Head morphometry and isoenzymatic profile of two Triatoma infestans Kl?g, 1834 (Hemiptera, Reduviidae) populations

The triatomine bug Triatoma infestans was probably originated in Bolivia and dispersed passively over large areas of South America, where it is the major vector of Trypanosoma cruzi. In its probable origin area this species shows two different patterns of behaviour, being found both in sylvatic and human related habitats. Such behaviour is not observed in other areas of its distribution, where it is exclusive to human related habitats. The main objective of the present study was to evaluate head morphometry characters and isoenzymes patterns of two T. infestans populations, one collected in Minas Gerais (Brazil) and other in the Cochabamba Valley (Bolivia), in order to elucidate the factors that could have an implication with the different colonization behaviour. The two populations presented differences in both morphometric (head size) and isoenzymes (specially PGM enzyme profile). The insects from the colonies reared for several years in laboratory conditions, showed reduction in head size starting from the third generation, maintaining this same size in all generations after, until 10 years after generation. The laboratory rearing conditions could be similar to human associated habitats, inducing certain level of genetic homogeneity. Our results showed increase of genetic homogeneity in Brazilian and laboratory-reared colonies from Bolivia, that may be due to a selection process due to passive dispersion, followed by several founder effects episodes and genetic drift.     

Biological cycle and preliminary data on vectorial competence of Triatoma boliviana in laboratory conditions

With more than 140 potential vectors of Chagas disease, it is important to better know the biology and especially the vectorial capacity of the triatomine species which live in the surroundings of human dwellings. In Bolivia where 17 triatomine species are reported, the principal vector is Triatoma infestans. In some valleys of the department of La Paz where T. infestans is not present, a new species (Triatoma boliviana) was described in 2007. This species lives in a sylvatic environment not far away from the dwellings, and occasionally some individuals are found inside the houses. This study was carried out to describe the biological cycle of T. boliviana and to determine its vectorial competence. The development of a cohort of 95 nymphs of first instar (N1) was followed through nymphal instars and adult stage until death in laboratory (22 °C). They were fed twice a week on an immobilized mouse. The median egg-to-adult development time was 8.4 months. The mortality by nymphal instar was lower than 7% except for N1 (67%) and N5 (18%). All nymph instars needed at least two feedings to molt (until six feedings for N5). The differentiation of a nymph into a female or a male could not be detected until the fifth instar for which the food intake was greater for a nymph developing into a female. Adults fed about once a week. The adult life span was around 400 days. The fecundity was 4.2 eggs/female/week, with a hatching rate of 50% and a hatching time of 39 days. In the same conditions, T. infestans showed a similar fecundity but a greater hatching rate and hatching time. A trial for rearing the adults at a higher temperature (26 °C) showed a drastic fall in the fecundity and in the hatching rate. The vectorial competence was analyzed for fifth instars and adults by three parameters: the ability to feed on human beings, the capacity to be infected by T. cruzi and the postfeeding defecation delay. Results showed a relatively high vectorial competence: (1) insects fed easily on the tested human being; (2) 100% of the specimens became infected by T. cruzi just by one infected meal; and (3) although the adults defecated after a median postfeeding delay greater than that of T. infestans, results on N5 suggest that they could be as good vectors as T. infestans males.     

Predominance of Trypanosoma cruzi genotypes in two reservoirs infected by sylvatic Triatoma infestans of an endemic area of Chile

We report results of Trypanosoma cruzi infection and parasite genotypes in the wild Octodon degus and synantropic reservoir Rattus rattus from an endemic area with sylvatic Triatoma infestans as the only detected vector. The infection status was determined by hemi-nested PCR directed to minicircles DNA and genotyping by hybridization tests with a panel of five specific probes, including two probes for TcI subgroups (clones 19 and 20). O. degus was found infected with 13.3% and mainly with sublineage TcIId, and less with TcIIb and TcI. Meantime the synantropic R. rattus was found infected with 27.7% and mainly with TcI and much less with TcIId, TcIIb and TcIIe.The results are discussed to explain the distribution of T. cruzi genotypes between these two reservoirs and the importance of sylvatic foci of T. infestans allowing the permanence of the wild and peridomestic cycle of Chagas disease.     

