Charles S. Richards

Genetic factors in susceptibility of Biomphalaria glabrata for different strains of Schistosoma mansoni

Biomphalaria glabrata selected for genetic differences in susceptibility to infection with a Puerto Rican strain of Schistosoma mansoni were exposed to miracidia of a strain of S. mansoni from St Lucia. The St Lucian strain was less infective than the Puerto Rican. Results suggested that in snails susceptible to the Puerto Rican S. mansoni differences in susceptibility to the St Lucian straing were determined by a single gene, with insusceptibility dominant.

The relationship between Schistosoma mansoni and Biomphalaria glabrata: genetic and molecular approaches

Biomphalaria glabrata is a major intermediate host for the helminth parasite Schistosoma mansoni. Beginning in the mid-20th century, studies were carried out with this snail species to identify the immunological and genetic components that might be involved in controlling schistosome development. A number of genetically well-defined snail stocks were derived as a direct result of these studies and have since played major roles in helping investigators to identify important cellular and humoral components in the snail/schistosome relationship. This review will explore the historical development of these stocks and describe some of the major advances in several areas of medical malacology that hawe been made possible be their use.

Schistosoma mansoni: susceptibility reversal with age in the snail host Biomphalaria glabrata.

Abstract A variety of genetic types of the snail Biomphalaria glabrata have been developed by selection. Susceptibility to infection by the trematode, Schistosoma mansoni, was the selective factor. Snails of one genetic type are consistently susceptible as juveniles but vary in susceptibility as adults. In one such stock, it was found that some snails remain susceptible as adults, a few become refractory as young adults and remain so, while most of those refractory as young adults revert to susceptibility in old age.

Schistosoma mansoni: temporary reduction of natural resistance in Biomphalaria glabrata induced by irradiated miracidia of Echinostoma paraensei.

Abstract Sporocysts developing in the heart of the snail host from irradiated Echinostoma paraensei miracidia are unable to form rediae and can survive for only a brief time. However, they still were able to reduce temporarily the strong natural resistance to Schistosoma mansoni in juveniles of a strain of Biomphalaria glabrata selected for genetic resistance to this parasite. S. mansoni primary sporocysts, unable to survive in single (control) infections in this host strain, developed successfully in most snails in which irradiated E. paraensei sporocysts were present. After the echinostome sporocysts were destroyed by host amebocytes, the snails regained their natural resistance against a new infection by miracadia of S. mansoni. Successful initiation of an infection with S. mansoni was achieved only in the presence of living irradiated echinostomes. Once the schistosome infection had become well established, however, developing primary and secondary sporocysts could survive and produce cercariae, although the protecting echinostomes had by then been destroyed. Early growth stages of the primary sporocysts apparently are more vulnerable to the snails defensive reaction and generally do not survive unless protected by irradiated E. paraensei sporocysts. After the S. mansoni sporocysts grow older, they develop their own capacity to interfere with the snails natural resistance and continue to survive and produce progeny without further protection by the echinostomes. Irradiated sporocysts have a lower capacity to interfere with the snails natural resistance than do nonirradiated sporocysts. Suitability, as distinguished in this paper from susceptibility, can be separated from resistance of the snail to trematodes by employing double infections.

GENETIC STUDIES OF PATHOLOGIC CONDITIONS AND SUSCEPTIBILITY TO INFECTION IN BIOMPHALARIA GLABRATA

During studies on the genetics of variation in susceptibility of B. galbrata to infection with S. mansoni, four types of proliferative amoebocytic accumulations have been observed. They occur in four different clonal stocks of B. glabrata, beginning as amoebocytic aggregations, namely, in the atrial cavity, pericardial cavity, periaortic space, and hemocoel between the stomach and intestine. Persistent amoebocytic accumulations involve the sinuses around the stomach, intestine, and hepatopancreas. In these snails, nests of undifferentiated cells occur in the anterior pericardial wall, which is considered to be a hemopoietic area. Crossing experiments indicate the involvement of genetic factors, possibly in combination with infectious agents.

Schistosoma mansoni: Use of a cloned ribosomal RNA gene probe to detect restriction fragment length polymorphisms in the intermediate host Biomphalaria glabrata

Adult susceptibility of Biomphalaria glabrata to Schistosoma mansoni infection is controlled by simple Mendelian genetics. In this study a molecular approach was used to determine the degree of genetic variation between well-defined lines of B. glabrata which are either resistant (10-R2) or susceptible (M-line) to S. mansoni infection. A cloned probe pSM389, which contains part of the S. mansoni small ribosomal RNA gene and a portion of the nontranscribed spacer was found to cross-hybridize with B. glabrata DNA and was used in Southern hybridizations to detect restriction fragment length polymorphisms (RFLPs) between the above snail stocks. Polymorphisms were noted with a variety of restriction enzymes, namely Bg/II, BamHI, AccI, AvaII, ClaI, EcoRI, EcoRV, KpnI, PvuII, and NcoI. Although most RFLPs were relatively minor, a significant difference was observed with EcoRV. Further analysis of the EcoRV RFLPs among other isolates of the resistant stock demonstrated that a high frequency of genetic variation exists even among isolates of the same origin, but maintained in separate laboratories. Interestingly, RFLPs in the EcoRV site were detected in DNA isolated from a single generation of selfed progeny of a single 10-R2 parent. RFLPs associated with this site were found to occur between B. glabrata and B. tenagophila, B. straminea, and B. schrammi, indicating that Southern blot analysis using ribosomal gene probes may be useful for the molecular differentiation of B. glabrata from other intermediate hosts and from morphologically similar species that are refractory to infection.

