Biological and genetic aspects of experimental hybrids from species of the Phyllosoma complex (Hemiptera: Reduviidae: Triatominae)

The present work is a thorough investigation of the degree of reproductive isolation between Meccus mazzottii and Meccus longipennis, Meccus picturatus, Meccus pallidipennis and Meccus bassolsae, as well as between M. longipennis and M. picturatus. We examined fertility and segregation of morphological characteristics in two generations of hybrids derived from crosses between these species. The percentage of pairs with (fertile) offspring was highest in the set of crosses between M. longipennis and M. picturatus, and lowest between M. mazzottii and M. picturatus. Most first-generation (F1) individuals from crosses involving M. mazzottii were morphologically similar to this species, while only F1 x F1 progeny of parental crosses between M. mazzottii and M. longipennis had offspring second generation that looked like M. mazzottii. The results indicate that different degrees of reproductive isolation apparently exist among the species of the Phyllosoma complex examined in this study. The biological evidence obtained in this study does not support the proposal that M. longipennis and M. picturatus are full species. It could indicate on the contrary, that both could be considered as subspecies of a single polytypic species. On the other hand, biological evidence supports the proposal that M. mazzottii is a full species.

Biological and genetic aspects of crosses between species of the genus Meccus (Hemiptera: Reduviidae Triatominae)

The degree of reproductive isolation between Meccus phyllosomus and the remaining five species of the genus Meccus, as well as between Meccus bassolsae and Meccus pallidipennis, Meccus longipennis and Meccus picturatus, was examined. Fertility and the segregation of morphological characteristics were examined in two generations of hybrids from crosses between these species. The percentage of couples with offspring (fertile) was high in the vast majority of sets of crosses, with the exception of that between ♀M. phyllosomus and ♂Meccus mazzottii. In sets of crosses involving M. bassolsae specimens, no first-generation (F1) individuals were morphologically similar to M. bassolsae, but instead shared the morphology of the other parental species. A similar phenomenon was observed in most sets of crosses involving M. phyllosomus. These results indicated that different degrees of reproductive isolation exist among the species of Meccus involved in this study. The biological evidence obtained in this study does not support the proposal that M. bassolsae is a full species. It could indicate that, on the contrary, it should be considered a subspecies of a single polytypic species. The biological evidence does support the proposal that M. phyllosomus is a full species.

Genetic variability of behaviorin Melipona quadrifasciata(Hymenoptera: Meliponinae)

Observation colonies containing only young workers from 10 matrix colonies were set up to investigate the genetic aspects involved in task division in Melipona quadrifasciata. Wide variation among origins was observed for all behaviors analyzed, but these differences were significant only for brood cell construction and propolis preparation

Biomphalaria tenagophila: dominant character of the resistance to Schistosoma mansoni in descendants of crossbreedings between resistant (Taim, RS) and susceptible (Joinville, SC) strains

The aim of the present work was to study parasitological, molecular, and genetic aspects in descendants of crossbreedings between a totally resistant Biomphalaria tenagophila strain (Taim, RS) and another one highly susceptible (Joinville, SC) to Schistosoma mansoni. Descendants F1 and F2 were submitted to S. mansoni infection (LE strain). The susceptibility rates for individuals from Group F1 were 0 to 0.6%, and from Group F2 was 7.2%. The susceptible individuals from Group F2 discharged a lower number of cercariae, when compared with the susceptible parental group, and in 2 out of 9 positive snails the cercarial elimination was discontinued. In order to identify genetic markers associated with resistance the genotype of parental snails and their offspring F1 and F2 were analyzed by means of the randomly amplified polymorphic DNA method. Nevertheless, it was not possible to detect any marker associated to resistance, but the results showed that in the mentioned species the resistance character is determined by two dominant genes.

Modern cancer epidemiological research: genetic polymorphisms and environment

Individual cancer susceptibility seems to be related to factors such as changes in oncogenes and tumor suppressor genes expression, and differences in the action of metabolic enzymes and DNA repair regulated by specific genes. Epidemiological studies on genetic polymorphisms of human xenobiotics metabolizing enzymes and cancer have revealed low relative risks. Research considering genetic polymorphisms prevalence jointly with environmental exposures could be relevant for a better understanding of cancer etiology and the mechanisms of carcinogenesis and also for new insights on cancer prognosis. This study reviews the approaches of molecular epidemiology in cancer research, stressing case-control and cohort designs involving genetic polymorphisms, and factors that could introduce bias and confounding in these studies. Similarly to classical epidemiological research, genetic polymorphisms requires considering aspects of precision and accuracy in the study design.

FATAL GROUP A STREPTOCOCCAL TOXIC SHOCK-LIKE SYNDROME IN A CHILD WITH VARICELLA: REPORT OF THE FIRST WELL DOCUMENTED CASE WITH DETECTION OF THE GENETIC SEQUENCES THAT CODE FOR EXOTOXINS SPE A AND B, IN SÃO PAULO, BRAZIL

A previously healthy seven-year-old boy was admitted to the intensive care unit because of toxaemia associated with varicella. He rapidly developed shock and multisystem organ failure associated with the appearance of a deep-seated soft tissue infection and, despite aggressive treatment, died on hospital day 4. An M-non-typable, spe A and spe B positive Group A Streptococcus was cultured from a deep soft tissue aspirate. The criteria for defining Streptococcal toxic shock-like syndrome were fulfilled. The authors discuss the clinical and pathophysiological aspects of this disease as well as some unusual clinical findings related to this case.

