Location of Schistosoma haematobium and early lesions in Meriones unguiculatus during the prepatent period

Objectives - The authors wanted to investigate the location and the develop ment of Schistosoma haematobium during the prepatent period. Methods - Meriones unguiculatus (n = 16) were exposed to 300 cercariae and sacrificed at regular intervals, d3 to d88, after infection. The control gr oup included three rodents presenting patent schistosomiasis. The rodents w ere submitted to a histological study. Results - At d3, schistosomulae were located only in the subcutaneous lymph atic capillaries. At d7 and d8, deposits of bilharzial pigment were observe d in the liver, next to the portal veins. From d10 to d33, single worms wer e mainly found in the portal veins and occasionally in the mesenteric veins . They deposited bilharzial pigment. Various lesions developed in the neigh boring liver parenchyma: peliosis, granulomatous phlebitis, patchy paraport al necrosis, and collapse. From d50 to d71, coupled worms were mostly found in the mesenteric and pancreatic veins. However, single worms remained in the portal veins. At d78, besides their usual dwelling, a few coupled worms were found in the vena cava and esophageal veins. The lungs developed gran ulomas containing parasitic debris. At d88, coupled worms were largely scat tered in the mesenteric, colic, and pancreatic veins. The first eggs were i dentified in the portal veins and pulmonary arteries. Few single worms rema ined in the portal veins. Comments - This data allowed us to suggest that Schistosomulae first penetr ate the lymphatic capillaries before crossing the venolymphatic barrier. Th e liver is the first affected viscus in the prepatent period. (C) 1999 Edit ions scientifiques et medicales Elsevier SAS.