The molecular epidemiology and phylogeography of Trypanosoma cruzi and parallel research on Leishmania: looking back and to the future.

Trypanosoma cruzi is the protozoan agent of Chagas disease, and the most important parasitic disease in Latin America. Protozoa of the genus Leishmania are global agents of visceral and cutaneous leishmaniasis, fatal and disfiguring diseases. In the 1970s multilocus enzyme electrophoresis demonstrated that T. cruzi is a heterogeneous complex. Six zymodemes were described, corresponding with currently recognized lineages, TcI and TcIIa-e--now defined by multiple genetic markers. Molecular epidemiology has substantially resolved the phylogeography and ecological niches of the T. cruzi lineages. Genetic hybridization has fundamentally influenced T. cruzi evolution and epidemiology of Chagas disease. Genetic exchange of T. cruzi in vitro involves fusion of diploids and genome erosion, producing aneuploid hybrids. Transgenic fluorescent clones are new tools to elucidate molecular genetics and phenotypic variation. We speculate that pericardial sequestration plays a role in pathogenesis. Multilocus sequence typing, microsatellites and, ultimately, comparative genomics are improving understanding of T. cruzi population genetics. Similarly, in Leishmania, genetic groups have been defined, including epidemiologically important hybrids; genetic exchange can occur in the sand fly vector. We describe the profound impact of this parallel research on genetic diversity of T. cruzi and Leishmania, in the context of epidemiology, taxonomy and disease control.

A new consensus for Trypanosoma cruzi intraspecific nomenclature: second revision meeting recommends TcI to TcVI.

In an effort to unify the nomenclature of Trypanosoma cruzi, the causative agent of Chagas disease, an updated system was agreed upon at the Second Satellite Meeting. A consensus was reached that T. cruzi strains should be referred to by six discrete typing units (T. cruzi I-VI). The goal of a unified nomenclature is to improve communication within the scientific community involved in T. cruzi research. The justification and implications will be presented in a subsequent detailed report.

Infection rates and genotypes of Trypanosoma rangeli and T. cruzi infecting free-ranging Saguinus bicolor (Callitrichidae), a critically endangered primate of the Amazon Rainforest.

Parasites of wild primates are important for conservation biology and human health due to their high potential to infect humans. In the Amazon region, non-human primates are commonly infected by Trypanosoma cruzi and T. rangeli, which are also infective to man and several mammals. This is the first survey of trypanosomiasis in a critically endangered species of tamarin, Saguinus bicolor (Callitrichidae), from the Brazilian Amazon Rainforest. Of the 96 free-ranging specimens of S. bicolor examined 45 (46.8%) yielded blood smears positive for trypanosomes. T. rangeli was detected in blood smears of 38 monkeys (39.6%) whereas T. cruzi was never detected. Seven animals (7.3%) presented trypanosomes of the subgenus Megatrypanum. Hemocultures detected 84 positive tamarins (87.5%). Seventy-two of 84 (85.7%) were morphologically diagnosed as T. rangeli and 3 (3.1%) as T. cruzi. Nine tamarins (9.4%) yielded mixed cultures of these two species, which after successive passages generated six cultures exclusively of T. cruzi and two of T. rangeli, with only one culture remaining mixed. Of the 72 cultures positive for T. rangeli, 62 remained as established cultures and were genotyped: 8 were assigned to phylogenetic lineage A (12.9%) and 54 to lineage B (87.1%). Ten established cultures of T. cruzi were genotyped as TCI lineage (100%). Transmission of both trypanosome species, their potential risk to this endangered species and the role of wild primates as reservoirs for trypanosomes infective to humans are discussed.

Old and Novel Functions of Caspase-2.

