Post mortem examinations on 125 zebras [Equus burchelli (Gray, 1824)] from the Kruger and Etosha National Parks revealed nodular and cystlike lesions of parasitic thrombophlebitis within the intrahepatic branches of the portal vein of most of the adults. These lesions contained either the larvae of the fifth stage of Delafondia vulgaris (Looss, 1900) Skrjabin, 1933. The lesion was usually a combination of thrombosis, its organization and host response to the parasite. The fifth stage specimens were larger than the sexually mature D. vulgaris present in the caecum and ventral colon. Though larger, none of the females in the liver contained ova in their uteri. Somewhat similar lesions due to fifth stage D. vulgaris were rarely observed in the pulmonary artery. Fourth stage larvae and the fifth stage of the parasite were found in the anterior mesenteric arteries and their branches of many of the zebras. Though enlarged and having thickened walls, the lumens were narrowed and none of the arteries appeared to have true aneurysms. These findings in zebras lend support to the contention of a previous investigator that it is the time factor and not the environment of the larva that determines its moults. It was obvious that some of the larvae of D. vulgaris migrate into the liver. Whether it is in the course of a normal migratory pattern or an aberrrant one was not determined. Those which become trapped in the lesions are at a dead end. The authors refer to the disease by the derivative from the generic name of the nematode, viz. "Delafondiasis".
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