Triatoma maculata, the Vector of Trypanosoma cruzi, in Venezuela. Phenotypic and Genotypic Variability as Potential Indicator of Vector Displacement into the Domestic Habitat

Enzootic Trypanosoma cruzi infection by Rhodnius prolixus shows transmission to humans and dogs in Vichada, Colombia

Background

Rhodnius prolixus is considered the most relevant Trypanosoma cruzi vector in Colombia and Venezuela due it is responsible for domestic transmission in both countries. However, a wild population of this species is distributed in the eastern plains of the Orinoco region and Amazonia jungle, where its epidemiological importance has not been sufficiently elucidated. This study aimed to assess epidemiological parameters of T. cruzi transmission in the Department of Vichada, Colombia.

Methods

We determined the characteristics of T. cruzi transmission using entomological studies in domestic and sylvatic ecotopes. We analyzed the T. cruzi infection in triatomine insects, identified blood meal sources, and conducted a serological determination of T. cruzi infection in scholar-aged children, domestic dogs, and wild hosts.

Results

Fifty-four triatomine bugs, 40 T. maculata and 14 R. prolixus were collected in peridomestic and sylvatic ecotopes. Infected R. prolixus was observed in La Primavera, Santa Rosalia, and Cumaribo municipalities. All the T. maculata bugs were not infected. Serological analysis indicated that two of 3,425 children were T. cruzi positive. The seroprevalence in domestic dogs was 10,5% (49/465). Moreover, 22 synanthropic mammals were sampled, being Didelphis marsupialis the most common. TcI genotype was detected in seropositive dogs, R. prolixus, and D. marsupialis.

Conclusion

The present work describes extra domestic R. prolixus and D. marsupialis in a sylvatic T. cruzi transmission cycle with transmission to humans and domestic dogs in Colombia’s Vichada Department.

Infections and Coinfections by Trypanosomatid Parasites in a Rural Community of Venezuela

INTRODUCTION

Trypanosoma cruzi, Trypanosoma rangeli and Leishmania spp. are parasites that coexist in several endemic areas. The identification of these parasites in hosts is important for the control programs.

METHODS

216 samples from human blood (101), blood of other mammals (45) and triatomine intestinal content and hemolymph (70), from an endemic area of Venezuela, were analysed. The samples were evaluated by; serology (only humans) and PCR for T. cruzi in human, other mammals and triatomines, PCR for T. rangeli in mammals-including human and triatomines and PCR for Leishmania in mammals-including human.

RESULTS

The 9.9% of the human samples were positive for T. cruzi by serology, 11.9% by PCR, 4% for T. rangeli PCR and none for Leishmania spp. PCR. 60% of the samples of other mammals showed DNA amplification for T. cruzi, 42.2% for T. rangeli and 4.4% for Leishmania spp. 61.4% of the triatomine samples showed DNA amplification for T. cruzi and 10% for T. rangeli.

CONCLUSIONS

High T. cruzi infection was detected in mammals and triatomines compared with T. rangeli. Low leishmanial infection was detected in other mammals. It is the first time that T. cruzi/T. rangeli coinfection, in humans, Canis familiaris (dog), and Bos Taurus (cow), were reported world-wide, and that this coinfection was described in Tamandua tetradactyla (anteater) from Venezuela. The coinfection T. cruzi/T. rangeli in mammals-including humans and triatomines, and coinfection T. cruzi/Leishmania spp. in non-human mammals, show the risk for trypanosomic zoonoses in this endemic area.