Although caspase-2 is a highly conserved protease that has received a lot of research attention, consensus about its roles and the molecular mechanisms that underpin them has been elusive. Recent improvements to our understanding of the activities of caspase-2 have been facilitated by the development and refinement of techniques allowing identification of cellular processes instigated by this caspase. Following DNA damage, caspase-2 can be activated in a molecular complex called the "PIDDosome"; however, other stimuli provoke caspase-2-dependent activities that do not appear to involve this complex. Further research is needed into the mechanisms that activate caspase-2, and the substrates that it cleaves to accomplish its functions. Apart from DNA damage, caspase-2 has also been implicated in responses to other cellular stresses including oxidative damage, endoplasmic reticulum stress, and aberrant mitotic signaling. Caspase-2 sensitized animals fed diets high in fat and sugar to glucose intolerance and liver disease, so drugs that target this protease may be useful to prevent or treat metabolic conditions. Caspase-2 loss enhanced the survival of retinal ganglion cells following optic nerve damage, prompting hope that caspase-2 inhibitors may help treat optic nerve injuries. Caspase-2 predisposed animals to neuroblastoma but tended to provide protection against oncogene-driven cancers. Intriguingly, caspase-2 facilitated host cell death following viral or bacterial infection, raising the possibility that its evolutionary retention may reflect its ability to induce defensive apoptosis following intracellular infection.

A biochemical comparison of glucosephosphate isomerase isozymes from Trypanosoma cruzi.

The glucosephosphate isomerase (D-glucose-6-phosphate Ketol-isomerase, EC 5.3.1.9) isozymes of Trypanosoma cruzi were characterized with respect to their native and subunit molecular size, isoelectric point and in vitro thermostability. The molecular weight data are consistent with a dimeric enzyme structure. The apparent native and subunit size homogeneity and differences in pI values imply that the electrophoretic mobility differences of isozymes in native gels are determined by their molecular charge. Minor differences in peptide maps indicate the existence of some heterogeneity in the primary structure of the isozymes. The stability of triple-banded glucosephosphate isomerase electrophoretic profiles was confirmed, supporting the view that these phenotypes represent non-interconvertible enzyme species.

First detection of Leishmania major in peridomestic Phlebotomus papatasi from Isfahan province, Iran: comparison of nested PCR of nuclear ITS ribosomal DNA and semi-nested PCR of minicircle kinetoplast DNA.

Two PCR methods were compared for their sensitivity in detecting cultured Leishmania major, before being used to estimate infection rates in female sandflies (Phlebotomus papatasi) collected from peridomestic animal shelters and the nearby burrows of the gerbil reservoir hosts, Rhombomys opimus, in Isfahan province, central Iran. A semi-nested PCR was used to amplify a fragment of minicircle kinetoplast (k) DNA with a length and sequence diagnostic for L. major, and a nested PCR was developed to amplify a fragment containing the internal transcribed spacers of the ribosomal RNA genes (ITS-rDNA) with a sequence diagnostic for L. major. The semi-nested PCR was less sensitive than the nested PCR when using DNA extracted from cultured promastigotes of L. major, but it was more sensitive for detecting L. major in wild-caught sandflies. At the edges of two Isfahan villages, infection rates were significantly higher in P.papatasi collected outside gerbil burrows (14/28) compared with those from peridomestic animal shelters (2/21). This is the first record of L. major detected in P.papatasi from peridomestic sites in Isfahan province.

Chromosome size polymorphisms of Leishmania donovani.

A minimum of 22 chromosomes were found in all Leishmania donovani stocks examined by orthogonal field alternation gel electrophoresis (OFAGE). Chromosome sizes ranged from approximately 270 to 4000 kb. Certain chromosomes were polymorphic in size between stocks and chromosomes present in some stocks had no apparent equivalent in others. Specific polymorphisms were useful in distinguishing the subspecies L. d. donovani, L. d. infantum and L. d. chagasi and African L. donovani stocks but there were karotypic differences within these taxa. Radiolabelled DNA derived from whole chromosomes was hybridised to OFAGE Southern blots. Chromosome 1 of L. d. donovani was homologous to two larger chromosomes in all stocks. Chromosome 2 of certain L. d. chagasi and L. d. infantum stocks was homologous to both chromosomes 2 and 3 of L. d. donovani: this suggested that translocation between chromosomes may have contributed to the size polymorphisms. The smallest chromosome seen (270 kb) was unique to the African stock HU3. It was not homologous to small chromosomes in L. d. donovani, L. d. infantum or L. d. chagasi. The small chromosome did hybridise to two small chromosomes in another African stock, Khartoum, and to a large chromosome present in all stocks. The beta-tubulin gene was mapped to chromosomes 21/22, 13 and 7 with strongest hybridisation to 21/22. alpha-Tubulin was mapped to chromosomes 9. The alpha- and beta-tubulin arrangement was highly conserved.

