Bacteria cultured from the gut of Meccus pallidipennis (Hemiptera: Reduviidae), a triatomine species endemic to Mexico.

The study of intestinal microbiota in vector insects like triatomines is paramount in parasitology because many parasitic species inhabit the vector's gut. Although knowledge on the gut microbiota in various vectors of the parasitic flagellate Trypanosoma cruzi has grown, research efforts have focused on South American triatomines. This study reports the isolation of bacterial microbiota in the anterior and posterior gut of Meccus pallidipennis (a triatomine species endemic to Mexico) by culture, as well as its identification by phenotypic and biochemical tests and its quantification by counting colony-forming units. The study was performed on fifth-instar nymph and adult specimens of M. pallidipennis, either laboratory-bred or collected in the field and either infected or not with T. cruzi. Overall, 17 bacterial species were identified, with the genera Bacillus and Staphylococcus being the most prevalent regardless of the origin of the insects. No differences were observed in the number of bacterial species in the gut of laboratory-bred and field-collected insects, neither with respect to life stage or infection status. In general, the Shannon-Weaver diversity index was higher in non-infected insects than in infected ones. Further studies using non-culture methods are required to determine whether bacterial species diversity is modified by laboratory breeding.

Relationships between altitude, triatomine (Triatoma dimidiata) immune response and virulence of Trypanosoma cruzi, the causal agent of Chagas' disease.

Little is known about how the virulence of a human pathogen varies in the environment it shares with its vector. This study focused on whether the virulence of Trypanosoma cruzi (Trypanosomatida: Trypanosomatidae), the causal agent of Chagas' disease, is related to altitude. Accordingly, Triatoma dimidiata (Hemiptera: Reduviidae) specimens were collected at three different altitudes (300, 700 and 1400 m a.s.l.) in Chiapas, Mexico. The parasite was then isolated to infect uninfected T. dimidiata from the same altitudes, as well as female CD-1 mice. The response variables were phenoloxidase (PO) activity, a key insect immune response, parasitaemia in mice, and amastigote numbers in the heart, oesophagus, gastrocnemius and brain of the rodents. The highest levels of PO activity, parasitaemia and amastigotes were found for Tryp. cruzi isolates sourced from 700 m a.s.l., particularly in the mouse brain. A polymerase chain reaction-based analysis indicated that all Tryp. cruzi isolates belonged to a Tryp. cruzi I lineage. Thus, Tryp. cruzi from 700 m a.s.l. may be more dangerous than sources at other altitudes. At this altitude, T. dimidiata is more common, apparently because the conditions are more beneficial to its development. Control strategies should focus activity at altitudes around 700 m a.s.l., at least in relation to the region of the present study sites.

Immune defence mechanisms of triatomines against bacteria, viruses, fungi and parasites.

Triatomines are vectors that transmit the protozoan haemoflagellate Trypanosoma cruzi, the causative agent of Chagas disease. The aim of the current review is to provide a synthesis of the immune mechanisms of triatomines against bacteria, viruses, fungi and parasites to provide clues for areas of further research including biological control. Regarding bacteria, the triatomine immune response includes antimicrobial peptides (AMPs) such as defensins, lysozymes, attacins and cecropins, whose sites of synthesis are principally the fat body and haemocytes. These peptides are used against pathogenic bacteria (especially during ecdysis and feeding), and also attack symbiotic bacteria. In relation to viruses, Triatoma virus is the only one known to attack and kill triatomines. Although the immune response to this virus is unknown, we hypothesize that haemocytes, phenoloxidase (PO) and nitric oxide (NO) could be activated. Different fungal species have been described in a few triatomines and some immune components against these pathogens are PO and proPO. In relation to parasites, triatomines respond with AMPs, including PO, NO and lectin. In the case of T. cruzi this may be effective, but Trypanosoma rangeli seems to evade and suppress PO response. Although it is clear that three parasite-killing processes are used by triatomines - phagocytosis, nodule formation and encapsulation - the precise immune mechanisms of triatomines against invading agents, including trypanosomes, are as yet unknown. The signalling processes used in triatomine immune response are IMD, Toll and Jak-STAT. Based on the information compiled, we propose some lines of research that include strategic approaches of biological control.

