Comparison of different PCR amplification targets for molecular diagnosis of Strongyloides stercoralis

Molecular techniques are an alternative for the diagnosis of strongyloidiasis, produced by Strongyloides stercoralis. However, it is necessary to determine the best amplification target for the populations of this parasite present in a geographical area and standardize a polymerase chain reaction (PCR) protocol for its detection. The objectives of this work were the comparison of different PCR targets for molecular detection of S. stercoralis and the standardization of a PCR protocol for the selected target with the best diagnostic results. DNA extraction was performed from parasite larvae by saline precipitation. Three amplification targets of the genes encoding ribosomal RNA 18S (18S rDNA) and 5.8S (5.8S rDNA) and cytochrome oxidase 1 (COX1) of S. stercoralis were compared, and the PCR reaction conditions for the best target were standardized (concentration of reagents and template DNA, hybridization temperature, and number of cycles). The analytical sensitivity and specificity of the technique were determined. DNA extraction by saline precipitation made it possible to obtain DNA of high purity and integrity. The ideal target was the 5.8S rDNA, since the 18S rDNA yielded non-reproducible results and COX1 never amplified under any condition tested. The optimal conditions for the 5.8S rDNA-PCR were: 1.5 mM MgCl2, 100 μM dNTPs, 0.4 μM primers, and 0.75 U DNA polymerase, using 35 cycles and a hybridization temperature of 60 °C. The analytical sensitivity of the PCR was 1 attogram of DNA, and the specificity was 100%. Consequently, the 5.8S rDNA was shown to be highly sensitive and specific for the detection of S. stercoralis DNA.

Hotspots and correlates of soil-transmitted helminth infections in a Venezuelan rural community: Which are the "wormy" houses?

OBJECTIVES

To determine spatial clustering and risk factors for occurrence and intensity of infection for soil-transmitted helminthiasis (STH), namely Ascaris lumbricoides, Trichuris trichiura, Strongyloides stercoralis and hookworms in a Venezuelan rural community.

METHODS

MIF-fixed faecal samples were individually collected for STH testing. The Getis-Ord statistic was used to determine significant STH clustering within 25/50/100 m radiuses around houses. Individual- and house-level factors associated with STH occurrence and intensity of infection were determined using generalized estimating equations.

RESULTS

Significant clusters of "wormy" houses for one or multiple parasites were found at distances of 25-50 m around 13 houses. Risk factors differed between occurrence and intensity of infection. Overcrowding in the house increased occurrence of S. stercoralis, T. trichiura and hookworm infections, while poor housing conditions increased A. lumbricoides infection risk. Overcrowding, poor faecal disposal system, economic dependency and lack of basic services differentially influenced the STHs. The "wormy" houses were mainly those built with waste materials, under economic dependency and lacking indoor water supply.

CONCLUSIONS

STH distribution in a community is clustered, with significant hotspots of STH occurrence and intensity of infection and different associated risk factors. Targeting the "wormy" houses is expected to affect STH morbidity more efficiently.

Diagnostic performance of parasitological, immunological and molecular tests for the diagnosis of Schistosoma mansoni infection in a community of low transmission in Venezuela

In Venezuela, areas endemic for schistosomiasis are of low transmission, with low parasite loads. Immunological tests often lack specificity and cannot differentiate past from present infections. Molecular tests are an alternative, although validation studies in endemic areas are needed. The aim of this study was to determine the performance of parasitological, immunological and molecular tests for the diagnosis of Schistosoma mansoni infection in low-transmission settings. A cross-sectional study was carried out in a rural community located in a schistosomiasis-endemic area of Venezuela to determine the prevalence and diagnostic performance of the Kato-Katz (KK) technique, Circumoval Precipitin Test (COPT), ELISA based on soluble egg antigen (ELISA-SEA) with and without treatment with sodium metaperiodate (ELISA-SEA-SMP), and PCR for amplification of the 121 bp highly repeated sequence of Schistosoma mansoni in faeces, urine and serum samples. The highest prevalence rates were obtained with ELISA-SEA (38.7%), COPT (33.3%), ELISA-SEA-SMP (31.5%), PCR on faeces (21.6%), and KK (17.1%), whereas PCR-based prevalence in urine was 6.2% and no positivity was detected in serum samples. Results showed that ELISA-SEA is the best method for the diagnosis of both current and former infections and that PCR on faeces is the best method for detecting recent transmission. The use of different tests that complement one another also allowed for a better diagnosis of Schistosoma mansoni infection, revealing a relatively high prevalence (33.8%) of schistosomiasis in a community of low transmission.