Use of RAPD-PCR to differentiate genetically defined lines of an intermediate host of Schistosoma mansoni, Biomphalaria glabrata.

The genetic differentiation among several laboratory-maintained pedigree snail lines of Biomphalaria glabrata (with different susceptibility phenotypes to Schistosoma mansoni infection) was assessed with the random amplified polymorphic DNA method. Out of the 20 primers tested, 2 (OPA-01 and OPA-06) gave reproducible markers with either individual or bulked DNA samples from resistant (BS-90, 10-R2, LAC-line) and susceptible (M-line) snails. Arbitrary primer, OPA-01, amplification of BS-90 DNA identified a 180-bp strain-specific fragment and a 400-bp marker in the susceptible M-line stock. In the 10-R2 and LAC snail lines, OPA-01 specific markers of 200 bp and 550 bp were identified. Amplification with primer OPA-06 identified several major strain-specific markers in the BS-90 (150 bp, 400 bp, 800 bp) and M-line (1,100 bp) snails. The heritability of the RAPD markers was evaluated in progeny snails derived from a cross between the BS-90 and M-line stocks. Results showed that markers were inherited in a dominant or codominant fashion. The 1,100-bp M-line marker was inherited in all susceptible progeny snails analyzed.

Elevation of aminopeptidase activity in Biomphalaria glabrata (Mollusca) parasitized by Echinostoma lindoense (Trematoda)

Abstract Comparisons of the levels of aminopeptidase activity in the hemocytes and serum of Biomphalaria glabrata at 20 and 30 days postexposure to irradiated Echinostoma lindoense miracidia with enzyme levels in control snails have revealed that there are significant elevations in the serum of snails at both time periods postexposure. Furthermore, there is a significantly higher level of aminopeptidase activity in the serum of snails at 30 days than at 20 days postexposure. Although the biologic function of the elevated levels of serum aminopeptidase in sensitized snails remains uncertain, it is possible that this lysosomal enzyme may degrade the surface proteins of secondarily introduced parasites and thus act as a form of acquired humoral immunity.

Schistosoma mansoni: Electrophoretic characterization of strains selected for different levels of infectivity to snails

Abstract Individual adult Schistosoma mansoni from strains selected for high or low infectivity to specific strains of the snail intermediate host, Biomphalaria glabrata , were subjected to enzyme electrophoresis on starch gels. Fourteen enzyme systems were analyzed in an attempt to find electrophoretic markers associated with genes for infectivity to snails. The S. mansoni strains were selected from different isolates from Puerto Rico in several strains of B. glabrata . Of an estimated 18 loci, 3 were polymorphic and the remainder monomorphic. For 1 of the 3 polymorphic enzyme loci, lactate dehydrogenase ( Ldh , EC 1.1.1.27), phenotype frequencies were correlated with infectivity to snails. In schistosome strains of low infectivity, frequencies of the Ldh-N phenotype ranged between 0.56 and 0.69, while in strains of high infectivity, Ldh-N frequencies were typically 0.91 to 1.00. Whether the correlation is accidental or due to some form of association, such as chromosomal linkage, between the locus responsible for variation in lactate dehydrogenase and a gene for infectivity to snails remains to be determined.

Host reactions in Biomphalaria glabrata to Schistosoma mansoni miracidia, involving variations in parasite strains, numbers and sequence of exposures.

Abstract M-line Biomphalaria glabrata snails are susceptible to Puerto Rican (PR-1) strain of Schistosoma mansoni , but are resistant to a St. Lucian (LC-1) strain. 10-R2 B. glabrata snails are resistant to both strains of S. mansoni . When 10-R2 snails were exposed repeatedly to PR-1 S. mansoni miracidia for 5 consecutive days, all of the sporocysts were encapsulated and destroyed by the snails. Thirty-four per cent of sporocysts examined in M-line snails with similar exposures were also degraded. In double concurrent infections of M-line B. glabrata with [ 3 H]leucine-labeled and unlabeled PR-1 and Lc-1 S. mansoni , the incompatible Lc-1 miracidia were selectively attacked and destroyed. This destruction occurred irrespective of the sequence of exposure of the 2 strains of miracidia, and whether or not the miracidia were labeled. Successful superinfection of M-line B. glabrata with homologous S. mansoni miracidia was obtained at least 4 days after the primary exposure to the miracidia.