Histological observation on the effects of praziquantel on schistosomulae of Schistosoma japonicum in mouse skin

Histological observation was carried out in mice given intragastrically praziquantel 300 mg/kg 1.5-2.0 h prior to the exposure to 500-1000 cercariae/mouse. 2 h after the infection, swelling and damage appeared in the tegument of schistosomulae, of which the parenchymal cells showed pyknosis and karyorrhexis. Invasion of neutrophilic granulocytes was seen in some dead larvae in hupodermis. The number of dead larvae surrounded and invaded by many inflammatory cells markedly increased both in dermis and hypodermis of the mice 6 h after the infection. All the dead larvae in the mouse skin were almost disintegrated 24-72 h after penetration. During the period of 2-168 h after the exposure to cercariae, no larvae were found in the skin of mice pretreated with a single oral dose of praxiquantel 500 mg/kg, while a great number of degenerated or necrosed cercariae was found adhered to the stratum corneum of the skin. An increase in acid mucopolysaccharide in epidermis of the pretreated mice was detected when compared with the control mice. These results suggest that praziquantel displays prophylactic and protective effects against S. japonicum in mice.