Case Report: Ocular Gnathostomiasis in Venezuela Most Likely Acquired in Texas

A 69-year-old male dentist in Caracas, Venezuela, was referred to our Cornea Clinic with a history of pain, photophobia, and blurred vision on his left eye. Routine biomicroscopic examination with a slit lamp showed a worm in the corneal stroma of his left eye. The worm was surgically removed and was identified morphologically as Gnathostoma binucleatum.

Diagnosis of intestinal parasites in a rural community of Venezuela: Advantages and disadvantages of using microscopy or RT-PCR

A cross-sectional study was carried out to determine the prevalence and diagnostic performance of microscopy and real time PCR (RT-PCR) for 14 intestinal parasites in a Venezuelan rural community with a long history of persistent intestinal parasitic infections despite the implementation of regular anthelminthic treatments. A total of 228 participants were included in this study. A multiplex RT-PCR was used for the detection of Dientamoeba fragilis, Giardia intestinalis, Cryptosporidium sp. and a monoplex RT-PCR for Entamoeba histolytica. Furthermore, a multiplex PCR was performed for detection of Ascaris lumbricoides, Strongyloides stercoralis, Necator americanus and Ancylostoma duodenale. Combined microscopy-PCR revealed prevalences of 49.3% for A. lumbricoides, 10.1% for N. americanus (no A. duodenale was detected), 2.0% for S. stercoralis, 40.4% for D. fragilis, 35.1% for G. intestinalis, and 7.9% for E. histolytica/dispar. Significant increases in prevalence at PCR vs. microscopy were found for A. lumbricoides, G. intestinalis and D. fragilis. Other parasites detected by microscopy alone were Trichuris trichiura (25.7%), Enterobius vermicularis (3.4%), Blastocystis sp. (65.8%), and the non-pathogenic Entamoeba coli (28.9%), Entamoeba hartmanni (12.3%), Endolimax nana (19.7%) and Iodamoeba bütschlii (7.5%). Age- but no gender-related differences in prevalences were found for A. lumbricoides, T. trichiura, G. intestinalis, and E. histolytica/dispar. The persistently high prevalences of intestinal helminths are probably related to the high faecal pollution as also evidenced by the high prevalences of non-pathogenic intestinal protozoans. These results highlight the importance of using sensitive diagnostic techniques in combination with microscopy to better estimate the prevalence of intestinal parasites, especially in the case of D. fragilis trophozoites, which deteriorate very rapidly and would be missed by microscopy. In addition, the differentiation between the pathogenic E. histolytica and the non-pathogenic E. dispar can be attained. However, microscopy remains an important diagnostic tool since it can detect other intestinal parasites for which no PCR is available.

Differential distribution and biochemical characteristics of hydrolases among developmental stages of Schistosoma mansoni may offer new anti-parasite targets

Schistosoma mansoni enzymes play important roles in host-parasite interactions and are potential targets for immunological and/or pharmacological attack. The aim of this study was to comparatively assess the presence of hydrolytic activities (phosphatases, glycosidases, aminopeptidases) in soluble (SF) and membrane (MF) fractions from different S. mansoni developmental stages (schistosomula 0 and 3h, juveniles, and adult worms of 28 and 45days-old, respectively), by using simple enzyme-substrate microassays. Our results show and confirm the prominent presence of alkaline phosphatase (AlP) activity in the MF of all the above parasite stages, highlighting also the relevant presence of MF-associated α-mannosidase (α-MAN) activity in juveniles. A soluble AlP activity, together with β-N-D-acetylglucosaminidase (β-NAG), and α-MAN activities, was detected in SF of schistosomulum 0h. Soluble β-NAG, α-MAN, acid phosphatase (AcP), leucin (LAP) and alanine (AAP) aminopeptidase activities were also seen in the SF of the other different developmental stages. This work shows different soluble and membrane-associated hydrolytic capacities in each S. mansoni developmental stage from schistosomula to adults that might be exploitable as potential new targets for immune and/or chemoprophylactic strategies.

