Is imidacloprid an effective alternative for controlling pyrethroid-resistant populations of Triatoma infestans (Hemiptera: Reduviidae) in the Gran Chaco ecoregion?

The prevention of Chagas disease is based primarily on the chemical control of Triatoma infestans (Klug) using pyrethroid insecticides. However, high resistance levels, correlated with control failures, have been detected in Argentina and Bolivia. A previous study at our laboratory found that imidacloprid could serve as an alternative to pyrethroid insecticides. We studied the delayed toxicity of imidacloprid and the influence of the blood feeding condition of the insect on the toxicity of this insecticide; we also studied the effectiveness of various commercial imidacloprid formulations against a pyrethroid-resistant T. infestans population from the Gran Chaco ecoregion. Variations in the toxic effects of imidacloprid were not observed up to 72 h after exposure and were not found to depend on the blood feeding condition of susceptible and resistant individuals. Of the three different studied formulations of imidacloprid on glass and filter paper, only the spot-on formulation was effective. This formulation was applied to pigeons at doses of 1, 5, 20 and 40 mg/bird. The nymphs that fed on pigeons treated with 20 mg or 40 mg of the formulation showed a higher mortality rate than the control group one day and seven days post-treatment (p < 0.01). A spot-on formulation of imidacloprid was effective against pyrethroid-resistant T. infestans populations at the laboratory level.

Domestic, peridomestic and wild hosts in the transmission of Trypanosoma cruzi in the Caatinga area colonised by Triatoma brasiliensis

The role played by different mammal species in the maintenance of Trypanosoma cruzi is not constant and varies in time and place. This study aimed to characterise the importance of domestic, wild and peridomestic hosts in the transmission of T. cruzi in Tauá, state of Ceará, Caatinga area, Brazil, with an emphasis on those environments colonised by Triatoma brasiliensis. Direct parasitological examinations were performed on insects and mammals, serologic tests were performed on household and outdoor mammals and multiplex polymerase chain reaction was used on wild mammals. Cytochrome b was used as a food source for wild insects. The serum prevalence in dogs was 38% (20/53), while in pigs it was 6% (2/34). The percentages of the most abundantly infected wild animals were as follows: Thrichomys laurentius 74% (83/112) and Kerodon rupestris 10% (11/112). Of the 749 triatomines collected in the household research, 49.3% (369/749) were positive for T. brasiliensis, while 6.8% were infected with T. cruzi (25/369). In captured animals, T. brasiliensis shares a natural environment with T. laurentius, K. rupestris, Didelphis albiventris, Monodelphis domestica, Galea spixii, Wiedomys pyrrhorhinos, Conepatus semistriatus and Mus musculus. In animals identified via their food source, T. brasiliensis shares a natural environment with G. spixii, K. rupestris, Capra hircus, Gallus gallus, Tropidurus oreadicus and Tupinambis merianae. The high prevalence of T. cruzi in household and peridomiciliar animals reinforces the narrow relationship between the enzootic cycle and humans in environments with T. brasiliensis and characterises it as ubiquitous.

The peri-urban interface and house infestation with Triatoma infestans in the Argentine Chaco: an underreported process?

Peri-urban infestations with triatomine bugs, their sources and their dynamics have rarely been investigated. Here, we corroborated the reported occurrence of Triatoma infestans in a peri-urban area and in neighbouring rural houses in Pampa del Indio, in the Argentine Chaco, and identified its putative sources using spatial analysis and demographic questionnaires. Peri-urban householders reported that 10% of their premises had triatomines, whereas T. infestans was collected by timed manual searches or community-based surveillance in only nine (3%) houses. Trypanosoma cruzi-infected T. infestans and Triatoma sordida were collected indoors only in peri-urban houses and were infected with TcV and TcI, respectively. The triatomines fed on chickens, cats and humans. Peri-urban infestations were most frequent in a squatter settlement and particularly within the recently built mud houses of rural immigrants, with large-sized households, more dogs and cats and more crowding. Several of the observed infestations were most likely associated with passive bug transport from other sources and with active bug dispersal from neighbouring foci. Thus, the households in the squatter settlement were at a greater risk of bug invasion and colonisation. In sum, the incipient process of domestic colonisation and transmission, along with persistent rural-to-urban migratory flows and unplanned urbanisation, indicate the need for active vector surveillance and control actions at the peri-urban interface of the Gran Chaco.

Factors associated with the occurrence of Triatoma sordida (Hemiptera: Reduviidae) in rural localities of Central-West Brazil

This study estimates the factors of artificial environments (houses and peridomestic areas) associated with Triatoma sordida occurrence. Manual searches for triatomines were performed in 136 domiciliary units (DUs) in two rural localities of Central-West Brazil. For each DU, 32 structural, 23 biotic and 28 management variables were obtained. Multiple logistic regression analysis was performed in order to identify statistically significant variables associated with occurrence of T. sordida in the study areas. A total of 1,057 specimens (99% in peridomiciles, mainly chicken coops) of T. sordida were collected from 63 DUs (infestation: 47%; density: ~8 specimens/DU; crowding: ~17 specimens/infested DU; colonisation: 81%). Only six (0.6%) out of 945 specimens examined were infected with Trypanosoma cruzi. The final adjusted logistic regression model indicated that the probability of T. sordida occurrence was higher in DU with wooden chicken coops, presence of > 30 animals in wooden corrals, presence of wood piles and presence of food storeroom. The results show the persistence of T. sordida in peridomestic habitats in rural localities of Central-West Brazil. However, the observed low intradomestic colonisation and minimal triatomine infection rates indicate that T. sordida has low potential to sustain high rates of T. cruzi transmission to residents of these localities.