Temperature modulation of growth rates and glucosephosphate isomerase isozyme activity in Trypanosoma cruzi.

In an attempt to understand the conditions which might influence the geographical distribution of Trypanosoma cruzi isozyme profiles (zymodemes), the thermal response of different glucosephosphate isomerase (GPI) phenotypes was studied. T. cruzi clones with single- and triple-banded GPI phenotype showed a similar response to temperature with respect to both growth rates and GPI kinetic parameters. However, the relative activity of each GPI isozyme was dependent on parasite incubation temperature. In view of the similar kinetic properties of the isozymes, enzyme regulation is not a consequence of an adaptative response to thermal conditions and the suggestion of a phenotype distribution determined selectively by temperature is not supported by the present study.

Molecular size of enzymes in Trypanosoma cruzi considered in relationship to the genetic interpretation of isozyme patterns.

The molecular size of seven Trypanosoma cruzi enzymes, chosen because of their frequent use in studying trypanosome populations, has been found to be similar to that of their mammalian equivalents. Malic enzyme (NADP-dependent malate dehydrogenase, decarboxylating, EC 1.1.1.40) from T. cruzi has an apparent molecular size of only half that of the mammalian enzyme. The probable subunit structure of these T. cruzi enzymes has been deduced from the molecular weights by comparison with mammalian data. The results are compatible with recent interpretations of isozyme data implying the existence of genetic diploidy in trypanosomes.

Specific serodiagnosis of visceral leishmaniasis using a Leishmania donovani antigen identified by expression cloning.

A lambda gt11 expression library was constructed using mRNA from the promastigote form of Leishmania donovani (African isolate MHOM/ET/67/HU3). The library was screened with serum obtained from a patient who contracted visceral leishmaniasis in the Sudan. Several cDNA clones which expressed beta-galactosidase/L. donovani antigen fusion proteins were isolated. One of these clones corresponded to a 60 kDa membrane-associated antigen. By a Western blot assay antibodies against the fusion protein were detected universally in the sera of visceral leishmaniasis patients. They were not detected in sera from patients with cutaneous leishmaniasis or other parasitic protozoan infections. The gene coding for this antigen was specific to the genus Leishmania as judged by DNA hybridisation, and its chromosomal location was conserved. A 20 kb mRNA was detected on Northern blots of promastigote RNA.

Characterisation of a Cryptosporidium parvum-specific cDNA clone and detection of parasite DNA in mucosal scrapings of infected mice.

A cDNA library was constructed using total RNA extracted from oocysts and sporozoites of the protozoan parasite Cryptosporidium parvum. The expression library was screened with an anti-C. parvum antiserum and a clone, Cp3.4, with a 2043 bp insert, was extracted. Southern blot analysis demonstrated a single copy gene that was located on a 1.6 Mb chromosome. The gene was found to be C. parvum specific as Cp3.4 did not cross-hybridise with chromosomal DNA from three other apicomplexan parasites. The cDNA encodes a polypeptide with a predicted membrane helix at its C-terminal end which is flanked by stretches of acidic amino acids. Overall, the polypeptide has a low isoelectric point (pI) of 3.94. A total of 21 glycine/proline-rich octapeptides were identified which represented variations of a consensus sequence. The function of this protein is yet unknown. Using Cp3.4-specific PCR primers, this C. parvum gene could be amplified from as little as 0.8 pg of purified parasite DNA in a single polymerase chain reaction. Less than 0.1 ng of DNA from the ileum mucosa of immunosuppressed adult mice that had been infected with C. parvum oocysts was required to detect the parasites. In non-immunosuppressed mice that were infected and which did not shed oocysts in numbers detectable by acid-fast staining, parasite development could be detected in 25 ng of total mucosa DNA. This PCR approach may be a valuable technique for the detection of parasite infections in situations where conventional staining methods fail, such as chronic, low-grade infections or the detection of parasites in potential reservoir hosts.

