Population structure and genetic diversity in the invasive freshwater snail Galba schirazensis (Lymnaeidae)

We studied the population genetic structure of the freshwater snail Galba schirazensis (Küster, 1862), a potential vector of infectious diseases such as fascioliasis. Galba schirazensis has now a worldwide distribution but a poorly known origin because this species has been distinguished only recently from the morphologically similar and cosmopolitan Galba truncatula (O.F. Müller, 1774). We developed specific microsatellite markers and sequenced a mitochondrial gene (cytochrome oxidase subunit I (CO1)) to study individuals of G. schirazensis from the Old World and the New World. We found very low genetic diversity within populations, no heterozygotes, and marked population structure — a pattern observed in other highly selfing lymnaeid species with recently enlarged distributions as a result of biological invasions. The total lack of observed heterozygosity in the few populations of G. schirazensis that displayed some allelic diversity suggests high selfing rates. We also found that the center of diversity, and by extension the origin area of this species, should be found in the New World, whereas Old World populations should rather result from a recent introduction of a genetically uniform population. The microsatellite markers developed here will help to clarify the history of expansion of G. schirazensis and might help to understand its role as a potential vector of infectious diseases.

Synthetic peptides for the immunodiagnosis of hepatitis A virus infection

VP1, VP2 and VP3 molecules of hepatitis A virus are exposed capsid proteins that have shown to be antigenic and are used for diagnosis in recombinant-antigen commercial kits. In this study, we developed a sequence analysis in order to predict diagnostic peptide epitopes, followed by their spot synthesis on functionalized cellulose paper (Pepscan). This paper with synthetic peptides was tested against a sera pool of hepatitis A patients. Two peptide sequences, that have shown an antigenic recognition, were selected for greater scale synthesis on resin. A dimeric form of one of these peptides (IMT-1996), located in the C-Terminus region of protein VP1, was antigenic with a recognition frequency of 87-100% of anti-IgG antibodies and 100% of anti-IgM antibodies employing the immunological assays MABA and ELISA. We propose peptide IMT-1996, with less than twenty residues, as a cheaper alternative for prevalence studies and diagnosis of hepatitis A infection.

Oral transmission of Chagas disease: typing of Trypanosoma cruzi from five outbreaks occurred in Venezuela shows multiclonal and common infections in patients, vectors and reservoirs

In Venezuela six episodes of oral transmission of Chagas disease (OChD) have been described, being the one reported in 2007 with a total of 103 people infected the largest worldwide. This work shows the use of three molecular markers (mini-exon gene and domains 24Sα and 18S of the ribosomal RNA) to characterize the infecting Trypanosoma cruzi strain of patients, reservoirs and vectors involved in five of the six OChD outbreaks. For this, 28 T. cruzi isolates were characterized by PCR, and the products of these reactions cloned and sequenced to reveal the existence of different TcI SL-IR genotypes. We also describe a new PCR assay able to discriminate between TcIb and TcId parasite populations. In summary, we have identified mostly parasites with the TcId haplotype and multiclonal populations with predominance of haplotype TcId (65.2%). Additionally, populations of haplotypes TcIb, TcIa and mixtures (TcId+TcIb, TcId+TcIa, TcIb+TcIa) are recurrent in samples obtained from children. The analysis of the SL-IR motif showed two clones depicting a different motif that could be an evidence for a possible hybrid haplotype between TcIa and TcIb (haplotype TcIa/Ib). Interestingly, in a single patient haplotype differences between T.cruzi isolates obtained pre and post-treatment were found. In conclusion, our findings show that in order to understand the pathogenic mechanisms involved in the orally acquired Chagas disease there is a need to join efforts to study T. cruzi haplotypes, their tissue tropisms and their susceptibility to chemoteraphy.

Distribution of Lymnaeidae (Mollusca: Pulmonata), intermediate snail hosts of Fasciola hepatica in Venezuela

An extensive malacological survey was carried out between 2005-2009 in order to clarify the exact number of lymnaeid species which may be intermediate hosts of Fasciola hepatica in Venezuela. Four species were discovered during this survey, including two local species: Lymnaea cubensis and Lymnaea cousini and two exotic species: Lymnaea truncatula and Lymnaea columella. The most common local species was L. cubensis which was found at 16 out of the 298 sampling sites. This species has a large distribution area throughout the Northern part of Venezuela and was encountered from sea level to an altitude of 1,802 m in state of Trujillo. The second local species L. cousini was collected at only two sites of the Andean Region at altitudes of 3,550 m and 4,040 m, respectively. The European L. truncatula was found at 24 sites all located in the states of Mérida and Táchira at an altitude varying between 1,540-4,000 m. The respective distribution areas of L. cubensis and L. truncatula do not appear to overlap, but more detailed malacological surveys are needed. The fourth lymnaeid species, L. columella was collected in a canal from Mérida at an altitude of 1,929 m and in an irrigation canal from the state of Guárico, at an altitude of 63 m. The role of these four lymnaeid species in the transmission of fascioliasis in Venezuela is discussed.

Detection of schistosomiasis cases in low-transmission areas based on coprologic and serologic criteria The Venezuelan experience

Low and very-low intensities of infection hinder the diagnosis of schistosomiasis. Therefore, new parameters should be established in order to more accurately identify active cases and true infection prevalence, for the adequate implementation of a control program. After the survey and analysis of the epidemiological characteristics of five Venezuelan communities, we propose three criteria for the definition of a "schistosomiasis case", based on different diagnostic methods: stool examination, ELISA-soluble egg antigen with sodium metaperiodate (SMP-ELISA), alkaline phosphatase immunoassay (APIA) and the circumoval precipitin test (COPT). Briefly, criterion I: persons with Schistosoma mansoni eggs in stools; criterion II: persons without eggs in stools, with positive COPT, without previous antischistosome chemotherapy in the last year; and criterion III: persons without eggs in stools, with negative COPT, with two positive immunoenzymatic tests (SMP-ELISA and APIA), and with no previous chemotherapy. The incorporation of serological tests to epidemiologic surveillance in areas of low-transmission tries to compensate the underestimation of prevalence based only on parasitological diagnosis.

