Potential correlation between carboxylic acid metabolites in Biomphalaria alexandrina snails after exposure to Schistosoma mansoni infection

Carboxylic acids play an important role in both aerobic and anaerobic metabolic pathways of both the snail and the parasite. Monitoring the effects of infection by schistosome on Biomphalaria alexandrina carboxylic acids metabolic profiles represents a promising additional source of information about the state of metabolic system. We separated and quantified pyruvic, fumaric, malic, oxalic, and acetic acids using ion-suppression reversed-phase high performance liquid chromatography (HPLC) to detect correlations between these acids in both hemolymph and digestive gland gonad complex (DGG's) samples in a total of 300 B. alexandrina snails (150 infected and 150 controls) at different stages of infection. The results showed that the majority of metabolite pairs did not show significant correlations. However, some high correlations were found between the studied acids within the control group but not in other groups. More striking was the existence of reversed correlations between the same acids at different stages of infection. Some possible explanations of the underlying mechanisms were discussed. Ultimately, however, further data are required for resolving the responsible regulatory events. These findings highlight the potential of metabolomics as a novel approach for fundamental investigations of host-pathogen interactions as well as disease surveillance and control.     

Karyological Studies of Biomphalaria tenagophila (d'Orbigny, 1835) (Gastropoda: Planobidae) from Rio de Janeiro,Brazil

The karyotypes of Biomphalaria tenagophila collected from Rio de Janeiro, Brazil were studied using the air-drying method. Somatic cells of this species had 2n=36. The 18 chromosome pairs were identified and classified into 3 groups. The diploid cell has 7 pairs of metacentric, 8 pairs of submetacentric, and 3 pairs of subtelocentric chromosomes. Observed chromosomes ranged from 2.4 to 6.4 µm, and the total length was 122.3 µm. This is the first report on the chromosome of B. tenagophila.     

Host reproductive fitness: the influence of increasing parasite pressure in a Biomphalaria glabrata/Schistosoma mansoni system

Summary

Host life history traits are often shaped by trade-offs between the current and potential future costs of parasitism. Reproductive tissues are not normally essential for host survival and diversion of resources elsewhere is a common effect of parasitic infection. Variations in reproductive output may therefore indicate overall fitness correlated to the host response to parasite pressure. Here, we investigated reproductive fitness in a Biomphalaria glabrata—Schistosoma mansoni system, a laboratory model for schistosomiasis. Five matched groups of unselected B. glabrata snails were individually exposed to doses of 1, 2, 5, 10 or 20 S. mansoni miracidia, respectively. A sixth group remained unexposed providing a control. Fertility (defined as actual reproductive performance, measured as the number of offspring produced) and fecundity (defined as potential reproductive capacity, measured as number of eggs and embryos formed) were monitored for each group at weekly intervals. Our results revealed that both parasite dose and infection status had a significant effect on the potential reproductive capacity of the host, but this was not always reflected in the actual reproductive success. Egg mass production showed a negative association with increasing parasite dose in patently infected snails. In contrast, snails exposed to the parasite, but within which infection did not establish, demonstrated a positive association between egg mass production and parasite dose. This suggests the existence of a fecundity compensation mechanism occurring within the post-patent period of infection. This is, to our knowledge, the first report of such an effect in a snail-trematode system and, indeed, in any host-parasite association.     

Dominant lethal effects of 2,4-D in Biomphalaria glabrata

Dominant lethal effects of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) were evaluated in the freshwater snail Biomphalaria glabrata. Wild-type snails were exposed during 10 days to 50, 75 and 100 ppm of 2,4-D dimethylamine salt (2,4-D DMA) and paired with non-exposed albino snails 1, 11, 25 and 40 days after the exposure. The offspring of the non-exposed albino snails was scored for lethal malformations.One day after the exposure, a significant effect was observed at 75 and 100 ppm without a dose–response relationship. After 11 days, the effect was observed only at the highest dose. After 25 days, significant increases in the dominant lethal effects occurred at 50 and 75 ppm; effects were directly related to the doses. Background levels of lethal malformations were resumed after 40 days.Although the major and direct measure of dominant lethal mutations is the rate of lethal malformations in the heterozygous offspring of the albino snails, the sensitivity of the assay was substantially increased with the evaluation of all non-viable embryos, that are the sum of those with lethal malformations, identified or not as wild-type.     

Low genetic diversity in a snail intermediate host (Biomphalaria pfeifferi Krass, 1848) and schistosomiasis transmission in the Senegal River Basin

Population genetic perturbations of intermediate hosts, often a consequence of human pressure on environmental resources, can precipitate unexpectedly severe disease outbreaks. Such disturbances are set to become increasingly common following range changes concomitant with climate shifts, dwindling natural resources and major infrastructure changes such as hydroprojects. Construction of the Diama dam in the Senegal River Basin (SRB) reduced river salinity, enabling the freshwater snail intermediate host Biomphalaria pfeifferi to rapidly expand its distribution. A serious public health problem ensued, with an epidemic of intestinal schistosomiasis occurring in the previously schistosome‐free Richard‐Toll region within 2 years. The current study aimed to assess the population variability of B. pfeifferi in the SRB, and speculate upon its subsequent impact on host‐parasite interactions following such engineered ecological change. Genetic variation at nine polymorphic microsatellite loci revealed little population differentiation in SRB snails compared with those from natural habitats in Zimbabwe, where Schistosoma mansoni transmission is much lower. ‘Open’ SRB habitats are associated with greater water contact, smaller population sizes and less genetic diversity, with sites downstream of Richard‐Toll showing greater inter‐ and intrapopulation variation, concomitant with less frequent human contact. These observations may be explained by rapid expansion into pristine habitat selecting for high fecundity genotypes at the expense of schistosome resistance, presenting S. mansoni with genetically homogenous highly fecund susceptible populations around the focal point, promoting development of a highly compatible host‐parasite relationship. Longitudinal study of such systems may prove important in predicting public health risks engendered by future environmental engineering projects.     

Intraspecific competition and the evolution of virulence in a parasitic trematode

Intrahost competition between parasite genotypes has been predicted to be an important force shaping parasite ecology and evolution and has been extensively cited as a mechanism for the evolution of increased parasite virulence. However, empirical evidence demonstrating the existence and nature of intraspecific competition is lacking for many parasites. Here, we compared within-host competitiveness between genetic strains of Schistosoma mansoni with high (HIGH-V) or low (LOW-V) virulence to their intermediate snail host, Biomphalaria glabrata. Groups of snails were exposed to either one or the other of two parasite strains, or a mixed infection of both strains, and the resulting progeny were identified using a molecular marker. In two separate experiments investigating simultaneous and sequential infections, we demonstrated that the lifetime reproductive success of parasite strain HIGH-V was reduced in the presence of a faster replicating parasite genotype, LOW-V, regardless of whether it was in a majority or minority in the initial inoculum of the simultaneous exposure or of its relative position in the sequential exposure experiment. Thus, we demonstrate competition between parasite genotypes and asymmetry in competitive success between parasite strains. Moreover, since the less virulent strain investigated here had a competitive advantage, we suggest that a high frequency of multiple infections could favor the evolution of less, rather than more, virulent parasites in this system.