Survival, induction and resuscitation of Vibrio cholerae from the viable but non-culturable state in the Southern Caribbean Sea

The causative agent of cholera, Vibrio cholerae, can enter into a viable but non-culturable (VBNC) state in response to unfavorable conditions. The aim of this study was to evaluate the in situ survival of V. cholerae in an aquatic environment of the Southern Caribbean Sea, and its induction and resuscitation from the VBNC state. V. cholerae non-O1, non-O139 was inoculated into diffusion chambers placed at the Cuare Wildlife Refuge, Venezuela, and monitored for plate, total and viable cells counts. At 119 days of exposure to the environment, the colony count was < 10 CFU/mL and a portion of the bacterial population entered the VBNC state. Additionally, the viability decreased two orders of magnitude and morphological changes occurred from rod to coccoid cells. Among the aquatic environmental variables, the salinity had negative correlation with the colony counts in the dry season. Resuscitation studies showed significant recovery of cell cultivability with spent media addition (p < 0.05). These results suggest that V. cholerae can persist in the VBNC state in this Caribbean environment and revert to a cultivable form under favorable conditions. The VBNC state might represent a critical step in cholera transmission in susceptible areas.

Household social determinants of ascariasis and trichuriasis in North Central Venezuela

Ascariasis and trichuriasis are highly prevalent parasitoses in tropical countries caused by Ascaris lumbricoides and Trichuris trichiura, respectively. Their prevalence is associated with poor sanitation and hygiene, among other biological and social factors. In this study, the associations of household social determinants with these soil-transmitted helminthiases in North Central Venezuela was assessed in the context of a National Study on Human Growth and Development (SENACREDH). This was a probabilistic, stratified, cross-sectional survey with a sample of 3388 individuals that weighted represents 4 675 433 inhabitants from the region. The prevalence of ascariasis and trichuriasis was 3.73% and 1.13%, respectively. In the univariate and multivariate analyses, these prevalences were significantly higher in those living in vulnerable houses [adjusted OR (AOR) = 1.479, 95% CI 1.428-1.532; and AOR = 10.519, 95% CI 9.971-11.097, respectively], houses located in rural areas (AOR = 2.067, 95% CI 2.035-2.101; and AOR = 1.918, 95% CI 1.868-1.970, respectively) and houses with a soil floor (AOR = 5.027, 95% CI 4.895-5.162; and AOR = 5.190, 95% CI 4.944-5.448, respectively), among other factors. People living in rural households with inappropriate building materials, insufficient basic public services such as water and waste disposal, and surrounding disease-prone environments are at higher risk of acquiring A. lumbricoides and T. trichiura infections.

Staphylococcus warneri meningitis in a patient with Strongyloides stercoralis hyperinfection and lymphoma: first report of a case

A case of meningitis due to Staphylococcus warneri in a patient with a hyperinfection with Strongyloides stercoralis possibly associated with rituximab treatment for mantel cell lymphoma is reported for the first time in the literature. The patient was a 59-year-old woman, with a 3-year history of an apparently well controlled lymphoma after treatment with chemotherapy-immunotherapy and then immunotherapy alone, and diagnosis of strongyloidiasis. Meningitis was diagnosed by cerebrospinal fluid culture and tested with an automated plate system. The patient was successfully treated with vancomycin; although fever and productive cough persisted. Severe gastrointestinal symptoms and pneumonia developed three weeks later. Hyperinfection syndrome by S. stercoralis was diagnosed, with abundant larvae in feces and expectoration.

Hyperinfection by Strongyloides stercoralis probably associated with Rituximab in a patient with mantle cell lymphoma and hyper eosinophilia

The first report to our knowledge, of hyperinfection by Strongyloides stercoralis (HS) and hypereosinophilia, associated to immune suppression by Rituximab (the only drug received for the last one year and 10 months), in a patient with mantle-cell lymphoma (MCL), is presented. The patient has a 3-year history of MCL, and developed two accesses of HS during 2008, including meningitis, pneumonia and presence of larvae of S. stercoralis in the lungs. We had a unique chance to look at cytotoxicity of filariform larvae in the expectoration after Ivermectin treatment, showing immobilization and death of larvae, associated with eosinophils attached to the cuticle of the parasite.

