ABSTRACT
Stictodora lari Cysts of S. lari seemingly do not elicit a host reaction until after weeks of infection in fish. The cyst and host encapsulation associated with metacercariae in freshwater fishes has been investigated by Leong and Howell (1971) and Howell (1973). Glass beads and metacercarial cysts of S. lari were implanted in the abdominal cavity of mosquitofish to study the sequence of the encapsulation by the host (Howell, 1973). Three days post-implantation the glass beads were encapsulated by host cells; whereas, cysts of S. lari remained unencapsulated until 21-23 days later. Howell (1973) proposed both an immunological explanation and a physical one: the cysts remained unencapsulated because they were either immunologically disguised as host tissue or they remained as such because the presence of spikes on the external surface of the cyst inhibit the attachment of host cells. He further asked why it takes so long for the host to encapsulate a parasite cyst? Basically, the cyst includes fish elements and he insinuates that "selective contamination" (e.g., Smithers and Terry, 1969) of the cyst masks the parasite from the host's defenses. Sommerville (1982) likened her results to those of Howell (1973) in, that there was very little inflammation and cited an 'avoidance of host response'.