Schistosoma: Cross-reactivity and antigenic community among different species

It is not unusual to find common molecules among different species of the genus Schistosoma. When those molecules are antigenic, they may be used in immunodiagnosis and vaccines, but they could also be applied to taxonomic and evolutionary studies. To study cross-reactivity and antigenic community among different species of schistosomes, plasmas from laboratory animals infected with Schistosoma bovis, S. guineensis, S. rodhaini, S. haematobium, and four strains of S. mansoni were evaluated with a crude extract of adult worms of S. mansoni by Western blot. Using the multiple antigen blot assay, plasmas from these infected animals were exposed to a selected group of synthetic peptides from Sm28GST, Sm28TPI, Sm elastase, Sm97, Sm32, Sm31, and Sm Cathepsin L. The results presented herein demonstrate differential cross-reactivity and antigenic community among the Mansoni and Haematobium groups of schistosomes, which is of relevance as an additional new tool for phylogenetic studies of schistosomes as well as for diagnosis and vaccine purposes.

Lymnaea cousini Jousseaume, 1887 (Gastropoda: Lymnaeidae): first record for Venezuela

Lymnaea cousini Jousseaume, 1887 was collected in Mucubaji, Merida State, Venezuela, from a permanent pond located at a very high altitude (3760 m). Identification of the collected specimens was made by comparison with the original description of the shell by Jousseaume and the description of the renal organ and reproductive system of topotypic specimens by Paraense.

Importance of including Blomia tropicalis in the routine diagnosis of Venezuelan patients with persistent allergic symptoms

BACKGROUND

Blomia tropicalis is a common mite found in the house dust of many tropical countries including Venezuela. The prevalence of skin test and specific serum immunoglobulin (Ig)E reactivity to B. tropicalis in Venezuela has not been previously evaluated.

METHODS

In the present study we evaluated the skin reactivity by skin prick test and specific IgE by a multiple antigen blot assay, against B. tropicalis and Dermatophagoides pteronyssinus, in a group of 115 subjects who attended the Allergy Clinic of the Institute of Biomedicine, Caracas, Venezuela, and we studied possible cross reactions between similar proteins of these two mites.

RESULTS

One hundred and six patients with persistent allergic respiratory symptoms showed a positive skin prick test to at least one of the mite extracts, with the frequency of positive reactions to B. tropicalis being as high as to D. pteronyssinus. Twelve patients reacted only to D. pteronyssinus and 13 different patients only to B. tropicalis. Specific IgE to each of the mite extracts was found with similar frequency, and the results coincided with the skin test reactivity.

CONCLUSIONS

The study indicated the importance of including B. tropicalis in routine diagnostic testing in tropical and sub-tropical situations.

Immunodiagnosis of parasitic diseases with synthetic peptides

Parasitic diseases remain as a major public health problem worldwide, not only based on their historically high morbidity and mortality rates, but also because risk factors associated with their transmission are increasing. Laboratory diagnosis and particularly immunodiagnosis is a basic tool for the demonstration, clinical management and control of these infections. Classically, the serological tests for the detection of antibodies or antigens are based on the use of crude and purified antigens. Synthetic peptides have opened a new field and perspectives, as the source of pure epitopes and molecules for diagnosis of malaria, Chagas' disease, leishmaniasis, schistosomiasis, hidatidosis, cysticercosis and fasciolosis based on the detection of antibodies and circulating antigens. Herein, are critically reviewed the relevant advances and applications of the synthetic peptides on immunodiagnosis of parasitic diseases. A variety of sequences, constructs (monomers, polymers, MAPs), immunological methods and samples have been used, demonstrating their diagnostic potential. However, in most parasitic infections it is necessary to use more than a single peptide in order to avoid the genetic restriction against certain epitopes, as well as to test them in well characteized groups of patients, in order to confirm their sensitivity and specificity. The concept of multidiagnosis with synthetic peptides, using a novel multi-dot blot assay is introduced. Finally, the chemical imitation of antigens, offers a tremendous posibilities in the diagnosis of parasitic infections in developing countries since this strategy is cheaper, simpler, reproducible, useful for large scale testing and in most cases, specific and sensitive.

Antigenic community between Schistosoma mansoni and Biomphalaria glabrata: on the search of candidate antigens for vaccines

We have previously confirmed the presence of common antigens between Schistosoma mansoni and its vector, Biomphalaria glabrata. Cross-reactive antigens may be important as possible candidates for vaccine and diagnosis of schistosomiasis. Sera from outbred mice immunized with a soluble Biomphalaria glabrata antigen (SBgA) of non-infected B. glabrata snails recognized molecules of SBgA itself and S. mansoni AWA by Western blot. Recognition of several molecules of the SBgA were inhibited by pre-incubation with AWA (16, 30, 36, 60 and 155 kDa). The only specific molecule of AWA, inhibited by SBgA, was a 120 kDa protein. In order to determine which epitopes of SBgA were glycoproteins, the antigen was treated with sodium metaperiodate and compared with non-treated antigen. Molecules of 140, 60 and 24 kDa in the SBgA appear to be glycoproteins. Possible protective effects of the SBgA were evaluated immunizing outbred mice in two different experiments using Freund's Adjuvant. In the first one (12 mice/group), we obtained a significant level of protection (46%) in the total worm load, with a high variability in worm recovery. In the second experiment (22 mice/group), no significant protection was observed, neither in worm load nor in egg production per female. Our results suggest that SBgA constitutes a rich source of candidate antigens for diagnosis and prophylactic studies.