Virulence profile of ten Paracoccidioides brasiliensis isolates: association with morphologic and genetic patterns

Ten isolates of Paracoccidioides brasiliensis were examined for differences in virulence in outbred mice intravenously inoculated with the fungus, associated with mycelial morphology, and genetic patterns measured by random amplified polymorphic DNA (RAPD). Virulence was evaluated by viable yeast cell recovery from lungs and demonstration of histopathologic lesions in different organs. The results showed that the isolates presented four virulence degrees: high virulence, intermediate, low and non-virulence. RAPD clustered the isolates studied in two main groups with 56% of genetic similarity. Strains with low virulence, Pb265 or the non-virulent, Pb192, showed glabrous/cerebriform morphology and high genetic similarity (98.7%) when compared to the other isolates studied. The same was observed with Bt79 and Bt83 that shared 96% genetic similarity, cottony colonies and high virulence. The RAPD technique could only discriminate P. brasiliensis isolates according to glabrous/cerebriform or cottony colonies, and also high from low virulence strains. Isolates with intermediate virulence such as Pb18, Pb18B6, Bt32 and Bt56 showed variability in their similarity coefficient suggesting that RAPD was able to detect genetic variability in this fungal specie. Virulence profile of P. brasiliensis demonstrated that both mycelial morphologic extreme phenotypes may be associated with fungal virulence and their in vitro subculture time. Thus, RAPD technique analysis employed in association with virulence, morphologic and immunologic aspects might prove adequate to detect differences between P. brasiliensis isolates.

Genetic Control of Mosquitoes: population suppression strategies

Over the last two decades, morbidity and mortality from malaria and dengue fever among other pathogens are an increasing Public Health problem. The increase in the geographic distribution of vectors is accompanied by the emergence of viruses and diseases in new areas. There are insufficient specific therapeutic drugs available and there are no reliable vaccines for malaria or dengue, although some progress has been achieved, there is still a long way between its development and actual field use. Most mosquito control measures have failed to achieve their goals, mostly because of the mosquito's great reproductive capacity and genomic flexibility. Chemical control is increasingly restricted due to potential human toxicity, mortality in no target organisms, insecticide resistance, and other environmental impacts. Other strategies for mosquito control are desperately needed. The Sterile Insect Technique (SIT) is a species-specific and environmentally benign method for insect population suppression, it is based on mass rearing, radiation mediated sterilization, and release of a large number of male insects. Releasing of Insects carrying a dominant lethal gene (RIDL) offers a solution to many of the drawbacks of traditional SIT that have limited its application in mosquitoes while maintaining its environmentally friendly and species-specific utility. The self-limiting nature of sterile mosquitoes tends to make the issues related to field use of these somewhat less challenging than for self-spreading systems characteristic of population replacement strategies. They also are closer to field use, so might be appropriate to consider first. The prospect of genetic control methods against mosquito vectored human diseases is rapidly becoming a reality, many decisions will need to be made on a national, regional and international level regarding the biosafety, social, cultural and ethical aspects of the use and deployment of these vector control methods.

Delayed phagocytosis and bacterial killing in Chediak-Higashi syndrome neutrophils detected by a fluorochrome assay: ultrastructural aspects

The few studies already published about phagocyte functions in Chediak-Higashi syndrome (CHS) has stated that neutrophils present slow rate of bacterial killing but normally ingest microorganisms. In the present study, both phagocytosis and killing of Staphylococcus aureus were verified to be in neutrophils from two patients with CHS when these functions were simultaneously evaluated by a fluorochrome phagocytosis assay. Electron microscopic examination showed morphologic differences among neutophils from CHS patients and normal neutrophils regarding the cytoplasmic structures and the aspects of the phagolysosomes. It was noteworthy the presence of giant phagolysosomes enclosing bacteria in active proliferation commonly observed in CHS neutrophils after 45 min of phagocytosis, wich corresponded with the impaired bactericidal activity of these leukocytes. The present results suggest that phagocytosis may also be defective in CHS, and point out to the sensitivity of the fluorochrome phagocytosis assay and its application in clinical laboratories.

Population genetic analysis of Colombian Trypanosoma cruzi isolates revealed by enzyme electrophoretic profiles

Although Colombia presents an enormous biological diversity, few studies have been conducted on the population genetics of Trypanosoma cruzi. This study was carried out with 23 Colombian stocks of this protozoa analyzed for 13 isoenzymatic loci. The Hardy-Weinberg equilibrium, the genetic diversity and heterogeneity, the genetic relationships and the possible spatial structure of these 23 Colombian stocks of T. cruzi were estimated. The majority of results obtained are in agreement with a clonal population structure. Nevertheless, two aspects expected in a clonal structure were not discovered in the Colombian T. cruzi stocks. There was an absence of given zymodemes over-represented from a geographical point of view and the presumed temporal stabilizing selective phenomena was not observed either in the Colombian stocks sampled several times through the years of the study. Some hypotheses are discussed in order to explain the results found.

