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OBJECTIVE: To estimate the prevalence of infection with Trypanosoma cruzi in Triatominae species frequently found in and around Mexican dwellings, and to assess the frequency of Triatominae in towns by state. MATERIAL AND METHODS: Between January 1993 and December 1999, 5,399 Triatominae bugs from 14 states of Mexico, were received in the Department of Entomology of the Institute for Epidemiologic Diagnosis and Referral (InDRE), for taxonomic determination and parasitoscopical search of Trypanosoma cruzi. Results obtained between 1993 and 1999 were analyzed globally. RESULTS: From 13 bug species associated with human dwellings, nine were naturally infected with T. cruzi. The highest percentage of infection occurred in Triatoma pallidipennis, T. picturata, Rhodnius prolixus and T. longipennis. Nayarit, Morelos, and Michoacán were the states with the highest percentage of infected bugs. The species T. dimidiata, T. gerstaeckeri, T. longipennis, T. mexicana and T. pallidipennis were first state records and Pastrongylus rufotuberculatus was a first local record. CONCLUSIONS: These findings stress the importance of studying the biology of Triatominae and the need for permanent surveillance, to allow for up-to-date distribution records of Triatominae species in and around human dwellings, those adapting to human dwellings, and frequencies of those naturally infected by T. cruzi.
Mepraia spinolai and Mepraia gajardoi (Hemiptera, Reduviidae) are only found in the arid regions of northern Chile. Mepraia is the only genus of Triatominae with marked wing polymorphism. Females of both species are micropterous, males of M. spinolai may be micropterous, brachypterous or macropterous, while males of M. gajardoi are always brachypterous. Because of this wing polymorphism, Mepraia can be used as a model to analyze morphological adaptations related to the flying activity and evolutionary relationships in the Triatominae. The study presented here analyses the antennal phenotype of the Mepraia species and carries out a comparison with the two species of Triatoma included in the spinolai complex (Triatoma eratyrusiformis and Triatoma breyeri). The analysis of the antennal phenotype of Mepraia showed a marked intraspecific phenotypic variability related with sex and wing condition. The number and length of multiporous trichoid sensilla (TH) on the pedicel are significantly higher and longer in winged males and are strongly reduced in females. The great length of the TH sensillum is an infrequent characteristic within Triatominae. The results show that phenetic distances between sexes are greater than between the two species. Similarity between the Mepraia species and T. eratyrusiformis was found as they all show long bristles (BR) and TH and two sized basiconic receptors (BA), a pattern that have not been observed in other species of Triatominae. These characters are not present in T. breyeri.
The susceptibility of 3rd instar nymph of Triatominae Rhodnius neglectus, R. robustus and Triatoma infestans to Trypanosoma cruzi Y and AMJM strains was verified using artificial xenodiagnosis. After the accomplishment of the xenodiagnosis, the faeces of the Triatominae were analyzed on two-day intervals from day 5 until day 31 post infection, using the abdominal compression technique. The results showed differences in the susceptibility of the Triatominae for the two strains studied, and the optimal period reading differed from day 11 to day 19 for the Y strain and from day 11 to day 15 for the AMJM strain. For the Y strain, all three Triatominae species showed good susceptibility, whereas in the AMJM strain, the highest susceptibility was observed with R. neglectus, followed by T. infestans and R. robustus.
We report 29 new localities with Triatominae in the Republic of México; these Triatominae belong to 8 different species. Infection by Trypanosoma cruzi in the majority of these localities with high rates of positivity was found. Biological observations concerning the collected Triatominae are given. The necessity of continued work in relation to geographical distribution, ecology, frequency of infection by T. cruzy, and the role played by Triatominae of the Republic of México in the transmission of the infection to the man is stressed.
The most representative sample of molecular data, especially 16S and 12S rDNAs, is used to study the phylogeny and evolution of 57 species of three tribes, Rhodniini, Linshcosteini, and Triatomini, of the subfamily Triatominae. For the first time both New World and Old World species are brought together in a single phylogenetic analysis. Maximum-parsimony and distance estimation place both the Asiatic representatives, Linshcosteus and Triatoma rubrofasciata, as sister groups. The Linshcosteus-T. rubrofasciata clade nests firmly within Triatomini, in most analyses branching as a basalmost lineage, thus supporting a monophyletic origin of Triatominae. A paraphyly of "Triatoma" with respect to Linshcosteus, Dipetalogaster, Eratyrus, and Panstrongylus and the paraphyly of "Rhodnius" with respect to Psammolestes is observed in most of the analyses. Reinterpretation of triatomine biogeography points to the origin of Triatominae in northern areas of South America, in Central America, or in the southern region of North America. A few taxonomic changes are proposed: (1) reinclusion of Linshcosteus in Triatomini, (2) inclusion of Psammolestes in Rhodnius, (3) elevation of the "T. flavida complex" to the full genus Nesotriatoma (including N. flavida, N. bruneri, and N. obscura), (4) inclusion of the "T. spinolai complex" in Mepraia (including M. spinolai, M. gajardoi, M. eratyrusiformis, and M. breyeri), and (5) inclusion of "T." dimidiata in Meccus (M. dimidiatus).