Schistosomiasis mansoni in areas of low transmission: epidemiological characterization of Venezuelan foci

Severe schistosomiasis is a rare event in Venezuela nowadays, after a successful national campaign by the Schistosomiasis Control Program. Unfortunately, this program has practically disappeared, and snail surveillance in field is not a priority, anymore. Thus, schistosomiasis has become a neglected disease in this country. However, surveys in different populations from the endemic area have shown particular epidemiological features described herein. In five communities we evaluated 2,175 persons and searched for the presence of Biomphalaria glabrata snails. Some markers were used for classifying schistosomiasis foci: mean age of the persons with Schistosoma mansoni eggs in the stools, serological tests, presence of B. glabrata snails, and intensity of infection. Places without B. glabrata snails and with few schistosomiasis cases were defined as "past transmission sites"; a site with abundant snails but few cases was defined as "potential risk"; "new transmission" foci were characterized by the presence of infected snails and young people passing eggs in the stools. A "re-emergent" focus has shared these last features, showing in addition a place where schistosomiasis had been reported before. Recent evidences of active transmission with the increasing dispersion of B. glabrata snails, point out the necessity for the re-establishment of the Schistosomiasis Control Program in Venezuela.

Schistosomiasis mansoni in low transmission areas: abdominal ultrasound

In endemic areas with low prevalence and low intensity of infection, the diagnosis of hepatic pathology due to the Schistosoma mansoni infection is very difficult. In order to establish the hepatic morbidity, a double-blind study was achieved in Venezuelan endemic areas, with one group of patients with schistosomiasis and the other one of non-infected people, that were evaluated clinically and by abdominal ultrasound using the Cairo classification. Schistosomiasis diagnosis was established based on parasitologic and serological tests. The increase of the hepatic size at midclavicular and midsternal lines (in hepatometry) and the hard liver consistency were the clinical parameters able to differentiate infected persons from non infected ones, as well as the presence of left lobe hepatomegaly detected by abdominal ultrasound. The periportal thickening, especially the mild form, was frequent in all age groups in both infected and uninfected patients. There was not correlation between the intensity of infection and ultrasound under the current circumstances. Our data suggest that in Venezuela, a low endemic area of transmission of schistosomiasis, the hepatic morbidity is mild and uncommon. The Cairo classification seems to overestimate the prevalence of periportal pathology. The specificity of the method must be improved, especially for the recognition of precocious pathology. Other causes of hepatopathies must be investigated.

Laboratory diagnosis of Schistosomiasis in areas of low transmission: a review of a line of research

After 57 years of successful control of schistosomiasis in Venezuela, the prevalence and intensity of infection have declined. Approximately 80% of the individuals eliminate less than 100 eggs/g of stools, therefore morbidity is mild and the majority are asymptomatic. The sensitivity of Kato-Katz decreases to approximately 60%. Available serological methods for the detection of circulating antigens only reach a 70% of sensitivity. Tests based on the detection of antibodies by immunoenzymatic assays have been improved. The circumoval precipitine test has shown a high sensitivity (97%), specificity (100%), and correlation with oviposition, being considered the best confirmatory diagnostic test. Additionally to the classical immunoenzymatic assays, the development of the alkaline phosphatase immunoassay, allowed to reach a 100% specificity with an 89% sensitivity. Recently, we have developed a modified ELISA in which the soluble egg antigen is treated with sodium metaperiodate (SMP-ELISA) in order to eliminate the glycosilated epitopes responsible for the false positive reactions. The specificity and sensitivity reaches 97% and 99%, respectively. Synthetic peptides from the excretory-secretory enzymes, cathepsin B (Sm31) legumain (Sm32) and cathepsin D (Sm45), have been synthesized. The combination of two peptides derived from the Sm31 have been evaluated, reaching a sensitivity of 96% when analyzed independently and with a 100% specificity. Antibodies raised in rabbits against peptides derived from the Sm31 and Sm32 are currently evaluated in two different antigen-capture-based assays. The development of a simple, cheap and reliable test that correlates with parasite activity is a major goal.

Immunogenicity of synthetic peptides from the Sm31 antigen (cathepsin B) of the Schistosoma mansoni adult worms

The chemical synthesis of peptides may simplify the production of molecules for diagnosis of Schistosoma mansoni. Seventeen polymeric, 20-amino acids long, peptides comprising the entire Sm31 molecule of the adult worm, were synthesized under the t-boc strategy and their immunogenicity was evaluated. Of these, 10 peptides were immunogenic in rabbits. The peptides containing the sequence Gly74-Ser93 (peptide IMT-172) and the sequence Val154-Ala173 (peptide IMT-180) were responsible for the recognition of the Sm31 molecule by Western blot. This was confirmed by the specific inhibition of recognition of each molecule with the homologous peptide. Additionally, antibodies against these peptides strongly fixed to the adult worm gut. The present results, together with the strong immunogenicity shown for the adult worm 31 kDa antigen, establish the basis for the development of an immunodiagnostic method using synthetic peptides.

Phylogenetic identification of Sparganum proliferum as a pseudophyllidean cestode by the sequence analyses on mitochondrial COI and nuclear sdhB genes

Sparganum proliferum is a larval cestode for which the adult stage is unknown. It is characterized by the continuous branching and budding when parasitized to humans, and causes fatal human sparganosis. However, the biological features of S. proliferum, including its taxonomic status, still remain obscure. Our previous investigation suggested that S. proliferum might be phylogenetically distinct from Spirometra erinaceieuropaei, by the analysis on mitochondrial NADH dehydrogenase subunit 3 (ND3) gene. However, mitochondrial DNA sequence in Platyhelminth is known to have heteroplasmy within a species. Therefore, in the present study, we have investigated the complete nucleotide sequences of mitochondrial cytochrome c oxidase subunit I (COI) gene and the partial nucleotide sequences of nuclear coded succinate dehydrogenase iron-sulfur protein subunit gene (sdhB). The results clearly demonstrated that S. proliferum is a distinct species from S. erinaceieuropaei, and that S. proliferum belongs to the order Pseudophyllidea.