Chagas Disease Expands Its Epidemiological Frontiers From Rural to Urban Areas

The infection with the hemoflagellate parasite Trypanosoma cruzi originates from America where the wildlife cycle remains to alternate between mammals and hematophagous triatomines. Transmission through contamination of the bite site by vector feces containing highly infectious forms of parasite or direct ingestion of T. cruzi-infected triatomines appear to be the dominant transmission mechanisms. Man joins the transmission when he enters this wild environment or takes the leaves of palms carrying vectors to build houses. Rural Chagas disease develops associated with populations of low economic resources, with infection and reinfection of vector bites since childhood, and the consequent evolution toward chronic cases in adults, when there is little therapeutic benefit to infected people. The progressive migration of people from rural to urban areas and the adaptation of vectors to the peripheries of cities due to displacement caused by deforestation or urbanization that has favored the presence of enzootic cycles with Panstrongylus geniculatus as the most widely distributed species and mammals (synanthropic and domestic) allow vector transmission by ingestion of food contaminated with excrements containing infectious trypomastigotes as the dominant transmission mechanism in the urban environment. Human-to-human transmissions through vertical mother–child infection, transfusions, organ transplants, and the possibility of sexual transmission, transform the epidemiology and the clinical evolution of Chagas disease in the urban environment. Vectors of American trypanosomiasis are no longer restricted to the endemic area, but its presence has been demonstrated in nonendemic areas of the United States, Asia, and other latitudes. The worldwide plague of bedbugs (Cimex lectularius) threatens the possibility of expansion of transmission since they are vectors susceptible to infection, transmission to mammals, trans-stadial penetration, and not being affected by T. cruzi infection at least experimentally. These factors, added to the presence of an unknown number of migrating Latin American asymptomatic carriers together with the presence of triatomines in other continents, have initiated the globalization of a pathology originating in the American continent. Only with an integrative approach, based on new and better tolerated and efficient drugs, vaccines and residual action insecticides, all of them included in an epidemiological surveillance program.

Domiciliation and sympatry of Triatoma maculata and Rhodnius prolixus, risk of Trypanosoma cruzi transmission in villages of Anzoátegui, Venezuela

The domiciliation of Triatoma maculata and Rhodnius prolixus and the entomological risk indicators for the transmission of Trypanosoma cruzi, an etiological agent of Chagas Disease-CD, were studied in rural villages of Anzoátegui state, Venezuela. Nightly home visits were made for 4 months/year, for 2 years, to search for and capture triatomines in human settlements. For six of the evaluated villages, 16.4% (11/67) of houses were found with triatomine infestation; obtaining 151 triatomines in all their ontogenetic stages, of which 54.3% (82/151) corresponded to T. maculata and 45.7% (69/151) to R. prolixus. In 7.5% of the evaluated houses, both species were presented in sympatry. Entomological indicators of transmission risk were higher for T. maculata in relation to R. prolixus. Inoculation of fecal flagellates of triatomines produced 2.92 × 10⁵ flagellates/mL of blood in mean and 100% mortality in the murine model. Molecular tests (satellite DNA, kDNA and DTUs studies) demonstrated the presence of T. cruzi, all compatible with TcI. The food source determined by IESPA, revealed that R. prolixus showed less eclecticism in relation to T. maculata in the use of blood sources. This could be an indicator of an older domiciliation with low dispersion between ecotopes. The sympatry of T. maculata and R. prolixus had been recorded in natural niches, but for the first time it is recorded inside the houses in rural villages of the Anzoátegui state. Human dwellings can constitute an adequate niche, with available food sources for both triatomines species and with the risk of establishing AT/CD as zoonosis or zooanthroponosis.

Geographic abundance patterns explained by niche centrality hypothesis in two Chagas disease vectors in Latin America

Ecoepidemiological scenarios for Chagas disease transmission are complex, so vector control measures to decrease human–vector contact and prevent infection transmission are difficult to implement in all geographic contexts. This study assessed the geographic abundance patterns of two vector species of Chagas disease: Triatoma maculata (Erichson, 1848) and Rhodnius pallescens (Barber, 1932) in Latin America. We modeled their potential distribution using the maximum entropy algorithm implemented in Maxent and calculated distances to their niche centroid by fitting a minimum-volume ellipsoid. In addition, to determine which method would accurately explain geographic abundance patterns, we compared the correlation between population abundance and the distance to the ecological niche centroid (DNC) and between population abundance and Maxent environmental suitability. The potential distribution estimated for T. maculata showed that environmental suitability covers a large area, from Panama to Northern Brazil. R. pallescens showed a more restricted potential distribution, with environmental suitability covering mostly the coastal zone of Costa Rica and some areas in Nicaragua, Honduras, Belize and the Yucatán Peninsula in Mexico, northern Colombia, Acre, and Rondônia states in Brazil, as well as a small region of the western Brazilian Amazon. We found a negative slope in the relationship between population abundance and the DNC in both species. R. pallecens has a more extensive potential latitudinal range than previously reported, and the distribution model for T. maculata corroborates previous studies. In addition, population abundance increases according to the niche centroid proximity, indicating that population abundance is limited by the set of scenopoetic variables at coarser scales (non-interactive variables) used to determine the ecological niche. These findings might be used by public health agencies in Latin America to implement actions and support programs for disease prevention and vector control, identifying areas in which to expand entomological surveillance and maintain chemical control, in order to decrease human–vector contact.