The rising importance of Triatoma rubrofasciata

The migration of invasive vector species has contributed to the worldwide extension of infectious diseases such as dengue (Aedes aegypti) and chikungunya (Aedes albopictus). It is probably a similar behaviour for certain vectors of Chagas disease which allowed it to become a continental burden in Latin America. One of them, Triatoma rubrofasciata has also been spreading throughout the tropical and subtropical world. Here, the recent and massive peridomestic presence of T. rubrofasciata in Vietnam cities is reported, and tentatively explained, highlighting the need for improved entomological surveillance.

Thermal preferences and limits of Triatoma brasiliensis in its natural environment - Field observations while host searching

The goal of this work was to explore the thermal relationship between foraging Triatoma brasiliensis and its natural habitat during the hottest season in the state of Ceará, Brazil. The thermal profiles were determined using infrared analysis. Although the daily temperature of rock surfaces varied in a wide range, T. brasiliensisselected to walk through areas with temperatures between 31.7-40.5ºC. The temperature of T. brasiliensisbody surface ranged from 32.8-34.4ºC, being higher in legs than the abdomen. A strong relationship was found between the temperature of the insect and the temperature of rock crevices where they were hidden (r: 0.96, p < 0.05). The species was active at full sunlight being a clear example of how the light-dark rhythm may be altered, even under predation risk. Our results strongly suggest a thermal borderline for T. brasiliensisforaging activity near 40ºC. The simultaneous determination of insect body and rock temperatures here presented are the only obtained in natural habitats for this or other triatomines.

Assessing the mitochondrial DNA diversity of the Chagas disease vector Triatoma sordida (Hemiptera: Reduviidae)

Triatoma sordida is a species that transmits Trypanosoma cruzi to humans. In Brazil, T. sordida currently deserves special attention because of its wide distribution, tendency to invade domestic environments and vectorial competence. For the planning and execution of control protocols to be effective against Triatominae, they must consider its population structure. In this context, this study aimed to characterise the genetic variability of T. sordida populations collected in areas with persistent infestations from Minas Gerais, Brazil. Levels of genetic variation and population structure were determined in peridomestic T. sordida by sequencing a polymorphic region of the mitochondrial cytochrome b gene. Low nucleotide and haplotype diversity were observed for all 14 sampled areas; π values ranged from 0.002-0.006. Most obtained haplotypes occurred at low frequencies, and some were exclusive to only one of the studied populations. Interpopulation genetic diversity analysis revealed strong genetic structuring. Furthermore, the genetic variability of Brazilian populations is small compared to that of Argentinean and Bolivian specimens. The possible factors related to the reduced genetic variability and strong genetic structuring obtained for studied populations are discussed in this paper.

Preferencia de los sitios y alturas de reposo de Triatoma gerstaeckeri Stal (Hemíptera: Reduviidae) bajo condiciones de laboratorio y campo [por] José Luis Torres Estrada

Tesis (Maestría en Ciencias con Especialidad en Entomología Médica) U.A.N.L.

Rural Triatoma rubrovaria from Southern Brazil harbors Trypanosoma cruzi of lineage IIc

Triatoma infestans, the main vector of Chagas disease, has nearly been eliminated from Brazil. Nevertheless, other triatominae species are involved in the domiciliation process, including Triatoma rubrovaria in Rio Grande do Sul State (RS). Previous studies showed that 1.6% of the T rubrovaria specimens collected at the rural district of Quarai, RS, were naturally infected by Trypanosoma cruzi. In this study, five T. cruzi isolates obtained from infected triatomines were characterized molecularly and biologically. Genotyping of the T cruzi isolates showed that they belong to lineage IIc of T cruzi (TCIIc). Biological characterization showed miotropism and myositis during acute and chronic phases of infection, respectively. Virulence and mortality rates were variable among isolates. To our knowledge, this study corresponds to the first characterization of T cruzi isolates from T rubrovaria and the first description of TCIIc in the sylvatic cycle of T cruzi from the southern region of Brazil.

A short proregion of trialysin, a pore-forming protein of Triatoma infestans salivary glands, controls activity by folding the N-terminal lytic motif

Triatoma infestans (Hemiptera: Reduviidae) is a hematophagous insect that transmits the protozoan parasite Trypanosoma cruzi, the etiological agent of Chagas` disease. Its saliva contains trialysin, a protein that forms pores in membranes. Peptides based on the N-terminus of trialysin lyse cells and fold into alpha-helical amphipathic segments resembling antimicrobial peptides. Using a specific antiserum against trialysin, we show here that trialysin is synthesized as a precursor that is less active than the protein released after saliva secretion. A synthetic peptide flanked by a fluorophore and a quencher including the acidic proregion and the lytic N-terminus of the protein is also less active against cells and liposomes, increasing activity upon proteolysis. Activation changes the peptide conformation as observed by fluorescence increase and CD spectroscopy. This mechanism of activation could provide a way to impair the toxic effects of trialysin inside the salivary glands, thus restricting damaging lytic activity to the bite site.

Phylogeny of Triatoma sherlocki (Hemiptera: Reduviidae: Triatominae) Inferred from Two Mitochondrial Genes Suggests Its Location Within the Triatoma brasiliensis Complex

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Description of eggs and nymphal instars of Triatoma baratai Carcavallo & Jurberg, 2000 based on optical and scanning electron microscopy (Hemiptera: Reduviidae: Triatominae)

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Dispersion capacity of Triatoma sherlocki, Triatoma juazeirensis and laboratory-bred hybrids

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)