Geographic variation of Trypanosoma cruzi discrete typing units from Triatoma infestans at different spatial scales

We assessed the diversity and distribution of Trypanosoma cruzi discrete typing units (DTU) in Triatoma infestans populations and its association with local vector-borne transmission levels at various geographic scales. At a local scale, we found high predominance (92.4%) of TcVI over TcV in 68 microscope-positive T. infestans collected in rural communities in Santiago del Estero province in northern Argentina. TcV was more often found in communities with higher house infestation prevalence compatible with active vector-borne transmission. Humans and dogs were the main bloodmeal sources of the TcV- and TcVI-infected bugs. At a broader scale, the greatest variation in DTU diversity was found within the Argentine Chaco (227 microscope-positive bugs), mainly related to differences in equitability between TcVI and TcV among study areas. At a country-wide level, a meta-analysis of published data revealed clear geographic variations in the distribution of DTUs across countries. A correspondence analysis showed that DTU distributions in domestic T. infestans were more similar within Argentina (dominated by TcVI) and within Bolivia (where TcI and TcV had similar relative frequencies), whereas large heterogeneity was found within Chile. DTU diversity was lower in the western Argentine Chaco region and Paraguay (D = 0.14–0.22) than in the eastern Argentine Chaco, Bolivia and Chile (D = 0.20–0.68). Simultaneous DTU identifications of T. cruzi-infected hosts and triatomines across areas differing in epidemiological status are needed to shed new light on the structure and dynamics of parasite transmission cycles.     

Active dispersal by wild Triatoma infestans in the Bolivian Andes

Triatoma infestans is the main vector of Chagas disease and target of control programmes in the Southern Cone countries. So far Bolivia is the only country where true T. infestans wild foci are documented. The dispersal ability for wild T. infestans was studied at microgeographical scale in Bolivian Andes, to assess the possibility for wild populations to actively recolonize insecticide-treated villages. Nine microsatellite loci were used to detect the extent of gene flow between neighbouring collecting sites. The detection of restricted gene flow between close but distinct sylvatic sites supports the hypothesis that wild T. infestans does not disperse by flying at high altitude (2,750 m asl). It gradually disperses over small distances by walking within a 'patch' of continuous land cover. The genetic differentiation detected between sylvatic and domestic populations suggests a limited short-term role of wild insects in the process of recolonization of insecticide-treated houses in the Andes.     

Insecticide resistance of Triatoma infestans (Hemiptera,Reduviidae) vector of Chagas disease in Bolivia

Objective To define the insecticide resistance status of Triatoma infestans to deltamethrin (pyrethroid), malathion (organophosphate) and bendiocarb (carbamate) in Bolivia. Methods Fifty populations of T. infestans were sampled in Bolivian human dwellings. Quantal response data were obtained by topical applications of 0.2 μl of insecticide–acetone solutions on nymphs N1 of the F1 generations. For most populations, dose–mortality relationships and resistance ratios (RR) were analysed. Discriminating concentrations were established for each insecticide with a susceptible reference strain and used on the other field populations. A tarsal‐contact diagnostic test using insecticide impregnated papers was designed to rapidly identify deltamethrin‐resistant populations in the field. Results Discriminating concentrations for topical applications were 5, 70 and 120 ng active ingredient per insect for deltamethrin, bendiocarb and malathion, respectively. The diagnostic concentration for deltamethrin was 0.30% for the 1‐h exposure by tarsal contact. All populations sampled in human dwellings exhibited significant levels of resistance to deltamethrin, from 6 to 491 and varied among regions. Resistant populations did not recover complete susceptibility to deltamethrin when the synergist piperonyl butoxide (PBO) was used. None of the sampled populations exhibited significant resistance to bendiocarb (all RR₅₀ < 1.8) or malathion (all RR₅₀ < 2.2). Conclusion In Bolivia, most ‘domestic’T. infestans populations are resistant to deltamethrin. Because insecticide vector control is the only selection pressure, resistance likely originates from it. Switching from pyrethroids to organophosphates or carbamates could be a short‐term solution to control this vector, but other alternative integrated control strategies should also be considered in the long term.     