An association is established between the Brazilian geographical pattern of the domiciliarity of the triatominae bugs and open lands characterized by natural savanna vegetation or artificial, man-made landscapes. The Brazilian open lands involved are the "caatingas'' and "cerrados", both wholly included in Brazilian territory, while the mixed Southern subtropical prairies belong to systems extending bevond national boundary lines. The other open lands are anthropic-lands opened mainly by the destruction of primitive forests of the tropical Atlantic system. Attempts were made to subject the four synanthropic species of epidemiological importance to model paleoecologic refuges and endemic centers. Triatoma sordida, Triatoma brasiliensis, and Triatoma pseudomaculata seem to have their endemic centers in the "cerrados" and "caatinga", while the Panstrongylus megistus may have originated in the tropical Atlantic forest system. The Triatoma infestans, however, seem to have originated in Bolivia, then were spread to large dispersal regions by man. Thus it can be assumed that domiciliarity is arrived at through an opportunistic mechanism stimulated by shelter and food availability factors. Once established, domiciliarity favors the species survival and dispersal, and this is of particular interest to control and surveillance programs because it increases the probability of the triatominae's success in synanthropic specialization. The present intense anthropic activities in the Amazonian system will lead to even greater expansion into the open lands; consequently, a triatominae domiciliarity spread can be expected, due to either autochthonous or man-introduced populations. A public health problem will then arise in a region where it has, heretofore, been unknown.
To determine and analyze the distribution of Triatominae sylvatic populations in the Federal District of Brazil, 150 Mauritia flexuosa palm trees were sampled in six veredas of different landscapes (sylvatic, rural and peri-urban) in the rainy season. Triatomines were morphologically identified and grouped by sex and nymphal stage and were examined to verify infection by Trypanosoma cruzi and Trypanosoma rangeli. Twenty eight (18.6%) palm trees were infested by Rhodnius neglectus and fourteen (9.5%) by Psammolestes tertius. The frequency of Triatominae in palm trees with and without nests was significantly different being higher in palm trees with bird and mammal nests in the crown. The higher average number of insects/palm tree was observed in rural areas with estimates of up to 838 insects/hectare. The species age makeup presented a different pattern, with nymphs predominant for Rhodnius neglectus and adults predominant for Psammolestes tertius. Also, many Rhodnius neglectus eggs were collected, which indicates a reproductive event in February 2003. Among the nests found in palm trees, that of the Phacellodomus ruber (Furnariidae) bird had the greatest abundance of Triatominae, occurring on 42% of palm trees. The relative abundance of Rhodnius neglectus and Psammolestes tertius was greater in rural areas which contained higher number of nests in palm trees and lesser density of palms per hectare. None of the 96 triatomines examined were infected by Trypanosoma cruzi or Trypanosoma rangeli, despite our finding of Rhodnius neglectus infection by those parasites in former studies.
The use of biochemical and genetic characters to explore species or population relationships has been applied to taxonomic questions since the 60s. In responding to the central question of the evolutionary history of Triatominae, i.e. their monophyletic or polyphyletic origin, two important questions arise (i) to what extent is the morphologically-based classification valid for assessing phylogenetic relationships? and (ii) what are the main mechanisms underlying speciation in Triatominae? Phenetic and genetic studies so far developed suggest that speciation in Triatominae may be a rapid process mainly driven by ecological factors.
The evolutionary history and times of divergence of triatomine bug lineages are estimated from molecular clocks inferred from nucleotide sequences of the small subunit SSU (18S) and the second internal transcribed spacer (ITS-2) of the nuclear ribosomal DNA of these reduviids. The 18S rDNA molecular clock rate in Triatominae, and Prosorrhynchan Hemiptera in general, appears to be of 1.8% per 100 million years (my). The ITS-2 molecular clock rate in Triatominae is estimated to be around 0.4-1% per 1 my, indicating that ITS-2 evolves 23-55 times faster than 18S rDNA. Inferred chronological data about the evolution of Triatominae fit well with current hypotheses on their evolutionary histories, but suggest reconsideration of the current taxonomy of North American species complexes.
Random amplified polymorphic DNA (RAPD) technique is a simple and reliable method to detect DNA polymorphism. Several factors can affect the amplification profiles, thereby causing false bands and non-reproducibility of assay. In this study, we analyzed the effect of changing the concentration of primer, magnesium chloride, template DNA and Taq DNA polymerase with the objective of determining their optimum concentration for the standardization of RAPD technique for genetic studies of Cuban Triatominae. Reproducible amplification patterns were obtained using 5 pmoL of primer, 2.5 mM of MgCl2, 25 ng of template DNA and 2 U of Taq DNA polymerase in 25 microL of the reaction. A panel of five random primers was used to evaluate the genetic variability of T. flavida. Three of these (OPA-1, OPA-2 and OPA-4) generated reproducible and distinguishable fingerprinting patterns of Triatominae. Numerical analysis of 52 RAPD amplified bands generated for all five primers was carried out with unweighted pair group method analysis (UPGMA). Jaccard's Similarity Coefficient data were used to construct a dendrogram. Two groups could be distinguished by RAPD data and these groups coincided with geographic origin, i.e. the populations captured in areas from east and west of Guanahacabibes, Pinar del Río. T. flavida present low interpopulation variability that could result in greater susceptibility to pesticides in control programs. The RAPD protocol and the selected primers are useful for molecular characterization of Cuban Triatominae.
