Development of Spirometra and Paragonimus Eggs in Harada-Mori Cultures

Abstract

The Harada-Mori type of hookworm culture which consists of a thin film of feces on a strip of filter paper in an upright test tube containing a shallow reservoir of water was found to be a simple and effective medium for incubating Spirometra and Paragonimus eggs. When the eggs of S. mansonoides in feces of experimentally infected cats were cultured by this method, essentially all of the eggs contained coracidia in 2 weeks at room temperature (22 to 26 C). When the feces-smeared filter paper from the culture was placed in water, there usually was prompt hatching and swarming of coracidia into the water. Eggs of P. kellicotti similarly incubated in feces of an experimentally infected cat contained fully developed miracidia in 17 to 20 days and these remained viable in cultures for 3 months. When placed in water, a high proportion of the miracidia hatched, especially if subjected to a sudden change of temperature. Hatching in water possibly was not necessary for infecting snails, however, for of 67 Pomatiopsis lapidaria allowed to feed directly on the leached culture feces, six became infected and shed cercariae in 60 to 68 days. The observations suggest that development of the eggs of these helminths may occur under nonaquatic natural conditions similar to those provided by the Harada-Mori culture. In the laboratory, the eggs of trematodes and cestodes having aquatic intermediate hosts usually are incubated in water. In nature, the infection of such hosts by miracidia and coracidia generally is believed to occur only in aquatic habits. However, the final hosts of many of these parasites frequently-more often than not in some instances-defecate at the water's edge rather than in the water, and a high proportion of the egg-bearing feces therefore rests on and becomes a part of the damp soil at the margin of streams and other bodies of water. Moreover, the intermediate hosts are in some instances amphibious-as, for example, those of Paragonimus kellicotti and Schistosoma japonicum--or are adapted to temporary ponds and to bodies of water having widely fluctuating water levels-as, for example, those of Fasciola hepatica, Fascioloides magna, and Schistosomatium douthitti. Under these conditions the intermediate hosts and the developmental stages of the parasites are for relatively long periods of time in or on the mud and wet ooze of nonaquatic habitats. The type of fecal culture described by Harada and Mori (1955) provides a habitat which in a number of respects resembles those of the mud-ooze situations just referred to. As a preliminary investigation of the possibilities of nonaquatic incubation of eggs and of subsequent natural infection of amphibious and aquatic hosts in and out of water the following observations were made.