The structure, organization, and expression of the Leishmania donovani gene encoding trypanothione reductase.

Trypanothione reductase (TR) is an NADPH-dependent flavoprotein oxidoreductase central to thiol metabolism in the trypanosomatids. We report here the cloning by expression of the Leishmania donovani gene. It is single copy, expresses a 2.6-kb transcript and a 52-kDa protein and is located on a 1.1-Mbp chromosome. The 491 amino acid sequence has 76% similarity to Crithidia fasciculata and 67% similarity to Trypanosoma cruzi, Trypanosoma congolense and Trypanosoma brucei TR. Residues recognising the adenosine pyrophosphate moiety of NADPH and FAD, and residues in the catalytic site segment (A47-A67) involving electron transfer from TR to trypanothione disulphide (T(S)2) were completely conserved. Thus inhibitors of TR are likely to be active against the enzyme from all the parasitic trypanosomatids. Two peptide inserts (39-47, 131-140) seen in other TR genes and a C-terminal extension of 19 residues were also present. When the gene was introduced back into L. donovani at high copy number using the pTEX expression vector, we detected elevated expression of TR RNA and a 14-fold increase in TR activity. Transfection and overexpression of the TR gene will facilitate studies of gene function and of the dependence of trypanosomatids on TR for protection against oxidative stress.

A sensitive repetitive DNA probe that is specific to the Leishmania donovani complex and its use as an epidemiological and diagnostic reagent.

Leishmania donovani (HU3 strain) metacyclic promastigotes generated in vitro were used to construct a cDNA library in the bacteriophage vector lambda gt10. A cDNA clone (Lmet 2), was isolated by differential screening with metacyclic-derived or log-phase promastigote-derived cDNA. The clone insert was comprised predominantly of four copies of an imperfect 60-bp repeat motif, which was represented in the genome by multiple tandem repeats distributed among at least six chromosomes. The corresponding mRNA transcript was a developmentally regulated 12-kb doublet. The Lmet 2 sequence was entirely specific to L. donovani donovani, L. donovani (East Africa), L. donovani infantum and L. donovani chagasi, even when genomic Southern blots and slot blots of other Leishmania species were washed at low stringencies. Twenty-two strains of L. donovani were clearly detected by radiolabelled Lmet 2 cDNA probe, with signals of approximately equal intensity, irrespective of geographical origin, which encompassed widely dispersed endemic regions. The probe could detect DNA from fewer than 100 organisms and identified small numbers of promastigotes in infected sand flies. Amastigotes were also detected in impression smears of organs from infected hamsters. The Lmet 2 probe is likely to be a valuable reagent for clinical diagnosis and epidemiological investigations.

Activated factor IX complex in treatment of surgical cases of hemophilia A with inhibitors.

Three patients with severe hemophilia A with inhibitors to factor VIII were treated with activated factor IX complex. Bleeding was controlled adequately during surgical procedures involving each of the three. Partial thromboplastin times showed a variable shortening and prothrombin times were significantly shortened to values less than normal. Hemostasis was substantiated by the use of epsilon aminocaproic acid. Neither anamnestic responses nor thrombotic complications were observed. A transient hypertension developed in two patients shortly after infusion with the activated factor IX complex.

Use of polymerase chain reaction-based single strand conformational polymorphism and denaturing gradient gel electrophoresis methods for detection of sequence variation of ribosomal DNA of Trypanosoma cruzi.

Polymerase chain reaction (PCR) was used to amplify the V1 region of the small sub-unit (18S) ribosomal DNA gene from representative strains of Trypanosoma cruzi. In order to screen for sequence variation, amplification products were subsequently analysed by single strand conformational polymorphism (SSCP) and denaturing gradient gel electrophoresis (DGGE) techniques. SSCP could not detect sequence variation within T. cruzi, although electrophoretic profiles were clearly distinct from both Leishmania donovani and Leishmania braziliensis. DGGE could differentiate strains of T. cruzi and it appears that there are at least 2 18S V1 sequences of this multi-gene family within each strain examined, contrasting with Leishmania spp. where only 1 was identified. This is the first application of PCR-linked SSCP and DGGE analysis for differentiating parasitic protozoa.