Giardia lamblia infection is associated with lower body mass index values

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Preliminary antigenic characterisation of an adult worm vomit preparation of Fasciola hepatica by infected human sera

Fascioliasis is an emerging/re-emerging vector-borne disease with the widest known distribution. Approximately 17 million people are infected around the world, being the Andean region the most affected area. There is an important necessity to develop sensitive and specific diagnostic tools to treat patients early and to avoid complications. In this paper we evaluated the immune response of infected humans against two antigenic preparations: the total soluble extract (FhTSE) and the adult worm vomit (FhAWV) in order to identify antigenic fractions specific for Fasciola hepatica. Both preparations were processed by SDS-PAGE and Western blot with human sera with fascioliasis (F), other parasitosis and healthy individuals. In the immunoblot of FhTSE, sera F recognised 16 bands with MW between eight and 110 kDa, from which those of 8, 9, 10, 38, 45 and 57 kDa were specific. In the preparation FhAWV, sera F recognised nine bands with MW from eight to 85 kDa, from which those of 8, 12, 15 and 24 kDa were specific. Some bands of cross-reaction were evident with sera from patients with other parasitoses, more frequent with the FhTSE. Bands within the MW mentioned, particularly that of eight kDa, have been shown to be specific by others, and deserve additional characterisation for their potential use in immunodiagnosis.

Human infection by Angiostrongylus costaricensis in Venezuela: first report of a confirmed case

A proven case of human infection caused by Angiostrongylus costaricensis is reported for the first time in Venezuela. The patient was a 57-year-old female surgically operated because of signs of peritonitis with a palpable mass at the lower right quadrant of the abdomen. WBC count reported 16,600 cells/mm³, with 46% eosinophils. The tumoral aspect of ileocolic area and peritoneal lymph nodes prompted the resection of a large area of the terminal ileum, cecum, part of the ascending colon and a small part of the jejunum, where a small lesion was found. The pathology showed thickened areas of the intestinal wall with areas of hemorrhage and a perforation of the cecum. Histology showed intense eosinophil infiltration of the whole intestinal wall, granulomas with giant cells and eosinophils. Some of the granuloma surrounded round or oval eggs with content characterized by a large empty area, cells or embryo in the center, and sometimes nematode larvae. A cross section of an adult nematode worm was observed inside a branch of mesenteric artery. The intestinal affected area, the characteristics of the lesions, the presence of eggs in the submucosa with nematode larvae inside, and the observation of a nematode inside a mesenteric artery, makes sufficient criteria for the diagnosis of an infection by Angiostrongylus costaricensis.

Preliminary characterization of an adult worm “vomit” preparation of Schistosoma mansoni and its potential use as antigen for diagnosis

Schistosoma mansoni is a parasitic trematode of the portal-mesenteric veins with a closed-end intestine. Adult worms regurgitate their intestinal content after digestion, together with constituents of the lining gut. Some of these molecules circulate in the blood and are antigenic. We obtain a "vomit" preparation and preliminary evaluate its biochemical composition and antigenic capacity. The "vomit" preparation was obtained after changes in temperature and solutions of incubation of adult worms between 4 and 37 degrees C. Supernatant was assayed for protein, carbohydrate concentration and enzymatic activities associated to the intestine and to the worm tegument. The antigenicity of the product was evaluated using Western blot (WB) analysis against sera of experimentally infected mice, before and after drug cure, sera from people infected with S. mansoni and from individuals infected with other parasitoses. More carbohydrate than protein was detected in the preparations. Cysteine proteinase (CP), N-acetyl-beta-D: -glucosaminidase and alkaline phosphatase activities were detected. The latter enzyme activity is a marker of the tegument, suggesting that in spite of careful conditions used to avoid the presence of tegumental material, manipulation of the worms always resulted in the release of tegumental molecules. Cationic exchange chromatography was useful to separate various components of this "vomit" preparation, particularly enzymes responsible for CP activity. Two highly immunogenic and specific duplets were observed in the WB analysis, 31/32- and 38/40-kDa components, the former probably referring to the intestinal CPs Sm31/Sm32. None of the two duplets disappeared after successful chemotherapy during the time of evaluation in mice or humans.

