BACKGROUND Trypanosoma cruzi is a protozoan parasite and an etiological agent of Chagas disease. There is a wide variability in the clinical outcome of its infection, ranging from asymptomatic individuals to those with chronic fatal mega syndromes. Both parasite and host factors, as well as their interplay, are thought to be involved in the process. OBJECTIVES To evaluate the resistance to complement-mediated killing in two T. cruzi TcI strains with differential virulence and the subsequent effect on their infectivity in mammalian cells. METHODS Tissue-culture derived trypomastigotes of both strains were incubated in guinea pig serum and subjected to flow cytometry in order to determine their viability and complement activations. Trypomastigotes were also incubated on host cells monolayers in the presence of serum, and infectivity was evaluated under different conditions of complement pathway inhibition. Relative expression of the main parasite-specific complement receptors between the two strains was assessed by quantitative real-time polymerase chain reaction. FINDINGS In this work, we showed that two TcI strains, one with lower virulence (Ninoa) compared to the other (Qro), differ in their resistance to the lytic activity of complement system, hence causing a compromised ability of Ninoa strain to invade mammalian cells. These results correlate with the three-fold lower messenger RNA (mRNA) levels of complement regulatory protein (CRP), trypomastigote-decay acceleration factor (T-DAF), and complement C2 receptor inhibitor trispanning (CRIT) in Ninoa compared to those in Qro. On the other hand, calreticulin (CRT) mRNA and surface protein levels were higher in Ninoa strain and promoted its infectivity when the lectin pathway of the complement system was inhibited. MAIN CONCLUSIONS This work suggests the complex interplay of CRP, T-DAF, CRIT, and CRT, and the diagnostic value of mRNA levels in the assessment of virulence potential of T. cruzi strains, particularly when dealing with isolates with similar genetic background.

Chagas disease is a major endemic disease caused by the protozoan parasite Trypanosoma cruzi. This parasitic disease is widely distributed throughout Latin America, affecting 10 million people. There are also reports of canine infection in the southern part of the United States. Dogs are considered the predominant domestic reservoir for T. cruzi in many areas of endemicity. In México, dog infection by this parasite has been poorly studied. In this work 209 dogs from six villages in Jalisco, México, were assessed to detect anti-T. cruzi antibodies by ELISA and Western blot. Seventeen (17) seropositive dogs (8.1 %) were detected by both tests, representing a seropositive value similar to that found in some southern states of México where the infection is present. No statistical differences were observed concerning the age and sex of infected and non-infected dogs. The major antigens recognized by positive sera were 26, 32, 66 and 80 kDa. These proteins are candidates to develop a specific diagnostic method for canine Chagas. No antibodies against HSP16 protein were found in T. cruzi seropositive sera. This is the first report of canine serology of Chagas disease in this central part of México. This report will contribute to the knowledge of the infection status of domestic reservoirs in the state of Jalisco, México.

El mal de Chagas es una enfermedad endémica causada por el parásito protozoario Trypanosoma cruzi. Este padecimiento está ampliamente distribuido en América, donde afecta a alrededor de 10 millones de personas. También existen comunicaciones de la infección canina desde el sur de los Estados Unidos hasta países de Sudamérica. Los perros son considerados los principales reservorios domésticos de T. cruzi en muchas áreas endémicas. En México, la infección canina ha sido estudiada escasamente. En el presente trabajo se evaluó mediante ELISA y Western blot la presencia de anticuerpos anti-T. cruzi en el suero de 209 perros de seis localidades del estado de Jalisco, México. Se encontraron 17 perros seropositivos (8,1 %) a ambas pruebas. No se observaron diferencias de significación estadística en la edad o el sexo de los perros infectados comparados con los no infectados. Los principales antígenos reconocidos por los sueros positivos fueron de 26, 32, 66 y 80 kDa. Estas proteínas son candidatos para desarrollar un método de diagnóstico específico para Chagas canino. No se encontraron anticuerpos contra la proteína HSP16 en los sueros positivos anti-T. cruzi. Este es el primer informe de serología canina en la región central de México y contribuirá al conocimiento de la infección en reservorios domésticos de Jalisco, México.

