The wide geographic distribution of Schistosoma mansoni, a digenetic trematode and parasite of humans, is determined by the occurrence of its intermediate hosts, freshwater snails of the genus Biomphalaria (Preston 1910). We present phylogenetic analyses of 23 species of Biomphalaria, 16 Neotropical and seven African, including the most important schistosome hosts, using partial mitochondrial ribosomal 16S and complete nuclear ribosomal ITS1 and ITS2 nucleotide sequences. A dramatically better resolution was obtained by combining the data sets as opposed to analyzing each separately, indicating that there is additive congruent signal in each data set. Neotropical species are basal, and all African species are derived, suggesting an American origin for the genus. We confirm that a proto-Biomphalaria glabrata gave rise to all African species through a trans-Atlantic colonization of Africa. In addition, genetic distances among African species are smaller compared with those among Neotropical species, indicating a more recent origin. There are two species-rich clades, one African with B. glabrata as its base, and the other Neotropical. Within the African clade, a wide-ranging tropical savannah species, B. pfeifferi, and a Nilotic species complex, have both colonized Rift Valley lakes and produced endemic lacustrine forms. Within the Neotropical clade, two newly acquired natural hosts for S. mansoni (B. straminea and B. tenagophila) are not the closest relatives of each other, suggesting two separate acquisition events. Basal to these two species-rich clades are several Neotropical lineages with large genetic distances between them, indicating multiple lineages within the genus. Interesting patterns occur regarding schistosome susceptibility: (1) the most susceptible hosts belong to a single clade, comprising B. glabrata and the African species, (2) several susceptible Neotropical species are sister groups to apparently refractory species, and (3) some basal lineages are susceptible. These patterns suggest the existence of both inherent susceptibility and resistance, but also underscore the ability of S. mansoni to adapt to and acquire previously unsusceptible species as hosts. Biomphalaria schrammi appears to be distantly related to other Biomphalaria as well as to Helisoma, and may represent a separate or intermediate lineage.
Schistosoma mansoni is the most widespread of the human-infecting schistosomes, present in 54 countries, predominantly in Africa, but also in Madagascar, the Arabian Peninsula, and the Neotropics. Adult-stage parasites that infect humans are also occasionally recovered from baboons, rodents, and other mammals. Larval stages of the parasite are dependent upon certain species of freshwater snails in the genus Biomphalaria, which largely determine the parasite's geographical range. How S. mansoni genetic diversity is distributed geographically and among isolates using different hosts has never been examined with DNA sequence data. Here we describe the global phylogeography of S. mansoni using more than 2500 bp of mitochondrial DNA (mtDNA) from 143 parasites collected in 53 geographically widespread localities. Considerable within-species mtDNA diversity was found, with 85 unique haplotypes grouping into five distinct lineages. Geographical separation, and not host use, appears to be the most important factor in the diversification of the parasite. East African specimens showed a remarkable amount of variation, comprising three clades and basal members of a fourth, strongly suggesting an East African origin for the parasite 0.30-0.43 million years ago, a time frame that follows the arrival of its snail host. Less but still substantial variation was found in the rest of Africa. A recent colonization of the New World is supported by finding only seven closely related New World haplotypes which have West African affinities. All Brazilian isolates have nearly identical mtDNA haplotypes, suggesting a founder effect from the establishment and spread of the parasite in this large country.
This review discusses the large-scale laboratory maintenance of Schistosoma mansoni. Emphasized are features which increase efficiency in such facilities, and problems most frequently encountered. Profiles are given of the long-term, high-level production of 3 strains of S. mansoni. Two of the strains, NMRI and PR-1, were of Puerto Rican origin and the other, LE, was from Brazil. Three to 8 million cercariae of each strain were usually obtained per week. The most obvious differences between the 3 strains were cercarial output per snail and snail mortality rates. Maintenance problems encountered were usually related to water quality, temperature, genetics of the parasite or snail host, predators or contaminants, feeding, or crowding of snails. Examination of the production data from these 3 life cycles led to identification of features that could be of benefit for increasing the productivity and efficiency of other S. mansoni life cycles used in research activities.
The role of cytokines on the in vitro proliferative response of peripheral blood mononuclear cells (PBMC) from Schistosoma mansoni infected patients to soluble egg (SEA) and adult worm antigens (SWAP) were evaluated. The results obtained demonstrated that the proliferative response of PBMC from chronic intestinal (INT) patients to SEA and SWAP is increased by the blockage of IL-10 with specific monoclonal antibodies (MAb). The effects of these antibodies were readily reversed by the addition of recombinant IL-10. In contrast, no effect was observed on the PBMC response of acute and hepatosplenic patients (HS) in the presence of anti-IL-10. Anti-IL-4 antibodies decreased the PBMC response of the intestinal (INT) and HS individuals to SEA and SWAP, and the PBMC response of acute patients to SEA but not to SWAP. Addition of anti-IL-5 MAb did not decrease the PBMC response of acute patients to SEA or SWAP. These results suggested that IL-10 has an important role in the modulation of the immune response in chronic asymptomatic patients and that this cytokine may be an important factor in controlling morbidity.