Biological and genetic aspects of crosses between phylogenetically close species of Mexican triatomines (Hemiptera: Reduviidae).

Reproductive isolation between Triatoma mexicana (Herrich-Scaeffer) and the six species of the Phyllosoma complex, belonging to the genus Meccus, was examined by analyzing the fertility of experimental hybrids. The percentage of couples with offspring was highest in the set of crosses between Meccus phyllosomus (Burmeister) and T. mexicana, and lowest in those between Meccus pallidipennis (Stål) and Meccus bassolsae (Alejandre-Aguilar, Nogueda-Torres, Cortés-Jiménez, Jurberg, Galvão, and Carcavallo) with respect to T. mexicana. Crosses between Meccus mazzottii (Usinger), Meccus picturatus (Usinger), and Meccus longipennis (Usinger) and T. mexicana had scarce offspring, whereas offspring from crosses between M. phyllosomus and T. mexicana were abundant. However, all F1 nymphs died in different instars before reaching sexual maturity. The biological evidence in this study suggests that different degrees of reproductive isolation exist between T mexicana and the different species of Meccus. Our data also support the current status of T. mexicana as a separate species.

Transmission Capacity of Trypanosoma cruzi (Trypanosomatida: Trypanosomatidae) by Three Subspecies of Meccus phyllosomus (Heteroptera: Reduviidae) and Their Hybrids.

Three behaviors of epidemiological importance: the time lapse for the onset of feeding, actual feeding, and defecation time for Meccus phyllosomus pallidipennis (Stål), Meccus phyllosomus longipennis (Usinger), Meccus phyllosomus picturatus (Usinger), and their laboratory hybrids were evaluated in this study. The mean time lapse for the beginning of feeding was between 0.5 and 8.3 min considering all instars in each cohort, with highly significant differences only among fifth-instar nymphs, females, and males of M. p. pallidipennis and M. p. longipennis relative to the hybrid cohorts. Four hybrid (LoPa [M. p. longipennis and M. p. pallidipennis] and LoPi [M. p. longipennis and M. p. picturatus] and their reciprocal experimental crosses) cohorts had similar mean feeding times to one of the parental subspecies, but longer than the other one. The remaining hybrid cohort (PaPi [M. p. pallidipennis and M. p. picturatus]) had longer feeding times than both of its parental subspecies. The specimens of the LoPa and LoPi hybrid cohorts defecated faster than the respective instars of the three parental cohorts. With exception of first- and fifth-instar nymphs, PaPi cohorts defecated faster than the remaining seven cohorts. More than 60% of defecation events occurred during feeding in the six hybrid cohorts. Our results indicate that hybrid cohorts have more potential to acquire infection and transmit Trypanosoma cruzi Chagas than their parental cohorts.

Cuticular hydrocarbon variability among Triatoma dimidiata (Hemiptera: Reduviidae) populations from Mexico and Guatemala.

The geographic variation in the cuticular hydrocarbon pattern among 11 populations of Triatoma dimidiata Latreille (Hemiptera: Reduviidae: Triatominae) from different regions of Mexico and Guatemala, was studied using capillary gas chromatography. T. dimidiata populations were differentiated based on the relative amounts of 71 hydrocarbon components. Insect population classification was mostly in agreement with their geographical vicinity; Mexican populations from the Yucatan peninsula grouped together with those from northern Guatemala, insects from the Mexican Gulf coast states were closely related to those collected from northern Oaxaca, and to a lesser extent, to insects from Chiapas. Insects from southern Oaxaca were clustered together with those from southern Guatemala. All these populations were clearly separated from Guatemalan specimens collected in caves from Alta Verapaz.

Customs which predispose to Chagas' disease and cysticercosis in Mexico.

Customs in small isolated populations of Mexico are described which influence the prevalence of cysticercosis and Chagas' disease. People in some villages prefer the taste of pork harboring cysticerci. Certain triatomids are thought to have aphrodisiac properties and are therefore eaten.

Parasite search in strawberries from Irapuato, Guanajuato and Zamora, Michoacan (Mexico).