Some Aspects of Protozoan Infections in Immunocompromised Patients: A Review

Protozoa are among the most important pathogens that can cause infections in immunocompromised hosts. These microorganisms particularly infect individuals with impaired cellular immunity, such as those with hematological neoplasias, renal or heart transplant patients, patients using high doses of corticosteroids, and patients with acquired immunodeficiency syndrome. The protozoa that most frequently cause disease in immunocompromised patients are Toxoplasma gondii, Trypanosoma cruzi, different Leishmania species, and Cryptosporidium parvum; the first two species cause severe acute meningoencephalitis and acute myocarditis, Leishmania sp. causes mucocutaneous or visceral disease, and Cryptosporidium can lead to chronic diarrhea with hepatobiliary involvement. Various serological, parasitological, histological and molecular methods for the diagnosis of these infections are currently available and early institution of specific therapy for each of these organisms is a basic measure to reduce the morbidity and mortality associated with these infections.

The association of genetic markers and malaria infection in the Brazilian Western Amazonian region

Almost all individuals (182) belonging to an Amazonian riverine population (Portuchuelo, RO, Brazil) were investigated for ascertaining data on epidemiological aspects of malaria. Thirteen genetic blood polymorphisms were investigated (ABO, MNSs, Rh, Kell, and Duffy systems, haptoglobins, hemoglobins, and the enzymes glucose-6-phosphate dehydrogenase, glyoxalase, phosphoglucomutase, carbonic anhydrase, red cell acid phosphatase, and esterase D). The results indicated that the Duffy system is associated with susceptibility to malaria, as observed in other endemic areas. Moreover, suggestions also arose indicating that the EsD and Rh loci may be significantly associated with resistance to malaria. If statistical type II errors and sample stratification could be ruled out, hypotheses on the existence of a causal mechanism or an unknown closely linked locus involved in susceptibility to malaria infection may explain the present findings.

Cellular and genetic mechanisms involved in the generation of protective and pathogenic immune responses in human Chagas disease

Perhaps one of the most intriguing aspects of human Chagas disease is the complex network of events that underlie the generation of protective versus pathogenic immune responses during the chronic phase of the disease. While most individuals do not develop patent disease, a large percentage may develop severe forms that eventually lead to death. Although many efforts have been devoted to deciphering these mechanisms, there is still much to be learned before we can fully understand the pathogenesis of Chagas disease. It is clear that the host's immune response is decisive in this process. While characteristics of the parasite influence the immune response, it is becoming evident that the host genetic background plays a fundamental role in the establishment of pathogenic versus protective responses. The involvement of three complex organisms, host, parasite and vector, is certainly one of the key aspects that calls for multidisciplinary approaches towards the understanding of Chagas disease. We believe that now, one hundred years after the discovery of Chagas disease, it is imperative to continue with highly interactive research in order to elucidate the immune response associated with disease evolution, which will be essential in designing prophylactic or therapeutic interventions.

Swimming against the current: genetic vaccination against Trypanosoma cruzi infection in mice

Vaccines have had an unquestionable impact on public health during the last century. The most likely reason for the success of vaccines is the robust protective properties of specific antibodies. However, antibodies exert a strong selective pressure and many microorganisms, such as the obligatory intracellular parasite Trypanosoma cruzi, have been selected to survive in their presence. Although the host develops a strong immune response to T. cruzi, they do not clear the infection and instead progress to the chronic phase of the disease. Parasite persistence during the chronic phase of infection is now considered the main factor contributing to the chronic symptoms of the disease. Based on this finding, containment of parasite growth and survival may be one method to avoid the immunopathology of the chronic phase. In this context, vaccinologists have looked over the past 20 years for other immune effector mechanisms that could eliminate these antibody-resistant pathogens. We and others have tested the hypothesis that non-antibody-mediated cellular immune responses (CD4+ Th1 and CD8+ Tc1 cells) to specific parasite antigens/genes expressed by T. cruzi could indeed be used for the purpose of vaccination. This hypothesis was confirmed in different mouse models, indicating a possible path for vaccine development.

Immune homeostasis to microorganisms in the guts of triatomines (Reduviidae): a review

Bacteria, fungi and parasites are in constant contact with the insect gut environment and can influence different aspects of the host gut physiology. Usually, some of these microorganisms develop and survive in the digestive tract. Therefore, the gut environment must be able to tolerate certain populations of these organisms for the establishment of interactions between non-pathogenic bacteria, parasites and the gut. This review provides a brief overview of the biological and molecular mechanisms that microorganisms use to interact with the gut epithelia in mosquitoes and speculates on their significances for the development of bacteria and Trypanosoma cruzi in the guts of triatomines.