Trichinella infections in animals and humans in sub-Saharan Africa: A review

The aim of this review is to provide information on Trichinella infection in humans, livestock and wildlife in sub-Saharan Africa mainly focusing on geographical distribution of species/genotypes, biology, host range, life cycles and to identify research gaps. Trichinella britovi, Trichinella nelsoni and Trichinella zimbabwensis and one genotype (Trichinella T8) are known to occur in sub-Saharan Africa. Distinct geographic ranges with overlapping of some taxa in some areas have been observed. Genetic variants of T. nelsoni has been reported to occur among parasites originating from Eastern and Southern Africa and sequence heterogeneity also occurs among T. zimbabwensis isolates originating from different regions of Zimbabwe and South Africa. Field observations so far indicate that sylvatic Trichinella infections in the region are common in carnivores (mammals and reptiles) and to a lesser extent in omnivores. Cannibalism, scavenging and predation appear to be the most important routes of transmission and maintenance of the sylvatic cycles of the Trichinella taxa. To date, human trichinellosis has been documented in only four sub-Saharan countries (8.7%, 4/46). Bushpigs and warthogs have been the source of human infection with T. britovi and T. nelsoni being the aetiological agents. An increase in bushmeat trade and the creation of Transfrontier Conservation Areas (TFCAs) may have increased the risk of human trichinellosis in the region. With the creation of TFCAs in the region, sampling of wildlife hosts from protected areas of most sub-Sahara African countries is required to fully map the distribution of Trichinella species/genotypes in this region. More structured field surveys are still needed to determine the sylvatic host distribution of the different Trichinella taxa. Biological data of the Trichinella taxa in both wild and domestic animals of sub-Saharan Africa is very limited and further research is required.     

Genetic structure of sylvatic, peridomestic and domestic populations of Triatoma dimidiata (Hemiptera: Reduviidae) from an endemic zone of Boyaca, Colombia

Randomly amplified polymorphic DNA (RAPD) technique was used to study the genetic structure of sylvatic, peridomestic and domestic populations of Triatoma dimidiata. The genetic flow among them was calculated to establish the epidemiological risk of non-domiciliated populations in the transmission of Chagas disease in an endemic area of Boyaca, Colombia. A total of 83 adult specimens were studied: 26 sylvatic, 27 peridomestic and 30 domestic insects. Wright's Fst was 0.071 and the effective migration rate (Nm) 3.3, suggestive of low genetic differentiation and a movement of at least three insects per generation. The calculated percentage of polymorphic loci was 99%, confirming a large average heterozygosity due to a permanent contact between insects of the three populations. These results imply that non-domiciliated populations of T. dimidiata represent an epidemiological risk in the transmission of Chagas disease owing to the fact that they can colonize human dwellings. Close surveillance of non-strictly domiciliated species of triatomines such as T. dimidiata should entail not only the domicile but also the peridomicile and should include control programs of animal reservoirs. Houses enhancement, educational programs, surveillance of reinfestation and of individuals at risk of infection should be priorities in the control policies in endemic regions such as Boavita, Boyaca.     