Prevalence of infection with hepatitis C virus in Venezuela, as assessed with an immuno-assay based on synthetic peptides

Information on infection with hepatitis C virus (HCV) in South America is scarce. The seroprevalences of antibodies to HCV among urban, rural and Amerindian populations from Venezuela, and the genotypes of the HCV isolates recovered, were therefore determined. A total of 2592 sera were tested with an immuno-assay which was developed in-house and based on synthetic peptides. Each reactive sample was then re-tested, using other enzyme immuno-assays and a reverse-transcription, nested PCR, and any sample confirmed positive (in any test) was considered HCV-positive. Genotypes were determined by analysis of RFLP. Overall, 39 (1.5%) of the samples were found HCV positive. The results of the immuno-assays indicated that the seroprevalence of HCV markers among the Amerindians investigated (23/1082, or 2.1%) was significantly higher than that among the other subjects (16/1510, or 1.1%; P = 0.02). No such difference was observed in the numbers of subjects confirmed positive by PCR, however (6/1082 v. 10/1510), and some of the anti-HCV reactivity observed among Amerindians may have been the result of cross-reactivity with parasitic infections. The relative low prevalence of active HCV infection (16/2582, or 0.6%) and the HCV genotypes observed (mainly genotype 1) are in agreement with the results of previous studies indicating that HCV is not autochthonous to South America. However, it is clear that the virus may now be found even in isolated Amerindian populations. The in-house, synthetic-peptide-based immuno-assay seems to be a valuable tool for epidemiological studies.

Schistosoma mansoni: immunodiagnosis is improved by sodium metaperiodate which reduces cross-reactivity due to glycosylated epitopes of soluble egg antigen

ELISA with soluble egg antigen (SEA) from Schistosoma mansoni is widely used in the diagnosis of schistosomiasis, but cross-reactivity with other intestinal helminths, overestimating the true prevalence, represents a great limitation. The role of glycoproteins of SEA in cross-reactions was investigated. SEA was oxidized with sodium metaperiodate (SMP) in ELISA and immunoblot. One hundred schistosomiasis-negative individuals sera were submitted to SMP-ELISA improving the specificity from 73% without SMP treatment to 97% with SMP. On the other hand, 94 S. mansoni-positive sera were evaluated showing that 99% were positive in ELISA either with or without SMP treatment, indicating the maintenance of high sensitivity under SMP treatment. By immunoblot, 24 sera from persons with schistosomiasis and 10 sera from schistosomiasis-free persons were assayed under reducing and nonreducing conditions with or without SMP, looking for specific infection markers and cross-reactivity markers. Reactivity from positive sera showed that specific molecules were mainly low-molecular-mass antigens and seem to have predominant proteic epitopes. The unspecific molecules reacting with some schistosomiasis-negative individuals harboring other intestinal parasites (false-positive sera) were mostly larger than 60 kDa and seemed to be basically glycosylated. Glycosylated epitopes have an important role in cross-reaction and SMP can successfully be used to reduce the false reactivity of SEA with no decrease in sensitivity, especially in ELISA as an immunodiagnostic screening surveillance method, which is useful in areas of low schistosomiasis transmission.

The last fifteen years of schistosomiasis in Venezuela: features and evolution

Control of schistosomiasis in Venezuela has been a topic of major interest and controversy among the metaxenic parasitosis. A small area of transmission of approximately 15,000 km2 was thought to be eradicated some years ago. However, some epidemiological characteristics of our transmission area have limited the success on the way toward eradication. Since 1945, when the Schistosomiasis Control Program started, the prevalence in the endemic area has decreased from 14% in 1943 to 1.4% in 1996. Until 1982, the surveillance of active cases was based on massive stool examination. Since then, the Schistosomiasis Research Group (SRG) recommended the additional use of serologic tests in the Control Program and the selective or massive chemotherapy depending on serological and parasitological prevalence of each community. At present, the real prevalence is underestimated due to the fact that approximately 80% of the individuals eliminate less than 100 eggs/g of feces. Those persons could be responsible for the maintenance of the foci going on and therefore limiting the impact of the control measures. Efforts of the SRG are being oriented toward improvement of immunodiagnostic tests by using defined antigens (enzymes) and chemically synthesized peptides, derived from relevant molecules of the parasite, either for antibodies or antigens search. On the other hand, introduction of snail competitors has been a biological weapon in the control of the intermediate host in certain areas. However, the recent reinfestation of water courses by Biomphalaria glabrata, the increased prevalence in some areas, together with important administrative changes at the Control Program of the Minister of Health, have arisen new questions and doubts, challenging the eradication strategy proposed during the last decade.

Restricted isotypic antibody reactivity to hepatitis C virus synthetic peptides in immunocompromised patients

An enzyme immunoassay based on three synthetic peptides from the core, NS4, and NS5 regions of hepatitis C virus allowed the detection of antibodies in 100% of immunocompetent infected patients and in 91% of immunocompromised patients (hemodialysis and hemophiliac patients). Immune impairment seemed to restrict the spectrum of antibody isotypes reacting to the core peptide.

The multiple antigen blot assay (MABA): a simple immunoenzymatic technique for simultaneous screening of multiple antigens

We describe a simple, reliable, reproducible and inexpensive technique termed multiple antigen blot assay (MABA) that permits the simultaneous screening of 28 different antigens based on a dot-blot ELISA methodology. Using an acrylic device (Miniblotter) containing 28 parallel troughs, multiple antigens are distributed and immobilized onto a nitrocellulose membrane. Strips are then cut perpendicularly and exposed to immune serum. The reaction is detected with secondary antibodies conjugated to horseradish peroxidase, and developed by a chemiluminescent substrate, the results being recorded on film. Positive reactions to the different antigens are seen as small black squares on each strip. We have used this qualitative technique to screen synthetic peptides derived from native schistosomal and malarial proteins, using immune rabbit sera as the detection antibody. This system can also be used in the clinical laboratory according to a dipstick-based diagnostic format for different infectious and non-infectious diseases, and can be designed to detect either antibodies or circulating antigens.

Schistosoma mansoni infection in owl monkeys (Aontus nancymai): evidence for the early elimination of adult worms

Detailed parasitologic, serologic, clinical and histopathologic studies were conducted in owl monkeys (Aotus nancymai) exposed to varying numbers of cercariae of Schistosoma mansoni. All the experimental animals had clinical symptoms suggestive of infection (weight loss diarrhoea, mucus in stools, etc.) which were not seen in uninfected individuals. The only A. vociferans included in this study passed S. mansoni eggs 8 weeks after infection. None of the A. nancymai passed eggs in their faeces. No adult worms were recovered following perfusion of the sacrificed experimental monkeys, suggesting that they were early eliminated. Serological techniques (ELISA-SEA and COPT) allowed diagnosis of infection, starting 9 weeks post challenge, in all but one A. nancymai exposed to 100 cercariae. Granulomas containing eggs were observed predominantly in liver and less extensively in intestine, suggesting that adult worms were mainly lodged in the intrahepatic portal system. We conclude that A. nancymai is susceptible to infection with S. mansoi, with the worms reaching sexual maturity, but being eliminated shortly after oviposition.

