Differences of susceptibility of five triatomine species to pyrethroid insecticides - implications for Chagas disease vector control

As pyrethroids are presently the favored group of insecticides to control triatomines, we performed a series of bioassays to determine the intrinsic activity of some of the main compounds used in the control campaigns, against five of the main species of triatomines to be controlled. Comparing the insecticides it can be seen that lambdacyhalothrin is more effective than the other three pyrethroids, both considering the LD50 and 99 for all the three species with comparable results. On Triatoma infestans the LD50 of lambdacyhalothrin was followed by that of alfacypermethrin, cyfluthrin and deltamethrin. On Rhodnius prolixus the sequence, in decreasing order of activity, was lambdacyhalothrin, alfacypermethrin, deltamethrin and cyfluthrin. Some modifications can be seen when we compare the LD99, that has more to see to what happens in the field. T. brasiliensis showed to be as sensible to lambdacyhalothrin as T. infestans, the most susceptible for this product. By the other side T. sordida is the least susceptible considering the LD99 of this insecticide.

Inter-specific and developmental differences on the array of antennal chemoreceptors in four species of triatominae (Hemiptera: Reduviidae)

The aim of the work was to investigate the pattern of chemoreceptor sensilla in adults and fifth stage nymphs of Rhodnius prolixus, R. neglectus, Triatoma infestans and T. sordida in order to study differences and similarities between genera and species. Three types of sensilla were analyzed by light microscopy: thin-walled trichoidea, thick-walled trichoidea and basiconica. The number of sensilla of each three types were counted. The length of the antennal segments were also used as a variable for the analysis. The statistical analysis showed that the number of these antennal chemoreceptors had significant differences between species and between adults and nymphs of each species. Discriminant analysis separates incompletely the fifth stage nymphs of the four species and showed similarity between them. Discriminant analysis performed with 12 variables of the antennae, allowed a complete separation of the adults of the four species.

Freshwater snails and schistosomiasis mansoni in the State of Rio de Janeiro, Brazil: I - metropolitan mesoregion

In order to elaborate a planorbid chart of the State of Rio de Janeiro a survey of freshwater gastropods in the Metropolitan Mesoregion of this State was performed and revealed the occurrence of 20 species: Antillorbis nordestensis (Lucena, 1954); Biomphalaria glabrata (Say, 1818); Biomphalaria schrammi (Crosse, 1864); Biomphalaria straminea (Dunker, 1848); Biomphalaria tenagophila (Orbigny, 1835); Burnupia sp.; Drepanotrema anatinum (Orbigny, 1835); Drepanotrema cimex (Moricand, 1839); Drepanotrema lucidum (Pfeiffer, 1839); Ferrissia sp.; Gundlachia ticaga (Marcus & Marcus, 1962); Heleobia davisi Silva & Thomé, 1985; Lymnaea columella Say, 1817; Melanoides tuberculatus (Müller, 1774); Physa cubensis Pfeiffer, 1839; Physa marmorata Guilding, 1828; Pomacea sp.; Pomacea canaliculata (Lamarck, 1822); Pomacea lineata (Spix, 1827) and Pomacea sordida (Swainson, 1823). Among the planorbid species B. tenagophila was the most frequent, occurring in all municipalities surveyed. The present study extends the distribution of B. straminea in the State of Rio de Janeiro and reports new records for A. nordestensis, B. schrammi, G. ticaga, H. davisi and the genera Burnupia and Ferrissia. An account about the current transmission areas of schistosomiasis mansoni in this Mesoregion is presented as well.