Similarity of the patterns of sensilla on the antennae of Triatoma melanosoma and Triatoma infestans

The patterns of sensilla on the antennae of sylvatic Triatoma melanosoma Lent, Jurberg, Galvao and Carcavallo 1994 were compared with those of three samples of Triatoma infestans (Klug 1834) - one of domestic populations in Paraguay, Bolivia, Argentina and Chile, one of the sylvatic 'dark morph' from the Bolivian Chaco, and one from sylvatic sites in the Cochabamba region of Bolivia. The results of multivariate analysis indicated that, in terms of their antennal sensilla, the T. melanosoma and the 'dark morph' of T. infestans were more similar to the domestic T. infestans than to the sylvatic T. infestans from Cochabamba. As in previous molecular and genetic studies, there was no evidence to indicate that the bugs identified as T. melanosoma and those identified as T. infestans belonged to different species. The taxonomic position of T. melanosoma should therefore be reconsidered.     

Domiciliation process of Rhodnius stali (Hemiptera: Reduviidae) in Alto Beni,La Paz,Bolivia

We report a systematic collection of Triatominae inside houses and in the peridomestic environment of Alto Beni, department of La Paz, Bolivia. This area is free of Triatoma infestans and although we detected previously seropositivity for Trypanosoma cruzi, the Alto Beni region is not officially considered as endemic for Chagas disease. From 11 houses of five localities, we collected adults, nymphs and eggs of a Rhodnius species, which was confirmed by morphological and morphometric analysis as Rhodnius stali. This little-known species has long been confused with R. pictipes, and was originally described from museum specimens labelled as R. pictipes. Our data show that R. stali is able to establish colonies in domestic and peridomestic habitats in Bolivia, and it is probably the vector responsible for Chagas disease seropositivity observed in the indigenous population of Alto Beni.     

Cancer of the Gallbladder in Bolivia: Suggestions Concerning Etiology

In order to investigate the very high incidence of gallbladder cancer in Bolivia, a series of patients with gallbladder cancer and/or cholelithiasis from a hospital in La Paz was compared to a series of patients with cholelithiasis from Philadelphia. Each group demonstrated a similar female predilection. Bolivian patients with gallbladder cancer were older than patients with cholelithiasis who, in turn, were older than the general population (p less than 0.001). Racial differences demonstrated previously were confirmed. Bolivian gallstones were uniformly cholesterol in type, in contrast to the US series, in which 27% of patients had black pigment stones. Bile specimens obtained from Bolivian patients with cholelithiasis had a lower concentration of bile salts, phospholipids, and cholesterol than bile specimens from US cholelithiasis patients (p less than 0.01, less than 0.001, and less than 0.001, respectively). These biochemical differences may help to explain the differing incidence of cholelithiasis and gallbladder cancer in the US and Bolivia.     

High prevalence of Trypanosoma rangeli and Trypanosoma cruzi in opossums and triatomids in a formerly-endemic area of Chagas disease in Southeast Brazil

In Brazil Trypanosoma rangeli has been detected in humans, sylvatic mammals and vectors in the Amazon Basin and in wild rodents in a Southern State. Here we report for the first time a high prevalence of T. rangeli in opossums and triatomids captured in peridomestic environments in a formerly-endemic area of Chagas disease in Southeast Brazil. Five molecular typing tools clearly indicate the presence of T. rangeli and Trypanosoma cruzi in mammalian reservoirs and triatomids. Twenty-one opossums (Didelphis albiventris) were captured and flagellates were detected in the blood of 57.1% (12/21) of the animals. Single infections with T. rangeli or T. cruzi were diagnosed, respectively, in 58.4 and 8.3% of the opossums. Mixed infections were observed in 33.3%. Forty-four triatomids (38 Rhodnius neglectus and 6 Panstrongylus megistus) were collected in palm trees within 50 m from human dwellings. Flagellates were observed in the digestive tract and feces of 50% of the insects. PCR assays performed in DNA samples obtained from 16 cultures of the intestinal tract revealed single infection with T. cruzi (68.7%) or T. rangeli (6.3%), as well as mixed infections (25%). T. rangeli was also detected in the hemolymph of two specimens. Genotyping revealed predominance of T. cruzi I. The data suggest that R. neglectus in conjunction with D. albiventris may be significant factors in the maintenance of the sylvatic and peridomestic cycles of T. rangeli in the region. The finding of T. cruzi and T. rangeli in triatomine species capable of domiciliation and therefore considered as alternative vectors for the parasite transmission opens up the possibility of re-establishment of Chagas disease following reinfestation of houses.     