Untangling the transmission dynamics of primary and secondary vectors of Trypanosoma cruzi in Colombia: parasite infection, feeding sources and discrete typing units

BACKGROUND

Trypanosoma cruzi is the causative agent of Chagas disease. Due to its genetic diversity has been classified into six Discrete Typing Units (DTUs) in association with transmission cycles. In Colombia, natural T. cruzi infection has been detected in 15 triatomine species. There is scarce information regarding the infection rates, DTUs and feeding preferences of secondary vectors. Therefore, the aim of this study was to determine T. cruzi infection rates, parasite DTU, ecotopes, insect stages, geographical location and bug feeding preferences across six different triatomine species.

METHODS

A total of 245 insects were collected in seven departments of Colombia. We conducted molecular detection and genotyping of T. cruzi with subsequent identification of food sources. The frequency of infection, DTUs, TcI genotypes and feeding sources were plotted across the six species studied. A logistic regression model risk was estimated with insects positive for T. cruzi according to demographic and eco-epidemiological characteristics.

RESULTS

We collected 85 specimens of Panstrongylus geniculatus, 77 Rhodnius prolixus, 37 R. pallescens, 34 Triatoma maculata, 8 R. pictipes and 4 T. dimidiata. The overall T. cruzi infection rate was 61.2% and presented statistical associations with the departments Meta (OR: 2.65; 95% CI: 1.69-4.17) and Guajira (OR: 2.13; 95% CI: 1.16-3.94); peridomestic ecotope (OR: 2.52: 95% CI: 1.62-3.93); the vector species P. geniculatus (OR: 2.40; 95% CI: 1.51-3.82) and T. maculata (OR: 2.09; 95% CI: 1.02-4.29); females (OR: 2.05; 95% CI: 1.39-3.04) and feeding on opossum (OR: 3.15; 95% CI: 1.85-11.69) and human blood (OR: 1.55; 95% CI: 1.07-2.24). Regarding the DTUs, we observed TcI (67.3%), TcII (6.7%), TcIII (8.7%), TcIV (4.0%) and TcV (6.0%). Across the samples typed as TcI, we detected TcIDom (19%) and sylvatic TcI (75%). The frequencies of feeding sources were 59.4% (human blood); 11.2% (hen); 9.6% (bat); 5.6% (opossum); 5.1% (mouse); 4.1% (dog); 3.0% (rodent); 1.0% (armadillo); and 1.0% (cow).

CONCLUSIONS

New scenarios of T. cruzi transmission caused by secondary and sylvatic vectors are considered. The findings of sylvatic DTUs from bugs collected in domestic and peridomestic ecotopes confirms the emerging transmission scenarios in Colombia.

Triatoma maculata colonises urban domicilies in Boa Vista, Roraima, Brazil

During a medical entomology course in Boa Vista, Roraima, colonies of Triatoma maculata closely associated with pigeon nests were observed in concrete air-conditioner box located on the external plastered and cemented walls of a modern brick-built apartment block. In only one eight-hole ceramic brick, located inside one air-conditioner box, 127 specimens of T. maculata were collected. T. maculata is a recognised vector of Trypanosoma cruzi in the surrounding area and its domiciliation increases the risk of Chagas disease transmission.

Trypanosoma cruzi, the Causal Agent of Chagas Disease: Boundaries between Wild and Domestic Cycles in Venezuela

Trypanosoma cruzi the etiological agent of American Trypanosomiasis or Chagas disease (ChD) is transmitted by triatomines vectors between mammals including man. T. cruzi has existed for circa 150 Ma in the Americas and nearly 10 million people are currently infected. The overlap between wild and domestic ecotopes where T. cruzi circulates is increasing. Host–parasite interactions have been determined by infection patterns in these cycles, all under natural or laboratorial conditions. This mini-review describes specific parasite niches, such as plant communities or biological corridors between domestic and wild landscapes, in order to help identify risk factors for ChD and define the boundaries between wild and domestic transmission cycles, with an emphasis on research undertaken in Venezuela.