Nuclear rDNA ITS-2 sequences reveal polyphyly of Panstrongylus species (Hemiptera: Reduviidae: Triatominae), vectors of Trypanosoma cruzi.

Panstrongylus species are widely distributed throughout the Americas, where they act as vectors of Trypanosoma cruzi, agent of Chagas disease. Their intraspecific relationships, taxonomic position and phylogeny in relation to other Triatomini were explored using ribosomal DNA (rDNA) internal transcribed spacer 2 (ITS-2) sequence polymorphisms and maximum parsimony, distance and maximum likelihood analyses of 10 populations representing six species of the genus (P. megistus, P. geniculatus, P. rufotuberculatus, P. lignarius, P. herreri and P. chinai). At the subspecific level, P. megistus appeared more homogeneous than P. rufotuberculatus and P. geniculatus (both with broader distribution). Several dinucleotide microsatellites were detected in the sequences of given species. Many of these microsatellites (GC, TA, GT and AT) showed different number of repeats in different populations and thus, may be very useful for population differentiation and dynamics analyses in future studies. The sequences of P. lignarius (considered sylvatic) and P. herreri (a major disease vector in Peru) were identical, suggesting that these species should be synonymised. Intrageneric analysis showed a clear separation of P. rufotuberculatus, with closest relationships between P. geniculatus and P. chinai, and P. megistus occupying a separate branch. Genetic distances between Panstrongylus species (0.11585-0.22131) were higher than those between Panstrongylus and other Triatomini (16 species from central and North America and South America) (0.08617-0.11039). The distance between P. megistus and P. lignarius/herreri (0.22131) was the largest so far recorded in the tribe. The pronounced differences in length and nucleotide composition suggest a relatively old divergence of Panstrongylus species. P. rufotuberculatus was closer to Mesoamerican Triatoma, Meccus and Dipetalogaster species than to other Panstrongylus. All Panstrongylus clustered with the Mesoamerican clade; P. rufotuberculatus clustered with the phyllosoma complex and T. dimidiata, with D. maxima and T. barberi in a basal position. The rest of Panstrongylus appeared paraphyletically in the tree. This is evidence suggesting polyphyly within the genus Panstrongylus, whose species may be related to the ancestors giving rise to central and North American Triatomini.

Identification of the C-terminal region of 70 kDa heat shock protein from Leishmania (Viannia) braziliensis as a target for the humoral immune response.

A Leishmania (Viannia) braziliensis (Lb) promastigote cDNA library in lambda gt11 was screened with patients' sera with the aim of identifying antigens specifically related to mucocutaneous leishmaniasis (MCL). One of the clones isolated, 133P, consistently reacted with MCL sera; it was sequenced and found to encode the C-terminal three-quarters of a protein belonging to the highly conserved Hsp70 family. Since Hsp70 proteins from different species tend to be less conserved through the C-terminal end, it was predicted that this region would be more antigenic and was likely to bear the discriminatory epitopes. In order to test this hypothesis, the N- and C-terminal halves of the polypeptide encoded by 133P, 133P-N and 133P-C, respectively, were expressed in Escherichia coli. Immunoblotting analysis demonstrated that 133P-C reacted more strongly with a pool of MCL sera than 133P-N, and both recombinant proteins reacted faintly with pools of cutaneous (CL) and visceral (VL) leishmaniasis sera. These results confirmed the predicted epitope location in the C-terminal region. The 133P-C fragment was also expressed as a fusion protein with glutathione-S-transferase (GST-133P-C), affinity-purified with glutathione-agarose and tested by ELISA with individual sera. From 46 Lb-infected patients, 41 sera (89%) were positive, no cross-reactivity was observed with healthy, Trypanosoma cruzior L. amazonensis-infected individuals. Despite a relatively high cross-reactivity with VL sera, the enhanced humoral response of MCL as compared with CL patients might be interesting for studies on disease aggravation.