BackgroundPhlebotomine sand flies (Diptera: Psychodidae) are insects of medical importance due to their involvement in the zoonotic transmission of Leishmania spp. to vertebrates. The aim of this work was to study the ecology of the sand fly fauna of two types of environments, a rural environment (the Transacreana Road) and an urban park (Horto Florestal Park), both located in the municipality of Rio Branco in the state of Acre, Brazil. Additionally, this study intended to investigate Leishmania infection and blood meal sources of these sand flies using molecular techniques.MethodsThe sand fly fauna was studied in different environments (i.e. forest and peridomestic environments in a rural area, and an urban forest) using Shannon traps and HP light traps to collect sand fly specimens over 13 consecutive months (December 2014 to January 2016). For investigating natural infection by Leishmania and the source of sand fly blood meals, DNA samples were extracted from female sand flies and subjected to polymerase chain reaction targeting ITS1 and cytb genes. DNA sequencing was subsequently used to identify species of Leishmania and the source of blood meals.ResultsA total of 2515 individual sand flies of 43 species were collected and identified, Trichophoromyia auraensis (839; 33.35%), Trichophoromyia spp. (537; 21.35%) and Evandromyia saulensis (187; 7.43%) were more abundant in the rural area (S = 41 species) than in the urban forest. No significant differences were found in species richness between forest and peridomestic environments in the rural area (H = 0.04; P > 0.05), but a larger number of species was found in the forest. Leishmania DNA was sequenced in 13 samples, confirming the presence of L. (V.) braziliensis in Th. auraensis (n = 1), Ev. saulensis (n = 2), Ev. walkeri (n = 1), Ps. llanosmartinsi (n = 1), Pi. nevesi (n = 2), Ps. davisi (n = 1), Ps. ayrozai (n = 1), Pa. aragaoi (n = 1), Ny. antunesi (n = 1) and Ev. infraspinosa (n = 1). Only Ps. ayrozai possessed a sequence similar to that of L. (V.) guyanensis (99%). Through microscopic analysis, five specimens of Ev. saulensis were found to possess flagellate forms in the hindgut, with an infection rate of 2.4%. Samples from 33 fed females were submitted to cytb gene amplification, for which sequencing determined that all were similar to the sequence deposited on GenBank for Gallus gallus (domestic chicken).ConclusionsThe high abundance of Trichophoromyia auraensis and Ev. saulensis, and the detection of L. (V.) braziliensis DNA, suggests that both species may be vectors of American tegumentary leishmaniasis. Psychodopygus ayrozai was found to be infected by L. (V) braziliesnsis and L. (V.) guyanensis, and although collected in low abundance, it may be a potential vector in the region. The sand fly fauna was found to be rich and diverse with predominance of the genus Psychodopygus. Identification of food sources of fed females showed that 100% amplified a gene region compatible with the domestic chicken, which although considered refractory in the disease...
Naturally infected Biomphalaria glabrata snails were collected at two sites near Belo Horizonte, Brazil, and Schistosoma mansoni cercariae isolated from single snails were used to infect individual mice. Genetic comparison of single worm DNA was accomplished by hybridization of Southern blots to a polymorphic repetitive DNA element. Genetic profiles of parasite individuals revealed a diverse array of parasite genotypes in naturally infected intermediate hosts. The observed distribution of schistosome genotypes among intermediate hosts indicates that over half of the infected snails harbour multiple miracidia. Snails were more likely to carry multiple infections than expected by chance. This degree of overdispersion combined with high levels of genetic variability facilitates multi-genotype transmission and helps maintain parasite genetic diversity.
Schistosoma infection in Biomphalaria glabrata can be detected by either exposing snails to light to induce cercarial shedding or by squeezing them between glass slides to detect parasites in the digestive gland and other regions. The methods available are inefficient for identification of prepatent infections and do not allow the diagnosis of infection in snails that die before arriving in the laboratory. Furthermore, infection is undetectable after migration of sporocysts from the head-foot region of the snail. We examined the use of polymerase chain reaction (PCR) amplification of minisatellite repeats from Schistosoma mansoni mitochondrial DNA (mtDNA) to identify snail infection. We found that amplification of mtDNA under low stringency conditions (LS-PCR) allowed for the identification of specific S. mansoni infection in Biomphalaria snails. To confirm these results, specific amplification reactions were performed using 2 sets of primers that allowed for the diagnosis of infection and an internal control of the reaction (multiplex PCR). Results obtained using multiplex PCR demonstrated the ability of the assay to detect S. mansoni-specific infection. Thus, LS-PCR as well as specific multiplex PCR allow for the detection of prepatent infections and show high specificity for S. mansoni in comparison with other trematode infections in either living or dead snails.
The present study describes the action of the latex of Euphorbia splendens var. hislopii (E. milli) on species of the genus Bulinus and on Biomphalaria pfeifferi, intermediate hosts of schistosomiasis in Africa, and the Brazilian snails B. glabrata, B. tenagophila, and B. straminea, intermediate hosts of schistosomiasis in Brazil. The impact of the latex on the egg masses and embryos of B. glabrata was also evaluated. Using the standardized methodology of the World Health Organization for testing plant-derived molluscicides, we obtained a 90% lethal dose (LD 90) ranging from 0.13 ppm for B. glabrata subjected to lyophilized latex to 4.0 ppm for B. pfeifferi tested with the natural latex. This material has proved to be one of the most potent and specific plant molluscicides discovered thus far, presenting advantages in terms of application so that it could be used in programs involving community participation in endemic areas in both Brazil and Africa.
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