Colonization and laboratory maintenance of Anopheles albimanus Wiedemann in Venezuela

Anopheles albimanus is one of the main vectors of malaria in Central America and the Caribbean, based on its importance, there are previous reports of the successful colonization of this species in Latin America countries. Mosquitoes were collected in the Aragua State of Venezuela colonized in the laboratory, using a simple and efficient maintenance method. Based on life table calculations under well established laboratory conditions, the Survival Rate Probability was constant and always close to 1 in immature stages, the Reproductive Net Rate (Ro) was 3.83, the generation time (Tc) was 24.5 days and the Intrinsic Growth Rate (rm) was 0.0558. This is the first report of the colonization of A. albimanus in Venezuela.

Natural Schistosoma mansoni infection in wild rats from Guadeloupe: parasitological and immunological aspects

Rattus rattus is the predominant rodent in the mangrove area of Guadeloupe. Between 1990 and 1991 we found 73 R. rattus and five R. norvegicus. Among the infected rats with Schistosoma mansoni, 59% for R. rattus and 80% for R. norvegicus, the comparison of the median of the worm load was not statistically different. Both species of infected rats showed adult worms and eggs in the lungs and 20% of them showed, at the same time, two and even three generations of worms. Neither adults nor eggs were seen in the intestinal wall or stools of R. norvegicus, instead R. rattus had eggs in the liver, in the intestinal wall and the stools. Therefore, R. norvegicus gets infection as well as R. rattus, but does not participate in the transmission of the schistosomiasis. In order to elucidate this difference, we looked at the humoral recognition of these two rats, to the molecular antigens of the three stages of the parasite: cercaria, adult worm (AWA) and egg (SEA). In general, R. norvegicus recognized cercarial antigens more frequently than R. rattus, 73, 81 and 172 kDa being statistically different. Regarding AWA, molecules 82, 86, 117 and 150 kDa were recognized more often by R. rattus as compared to R. norvegicus. The reverse was true for the 18, 33 and 61 kDa. Only the differences between 61 and 150 kDa molecules were statistically significant. With respect to SEA, R. norvegicus recognized more 28, 45, 47, 49, 64 and 92 kDa molecules than R. rattus, but the latter recognized the 140 kDa molecules of SEA to a higher degree (95 and 140 kDa were significantly different). It is plausible that the immune response to cercarial invasion is more effective in R. norvegicus in allowing the parasites to reach adulthood, but it does not let them live in the mesenteric veins and therefore to lay their eggs in the intestinal wall and feces.

Evaluation of alkaline phosphatase immunoassay and comparison with other diagnostic methods in areas of low transmission of schistosomiasis

The alkaline phosphatase immunoassay (APIA) is an antibody detection technique which permits the diagnosis of schistosomiasis using a butanolic extract preparation from adult worms. APIA has demonstrated high sensitivity and specificity in previous reports with well characterized human sera. Its potential as a diagnostic tool for epidemiological surveillance was assessed in comparison with three other diagnostic tests: stool examination, ELISA with soluble egg antigen (SEA) and the circumoval precipitin test (COPT). APIA was 100% specific in an area without Schistosoma mansoni transmission and had 89% sensitivity in an endemic area where 69% of the infected subjects excreted less than 100 eggs g of faeces. It was found to be less sensitive in children under 5 years of age who were positive by the COPT test. APIA can be applied as an initial screening test, based on its high sensitivity, specificity, absence of cross-reactivity with intestinal parasites and the fact that it is a technique suitable for use in epidemiological surveillance.

Highly endemic human T-lymphotropic virus type II (HTLV-II) infection in a Venezuelan Guahibo Amerindian group

Sera from 166 Guahibo Indians (55% of the population) living in southwest Venezuela were screened by enzyme-linked immunoassay for antibodies to human T-cell lymphotropic virus (HTLV) I and II. Positive samples were confirmed by immunofluorescence and Western blot. Forty-one Guahibos (24.8%) were found to be seropositive. Polymerase chain reaction (PCR) analysis of proviral DNA in mononuclear cell lysates revealed the virus to be HTLV-II. Prevalence increased with age, and sexual contact with HTLV-II-seropositive partners was identified as a risk factor for infection. PCR amplification of a region of the pol gene, utilizing the primer pair SK110/SK111, with subsequent digestion of the 140-base-pair amplification products with HinfI and MseI restriction enzymes, showed an HTLV-II subtype-b restriction pattern in all cases. These data suggest that the substrain infecting this Guahibo community belongs to the b subtype, the most frequent among Paleo-Amerindian populations.

The immunopathology of human Schistosomiasis-III. Immunoglobulin isotype profiles and response to praziquantel

Immunoglobulin (Ig) isotype (IgG, IgG1, IgG2, IgG3, IgG4, IgM, IgD and IgE) levels were investigated, both pre- and post-treatment with praziquantel (PZQ), in 43 adults and children chronically infected with Schistosoma mansoni, by means of a two-site, isotype-specific immunoenzymometric assay. The patients were classified as responders (R) or non-responders (NR) on the basis of their circumoval precipitin test (COPT) results 12 months after treatment. In comparison with controls, pre-treatment R children showed significantly higher levels of IgG, IgG1, IgG4 (p < 0.001) and IgE (p < 0.01); and diminished IgG2 (p < 0.05), while NR children showed significantly elevated levels only of IgE (p < 0.05). Twelve months after therapy, R children maintained significantly lower levels of IgG2, but showed significantly decreased levels of IgG, IgG1, IgG4, and IgE, while the Ig isotype profile of NR children was unaltered. Adult R and NR showed similar isotype profiles before chemotherapy, with the exception of significantly elevated IgM levels in R. Twelve months after therapy, R adults showed significantly decreased levels of IgG, IgG1, and IgG4, while NR adults showed only diminished IgG4 levels. These results reveal different Ig isotype profiles in untreated adults and children chronically infected with S. mansoni. The results further show that the pre-treatment Ig isotype profile may be significantly modified after an effective R to chemotherapy, accounted for by down regulation of the IgG1 isotype in association with negative seroconversion of the COPT in R patients. The COPT reaction has been associated with the highly specific egg glycoprotein antigen omega 1, which shows a significant reduction in reactivity six months after treatment. IgG1 may thus play a main role in the response against the omega 1 antigen.