Functional status in depressed patients: the relationship to disease severity and disease resolution.

BACKGROUND: We set out to measure the impact of depression and its clinical resolution on patients' functional status. METHOD: The Work and Social Disability Scale (WSDS), a five-category investigator-rated scale measuring patient functional status, was completed at baseline and study discontinuation in a 56-day, open, uncontrolled study evaluating the safety of a sustained release (SR) formulation of bupropion in 3167 patients at 105 sites. To be included in the study, patients had to be 18 years or older, have a diagnosis of depression, and be considered appropriate for treatment with bupropion SR. The proportion of patients in each WSDS category, for those patients taking more than 7 days of bupropion SR (N = 2915), was assessed at screen and study discontinuation. The percentage of patients with improved WSDS scores at 56 days was also measured for all patients and correlated with patient and treatment characteristics. RESULTS: Of the patients entering the trial, 61.8% were markedly or severely impaired in their work or social activities, and only 5.4% were mildly or not impaired. At study discontinuation, more than 54% of patients were judged by the investigator to have very much or much improvement in their clinical symptoms. Results on the WSDS correlated with the clinical improvements; only 22.3% were markedly or severely impaired; and 50.0% were mildly or not impaired at study discontinuation. In addition, 63.9% of patients had less work or social disability at the end of the trial than at study entry. Functional status improved more in patients who had not previously been treated for the episode, had more severe depression at study entry, and had a higher dose and duration of treatment with bupropion SR. CONCLUSION: The results show that depression results in significant impairment in patients' functional status. Functional status improved in patients treated with bupropion SR for up to 56 days. This improvement was highly correlated with improvement in clinical symptoms and was related to patient characteristics at study entry as well as to treatment patterns during the study.

Value of microscopy in the diagnosis of dysentery associated with invasive Entamoeba histolytica.

AIMS: To assess the reliability of the detection of erythrophagocytic amoebic trophozoites in stool samples in the diagnosis of dysentery associated with invasive Entamoeba histolytica. METHODS: Amoebic culture was carried out on single stool samples collected from patients from Mexico, Colombia, and Bangladesh. The stools had been examined by light microscopy. Amoebic dysentery was diagnosed when erythrophagocytic E histolytica trophozoites were observed in a case of bloody diarrhoea. E histolytica isolates were characterised by isoenzyme electrophoresis and results correlated with microscopical findings in stools. Statistical analysis was performed using the chi 2 test. RESULTS: Where erythrophagocytic amoebae had been observed in dysenteric stool specimens the E histolytica phenotype was invariably invasive (p < 0.0001). Observation of erythrophagocytic amoebae in dysentery is 100% specific and predictive of infection with invasive E histolytica. When amoebic culture-positive cases only are considered it is 96% sensitive. In this study E histolytica of zymodeme XIV was more commonly associated with amoebic dysentery than zymodeme II. There was no significant difference between the carriage rate of invasive and non-invasive E histolytica in non-dysenteric diarrhoea. Asymptomatic subjects carried non-invasive E histolytica more frequently than invasive E histolytica. Patients with non-amoebic dysentery, when shown to be infected with E histolytica, carried non-invasive strains (12%). CONCLUSIONS: Sensitivity and specificity of microscopical examination of a single stool specimen for diagnosing amoebic dysentery is very high; intestinal carriage of invasive E histolytica detected by culture is not necessarily an indication of active disease as patients with diarrhoea and asymptomatic subjects shed invasive and non-invasive E histolytica. There are possibly two subpopulations of invasive E histolytica with different pathogenic potential which can be differentiated by zymodeme analysis.

A simple method of tracking mammals and locating triatomine vectors of Trypanosoma cruzi in Amazonian forest.

A simple method of tracking mammals from capture points to their refuges was developed to study Trypanosoma cruzi reservoir-vector associations in Belém forest. A device containing a spool of fine line was carried by released mammals so that the line unwound under minimum tension as the animal proceeded and could be followed the day after release. Twenty-three triatomine bugs of five species were found with 3 of 15 mammals retrieved.