The survival of Taenia pisiformis eggs under laboratory conditions and in the field environment.

This study reports on the long-term survival of Taenia pisiformis eggs held under controlled laboratory conditions and in the external environment. Egg viability was assessed by feeding the ova to susceptible rabbits. In the laboratory experiment dried eggs were stored under 4 different temperature and relative humidity regimes. At various time intervals eggs were removed from these environments and fed to rabbits which were subsequently killed and the number of viable cysticerci within them counted. The results show that a high temperature (38 degrees C) and to a lesser extent, a low humidity (33%) are quickly lethal to eggs and few survive for more than 7 days. However, at 4 degrees C and a relative humidity of 90%, some eggs were still viable after 300 days. At the lower temperature there was a noticeable interaction between temperature and relative humidity. For the field study a small area of pasture was enclosed by a rabbit-proof fence and hessian screen. The pasture was first shown to be substantially free of extraneous contamination with T. pisiformis ova and was then artificially seeded with a large number of eggs. Fresh groups of susceptible rabbits were grazed on this pasture at intervals thereafter. The results, expressed as the mean number of cysticerci recovered from rabbits, show that eggs remain viable for several months during winter and early spring, but in summer no viable eggs could be demonstrated after a period of 2 weeks.