A seasonal research was carried out in Irapuato, Guanajuato and Zamora, Michoacan, Mexico, the location of the most important producers of strawberries, in order to assess fecal contamination through the finding of protozoan cysts and helminth eggs, specifically of Taenia sp eggs. Three techniques were used: direct observation, flotation and sedimentation. Low numbers of protozoan cysts and only one Ascaris egg were found. What is most interesting is that no Taenia eggs were identified. Results indicate that although strawberries are contaminated with human feces, contamination is minimal.

Importance of Triatoma pallidipennis (Hemiptera: Reduviidae) as a vector of Trypanosoma cruzi (Kinetoplastida: Trypanosomatidae) in the state of Morelos, Mexico, and possible ecotopes.

We performed a transversal-type epidemiological study in the state of Morelos, Mexico, to determine the presence of triatomines, their ecotopes, and importance in transmission of Trypanosoma cruzi Chagas. Sampling sites included domestic, peridomestic, and wild areas with collection based on the person per hour technique. We determined the entomological indices related to infestation, density, overcrowding, colonization, infection, and dispersion, which were used to calculate transmission risk. During the study, observations were made on the predominant building material, presence of cracks and illumination as factors fostering colonization. The most important results were related to infection indices, which were higher for domestic type triatomines (29%), whereas it was 4% for peridomestic sites, and 20% for sylvatic areas. The actual risk of human contact with the vector was of 0.51%, and the predominating ecotopes were stone heaps.

Chromosomal variation and genome size support existence of cryptic species of Triatoma dimidiata with different epidemiological importance as Chagas disease vectors.

The wide geographical distribution of Triatoma dimidiata, one of the three major vectors of Chagas disease, ranges from Mexico to northern Peru. Since this species occupies a great diversity of artificial and natural ecotopes, its eradication is extremely difficult. In order to assist control efforts, we used chromosome analyses and DNA amount as taxonomic markers to study genetic variability in populations of T. dimidiata from Mexico, Guatemala, El Salvador and Colombia. We differentiated three groups or cytotypes defined by characteristic chromosome C-banding patterns and genome size measured by flow cytometry. The three cytotypes are restricted to different geographic locations. Cytotype 1 occurs in Mexico (excluding Yucatán), Guatemala (excluding Petén), El Salvador and Colombia. Cytotype 2 occurs in Yucatán and cytotype 3 occurs in Petén. Cytotype 1, commonly associated with domestic and peridomestic environments but also inhabiting sylvatic ecotopes, is the most widespread and with major epidemiological significance. In contrast, the Yucatán cytotype inhabits wild ecotopes but increasingly enters houses, while the Petén cytotype appears exclusively sylvatic. We suggest that these cytotypes represent cryptic species of T. dimidiata with different epidemiological relevance as Chagas disease vectors. Poor ability to colonize human dwellings, together with their restricted geographic distribution, indicate that the Yucatán and Petén putative species probably have much less epidemiological significance than cytotype 1. Thus, the genetic markers we describe are powerful tools to differentiate cryptic species in T. dimidiata with different epidemiological significance, contributing to planning the most effective control measures.

First case of natural infection in pigs. Review of Trypanosoma cruzi reservoirs in Mexico.

An epidemiological research project was performed in the State of Morelos including collection of samples for blood smears and culture, serological tests, and xenodiagnoses from a total of 76 domestic and peridomestic mammals. Two strains of Trypanosoma cruzi were isolated by haemocultures; one from a pig (Sus scrofa), the first case of natural infection reported in Mexico, and the other from a dog (Canis familiaris). This study summarizes current information in Mexico concerning confirmed reservoirs of T. cruzi.

The ITS-2 of the nuclear rDNA as a molecular marker for populations, species, and phylogenetic relationships in Triatominae (Hemiptera: Reduviidae), vectors of Chagas disease.

