The snail hosts of schistosomiasis: some evolutionary and ecological perspectives in relation to control

Despite opportunities for radiation provided by spatio-temporal isolation, the basic morphological plan of pulmonate snails has remained conservative. In consequence of the resulting dearth of morphological characters and their plasticity, there is a case for using biochemical characters such as exogenous chemicals released by the snails (e.g. amino acids) and their chemoreception niche as taxonomic aids to classify snails of medical importance. As these same chemicals are used by snails to distinguish conspecifics they could also be used as "environmental antibodies" in controlled release formulations (CRF's) designed to remove target snails in a specific, cost-effective and ecologically acceptable manner. The snails, surface-living bacteria, algae and macrophytic plants are considered as co-evolved, interactive modular systems with strong mutualistic elements. Recently, anthropogenic perturbations such as deforestation, and damming of flowing waters, have benefited these modules whereas others such as river canalization, acid deposition, accumulation of pesticide residues and eutrophication have harmed them. Research is needed to elucidate the factors which limit the growth of snails in primitive habitats, uninfluenced by man, as well as in those subject to harmful anthropogenic factors. The understanding thus gained could be applied to develop cost-effective primary health care strategies to reduce or prevent transmission of schistosomiasis and other water related diseases.

A molecular genetic study of the variations in metabolic function during schistosome development

During their complex life cycle schistosomes alternate between the use of stored glycogen and reliance on host glucose to provide for their energy needs. In addition, there is dramatic variation between the relative contribution of aerobic versus anaerobic glucose metabolism during development. We have cloned a set of representative cDNAs that encode proteins involved in glucose uptake, glycolysis, Kreb's cycle and oxidative phosphorylation. The different cDNAs were used as probes to examine the expression of glucose metabolism genes during the schistosome life cycle. Steady state mRNA levels from whole cercariae, isolated cercarial tails, schistosomula and adult worms were analysed on Northern blots and dot blots which were quantified using storage phosphor technology. These studies reveal: (1) Transcripts encoding glycogen metabolic enzymes are expressed to much higher levels in cercarial tails than whole cercariae or schistosomula while the opposite pattern is found for glucose transporters and hexokinase transcripts; (2) Schistosomula contain low levels of transcripts encoding respiratory enzymes but regain the capacity for aerobic glucose metabolism as they mature to adulthood; (3) Male and female adults contain similar levels of the different transcripts involved in glucose metabolism.

Genetic variability and differentiation between populations of Rhodnius prolixus and R. pallescens, vectors of Chagas' Disease in Colombia

Enzyme polymorphism in Rhodnius prolixus and R. pallescens (Hemiptera, Reduviidae), principal vectors of Chagas' disease in Colombia, was analyzed using starch gel electrophoresis. Three geographic locations were sampled in order to determine gene flow between populations and to characterize intra- and interspecific differences. Of 25 enzymes assayed 10 were successfully resolved and then used to score the genetic variation. The enzymes PEPD, GPI, PGM and ICD were useful to differentiate these species and PGD, PGM and MDH distinguished between sylvatic and domiciliary populations of R. prolixus. Both polymorphism and heterozygosity indicated greater genetic variability in sylvatic habitats (H = 0.021) compared to domiciliary habitats (H = 0.006) in both species. Gene flow between sylvatic and domiciliary populations in R. prolixus was found to be minimal. This fact and the genetic distance between them suggest a process of genetic isolation in the domiciliary population.

A possible correlation between the host genetic background in the epidemiology of Hepatitis B virus in the Amazon region of Brazil

The Amazon region of Brazil is an area of great interest because of the large distribution of hepatitis B virus in specific Western areas. Seven urban communities and 24 Indian groups were visited in a total of 4,244 persons. Each individual was interviewed in order to obtain demographic and familial information. Whole blood was collected for serology and genetic determinations. Eleven genetic markers and three HBV markers were tested. Among the most relevant results it was possible to show that (i) there was a large variation of previous exposure to HBV in both urban and non-urban groups ranging from 0 to 59.2%; (ii) there was a different pattern of epidemiological distribution of HBV that was present even among a same linguistic Indian group, with mixed patterns of correlation between HBsAg and anti-HBs and (iii) the prevalence of HBV markers (HBsAg and anti-HBs) were significantly higher (P=0.0001) among the Indian population (18.8%) than the urban groups (12.5%). Its possible that the host genetic background could influence and modulate the replication of the virus in order to generate HB carrier state.