The efficacy of human schistosomicide treatment may depend on the rate of transmission

The efficacy of different treatment protocols in humans infected with Schistosoma mansoni at sites with different transmission conditions was evaluated by the disappearance of anti-worm intestine IgM antibodies in an indirect fluorescence antibody test (IgM-IFT) and anti-egg antibodies in the circumoval precipitin test (COPT). Patient sera coming from sites of active low transmission (ALT), active high transmission (AHT) and low interrupted transmission (LIT) from Venezuela were studied. Chemotherapy protocols were (1) ALT, 60 mg/kg praziquantel (Pzq60); (2) AHT, one dose of 40 mg/kg Pzq followed by one dose of 20 mg/kg oxamniquine for one group and one dose of 40 mg/kg Pzq alone for the other group; (3) LIT, one dose of 40 mg/kg Pzq repeated every 3 months up to three doses. Cure rates occurred mostly between 3 and 12 months with the exception of Pzq60-ALT where it was evident before 3 months. Higher cure rates were evident in both places of low transmission (ALT and LIT) and the lowest in the AHT regardless of the treatment protocol. Cure was more evident with COPT compared to IgM-IFT. The rate of serological cure appears then to depend on the previous state of transmission. The differential cure rate evaluated by both techniques is probably due to the persistence of antibodies against antigens in different stages of the parasite.

Human infection by Fasciola hepatica in Venezuela: report of a geriatric case

A new case of human infection due to Fasciola hepatica is reported in the Venezuelan parasitological literature. The patient is an 81-year-old female asymptomatic, with an eosinophilia of 21% and critrosedimentation rate of 26 mm/h and was found during a routine check up. These values were normal at the time of treatment (4 months later), as were several tests of hepatic function, blood chemistry and peripheral blood haematological values. The number of eggs of the parasite were between 90 and 130/g of facees. The patient was successfully treated with the human formulation of trielabendazole at 2 single doses of 10 mg/kg, each separated by 24 h. The same laboratory tests mentioned above did not show modifications, except for a slight increase in the cosinophil counts at 2 and 11 days and erythrosedimentation rate at 11 days post-treatment. Coproparasitological observations carried out at 12, 18, 60 and 120 days post-treatment were negative. No clinical symptoms were registered up to 2 months after treatment. The patient most probably acquired the infection at home through the ingestion of commercially available lettuce from an endemic area of bovine fascioliasis, very distant from home, and between 4 and 7 months previous to treatment. We stress the need to investigate F. hepatica infections which he been neglected, probably because of limited knowledge by health workers, lack of specific symptoms and absence of more sensitive diagnostic procedures.

Evolutionary relationships and biogeography of Biomphalaria (Gastropoda: Planorbidae) with implications regarding its role as host of the human bloodfluke, Schistosoma mansoni

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.

Lacto-N-fucopentaose III (Lewis x), a target of the antibody response in mice vaccinated with irradiated cercariae of Schistosoma mansoni

Carbohydrates on soluble egg antigens are major epitopes for the antibody responses of patients and mice infected with Schistosoma mansoni. Recently, protective sera of mice vaccinated with irradiated cercariae were shown to recognize carbohydrate epitopes on schistosomal glutathione S-transferase. The present study demonstrates that carbohydrate epitopes are major targets of sera from C57BL/6J and CBA/J mice vaccinated with 15- or 50-kilorad-irradiated cercariae of S. mansoni. Antibody titers to carbohydrate epitopes increased with the number of vaccinations and were considerably higher in C57BL/6J mice than in CBA/J mice. The specificity of this anticarbohydrate response was determined by measuring antibody binding to defined oligosaccharide residues known to be present on the parasite. A predominant target of the humoral anticarbohydrate response of vaccinated mice was lacto-N-fucopentaose III, a molecule relevant for cell trafficking. We observed no binding to its nonfucosylated homolog, lacto-N-neotetraose, or to oligosaccharides present on keyhole limpet hemocyanin. The strongest antibody response to lacto-N-fucopentaose III was observed for C57BL/6J and CBA/J mice repeatedly vaccinated with 15-kilorad-irradiated cercariae, which also achieve the highest levels of protection. Immunoglobulin M was the predominant antibody class binding to lacto-N-fucopentaose III. We conclude that in the irradiated-cercariae vaccine model, C57BL/6J and CBA/J mice produce anticarbohydrate antibodies against various stages of S. mansoni and that the oligosaccharide lacto-N-fucopentaose III is one target of this response. Lacto-N-fucopentaose III and its specific antibodies may profoundly affect host resistance and parasite homing.

