On the diversity of mollusc intermediate hosts of Angiostrongylus costaricensis Morera & Cespedes, 1971 in southern Brazil

Veronicellid slugs are considered the most important intermediate hosts of Angiostrongylus costaricensis, an intra-arterial nematode of rodents. Studies undertaken in three localities in southern Brazil led to identification of molluscs other than veronicellid slugs as hosts of A. costaricensis: Limax maximus, Limax flavus and Bradybaena similaris. These data indicate a low host specificity of larval stages of A. costaricensis, as it has been reported to other congeneric species.

Degree of host-parasite compatibility between Schistosoma mansoni and their intermediate molluscan hosts in Brazil

The compatibility of Biomphalaria tenagophila, B. straminea and B. glabrata from Minas Gerais with different strains of Schistosoma mansoni was evaluated using the method of Frandsen (1979b) in standardized experiments. One hundred and fifty of each species of snail were individually exposed in the laboratory to 50 miracidia of S. mansoni lines LE, SJ and AL. The cercariae from the infected snails were counted and used to calculate TCP/100 indices, which were compared with those of Frandsen (1979b). For B. tenagophila the TCP/100 indices varied from 37,996 to 74,266 (class II and III). The snail was poorly compatible with LE (class II) and compatible with SJ and AL (class III). For B. straminea the indices varied from 9,484 to 20,508. The snail was not very compatible with SJ (class I) and poorly compatible with LE and AL (class II). For B. glabrata the indices varied from 588,828 to 1,039,065. The snails was extremely compatible (class VI) with the three lines of S. mansoni. These results confirm the epidemiological importance of B. glabrata in Brazil followed by B. tenagophila and B. straminea.

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.

DNA polymorphism of schistosomes and their snail hosts

Analysis of the genomes of schistosomes and one of their intermediate hosts, Biomphalaria glabrata, using Random Amplified Polymorphic DNA (RAPD) demonstrated that intraspecific genetic polymorphism in the parasite is limited but in the snail is highly pronounced. This suggests an important role for the snail in the determination of the epidemiology of the disease. In addition to their intraspecific stability, schistosome derived RAPDs exhibit a high level of interspecific polymorphism and are thus ideal for the construction of phylogenetic trees. For the detection of intraspecific polymorphisms extensive variation in the mitochondrial DNA is being exploited for the development of a PCR based test for Schistosoma mansoni. Gene level polymorphisms are being analyzed by Low Stringency Single Specific Primer PCR.

Development of a vaccine strategy against human and bovine schistosomiasis: background and update

Schistosomiasis is a chronic and debilitating parasitic disease that affects over 200 million people throughout the world and causes about 500,000 deaths annually. Two specific characteristics of schistosome infection are of primordial importance to the development of a vaccine: schistosomes do not multiply within the tissues of their definitive hosts (unlike protozoan parasites) and a partial non-sterilizing immunity can have a marked effect on the incidence of pathology and on disease transmission. Since viable eggs are the cause of disease pathology, a reduction in worm fecundity whether or not accompanied by a reduction in parasite burden is a sufficient goal for vaccine induced immunity. We originally showed that IgE antibodies played in experimental models a pivotal role for the development of protective immunity. These laboratory findings have been now confirmed in human populations. Following the molecular cloning and expression of a protein 28 kDa protein of Schistosoma mansoni and its identification as a glutathion S-transferase, immunization experiments have been undertaken in several animal species (rats, mice, baboons). Together with a significant reduction in parasite burden, vaccination with Sm28 GST was recently shown to reduce significantly parasite fecundity and egg viability leading to a decrease in liver pathology. Whereas IgE antibodies were shown to be correlated with protection against infection, IgA antibodies have been identified as one of the factors affecting egg laying and viability. In human populations, a close association was found between IgA antibody production to Sm28 GST and the decrease of egg output. The use of appropriate monoclonal antibody probes has allowed the demonstration that the inhibition of parasite fecundity following immunization was related to the inhibition of enzymatic activity of the molecule. Epitope mapping of Sm28 GST has indicated the prominent role of the N and C terminal domains. Immunization with the corresponding synthetic peptides was followed by a decrease of 70% of parasite fecundity and egg viability. As a preliminary step towards phase I human trials, vaccination experiments have been performed in cattle, a natural model for Schistosoma bovis. Vaccination of calves with the S. bovis GST has led to a reduction of ever 80% of egg output and tissue egg count. Significant levels of protection were also observed in goats after immunization with the recombinant S. bovis GST. Increasing evidence of the participation of IgA antibodies in protective immunity has prompted us toward the development of mucosal immunization. Preliminary results indicate that significant levels of protection can be achieved following oral immunization with live attenuated vectors or liposomes. These studies seem to represent a promising approach towards the future development of a vaccine strategy against one of major human parasitic diseases.

