Distribution of Schistosome Infections in Molluscan Hosts at Different Levels of Parasite Prevalence

Abstract

Biomphalaria glabrata snails infected with Schistosoma mansoni were collected during consecutive seasons from a site in Brazil known to have a very high percentage of infected snails. Schistosoma mansoni cercariae from single snails were used to infect individual mice, and the recovered adult worms were genetically assessed using a mtVNTR marker. The number of unique parasite genotypes found per snail was compared to expected abundance values, based on the infection prevalence at the site, to determine the distribution of S. mansoni infections within the snail population. The observed distributions and those from previous studies were used to examine the relationship between schistosome prevalence and aggregation across a wide range of prevalence values. Our analysis showed that prevalence was inversely related to the degree of parasite overdispersion, and at high prevalence, S. mansoni infections were randomly distributed among snails.

Interactions between Natural Populations of Human and Rodent Schistosomes in the Lake Victoria Region of Kenya: A Molecular Epidemiological Approach

“…Both species were overdispersed in their snail hosts, a pattern that is typical for schistosome populations in snails when prevalence is low [43]. One of the factors that likely leads to the observed pattern is the aggregation of miracidia in microhabitats occupied by particular snails [47] and low probability of contact between miracidia and snails since infection is relatively rare in this system.…”

“…Both raw prevalence and estimated prevalence values are given in Table 2. To test if prevalence (raw values) and mean intensity (number of genotypes per snail) of infection was positively correlated as noted in previous studies [43], a Pearson's correlation was calculated on the log transformed values using the same software. Also, an analysis of covariance (ANCOVA) that examined the difference in the total number of cercariae released between species and its relationship to snail size was performed.…”

Preliminary study on sex-related inflammatory reactions in mice infected with Schistosoma mansoni

“…Indeed, numerous unisexual mollusc infections are found in the field (69% Eppert et al 2002;71% Minchella et al 1995;95% Sire et al 1999). Thus, human unisexual primary infections in the field are highly possible in areas where schistosomiasis is emergent or the transmission rate is low, such as Venezuela (Noya et al 2002) or Oman (Mone´et al 2003).…”

Towards interruption of schistosomiasis transmission in sub-Saharan Africa: developing an appropriate environmental surveillance framework to guide and to support ‘end game’ interventions

“…Only the tiny fraction of miracidia and cercariae that transition successfully between hosts could be considered successful, as some element of chance has favoured their progression, but it is by sufficiently saturating the environment that these rather unlikely transmission events become statistically inevitable [24, 32]. Furthermore, evolved subtleties in the chemotaxis and chronobiology of the larval stages favour the odds of transmission and fine-tune other life history traits, honed by natural selection for eons.…”