Inter-relation of sylvatic and domestic transmission of Trypanosoma cruzi in areas with and without domestic vectorial transmission in Minas Gerais, Brazil

During the period 1980-1986, we captured triatomine bugs and mammalian reservoir hosts from sylvatic and domestic situations in different municipalities of the State of Minas Gerais. Trypanosoma cruzi was isolated from captured bugs, mammals and patients. After cultivation in LIT medium, the electrophoretic enzyme profiles were determined. We obtained atotal of 32 parasite isolates from regions with active domestic transmission, and 24 isolates form areas under control. For the first areas the results suggest introduction of T. cruzi from sylvatic habitats, through incursion of infected opossums and/or sylvatic T. sordida, which appears to have given rise to at least one acute human infection. Of particular interest is the finding of sylvatic opossums and a T. sordida nymph infected with ZB, that could indicate return of parasites from chronic human infections to sylvatic transmission cycles. For the areas under control we also interpret the results as interaction between sylvatic and domestic cycles of transmission, here through the invasion of houses by bugs carrying the Z1 zymodeme from the sylvatic environment. The Multivariate Correspondence Analysis gives a spatial description between the different parasite isolates and confirms the existence of a bridge in the opposite direction in the region with active vectorial transmission including the exporting of Z2 through the peridomestic environment into the sylvatic cycle. For the others areas this bridge corresponds especially to Panstrongylus megistus, importing Z1 into the domestic environment.

Eurytrema coelomaticum: influence of the infection on the reproduction and nucleic acids contents in the albumen gland and ovotestis of Bradybaena similaris

The number of eggs laid per snail in Bradybaena similaris and the nucleic acids (DNA and RNA) in the albumen gland and ovotestis were quantified in snails infected with sporocysts of the digenetic trematode Eurytrema coelomaticum. The total number of eggs laid per mollusc was reduced by 96.32% at the end of the larval development. The DNA concentration increased by 700% and the RNA concentration was reduced by 8,38% by the time when the daughter sporocysts of E. coelomaticum were released from B. similaris. The relation between these values and the inhibition of the reproduction observed in infected molluscs is discussed.

Interaction between Didelphis albiventris and Triatoma infestans in relation to Trypanosoma cruzi transmission

This paper attempts to prove if a high Trypanosoma cruzi prevalence of opossums might be reached with few potential infective contacts. One non-infected Didelphis albiventris to T. cruzi and 10 infected nymphs of Triatoma infestans were left together during 23 hr in a device that simulated a natural opossum burrow. Twenty-six replicates were perfomed using marsupials and triatomines only once. Potentially infective contacts occurred in all the trials. From the 26 opossums used in trials, 54% did not eat any bug. Of the 260 bugs used, 21% were predated. In the 25 trials involving 205 surving bugs, 36 % of them did not feed. In 15/25 cases, maior ou igual a 60% of the triatomines were able to feed. The parasitological follow-up of 24 opossums showed that among 10 that had eaten bugs, 4 turned out infected and among the 14 that had not predate, 3 (21%) became positive. In sum, 7/24 (29%) of the marsupials acquired the infection after the experiment. This infection rate was similar to the prevalences found for the opossum population of Santiago del Estero, Argentina, suggesting that the prevalences observed in the field might be reached if each marsupial would encounter infected bugs just once in its lifetime.

Dried blood spots collected on filter paper: an international resource for the diagnosis and genetic characterization of human immunodeficiency virus Type-1

The collection of dried blood spots (DBS) on filter paper provides a powerful approach for the development of large-scale, population-based screening programs. DBS methods are particularly valuable in developing countries and isolated rural regions where resources are limited. Large numbers of field specimens can be economically collected and shipped to centralized reference laboratories for genetic and (or) serological analysis. Alternatively, the dried blood can be stored and used as an archival resource to rapidly establish the frequency and distribution of newly recognized mutations, confirm patient identity or track the origins and emergence of newly identified pathogens. In this report, we describe how PCR-based technologies are beginning to interface with international screening programmes for the diagnosis and genetic characterization of human immunodeficiency virus type 1 (HIV-1). In particular, we review recent progress using DBS specimens to resolve the HIV-1 infection status of neonates, monitor the genetic evolution of HIV-1 during early infancy and establish a sentinel surveillance system for the systematic monitoring of HIV-1 genetic variation in Asia.