The nucleotide sequences of the rDNA second internal transcribed spacer (ITS-2) of 31 populations of 12 and 3 species of the two main Triatominae tribes Triatomini and Rhodniini, including the most important Chagas disease vectors, were obtained. Sequence comparisons and parsimony, distance, and maximum-likelihood analyses indicate that ITS-2 is a useful marker for resolving supraspecific, specific, subspecific, and even sometimes population-level relationships in Triatominae. Results were markedly different between species of Triatomini and Rhodniini, suggesting polyphyly. Phylogenetic trees support an old divergence between South American and North-Central American Triatomini and query the validity of some genera (Dipetalogaster, Psammolestes). The very low sequence variation between species of the phyllosoma complex suggests that subspecific ranking would be more appropriate. Triatoma dimidiata proves to be a clearly differentiated species, with several populations evidencing a clinal variation along a north-south axis and a population from Yucatan showing differences consistent with specific status.

Chagas disease in Mexico.

Mexico - the northernmost country of Latin America - has long been thought to have an unusually low prevalence of Chagas disease compared with other Latin American countries. This has seemed unusual because of the large number of vector species and subspecies reported from the country, and the social and ecological conditions that seem to parallel those in other countries where Chagas disease is recognized as a major public health priority. This review seeks to clarify the question, and suggests that the epidemiological, parasitological, and entomological pattern of Chagas disease in Mexico may also parallel that of other endemic regions, but has been masked by poor awareness of the disease both at local and institutional levels.

[Qualitative and quantitative study of Taenia solium posoncospheres in the muscular tissue of pigs with and without cysticercosis]. / Estudio cualitativo y cuantitativo de la presencia de posoncosferas de Taenia solium en el tejido muscular de cerdos con y sin cisticercosis.

It was determined the presence of posoncospheres in muscular tissues in 20 natural cysticercotic pigs and in 20 pigs apparently free of Taenia solium metacestodes. Ten differents anatomical regions were dissected, giving 400 samples in total. The animals were slaughtered in Ecatepec, Mexico State, Mexico. The samples were kept in bottles with saline and were processed in the Laboratorio de Biología de Parásitos, Facultad de Medicina, Universidad Nacional Autónoma de México (UNAM); cysticercus were counted and later on the resulting muscular mass was grinded and observations were made in the sediment, for posoncospheres search. Mann-Whitney statistical method revealed meaningful differences between postoncospheres in cysticercotic pigs and not apparently cysticercotic pigs. The Linear Correlation Analysis showed no relation between cysticercus quantity and postoncospheres quantity in the same samples. Postoncospheres were found in cysticercotic animals and in those apparently free of cysticercus, in the last group the quantity was bigger.

[Neurocysticercosis and occupational medicine]. / Neurocisticercosis y medicina ocupacional.

Twenty individuals classified as disabled due to diagnosed cerebral cysticercosis were studied to correlate the presence of neurocysticercosis with the history of having worked in contact with organic solvents as possible triggering agents of the pathology. The study was performed by direct or indirect interrogatory, review of the case histories, serologic examinations, and psychological evaluation of the intellectual performance level and psychopathological index. Of the 20 subjects, 50% had been exposed to organic solvents in their work; all had been in contact with the infecting parasite, either through frequent consumption of pork meat, or through contact with fecal mass. The titers of the haemagglutination test varied from 1:2 to 1:256, being the diagnosis value of > or = 1:16. There was also a variation as a function of the antigen used for the sera tests performed in the sampled subjects, such as complete or incomplete somatic antigen, vesicular fluid, and excretions and secretions. Other variations found, such as symptoms and the results of the psychological evaluation are depicted in tables. It is concluded that in these cases, neurocysticercosis is an invalidating disease, and the presence of organic solvents is emphasized as an important factor of the disease or as a triggering factor.

[Immune humoral response in pigs infected with eggs and posoncospheres of Taenia solium]. / Estudio de la respuesta inmune humoral en cerdos infectados con huevos y posoncosferas de Taenia solium.