Plasmodium falciparum: surface modifications of infected erythrocytes from clinical isolates. Evidence of antigenic diversity using Venezuelan human malarial sera

Infections of human erythrocytes with the mature asexual blood stages of Plasmodium falciparum result in antigenic changes in the host cell membrane that, by virtue of their position, length of exposure, and close association with functional changes critical to pathogenesis, are a potential important target for host effector mechanisms. These parasite-induced antigens expressed on the surface of infected erythrocytes have been shown to exhibit considerable polymorphism. An antibody-mediated agglutination assay using malaria serum samples from different regions of Venezuela has been developed to examine the extent of antigenic diversity of infected red blood cells (IRBC) taken from subjects with naturally acquired P. falciparum infections. An important humoral immune recognition of surface molecules from red blood cells infected with a wide variety of clinical isolates of P. falciparum was observed even when sera from individuals experiencing a single episode of malaria were used. A process of in vivo antigenic variation of surface molecules is postulated, since agglutination of IRBC was observed with acute heterologous but not autologous sera. When sera obtained from Amerindians inhabiting the Venezuelan Amazon were assayed, a strong immune response to different parasite isolates, including those of another geographic region, was observed, suggesting the recognition of highly conserved immunogenic parasitic epitopes in people exposed to multiple malaria infections.

Do intestinal parasites interfere with the seroepidemiologic surveillance of Schistosoma mansoni infection?

In view of the known cross-reactivity of sera from patients with intestinal parasites to some Schistosoma mansoni antigens, field work was conducted in an area of Venezuela non-endemic for schistosomiasis using the routine immunoenzymatic assay (ELISA) with soluble egg antigen (SEA). False positive reactions represented 15.3% of the total population as determined by SEA-ELISA. SEA-immunoblotting of the false positive sera indicated that protein fractions of 91 and 80 kDa appear to be responsible for cross-reactivity. Sera from hookworm infected individuals produced a higher frequency and intensity of cross-reaction than other sera. SEA-fractions of 105, 54, 46, 42, 32, 25 and 15 kDa were the most specific.

Skeletal muscle ultrastructural pathology in Serinus canarius infected with Plasmodium cathemerium

Serinus canarius infected with Plasmodium cathemerium was used as an animal model in order to study the skeletal muscle compromise in malaria. Pectoral muscle biopsies were obtained from 7 infected female birds. The transmission electron microscopic study showed alterations of contractile and sarcotubular systems, mitochondrial abnormalities, lysosomal proliferation and nuclear pyknosis. The sarcolemma looked disrupted and separated from the necrotic fibres. Capillary abnormalities included endothelial degeneration with proliferation of lysosomal structures, penetration of endothelial cell by the parasites and necrosis. A mononuclear cell infiltrate formed by plasmocytes, lymphocytes and macrophages was observed. This investigation shows that skeletal muscle is an important target tissue for some malaria parasites.

Humoral immune response of children with chronic schistosomiasis. Isotype recognition of adult worm antigens

In areas of low transmission of schistosomiasis, the evaluation of the success of control depends on reliable diagnostic tests. Under such conditions, some of the serological tests better estimate the real prevalence of this parasitosis than the classical stool examinations. On the search of highly sensitive and specific antigenic fractions for use in serological tests, an immunoblot technique with a luminescent substrate was used in order to evaluate, under dissociating and reducing conditions, the Schistosoma mansoni adult worm antigen (AWA). The sera of 30 infected Venezuelan children were assayed for specific recognition of AWA by IgG, IgM, IgE, IgA, and the four IgG subclasses. Eight highly specific polypeptide molecules from the parasite of 118, 114, 105, 74, 71, 45, 36, and 30 kDa were recognized by total IgG. Additionally, IgG1 and IgG2 recognized a molecule of 100 kDa and IgM one of 77 kDa. The present data suggests that certain molecules from the adult worm, specially the 36 kDa, might be relevant in the specific immunodiagnosis of this parasitic disease. The fact that the children antibodies were able to recognize the primary structure of these antigens, will allow us to chemically synthesize the relevant linear epitopes.

Effect of chemotherapy on immune response to egg antigens of Schistosoma mansoni in chronically infected children from areas of low transmission

In an attempt to identify antigenic molecules from Schistosoma mansoni eggs, a serological study was performed on children of a Venezuelan town (Caraballeda) in which the transmission of schistosomiasis had been interrupted two years prior to sera sampling. Infected children received treatment with Praziquantel and, based on the disappearance of eggs in the stools plus negativization of the circumoval precipitin test (COPT) one year after treatment, they were classified as either responders or non-responders to chemotherapy. Western blots of soluble egg antigen (SEA) with a very sensitive chemiluminescent substrate were performed. Sera from responder children recognized a 25 kDa band of SEA which diminished significantly after treatment. This was less frequent in non-responder children. When the sera of responder and non-responder children were compared before treatment, we found that the recognition of the 40 and 41 kDa proteins could be predictive of response to chemotherapy. All these antigens, used in ELISA-type techniques, might be of importance in the evaluation and follow-up of large scale schistosome control programmes.