Anatomy of the Spermatophore in Triatomines (Hemiptera,Reduviidae, Triatominae) and Its Applications to the Study of Chagas Disease Vector Biology

The present study focused on spermatophore structure, transfer, and subsequent destination inside bloodfeeding females of the species Triatoma infestans and Rhodnius neglectus. The morphology of the spermatophore differed between the species studied, such that in T. infestans, the shape was ovaloid, whereas in R. neglectus, the shape resembled a rod. Structures'' spine-like cuticulars distributed across the inner surface of the vagina of both species were observed; however, the role of these cuticulars is unknown in Triatominae. In both species, there was an opening in the spermatophore exactly where the common oviduct is connected, thereby making it possible to confirm that the process of spermatozoid migration takes place through this opening. The results obtained show that the spermatophores of T. infestans and R. neglectus differ in size, shape, and structure. Therefore, they can be used as taxonomic markers and may provide information regarding physiology and evolution.     

Infestation of peridomestic Attalea phalerata palms by Rhodnius stali,a vector of Trypanosoma cruzi in the Alto Beni,Bolivia

Objectives To determine (i) whether peridomestic Attalea phalerata palms in fragmented human‐occupied areas of the Alto Beni, Bolivia, are infested by triatomines; (ii) the specific status of triatomines captured in the area; and (iii) the rate of natural Trypanosoma cruzi infection among those triatomines. Methods One hundred and twenty‐five live‐bait traps were used to sample 47 A. phalerata palms in three Alto Beni localities. Active search for vectors was also performed in 10 chicken coops and three rice storage units. Only Rhodnius specimens were found. As nymphs of closely related Rhodnius species are morphologically undistinguishable, and because of controversy in the literature regarding which Rhodnius species occur in Bolivia, collected insects were identified through molecular taxonomy. Phylogenetic analyses of DNA sequences obtained for a fragment of the mitochondrial cytochrome b gene and for the nuclear ITS‐2 ribosomal region were used as molecular markers. Natural infection rates were determined using a pair of primers that PCR‐amplify a 330‐bp fragment of the parasite’s kDNA. Results Twelve nymphs were captured in five A. phalerata palms (from two of the three localities studied), and an adult was collected from a chicken coop in Iniqua (and morphologically identified as Rhodnius stali). All nymphs (as well as the adult) were molecularly identified as R. stali based on the two molecular markers used. A single nymph was found to be infected with T. cruzi. Conclusions Attalea phalerata palms represent an important sylvatic ecotope occupied by R. stali in the Alto Beni region of Bolivia, where there are signs of T. cruzi transmission to humans, despite the preliminary indication of low level of natural infection of the vectors.     

Ecohealth Interventions Limit Triatomine Reinfestation following Insecticide Spraying in La Brea,Guatemala

In this study, we evaluate the effect of participatory Ecohealth interventions on domestic reinfestation of the Chagas disease vector Triatoma dimidiata after village-wide suppression of the vector population using a residual insecticide. The study was conducted in the rural community of La Brea, Guatemala between 2002 and 2009 where vector infestation was analyzed within a spatial data framework based on entomological and socio-economic surveys of homesteads within the village. Participatory interventions focused on community awareness and low-cost home improvements using local materials to limit areas of refuge and alternative blood meals for the vector within the home, and potential shelter for the vector outside the home. As a result, domestic infestation was maintained at ≤ 3% and peridomestic infestation at ≤ 2% for 5 years beyond the last insecticide spraying, in sharp contrast to the rapid reinfestation experienced in earlier insecticide only interventions.     