Due to the importance of cysticercosis in Mexico and Latin America and to the fact that in the last years another mechanism of infection for this disease has been proposed, i.e. through postoncospheres and immunosuppression of the host, we have considered relevant to perform the present work, which consisted in assessing the immune response induced by dexamethasone as well as that produced by parasites in pigs infected with T. solium eggs, or postoncosphere-infected, and in postoncosphere-infected and dexamethasone-treated animals. We used 10 recently weaned pigs, three were used as controls, two of them without the drug and one with it; two were infected with T. solium eggs; five with postoncospheres receiving also dexamethasone three of them. We evaluated the humoral response against parasite antigen using indirect haemagglutination (IH) and ELISA methods. Results of the immune humoral response revealed titres of up to 1:128 in T. solium eggs infected animals, of 1:16 in postoncosphere infected animals, and of 1:32 towards the end of the experiment in postoncosphere plus dexamethasone animals. Absorbance titres with ELISA confirmed these findings. Data obtained by IH show that the antibody titres of the pigs challenged with postoncospheres and postoncospheres plus dexamethasone are positive as compared to the titres obtained in the pigs infected with T. solium eggs. Results from the ELISA confirmed this finding, since, from weeks 14 to 17, the pigs became positive, behaving as those pigs that developed cysticercosis. This is relevant as it indicates that the antiposcosphere antibodies recognized antigens of T. solium larvae.

[Validation of data collection for an American trypanosomiasis epidemiologic study in the State of Morelos, México]. / Validación del proceso de obtención de datos para un estudio sobre trypanosomiasis americana en el estado de Morelos, México.

The purpose of this paper is to show up the importance of the standardization concepts in American Trypanosomiasis epidemiological studies. The consistence in the measurement of some dwelling characteristics was evaluated. A validation of the Queretaro antigen for indirect hemagglutination reaction as a diagnostic test and the interobserver concordance for the serologic readings were also made. The observers were instructed in some sessions. The pretests were made in the laboratory with positive and negative sera, with sera from the studied population. Results show that the interobserver concordance after the instruction, for the dwelling variables ranged from 70% to 100%. Sensitivity of the Queretaro antigen was 100%, specificity 55%, the predictive value of a positive test 55%, and the predictive value of a negative test 93%. The interobserver concordance was 47%. The pretest and the pilot study are very important in getting the objectives of the principal study.

Tres especies de triatominos y su importancia como vectores de Trypanosoma cruzi en México / Importance of three triatoma vectors of Trypanosoma cruzi in Mexico

Observations made in the field and in the laboratory on three vectors of Trypanosoma cruzi: Triatoma barberi, T. pallidipennis and T. dimidiata are here presented. Results are compared in relation with their ecotopes, vectorial capacity, biological characteristic, entomological indexes and capture places. In relation with their ecotopos T. barberi has preference for the interior of the human home, in walls, directly in contact with beds; T. pallidipennis, when it is inside the houses, prefers floors and among clothes, although their main ecotope is wild; T. dimidiata has localization in floors, specially under the beds, in the angle between wall and floor; T. barberi and T. dimidiata are attracted by the light. The cycles of life were of 523, 171 and 510 days, respectively for Triatoma barberi, T. pallidipennis and T. dimidiata. The vectorial capacity was determined according to the time taken in defecating during or after its sucking blood: T. barberi defecates during its feeding, while T. pallidipennis and T. dimidiata make it from 10 to 20 and of 20 to 30 minutes after starting the process, respectively. The indexes of natural infection were of 56.6 for T. barberi, 29 for T. pallidipennis and 15.6 for T. dimidiata, The metacyclogenics indexes that indicate percentages of metacyclics trypomastigotes in later intestine of vectors was in T. barberi 76.6, T. pallidipennis 15 and T. dimidiata 26, with what it can be concluded that the first species is the best transmitter of T. cruzi in Mexico.(AU)