A population-based clinical trial with the SPf66 synthetic Plasmodium falciparum malaria vaccine in Venezuela

A phase III malaria vaccine trial in 13 villages in an endemic area, South Venezuela, compared incidence rates of Plasmodium falciparum and Plasmodium vivax infections in 1422 vaccinated and 938 nonvaccinated subjects over 18 months. The SPf66 vaccine was given in three doses, on days 0, 20, and 112. Vaccination was complete in 976 subjects (68.7%). Minor side effects requiring no treatment were reported by 123 (12.6%), with an apparent increase in frequency from the first to the third vaccine dose. No autoimmune evidence was observed in a sample of subjects. Antibodies against SPf66 were present at low titers in 24.7% of tested subjects before vaccination, increasing to 53.6% after the second dose and to 73.6% after the third dose; 26.4% of subjects initially seronegative never seroconverted. The SPf66 malaria vaccine showed a protective efficacy of 55% (95% confidence interval, 21%-75%) against P. falciparum and of 41% (19%-57%) against P. vivax malaria.

Pre- and post-treatment immunodiagnostic evaluation in human schistosomiasis mansoni

Schistosomiasis control seems to be different in countries were low parasitic burden and asymptomatic clinical patients are the features of majority of cases. Immunological methods must substitute the traditional coprologic techniques used for some decades in the Control Program. Circumoval Precipitin Test (COPT), intradermal test and ELISA with soluble egg antigen (SEA) are evaluated for using as tools for seroepidemiologic studies. COPT and ELISA were performed after treatment to known their utility when impact of chemotherapy must be assessed. One hundred sixty five persons were followed up 3, 6, 9 and 12 months after treatment. The mean sensitivity of COPT studied by age groups was 95.6% which is very important considering that 88.4% of the studied population excreted less than 100 eggs/gr of feces, while sensitivity of intradermal test was 58.2%. Children showed the highest reactivity to COPT. When treatment is effective, COPT reactivity progressively diminish until become negative one year later. In the non cure group, the COPT reactivity diminished but never below 20%. ELISA-SEA did not modify one year after treatment. Effort should be made to isolate fractions of eggs of Schistosoma mansoni whose antibodies disappear after treatment.

First description of endemic HTLV-II infection among Venezuelan Amerindians

We describe for the first time the presence of human T lymphotropic virus type II (HTLV-II) infection in Venezuela, among the Pume Amerindians living in the southern plains of the country. Antibodies to HTLV-II antigens were assessed by enzyme immunoassays (Elisa), Western blot, radioimmuno-precipitation, and immunofluorescence; titration studies against HTLV-I- and HTLV-II-infected cell lines were very useful in the differentiation of HTLV-I and HTLV-II antibodies. The HTLV-II general prevalence was 5%; however, there is a striking difference in prevalence between the truly isolated villages (0%) when compared to those living along the riverside and thus in contact with outsiders (9%). Preliminary evidence suggests sexual contact as the main source of transmission. These findings might suggest that HTLV-II in Venezuela originated through contact with outsiders rather than ancient infection related to the origins of the Pume.

Mapping of antigenic determinants of the T. cruzi hsp70 in chagasic and healthy individuals

In the present paper we describe the analysis of the immunological recognition by sera of healthy individuals and chagasic patients of the Trypanosoma cruzi heat shock 70 kDa protein. By a Falcon Assay Screening Test, using as antigen an ATP-agarose purified T. cruzi hsp70, it has been found that the sera of infected patients as well as of that of healthy individuals show reactivity against the hsp70 protein but that the reactivity of the sera of patients is in general significantly higher than that of healthy individuals. The analysis of the reactivity of the chagasic sera against a collection of peptides covering 92% of the protein has shown that more than 50% of the peptides gave a positive response but only against a few peptides did we observe high reactivity in a wide spectrum of sera. Only four peptides (numbers 9, 12, 14 and 47) were recognized by all sera tested with high reactivity values. The sera of healthy individuals also showed reactivity against a large percentage of peptides but with lower values. It was observed that particular peptides showing high reactivity against the sera of healthy donors also show high reactivity against patients' sera. However, the general pattern of reactivity against the peptides is different in chagasic and healthy sera. The immunodominant peptides map in the highly conserved as well as in the less conserved part of the hsp70 molecule. The 1/3 C-terminal, being the least conserved part of the molecule, seems to be the least immunogenic. Mapping of the epitopes led to the identification of particular immunogenic motifs within individual peptides.

Detection of antibodies to a 70 kDa Plasmodium falciparum exoantigen in malarious subjects using synthetic peptides

Indirect fluorescent antibody (IFA) tests and enzyme-linked immunosorbent assays (ELISA) were used to measure antibodies to Plasmodium falciparum in patients with acute malaria from Bolivar State, Venezuela. Antibody titers increased significantly with repeated malarial episodes. IgG antibody responses to 4 synthetic peptides (termed C2, C3, C5, C10) derived from a 70 kDa P. falciparum (Indochina I/CDC strain) exoantigen were evaluated by a peptide-ELISA with overall positivity rates of 20%, 40%, 20% and 58%, respectively. Seropositivity to peptide C10 was consistently over 50% (range 53-75%) among patients of different ages. Overall IgM reactivity to the respective peptides was 53%, 30%, 83% and 70%. IgM reactivity was generally greater in patients with primary malarial infections. The ELISA is a useful adjunct to the IFA in measuring naturally-occurring antibodies to specific parasite proteins.

Maintenance of Sparganum proliferum in vitro and in experimental animals

Successful in vitro and in vivo maintenance of Sparganum proliferum is described for the first time. Various experimental animals including hamsters, mice and a monkey were evaluated. Albino mice inoculated either subcutaneously or intraperitoneally allowed the survival and multiplication of larvae for as long as 72 weeks. Intensity of infection was proportional to the length of exposure; however, the number of larvae collected from inoculated animals varied widely when infection lasted for 6 or more months. Inoculation of single larval segments appears as effective as that of complete larvae. Although Minimal Essential Medium allowed the survival of S. proliferum for as long as 14 weeks, growth was observed only during the first 4 weeks of culturing. Despite initial in vitro growth of larvae, neither differentiation into a more developed stage nor multiplication was obtained.

Sparganum proliferum: an overview of its structure and ultrastructure

A detailed study of the structure and ultrastructure of Sparganum proliferum was made possible for the first time thanks to the successful in vitro and in vivo maintenance of this rare parasite. Although S. proliferum exhibits many of the classical tegumental and parenchymal structures previously described for other larval cestodes, these are either arranged in a distinct fashion or, in some cases, may be completely different. Among the latter and of special interest are the single or multiple parenchymal cavities, surrounded by tegument, which in some instances appear to act as a primitive digestive tract.