Triatomines Involved in Domestic and Wild Trypanosoma cruzi Transmission in Concepción, Corrientes, Argentina

An entomological and serological survey was performed in three localities of the Department of Concepción, Province of Corrientes, Argentina in 1998 and 1999, to identify triatomines species involved in domestic and wild transmission of Chagas disease. Triatomines were collected by man/hour capture in 32 houses randomly selected and 44 nearby outdoor ecotopes. Trypanosoma cruzi infection in triatomines was assessed by direct microscopic observation (400x) of feces and polymerase chain reaction. Serological techniques used for people were Indirect Hemagglutination Test and Indirect Fluorescent Test. Triatomines were collected in 28.1% of the houses and 31.8% of the wild biotopes. Triatoma infestans (Klug 1834) was exclusively found indoors and T. cruzi infected 60% of them. Triatoma sordida (Stål 1859) was mainly found in extradomestic ecotopes where trypanosome infection rate reached 12.7%. Serological study of 98 local people showed that 29.6% were seroreactive; most of their houses were closed to wild biotopes colonized by T. sordida. Results indicate that there is an active T. infestans mediated transmission of Chagas disease in this zone that yields important human prevalence and that the populations of T. sordida in wild biotopes not only sustain the wild T. cruzi cycle but also represent an actual risk for people living in the area.

The impact of Chagas disease control in Latin America: a review

Discovered in 1909, Chagas disease was progressively shown to be widespread throughout Latin America, affecting millions of rural people with a high impact on morbidity and mortality. With no vaccine or specific treatment available for large-scale public health interventions, the main control strategy relies on prevention of transmission, principally by eliminating the domestic insect vectors and control of transmission by blood transfusion. Vector control activities began in the 1940s, initially by means of housing improvement and then through insecticide spraying following successful field trials in Brazil (Bambui Research Centre), with similar results soon reproduced in São Paulo, Argentina, Venezuela and Chile. But national control programmes only began to be implemented after the 1970s, when technical questions were overcome and the scientific demonstration of the high social impact of Chagas disease was used to encourage political determination in favour of national campaigns (mainly in Brazil). Similarly, large-scale screening of infected blood donors in Latin America only began in the 1980s following the emergence of AIDS. By the end of the last century it became clear that continuous control in contiguous endemic areas could lead to the elimination of the most highly domestic vector populations - especially Triatoma infestans and Rhodnius prolixus - as well as substantial reductions of other widespread species such as T. brasiliensis, T. sordida, and T. dimidiata, leading in turn to interruption of disease transmission to rural people. The social impact of Chagas disease control can now be readily demonstrated by the disappearance of acute cases and of new infections in younger age groups, as well as progressive reductions of mortality and morbidity rates in controlled areas. In economic terms, the cost-benefit relationship between intervention (insecticide spraying, serology in blood banks) and the reduction of Chagas disease (in terms of medical and social care and improved productivity) is highly positive. Effective control of Chagas disease is now seen as an attainable goal that depends primarily on maintaining political will, so that the major constraints involve problems associated with the decentralisation of public health services and the progressive political disinterest in Chagas disease. Counterbalancing this are the political and technical cooperation strategies such as the "Southern Cone Initiative" launched in 1991. This international approach, coordinated by PAHO, has been highly successful, already reaching elimination of Chagas disease transmission in Uruguay, Chile, and large parts of Brazil and Argentina. The Southern Cone Initiative also helped to stimulate control campaigns in other countries of the region (Paraguay, Bolivia, Peru) which have also reached tangible regional successes. This model of international activity has been shown to be feasible and effective, with similar initiatives developed since 1997 in the Andean Region and in Central America. At present, Mexico and the Amazon Region remain as the next major challenges. With consolidation of operational programmes in all endemic countries, the future focus will be on epidemiological surveillance and care of those people already infected. In political terms, the control of Chagas disease in Latin America can be considered, so far, as a victory for international scientific cooperation, but will require continuing political commitment for sustained success.

Relationship between antennal sensilla pattern and habitat in six species of Triatominae

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.