Isotype responses to candidate vaccine antigens in protective sera obtained from mice vaccinated with irradiated cercariae of Schistosoma mansoni

In experimental schistosomiasis, sera of mice multiply vaccinated with radiation-attenuated cercariae of Schistosoma mansoni passively transfer resistance against cercarial challenge to naive mice. To further characterize these sera, we tested their protective capacities in two mouse strains (C57BL/6J and CBA/J) and compared the antigen-specific isotype compositions of the different protective sera by means of the enzyme-linked immunosorbent assay. By using an array of purified schistosomal antigens, the patterns of antibody titers and isotypes differed for each experimental group and antigen. In the most-protective C57BL/6J sera, high levels of immunoglobulin G1 (IgG1), IgG2a, and IgG2b bound to heat shock protein 70 and the integral membrane protein Sm23, whereas recognition of these antigens by less-protective CBA/J sera was lower. Glutathione S-transferase (GST) was recognized predominantly by IgM antibodies of all vaccinated groups, and a significant portion of this response was directed against carbohydrate epitopes. Antibodies specific for triosephosphate isomerase, paramyosin, and Sm32 (hemoglobinase) were present in less-protective sera and thus seem less relevant for passive transfer of resistance. The results of this study suggest a contribution of IgG antibodies specific for heat shock protein 70 and Sm23, and possibly a contribution of GST-specific IgM antibodies, to the protective effect of sera from C57BL/6J mice vaccinated with irradiated cercariae.

Compatibility of one Brazilian and two Venezuelan strains of Schistosoma mansoni with various strains of Biomphalaria glabrata

For evaluation of the degree of genetic heterogeneity in parasite and snail strains, the compatibility between Biomphalaria glabrata and Schistosoma mansoni from different geographical areas was studied. Venezuelan snails from Bárbula, Manuare (areas of schistosome transmission) and Tinaquillo (non-transmission area) and Brazilian BH snails were exposed to infection with miracidia of both the Venezuelan YT and SM strains and the Brazilian BH strain of S. mansoni. Snail-parasite compatibility was evaluated by quantifying the number of snails shedding cercariae during a period of 35 to 60 days post-infection. The best compatibility appeared to be between the Brazilian parasites and the Brazilian or Venezuelan snails. In contrast, the Brazilian snails appeared to be resistant to infection by the Venezuelan parasites tested. Paradoxically, the compatibility between the sympatric pair of Venezuelan parasites and Venezuelan snails appeared to be lower in comparison with the allopatric association of the Brazilian parasite and the Venezuelan snails. The results suggest an important degree of heterogeneity in the snail and parasite isolates studied and yield biological markers for both organisms.

Isoenzyme studies in one Brazilian and two Venezuelan strains of Schistosoma mansoni

1. Enzyme polymorphism, analyzed by starch gel electrophoresis, was found to be zero for acid phosphatase, phosphoglucomutase, phosphoglucose isomerase, glucose 6-phosphate dehydrogenase, lactate dehydrogenase, malate dehydrogenase and malic enzyme, in one Brazilian and two Venezuelan strains of Schistosoma mansoni. 2. All loci studied were monomorphic within strains, but the isoenzymic patterns were, however, different among the strains. 3. Results suggest a drastic loss of the genetic variability usually found in natural populations.

Experimental chemotherapy of Schistosoma mansoni with praziquantel and oxamniquine: differential effect of single or combined formulations of drugs on various strains and on both sexes of the parasite