Isolation of fungi from nature in the region of Botucatu, state of São Paulo, Brazil, an endemic area of paracoccidioidomycosis

In an attempt to isolate Paracoccidioides brasiliensis from nature 887 samples of soil from Botucatu, SP, Brazil, were collected cultured in brain heart infusion agar supplemented with dextrose, in potato dextrose agar and in yeast extract starch dextrose agar, all with antibiotics, at 25º and 37ºC. Five thermo-dependent dimorphic fungi morphologically resembling P. brasiliensis were isolated; two from armadillo holes; further studies of the biology, antigenicity and genetic features of the five dimorphic fungi are necessary to clarify their taxonomy and their possible relation to P. brasiliensis. In addition, 98 dematiaceous fungi and 581 different species of Aspergillus spp. were also isolated. Our findings emphasize that armadillos and their environment are associated with thermo-dimorphic fungi and confirm the ubiquity of pathogenic dematiaceous fungi and Aspergillus spp.

Comparison of Some Molecular-genetic Techniques for Identification of Leishmania Circulating in Natural Foci of Zoonotic Cutaneous Leishmaniasis in the Central Asia Region

Different molecular-genetic methods were used to identify a cohort of Leishmania strains from natural foci of zoonotic cutaneous leishmaniasis located in Central Asia, on the former USSR territory. The results obtained using isoenzymes, PCR, restriction fragment length polymorphisms of kDNA and molecular hybridization techniques are discussed in terms of their applicability, discrimination power and feasibility for answering questions related to molecular epidemiological research and for detecting mixed Leishmania infections

The Potential for Dispersal of Onchocerciasis in Ecuador in Relation to the Distribution of the Vector Simulium exiguum (Diptera:Simuliidae)

The future dispersal of onchocerciasis in Ecuador is dependent on the distribution of cytotypes of the vector species complex Simulium exiguum. Over the last 14 years, collections of larvae have been made from over 25 rivers, between 80-1600 m altitude, from various sites on both sides of the Andes. Analysis of larval polytene chromosomes was used to determine the distributions of each cytotype. On the western side of the Andes, the Cayapa cytotype (the only cytotype directly incriminated as a vector) has a distribution from Santo Domingo de los Colorados northwards. The Quevedo and Bucay cytotypes occur from Santo Domingo de los Colorados southwards. On the eastern side of the Andes, the Aguarico cytotype occurs in the Rio Aguarico and a new cytotype is present in the tributaries of the Rio Napo. Whether the disease will spread south of Santo Domingo and on the eastern side of the Andes depends on vector capacity of the cytotypes and the dispersal patterns of individuals infected with onchocerciasis. At present the Aguarico, Bucay and Quevedo cytotypes are known to be efficient hosts, but their biting preferences and biting densities have not yet been evaluated

Genetic Variability and Microdistribution of Triatoma infestans Genotypes and Trypanosoma cruzi Clones in Arequipa Region (Peru)

The genetic variability of Triatoma infestans and Trypanosoma cruzi populations was studied by isoenzyme analysis in two distinct areas of Arequipa province (Peru); one, Santa Rita de Siguas, being an endemic area for Chagas' disease, the second, Arequipa, recently infected. Analysis of T. infestans genetic variability indicates, (i) temporal stability of genotypes found in Santa Rita de Siguas, (ii) high genetic differences between Arequipa and Santa Rita de Siguas populations suggesting minor contact between them, (iii) multiple origin of the T. infestans population in Arequipa, and (iv) poor dispersal capacity of T. infestans: the panmictic unit could be reduce to a house. Parasite isoenzyme analysis was performed in 29 Peruvian stocks of T. cruzi, mainly isolated from bugs taken in a single locality, Santa Rita de Siguas. The results show, (i) a high genetic polymorphism, (ii) nine different multilocus genotypes were detected and clustered in two different clades, (iii) most of the parasite isolates pertained to one of the clade and were genetically similar to those analyzed 12 years before. This sample allowed the study of the mating system of T. cruzi in strict sympatic conditions and gave more strength to the hypothesis of the clonal structure of T. cruzi populations