Freshwater snails and Schistosomiasis mansoni in the state of Rio de Janeiro, Brazil: IV - Sul Fluminense Mesoregion

In this paper, the forth of a series dealing with the survey of freshwater gastropods of the state of Rio de Janeiro, the results of collections carried out in the Sul Fluminense Mesoregion from 2000 to 2002 are presented and revealed the occurrence of 18 species: Antillorbis nordestensis; Biomphalaria glabrata; Biomphalaria peregrina; Biomphalaria straminea; Biomphalaria tenagophila; Drepanotrema anatinum; Drepanotrema cimex; Drepanotrema lucidum; Ferrissia sp.; Gundlachia ticaga; Gundlachia sp.; Heleobia sp.; Lymnaea columella; Melanoides tuberculatus; Physa acuta; Physa marmorata; Pomacea sordida and Pomacea sp. As to the snail hosts of Schistosoma mansoni the most frequent species was B. tenagophila, found in all municipalities surveyed, except Parati. Besides new records the present study extends the distribution of B. peregrina and B. straminea in the state. No specimens were found harbouring larval forms of S. mansoni although different kinds of cercariae had been observed. An account about the current schistosomiasis transmission sites in this Mesoregion is presented as well.

Freshwater snails and schistosomiasis mansoni in the state of Rio de Janeiro, Brazil: V - Norte fluminense mesoregion

In this paper, the fifth of a series dealing with the survey of freshwater gastropods of the state of Rio de Janeiro, the results of collections carried out in the Norte Fluminense Mesoregion from 2002 to 2003 are presented and revealed the occurrence of 19 species: Antillorbis nordestensis; Burnupia sp.; Biomphalaria tenagophila; Drepanotrema anatinum; Drepanotrema cimex; Drepanotrema depressissimum; Drepanotrema lucidum; Ferrissia sp.; Gundlachia ticaga; Gundlachia sp.; Heleobia sp.; Hebetancylus moricandi; Idiopyrgus sp.; Lymnaea columella; Melanoides tuberculatus; Physa acuta; Physa marmorata; Pomacea sordida, and Pomacea sp. Concerning the snail hosts of Schistosoma mansoni only B. tenagophila was found, in contrast with other previuosly studied mesoregions.No specimens were found harbouring larval forms of S. mansoni although different kinds of cercariae had been observed.An account about the current schistosomiasis transmission sites in this Mesoregion is presented as well.

Climatic factors influencing triatomine occurrence in Central-West Brazil

We estimated the geographic distributions of triatomine species in Central-West Region of Brazil (CW) and analysed the climatic factors influencing their occurrence. A total of 3,396 records of 27 triatomine species were analysed. Using the maximum entropy method, ecological niche models were produced for eight species occurring in at least 20 municipalities based on 13 climatic variables and elevation. Triatoma sordida and Rhodnius neglectus were the species with the broadest geographic distributions in CW Brazil. The Cerrado areas in the state of Goiás were found to be more suitable for the occurrence of synanthropic triatomines than the Amazon forest areas in the northern part of the state of Mato Grosso. The variable that best explains the evaluated models is temperature seasonality. The results indicate that almost the entire region presents climatic conditions that are appropriate for at least one triatomine species. Therefore, it is recommended that entomological surveillance be reinforced in CW Brazil.

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.

The main sceneries of Chagas disease transmission. The vectors, blood and oral transmissions - A comprehensive review

This review deals with transmission ofTrypanosoma cruziby the most important domestic vectors, blood transfusion and oral intake. Among the vectors,Triatoma infestans,Panstrongylus megistus, Rhodnius prolixus,Triatoma dimidiata, Triatoma brasiliensis,Triatoma pseudomaculata, Triatoma sordida,Triatoma maculata, Panstrongylus geniculatus,Rhodnius ecuadoriensis and Rhodnius pallescens can be highlighted. Transmission of Chagas infection, which has been brought under control in some countries in South and Central America, remains a great challenge, particularly considering that many endemic countries do not have control over blood donors. Even more concerning is the case of non-endemic countries that receive thousands of migrants from endemic areas that carry Chagas disease, such as the United States of America, in North America, Spain, in Europe, Japan, in Asia, and Australia, in Oceania. In the Brazilian Amazon Region, since Shaw et al. (1969) described the first acute cases of the disease caused by oral transmission, hundreds of acute cases of the disease due to oral transmission have been described in that region, which is today considered to be endemic for oral transmission. Several other outbreaks of acute Chagas disease by oral transmission have been described in different states of Brazil and in other South American countries.

