SCHISTOSOMA-MANSONI - DISTRIBUTION PATTERNS OF MIRACIDIA AMONG BIOMPHALARIA-GLABRATA SNAIL AS RELATED TO HOST SUSCEPTIBILITY AND SPOROCYST REGULATORY PROCESSES

Parasite prevalences, miracidia developmental capacity, mother sporocy st mean intensities, sporocyst distribution patterns, and cercarial pr oduction levels were determined after individual exposure of Biomphala ria glabrata snails to increased doses of Schistosoma mansoni miracidi a for two geographical strains (Brazilian, BRE, and Guadeloupean, GUA) of host and parasite. For a high level (100%) of host-parasite suscep tibility and in the absence of mother sporocyst regulatory processes f or the BRE combination, parasites were randomly dispersed among snail hosts with a frequency distribution conforming to a positive binomial. In contrast, for a moderate level (65%) of host-parasite susceptibili ty and in the presence of mother sporocyst regulatory processes for th e GUA combination, parasites were overdispersed among snail hosts with a frequency distribution conforming to the negative binomial. Levels of cercarial production were found to be strain dependent, to be deter mined during early development of mother sporocysts, and to be correla ted with the number of developed mother sporocysts. Results were analy zed in the general context of the infrapopulation dynamics of the intr amolluscan stages of trematode and are discussed in terms of their con sequences on the distribution of the genetic diversity of adult schist osomes among the definitive host population. (C) 1997 Academic Press.