New approaches for the control and eradication of schistosomiasis in Venezuela

Schistosomiasis in America with the exception of Brazil, behaves as a chronic mild disease with few clinical manifestations due to low parasite burden. These features restrict the clinical and parasitological diagnosis. The most commonly used stool examination method, Kato-Katz, becomes insensitive when the majority of individuals excrete less than 100 eggs/g of feces. In view that antigen-detecting techniques have not been able to reveal light infections, the antibody detecting assays remain as a very valuable diagnostic tool for epidemiological surveillance. The Venezuelan Schistosomiasis Research Group (CECOICE) has designed a mass chemotherapy strategy based on sero-diagnosis. Since blood sampling is one of the important limiting factors for large seroepidemiological trials we developed a simple capillary technique that successfully overcame most of the limitations of blood drawing. In this sense, ELISA seems to be the most adequate test for epidemiological studies. Soluble egg Schistosoma mansoni antigen (SEA) has been largely used in Venezuela. The sensitivity of ELISA-SEA in our hands is 90%, moreover its specificity reach 92% when populations from non-endemic areas but heavily infected with other intestinal parasites are analyzed. The Schistosomiasis Control Program is currently carrying out the surveillance of endemic areas using ELISA-SEA as the first screening method, followed by the Circumoval Precipitin test for validation assay. The results with these two serological techniques allowed us to defined the criteria of chemotherapy in populations of the endemic areas. On the search of better diagnostic technique, Alkaline Phosphatase Immunoenzyme Assay (APIA) is being evaluated in field surveys.

[Comparative analysis between the circumoval precipitin test and ELISA with raw antigens for the diagnosis of schistosomiasis in Venezuela]

Schistosomiasis has special characteristics in Venezuela, since the majority of the infected population is asymptomatic and the elimination of eggs is very low, difficulting in this way parasitologic diagnosis. It is thus necessary to develop sensitive and specific immunologic methods to be applied in field surveys. The present study compares two serologic tests for Schistosomiasis, the enzyme linked immunosorbent assay (ELISA) with eggs (SEA) and adult (AWA) antigens and the traditional circumoval precipitation test (COPT). Sensitivity and specificity of the test were performed being 100% and 92% in COPT, 79% and 71% in ELISA-SEA and 71% and 91% in ELISA-AWA respectively. Advantages and disadvantages of each test are discussed.

Immunopathology of human schistosomiasis mansoni. II. NK activity and stimulation by specific antigen

Sixteen S. mansoni infected and untreated patients (5 with recent infection and 11 with chronic disease) were evaluated for their in vitro natural killer (NK) activity against the NK sensitive target K562 cell line. NK levels in 9 out of 11 patients (82%) with chronic disease were significantly lower (mean = 15 ± 6%),compared with patients recently infected (mean = 41 ± 9% p < 0.001) and with the control group (mean = 38 ± 13% p < 0.001). However, both patients and controls NK activity was stimulated by soluble adult worm antigens (SAWA), indicating that NK function even in the chronic stage of the infection is able to respond to the parasite antigens. These results suggest the possibility of NK cell participation as effector mechanism against S. mansoni.

Immunopathology of human schistosomiasis mansoni. I. Immunomodulatory influences on T cell function

Cell mediated immune response was studied in patients with recent and chronic Schistosoma mansoni infection. Precultured peripheral mononuclear cells showed significantly higher responses to S. mansoni adult worm antigen (SAWA) when compared to fresh cell preparations. The addition of each patient serum to the precultured cells reactions to SAWA or recall antigens demonstrated a strong inhibitory serum action, which was also noted on allogeneic cells derived from healthy subjects. The CD4 subset was the main responding cell to SAWA being this reactivity highly suppressed by the presence of the monocyte macrophage accessory cells. We stressed the simultaneous inhibitory action of humoral and cellular factors on the specific cell response to S. mansoni.

Seizures and praziquantel. A case report

A 27 year Old male developed seizures after receiving a single 20 mg/kg dose of praziquantel for the treatment of an intestinal Hymenolepis nana infection. On further clinical and laboratorial evaluations, he was found to suffer from an until then asymptomatic parenchymal brain cysticercosis. Praziquantel must be used with caution in those areas where cysticercosis represents a mayor public health problem. The occurrence of unexpected seizures in an individual being treated with the compound, must prompt clinicians to rule out cysticercosis of the CNS.

Hyperreactive malarial splenomegaly in Venezuela

A cross-sectional seroepidemiological survey seeking hyperreactive malarial splenomegaly was carried out in isolated Yanomami hamlets in Amazonas Territory in Venezuela. All 110 inhabitants greater than 1 year of age were evaluated clinically and 98 were studied immunologically. The spleen index for individuals greater than 10 years of age was 44%. Only 3 patients had Plasmodium spp. on thick blood smears. All had serological evidence of infection with Plasmodium falciparum and P. vivax. Twenty-three patients were considered to show hyperreactive malarial splenomegaly. Clinical manifestations of the syndrome did not differ from those described in other parts of the world.

A field study of paragonimiasis in Venezuela

In a natural focus of paragonimiasis in the northeastern region of Venezuela, 130 people were clinically, parasitologically and immunologically evaluated. A specific intradermal test was positive in 13%. Besides an index case, three other active cases of paragonimiasis were identified. Adult Paragonimus worms and metacercariae were recovered from Didelphis marsupialis and Eudaniela garmani, respectively. Previous reports of Paragonimus infection in Venezuela are discussed.

Pathological and parasitological aspects of the first autochthonous case of human paragonimiasis in Venezuela

A worm found in histopathologic sections of a lung piece of a young Venezuelan male was identified as a Paragonimus sp. Definitive identification of the species was not possible since only a deteriorated segment of the worm was recovered, nevertheless comparison with other known species is discussed. This is the first report of an indigenous case of human paragonimiasis in Venezuela.