Effects of carbon dioxide, temperature, pH and the number of worms on the in vitro survival, histology and histochemistry of Paramphistomum cervi (Paramphistomatidae: Digenea).

Survival of immature and mature stages of Paramphistomum cervi, collected from the intestine and the rumen of sheep has been studied in in vitro using Tyrode's, Hank's, Eagle's, Stephenson's saline and Hedon--Fleig media. Twenty-five ml quantities of carbon dioxide (CO2)-rich Hedon--Fleig solution at pH 6.7, at 37 degrees C supported the maximum survival of 5 worms of both immature and mature flukes for periods of 9 and 10 days, respectively. Alterations to the pH of the medium, the incubation temperature and the number of worms significantly affected the period of their in vitro survival. The tissues of immature and mature worms did not show any marked histological and histochemical change until 24 h of in vitro survival in Hedon--Fleig solution when the testes of adult worms started undergoing degeneration. There was a progressive depletion of stored lipids and carbohydrates in the parenchymatous tissue during the course of in vitro survival. After the second day of in vitro maintenance, the maturation of the worms' vitelline follicles was affected, and thereafter they started to degenerate. On Day 4, degeneration of some gastrodermal cells, and a ruptured body wall were observed in some worms. Though the degenerative changes in the tissues of worms appeared at 24 h and continued to increase during in vitro maintenance, the worms survived for 9-10 days.