In order to determine the role of rat fleas in the life cycle of Hymenolepis diminuta, between November 2009 and March 2010, 27 rats were captured in Cercado de Lima and their ectoparasites were examinated, using standard parasitological procedures. In examined rats, 22 (81.5%) were infected with the parasite H. diminuta, 85,2% were infested with siphonapters of the species Xenopsylla cheopis. Of the 158 fleas that were found, 12% housed cysticercoids in its hemocoel, which were inoculated into albino rats of Holtzman strain, and then developed to adult stage of Hymenolepis diminuta. The results of this study are conclusive and constitute the first record of the role of X. cheopis as natural intermediate host in Peru, making it necessary to reconsider the risk factors and preventive measures.

Con el objetivo de determinar el rol de las pulgas de las ratas en el ciclo biológico de Hymenolepis diminuta, entre noviembre del 2009 y marzo del 2010, se capturaron 27 ratas del Cercado de Lima y examinaron sus ectoparásitos, empleando los procedimientos parasitológicos estándares. De las ratas examinadas, 22 (81,5%) de las ratas examinadas estuvieron infectadas con el parásito H. diminuta, el 85,2% de ratas estuvo infestado por sifonápteros de la especie Xenopsylla cheopis. De las 158 pulgas encontradas, el 12% albergaba cisticercoides en su hemocele, los que al ser inoculados en ratas albinas de la cepa Holtzman, desarrollaron hasta el estadio de adultos de la especie Hymenolepis diminuta. Los resultados del presente trabajo son concluyentes y constituyen el primer registro del rol de X. cheopis como hospedero intermediario natural en Perú, por lo que es necesario reconsiderar los factores de riesgo y las medidas de prevención.

In nearly all of the previous multicentre studies evaluating serological tests for Trypanosoma cruzi infection, sera samples from Central or South American countries have been used preferentially. In this work we compared the reliability of the serological tests using Mexican sera samples that were evaluated in four independent laboratories. This included a reference laboratory in Brazil and three participant laboratories, including one in Central America and two in Mexico. The kappa index between Brazilian and Honduran laboratories reached 1.0 and the index for the Mexican laboratories reached 0.94. Another finding of this study was that the source of antigen did not affect the performance of the serological tests.

Two allelic genomic fragments containing ribosomal protein S4 encoding genes (rpS4) from Trypanosoma cruzi (CL-Brener strain) were isolated and characterized. One allele comprises two complete tandem repeats of a sequence encoding an rpS4 gene. In the other, only one rpS4 gene is found. Sequence comparison to the accessed data in the genome project database reveals that our two-copy allele corresponds to a variant haplotype. However, the deduced aminoacid sequence of all the gene copies is identical. The rpS4 transcripts processing sites were determined by comparison of genomic sequences with published cDNA data. The obtained sequence data demonstrates that rpS4 genes are expressed in epimastigotes, amastigotes, and trypomastigotes. A recombinant version of rpS4 was found to be an antigenic: it was recognized by 62.5% of the individuals with positive serology for T. cruzi and by 93.3% of patients with proven chronic chagasic disease.

Homologies of minicircle kDNA of 27 Mexican stocks were studied by cross-hybridization with four kDNA probes derived from three reference stocks belonging to groups Trypanosoma cruzi I (SO34 cl4 and Silvio) and T. cruzi II (MN) and one Mexican stock. High homologies were only observed with Silvio (six stocks) and Mexican probes (11 stocks). After 30 min exposure (low homology) additional stocks were recognized with SO34 cl4 (three stocks) and Silvio (six stocks) probes; with the Mexican probe only five stocks remained non-reactive. All the stocks were typed by isoenzyme (16 loci) and Mexican stocks belonged to T. cruzi I. Hybridization patterns were not strictly correlated with the observed clustering and cross-hybridization of kDNA minicircles is not available to distinct Mexican stocks.