Natural hosts of Notocotylus breviserialis (Digenea, Notocotylidae) parasite of brazilian waterfowl

Notocotylus breviserialis has been collected from Anas bahamenis L. and Amazonetta brasiliensis (Gmelin), in Maricá, state of Rio de Janeiro, Brazil. It is the first time that this digenean is collected as adult in its natural hosts, and this is its first record for the neotropical region. The prevalence of N. breviserialis was 5.56% and 18.18% in A. bahamensis and in A. brasiliensis, respectively. New morphological data about the location of the vitelline glands and previtellinic space measurements are presented.

A low stringency polymerase chain reaction approach to the identification of Biomphalaria glabrata and B. tenagophila, intermediate snail hosts of Schistosoma mansoni in Brazil

The low stringency-polymerase chain reaction (LS-PCR) with a pair of specific primers for the amplification of the 18S rRNA gene was evaluated as a means of differentiating between the two Schistosoma mansoni intermediate host species in Brazil: Biomphalaria glabrata and B. tenagophila. Individual snails obtained from different states of Brazil were used and the amplification patterns obtained showed a high degree of genetic variability in these species. Nevertheless, 4 and 3 clearly defined specific diagnostic bands was observed in individuals from B. glabrata and B. tenagophila respectively. The detection of snail specific diagnostic bands suggests the possibility of reliable species differentiation at the DNA level using LS-PCR.

Abdominal Angiostrongylosis in Southern Brazil - Prevalence and Parasitic Burden in Mollusc Intermediate Hosts from Eighteen Endemic Foci

Angiostrongylus costaricensis is a parasitic nematode of rodents and molluscs are the intermediate hosts. Nocturnal collection of molluscs and search for infective third stage larvae of A. costaricensis was carried out in 18 endemic foci identified by the notification of a confirmed diagnosis in human biopsies or surgical specimens. Molluscs were digested in acidic solution and isolation of larvae eventually present was done in a Baermann funnel. Larvae identified by the presence of a delicate groove in the tail were counted to assess the individual parasitic burden. Four species were found infected, with ranges of prevalence in parenthesis: Phyllocaulis variegatus (7% to 33.3%); Bradybaena similaris (11.7% to 24.1%); Belocaulus angustipes (8.3% ) and Phyllocaulis soleiformis (3.3% to 14.2%). Parasitic burden varied from 1 to 75 with P. variegatus, 1 to 98 with B. similaris, 1 to 13 with B. angustipes and 1 larvae in each of two specimens of P. soleiformis. P. variegatus was present in all sites and was found infected with the highest prevalence figures and the highest individual parasitic burdens. These data stress the importance of veronicellid slugs as intermediate hosts for A. costaricensis in the endemic areas in Rio Grande do Sul, Brazil

Zinc Sulphate in the Treatment of Cutaneous Leishmaniasis: an in Vitro and Animal Study

This study was designed to evaluate the effectiveness of zinc sulphate both in vitro and in an animal model against both strains of old world cutaneous leishmaniasis. The in vitro sensitivities of promastigotes and axenic amastigotes of both Leishmania major and L. tropica to zinc sulphate was determined, the LD50 calculated and compared to the standard treatment for cutaneous leishmaniasis pentavalent antimony compounds. The results show that the two forms of both strains were sensitive to zinc sulphate and their respective LD50 were lower compared to the pentavalent antimony compound. Furthermore the sensitivities of the forms of both strains were tested using a simple slide method and compared to results of the standard method. To confirm this result, zinc sulphate was administered orally to mice infected with cutaneous leishmaniasis both therapeutically and prophylactically. Results showed that oral zinc sulphate was effective in both treatment and prophylaxis for cutaneous leishmaniasis. These results encourage the use of oral zinc sulphate in the treatment of cutaneous leishmaniasis clinically.