Se presentan observaciones hechas en el campo y en el laboratorio sobre tres vectores de Trypanosoma cruzi: Triatoma barberi, T. pallidipennis y T. dimidiata. Se comparan resultados en relación con sus ecotopos, capacidad vectorial, características biológicas, índices entomológicos y sitios de captura. En relación con sus ecotopos, T. barberi tiene preferencia por el interior del domicilio humano, en paredes, directamente en contacto con las camas; T. pallidipennis, cuando se encuentra dentro de las casas, prefiere pisos y entre la ropa, aunque su principal ecotopo es silvestre; T. dimidiata tiene localización en pisos, especialmente bajo las camas, en el ángulo entre pared y piso; T. barberi y T. dimidiata son atraídas por la luz. Los ciclos de vida fueron de 523, 171 y 510 días, respectivamente para Triatoma barberi, T. pallidipennis y T. dimidiata. La capacidad vectorial se determinósegún el tiempo que tarda en defecar durante o después de su ingesta de sangre: T. barberi defeca durantesu alimentación, mientras que T. pallidipennis y T. dimidiata lo hacen de 10 a 20 y de 20 a 30 minutos después de iniciado el proceso, respectivamente. Los índices de infección natural fueron de 56.6 para T.barberi, 29 para T.pallidipennis y 15.6 para T. dimidiata. Los índices metaciclogénicos, que indican porcentajes de tripomastigotesmetacíclicos en intestino posterior de los vectores fueron en T. barberi 76.6, T. pallidipennis 15 y T. dimidiata 26,con lo que se concluye que la primera especie es el mejor transmisor de T. cruzi en México.(AU)

Tres especies de triatominos y su importancia como vectores de Trypanosoma cruzi en México / Importance of three triatoma vectors of Trypanosoma cruzi in Mexico

Observations made in the field and in the laboratory on three vectors of Trypanosoma cruzi: Triatoma barberi, T. pallidipennis and T. dimidiata are here presented. Results are compared in relation with their ecotopes, vectorial capacity, biological characteristic, entomological indexes and capture places. In relation with their ecotopos T. barberi has preference for the interior of the human home, in walls, directly in contact with beds; T. pallidipennis, when it is inside the houses, prefers floors and among clothes, although their main ecotope is wild; T. dimidiata has localization in floors, specially under the beds, in the angle between wall and floor; T. barberi and T. dimidiata are attracted by the light. The cycles of life were of 523, 171 and 510 days, respectively for Triatoma barberi, T. pallidipennis and T. dimidiata. The vectorial capacity was determined according to the time taken in defecating during or after its sucking blood: T. barberi defecates during its feeding, while T. pallidipennis and T. dimidiata make it from 10 to 20 and of 20 to 30 minutes after starting the process, respectively. The indexes of natural infection were of 56.6 for T. barberi, 29 for T. pallidipennis and 15.6 for T. dimidiata, The metacyclogenics indexes that indicate percentages of metacyclics trypomastigotes in later intestine of vectors was in T. barberi 76.6, T. pallidipennis 15 and T. dimidiata 26, with what it can be concluded that the first species is the best transmitter of T. cruzi in Mexico.

Se presentan observaciones hechas en el campo y en el laboratorio sobre tres vectores de Trypanosoma cruzi: Triatoma barberi, T. pallidipennis y T. dimidiata. Se comparan resultados en relación con sus ecotopos, capacidad vectorial, características biológicas, índices entomológicos y sitios de captura. En relación con sus ecotopos, T. barberi tiene preferencia por el interior del domicilio humano, en paredes, directamente en contacto con las camas; T. pallidipennis, cuando se encuentra dentro de las casas, prefiere pisos y entre la ropa, aunque su principal ecotopo es silvestre; T. dimidiata tiene localización en pisos, especialmente bajo las camas, en el ángulo entre pared y piso; T. barberi y T. dimidiata son atraídas por la luz. Los ciclos de vida fueron de 523, 171 y 510 días, respectivamente para Triatoma barberi, T. pallidipennis y T. dimidiata. La capacidad vectorial se determinósegún el tiempo que tarda en defecar durante o después de su ingesta de sangre: T. barberi defeca durantesu alimentación, mientras que T. pallidipennis y T. dimidiata lo hacen de 10 a 20 y de 20 a 30 minutos después de iniciado el proceso, respectivamente. Los índices de infección natural fueron de 56.6 para T.barberi, 29 para T.pallidipennis y 15.6 para T. dimidiata. Los índices metaciclogénicos, que indican porcentajes de tripomastigotesmetacíclicos en intestino posterior de los vectores fueron en T. barberi 76.6, T. pallidipennis 15 y T. dimidiata 26,con lo que se concluye que la primera especie es el mejor transmisor de T. cruzi en México.