquire coccidiosis when they ingest sporulated oocysts along with feed and water. The disease is exacerbated due to poor nutritional conditions of chicken. In addition, environmental and climatic factors also add to the spread of the infection. Faecal discharge of birds help oocysts to sporulate and become infective under warm and humid conditions. Crowding of birds due to intensive rearing creates favourable conditions for sudden outbreaks of severe forms of coccidiosis. 

Two salvage enzymes from Eimeria have been characterized. HGXPRTase is present in crude extracts of oocysts of E. tinella (11). Adenosine kinase is found in sporulated oocysts of three avian species of Eimeria (65). 

Eimeria tenella. It appears that the sporulated oocysts of E. tenella are capable of de novo pyrimidine synthesis since sporozoites incorporate " C-labeled aspartate and orotate into pyrimidine nucleotides (103). Besides de novo synthesis, E. tenella is also capable of pyrimidine salvage. E. tenella will incorporate uracil, cytidine and uridine but not thymidine into its nucleic acids (104). This parasite is dependent on UMP for the synthesis of TMP and thymidylate synthase activity is present in extracts of E. tenella (105). As with both Plasmodium and the kinetoplastids, the thymidylate synthase of E. tenella exists as a bifunctional protein (91). 

A low catalase activity has been found in sporulated oocysts and in sporozoites of Eimeria tenella (34) but its location was not determined. Only low levels of catalase were found in P. berghei, probably as a result of contamination of the preparations with host cell material (35). Toxoplasma gondii tachyzoites have an abundant catalase activity (36). 

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