Microgeographical study of insecticide resistance in Triatoma infestans from Argentina

Chagas disease is a chronic parasitic infection restricted to America where it is currently estimated that 90 million people are at risk of acquiring the infection. Chemical control with pyrethroid insecticides has been effective to reduce disease transmission in several areas of the Southern Cone, although insecticide resistance has evolved and diminished the campaigns’ results. Considering previous reports on the different levels of resistance between Triatoma infestans from different geographical areas, the objective of this work was to determine if T. infestans populations are toxicologically structured within localities. Response to the insecticide was measured and compared between houses of two Argentine localities. Different toxicity of deltamethrin was detected between dwellings of Chaco province, accounting for both susceptible and resistant houses within the same locality. However no difference was found among houses of Salta province. The results obtained in this work suggest that geographical structure is present not only at the between localities level, but also at the microgeograhical level.     

Feeding performance of Triatoma brasiliensis (Hemiptera: Reduviidae) on habitual hosts: Thrichomys laurentius (Rodentia: Echimyidae) and humans

Triatoma brasiliensis is an important vector of Trypanosoma cruzi in the semiarid zones of Northeastern Brazil where it is commonly found in human dwellings, peridomiciliary areas, and the wild environments. To better understand features that may be influencing the interaction of T. brasiliensis with its hosts, in the present work we compared the feeding performance of sylvatic and domestic populations of T. brasiliensis on humans and on Thrichomys laurentius, a wild rodent found in the natural ecotopes of T. brasiliensis. The analyses were performed using the electronic monitoring of the cibarial pump. The blood sources considerably affected the feeding parameters. Insects fed on T. laurentius had lower ingestion rate, gained less weight, had longer interruption time, remained less time in contact with the host, and had the contractions of the pump in a lower frequency during the feeding process in comparison to insects fed on humans. These results indicate that humans are better blood sources for T. brasiliensis than T. laurentius. The fact that there was no difference between the feeding performance of sylvatic and domestic insects suggests that feeding is not a barrier for the domiciliation. Together, these findings suggest that shelter and faster blood meals are qualities of human dwellings that facilitate the domiciliation of T. brasiliensis.     

Regional Variation in the Correlation of Antibody and T-Cell Responses to Trypanosoma cruzi

Chagas disease, caused by the protozoan parasite Trypanosoma cruzi, is a major cause of morbidity and mortality in Central and South America. Geographic variations in the sensitivity of serologic diagnostic assays to T. cruzi may reflect differences in T. cruzi exposure. We measured parasite-specific T-cell responses among seropositive individuals in two populations from South America with widely varying antibody titers against T. cruzi. Antibody titers among seropositive individuals were significantly lower in Arequipa, Peru compared with Santa Cruz, Bolivia. Similarly, the proportion of seropositive individuals with positive T-cell responses was lower in Peru than Bolivia, resulting in overall lower frequencies of interferon-γ (IFNγ)-secreting cells from Peruvian samples. However, the magnitude of the IFNγ response was similar among the IFNγ responders in both locations. These data indicate that immunological discrepancies based on geographic region are reflected in T-cell responses as well as antibody responses.     

Field evaluation of enzyme-linked immunosorbent assay for the serodiagnosis of tuberculosis

An enzyme-linked immunosorbent assay (ELISA) was evaluated as a serodiagnostic test for active tuberculosis in La Paz, Bolivia. ELISA was compared with sputum smear in 277 persons presenting to the Instituto de Torax and was used for screening in 1,458 military personnel. The test was performed under field conditions on 4-microliter samples of capillary blood obtained by finger prick. ELISA was found to have a sensitivity of 69% and a specificity of 88%. Sputum smear had a sensitivity of 79% and a specificity of 100%. ELISA was found to have undiminished sensitivity and specificity in patients who were sputum-negative, and the two tests could be combined to achieve a sensitivity of 92% and specificity of 88%. Positive and negative predictive values were highest for populations with tuberculosis prevalences in the range of that seen among patients presenting to the Instituto de Torax in Bolivia, but ELISA also led to the diagnosis of tuberculosis in 5 of 1,458 soldiers tested in the screening program.