The susceptibility of two Venezuelan (YT and SM) and one Brazilian (BH) strain of Schistosoma mansoni to single oral doses of praziquantel (Pz; 250 or 500 mg/kg), oxamniquine (Ox; 40, 60, or 100 mg/kg) or to low-dose combinations of both drugs (33 mg/kg Pz and 25 mg/kg Ox; 66 mg/kg Pz and 12.5 mg/kg Ox; 250 mg/kg Pz and 40 mg/kg Ox) was experimentally evaluated in mice. At lower doses of either drug, adult worms of the SM isolate were less susceptible than those of the BH and YT isolates. However, no difference in liver or intestinal egg counts (IECs) could be detected among the isolates after this treatment. At such doses, Pz was better than Ox at reducing IECs. In spite of lowered IECs, eggs continued to accumulate in the liver after Ox treatment. At higher individual doses or following treatment with low-dose combinations of both drugs, no difference in susceptibility could be detected among the parasite isolates. Under such conditions, oviposition was drastically reduced in all three isolates. We confirm that Ox preferentially kills male parasites and present for the first time evidence for the preferential killing of female worms by Pz. We propose that the synergistic effect obtained in the present study and in other investigations using low-dose combinations of both drugs may be due to the preferential cytotoxicity of each drug against a different parasite sex.

The Venezuelan experience in the control of schistosomiasis mansoni

Schistosomiasis mansoni endemic zone of Venezuela is located in the valleys of the north central mountain region, with an extension of 15,000 km2 and inhabited by 5.1 million persons. The disease was discovered in 1906, but an organized Control Program was not established until 1943. Its basic activity has been the control of the snail vector, but prevention of man-water contact, prevention of snail infection, treatment of infected people and sanitary instruction, have also been carried out. Prevalence has diminished from 14.7% (1943-60) to 0.9% (1981-84). At present few active foci still persist, but a low transmission rate and low morbidity makes it difficult to know the exact number of infected people, which has been estimulated to be about 50,000.

Ultrastructural observations on the in vitro interaction of rat neutrophils with schistosomula of Schistosoma mansoni in the presence of antibody and/or complement

Rat peritoneal neutrophils adhere to schistosomula of Schistosoma mansoni in vitro in the presence of antibody, complement, or both. Ultrastructural studies have demonstrated that cell adherence is not intimate, and that electron-dense secretions are not liberated onto the parasite surface in the manner described for eosinophils. Cytochemical techniques confirm that peroxidase is confined within intracellularly located neutrophil secretion granules. The metabolic burst is shown to operate during Fc-mediated interactions, but since morphological damage depends upon the presence of complement in the system, toxic oxygen products would seem not to be involved in the initiation of surface perturbation. Complement-dependent, neutrophil-mediated schistosomular damage is characterized by vesiculation of the tegumental outer membrane, an increase in density of the tegumental cytoplasm and the eventual development of focal lesions. The cells migrate laterally to push aside damaged surface tissues and then adhere intimately to the exposed musculature. Damage appears earlier when both antibody and complement are present in the system, and this correlates with higher killing efficiency. The frequently observed association of contaminant eosinophils with areas of parasite damage indicates that eosinophils and neutrophils may cooperate to effect schistosomular killing. In the presence of antibody alone, attached neutrophils exhibit intense phagocytic activity towards the antigen-antibody complex formed at the parasite surface. This phenomenon may account for the eventual detachment of cells and lack of significant parasite damage recorded in this system.

Neutrophil-mediated cytotoxicity to schistosomula of Schistosoma mansoni in vitro: studies on the kinetics of complement and/or antibody-dependent adherence and killing

The capacity of rat peritoneal neutrophils to adhere to and kill schistosomula of Schistosoma mansoni in vitro has been investigated. Neutrophils adhere readily to schistosomula in the presence of antibody plus complement (C) and C alone (fresh normal rat serum), but not with heat-inactivated normal rat serum. However, schitosomular killing is only achieved with neutrophils and fIRS or fNRS. In the presence of hiIRS the cells detach after 6 h without producing a significant level of parasite death. The system involving neutrophils plus fIRS is the most efficient in terms of serum dilution and the rate of schistosomular killing. The complement-dependent antibody involved in this system belongs to the class IgG and occurs in rat serum at peak titres, 6-8 wk after a primary schistosome infection. Neutrophil adherence in the presence of fNRS depends upon the generation of C3b molecules at the parasite surface via the alternative pathway of C activation. Studies on the antibody alone system indicate that the lack of significant schistosomular killing might result from the absence of factors which stimulate cell migration, since if a chemokinetic agent is introduced into the assay a 30% increase in mortality is recorded. The possible participation of neutrophils in the destruction of a primary and/or challenge infection in vivo is discussed.