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.
The members of the subfamily Triatominae (Hemiptera: Reduviidae) comprise a great number of species of medical importance in the transmission of the T. cruzi (American trypanosomiasis). The aim of this study was to contribute to the knowledge about the chemical composition in proteins, lipids, lipoproteins, and carbohydrates of vectors of Chagas' disease corresponding to twelve members of the subfamily Triatominae. This study was carried out in ninphs of the fifth instar and adult males of the species: T. delpontei, T. dimidiata, T. guasayana, T. infestans, T. mazzotti, T. pallidipennis, T. patagonica, T. platensis, T. rubrovaria, T. sordida of the Triatoma genus, and D. maximus and P. megistus of the Dipatalogaster and Panstrongylus genera respectively. The results show on one hand, qualitative differences in the protein composition, and on the other hand, similarity in the lipoprotein profiles. Lipids, proteins, and carbohydrates did not show significant differences between species or/and stages.
Large-scale trials of a trapping system designed to collect silvatic Triatominae are reported. Live-baited adhesive traps were tested in various ecosystems and different triatomine habitats (arboreal and terrestrial). The trials were always successful, with a rate of positive habitats generally over 20% and reaching 48.4% for palm trees of the Amazon basin. Eleven species of Triatominae belonging to the three genera of public health importance (Triatoma, Rhodnius and Panstrongylus) were captured. This trapping system provides an effective way to detect the presence of triatomines in terrestrial and arboreal silvatic habitats and represents a promising tool for ecological studies. Various lines of research are contemplated to improve the performance of this trapping system.
In order to determine if habitat similarity is correlated with a similarity of sensilla pattern, we analyzed six species of Triatominae present in two biogeographic regions of Brazil: the "caatinga" and the "cerrado". In broad terms Triatoma infestans (cerrado) and T. brasiliensis (caatinga) are found in human domiciles, T. sordida (cerrado) and T. pseudomaculata (caatinga) colonize peridomestic habitats, and Rhodnius neglectus (cerrado) and R. nasutus (caatinga) inhabit palm tree crowns. The number and distribution of four sensilla types (bristles, thin and thick walled trichoidea, and basiconica) were compared in these species. Sexual dimorphism of sensilla patterns was noted in T. sordida, T. brasiliensis and T. pseudomaculata. A principal component analysis showed three main groups: (i) species that live in the palms, (ii) domiciliated species and (iii) those living in the peridomestic habitat. T. infestans almost exclusively domestic, was placed at the centre of the canonical map and some individuals of other species overlapped there. These results support the idea that the patterns of antennal sensilla are sensitive indicators of adaptive process in Triatominae. We propose that those species that inhabit less stable habitats possess more types of sensilla on the pedicel, and higher number of antennal sensilla.
An important epidemiological challenge in controlling the Triatominae (Hemiptera: Reduviidae), vectors of Chagas disease, is identifying the origin of insects re-infesting treated areas, especially when reinfestation occurs during the first 1 or 2 years following insecticide application and in the absence of insecticide resistance. When using strict insect characteristics, the standard approach is to compare reinfesting specimens with those collected prior to treatment. Because of the long generation time of Triatominae, the experimental intent is to reject the hypothesis of a previous population, the one prior to insecticide application, to be the parental population of the reinfesting population. Biometric techniques are based on the hypothesis of more similarity between offspring and parents, and have been tested in the field. Reinfesting specimens are very few when discovered, which might cause sampling problems. The present study used museum material to test the performance of modern morphometrics to assess the origin of a single individual. A configuration of 13 landmarks was used to assign a single wing to its known parental line or relatives. For the 313 wings tested, correct attribution to the parental line was four times higher than expected at random. Moreover, most of the apparently wrong assignments were not random, but driven by lower levels of kinship. These results suggest that the geometry of the wing contains helpful information to identify the possible source of reinfesting specimens.
Brazil has just been certificated by Pan American Health Organization as 'free of Chagas disease transmission due to Triatoma infestans'. During the early 1980s, this species of blood-sucking bug alone was considered responsible for approximately 80% of Chagas disease transmission. But it was not always so. The species originally abundant in houses of central and eastern Brazil was Panstrongylus megistus, which seems to have been progressively displaced from houses by T. infestans during the past century. Indeed, T. infestans seems able to displace other Triatominae in artificial environments. Recent studies suggest that it might simply be because T. infestans feeds more efficiently than its Triatominae competitors.