No abstract

No abstract

Studies were done on laboratory-raised Rana pipiens tadpoles experimentally infected with Echinostoma trivolvis cercariae. Tadpoles exposed individually to 250 cercariae died within 24 h. They were edematous at death and their kidneys were heavily infected with metacercarial cysts. Of 20 tadpoles exposed to 100 cercariae each, 9 survived the infection, and their growth was compared for 4 weeks postinfection (p.i.) with that of 20 control tadpoles that had not been exposed to cercariae. There was a significant weekly decline in the total length and body weight of the infected versus control tadpoles. Surviving tadpoles retained their metacercarial infections in the kidneys following metamorphosis to frogs. Following exposure of tadpoles to cercariae, cercarial bodies were first seen in the kidneys by 0.5 h p.i. Metacercariae that were molding their inner and outer cyst walls were first seen at 2.3 h, and by 8.5 h the inner and outer cyst walls were clearly defined. Domestic chicks exposed to cysts aged 2.5 and 4.0 h did not become infected, whereas ovigerous adults of E. trivolvis were recovered from chicks fed 12-h-old cysts. Cercariae aged 6 to 8 h were more infective to tadpoles than were either 1- or 20-h-old cercariae. The E. trivolvis-R pipiens tadpole model is suitable for the study of host-parasite relationships of echinostome larvae in a cold-blooded vertebrate host.

Infections with gastrointestinal (GI) nematodes are prevalent worldwide, despite the fact that anti-helminthic medications are regarded as safe, efficient, and widely available globally. In this review, we highlight the potential therapeutic benefits that may be realized through the clinical use of Trichuris suis and other helminths for Crohn's disease (CD). Long-lived helminthic parasites are remarkable in their ability to down-regulate host immunity, protecting themselves from elimination, and also minimize severe pathological host changes. This review summarizes what is known about the underlying mechanisms that may account for the observed patterns in humans treated with helminths for CD. The Th2 arm of the immune system is emphasized as a component of primary importance in the association between the host immune system and GI nematode infections. Although GI nematode infections in humans cause significant morbidity and mortality, the existence and nature of protective mechanisms these helminths may confer remain largely unclear.