Genetic variability and identification of the intermediate snail hosts of Schistosoma mansoni

Studies based on shell or reproductive organ morphology and genetic considerations suggest extensive intraspecific variation in Biomphalaria snails. The high variability at the morphological and genetic levels, as well as the small size of some specimens and similarities between species complicate the correct identification of these snails. Here we review our work using methods based on polymerase chain reaction (PCR) amplification for analysis of genetic variation and identification of Biomphalaria snails from Brazil, Argentina, Uruguay and Paraguay. Arbitrarily primed-PCR revealed that the genome of B. glabrata exihibits a remarkable degree of intraespecific polymorphism. Low stringency-PCR using primers for 18S rRNA permited the identification of B. glabrata, B. tenagophila and B. occidentalis. The study of individuals obtained from geographically distinct populations exhibits significant intraspecific DNA polymorphism, however specimens from the same species, exhibit some species specific LSPs. We also showed that PCR-restriction fragment of length polymorphism of the internal transcribed spacer region of Biomphalaria rDNA, using DdeI permits the differentiation of the three intermediate hosts of Schistosoma mansoni. The molecular biological techniques used in our studies are very useful for the generation of new knowledge concerning the systematics and population genetics of Biomphalaria snails.

Molecular characterisation of intermediate snail hosts and the search for resistance genes

The relationship between schistosomes and their intermediate hosts is an extremely intricate one with strains and species of the parasite depending on particular species of snail, which in turn may vary in their susceptibility to the parasites. In order to gain a better understanding of the epidemiology of the disease we have been investigating the use of molecular markers for snail identification and for studying host-parasite relationships. In this paper we will draw on examples concerning schistosomiasis in West and East Africa to illustrate how a molecular analysis can be used as part of a "total evidence" approach to characterisation of Bulinus species and provide insights into parasite transmission. Particular emphasis is given to ribosomal RNA genes (rRNA), random amplified polymorphic DNA (RAPDs) and the mitochondrial gene cytochrome oxidase I (COI). Snails resistant to infection occur naturally and there is a genetic basis for this resistance. In Biomphalaria glabrata resistance to Schistosoma mansoni is known to be a polygenic trait and we have initiated a preliminary search for snail genomic regions linked to, or involved in, resistance by using a RAPD based approach in conjunction with progeny pooling methods. We are currently characterising a variety of STSs (sequence tagged sites) associated with resistance. These can be used for local linkage and interval mapping to define genomic regions associated with the resistance trait. The development of such markers into simple dot-blot or specific PCR-based assays may have a direct and practical application for the identification of resistant snails in natural populations.

The Office International des Epizooties ad hoc Group on Non Tsetse Animal Trypanosomoses: Its Origin, Scope and Perspectives

A summary of the goals and activities of the ad hoc group on Non Tsetse Transmitted Animal Trypanosomosis belonging to the Office International des Epizooties is presented.

Review on the Molecular Tools for the Understanding of the Epidemiology of Animal Trypanosomosis in West Africa

The epidemiology of animal trypanosomosis around Bobo-Dioulasso (Burkina Faso, West Africa) benefited a lot in the last years from the progress of molecular tools. The two most used molecular techniques were the polymerase chain reaction for the diagnosis of the disease in cattle and the characterization of the trypanosomes in the host and the vector on one hand, and the microsatellite DNA polymorphism in tsetse flies to study the intraspecific genetic variability of the vector on the other hand. The results obtained in the Sideradougou area during a recent two year survey with these techniques, associated with many other georeferenced informations concerning vector and cattle distribution, natural environment, landuse, ground occupation, livestock management, were combined in a Geographical Information System. This new approach of a complex pathogenic system led to a better evaluation of the risk of trypanosome transmission.