Análise das relações taxonômicas e sistemáticas entre espécies de triatomíneos (Hemiptera, Reduviidae) de colônias mantidas pelo Serviço Especial de Saúde de Araraquara, inferida de seqüências do 16S rDNA mitocondrial

Foram analisadas seqüências de nucleotídeos do gene 16S do rDNA mitocondrial em 14 populações de triatomíneos mantidos em colônias no insetário SESA de Araraquara- SP, comparando-as com seqüências do mesmo gene disponíveis no GenBank. Os fragmentos variaram de 311 a 317 pb com baixa variação intra-específica entre as distâncias genéticas (0% a 0,6%), exceto para os relacionamentos entre espécimes de Triatoma sordida (1%) e espécimes de T. brasiliensis (1,3%) atribuídos a populações geográficas diferentes. A parafilia de Rhodniini e do gênero Panstrongylus foi evidenciada pelas analises, confirmando resultados anteriores entre estes e os estreitos relacionamentos de R. prolixus com R. robustus e de T. infestans e T. platensis. O relacionamento entre T. maculata e T. pseudomaculata não foi solucionado, uma vez que, esses táxons apareceram tanto em monofilia quanto em parafilia: T. pseudomaculata (SESA) está agrupado com T. maculata (seqüência do GenBank) e associados a T . brasiliensis (SESA), enquanto T. maculata (SESA) aparece agrupado com T. pseudomaculata do SESA e do GenBank. Os resultados evidenciam a utilidade do gene 16S como marcador de espécies de triatomíneos e sua importância em questões de sistemática e taxonomia. Há necessidade de novos estudos envolvendo outros marcadores associados a caracteres sistemáticos clássicos de morfologia, ecologia e comportamento para decisões sistemáticas adequadas uma vez, que teriam impacto não apenas sistemático mas, para as estratégias de controle.

Chromatoid body: Remnants of nucleolar proteins during spermatogenesis in triatomine (Heteroptera, Triatominae)

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

Pattern of nucleolar activity during spermiogenesis in triatomines (Heteroptera, Reduviidae) as analysed by silver staining

Nucleoli are the sites of biosynthesis of ribosomal precursors. In this work the nucleolar activity at interphase and the meiotic cells of the testis in five species of triatomines were analysed by means of silver staining. Several nucleolar blocks in the polyploid nuclei of testicular tubules were observed, whereas only one nucleolar body could be seen in the spermatogonial nuclei of all five species. A single nucleolar body was evident in the 'confused stage' of Triatoma brasiliensis, T. delpontei, T. lecticularia and T. rubrovaria, while T. sordida presented two nucleolar dots. The existence of small, silver-stained dots in some metaphase I chromosomes of T. brasiliensis and T. sordida is reported. The number of nucleolar dots present in spermatids of each species varied within and among species. It is suggested that in addition to providing information on rRNA biosynthesis, studies of nucleolar organizing activity can also be important sources of data on differentiation patterns and species development.

Chagas disease and triatomine biology (Heteroptera, Triatominae), with emphasis on aspects of spermatogenesis

A century after the discovery of Chagas disease, it is still one of the most important parasitic diseases affecting humans. The subfamily Triatominae is important in medical health, because these insects are vectors of Trypanosoma cruzi, the etiologic agent of Chagas disease. These insects are also of important cytological relevance because they have particular cell characteristics, such as persistence of nucleolar material in spermatogenesis. The germ cells of the animal kingdom have chromatoid bodies (CBs) in their cytoplasm that can originate from nucleolar material that is fragmented in the early stages of spermatogenesis and plays an important role in cellular communication between the spermatids during spermiogenesis. Currently, there are few studies on the function and formation of the CB in nucleologenesis, especially with emphasis on the ultrastructure of the cells involved in spermatogenesis of insects. Considering the importance of knowledge about the triatomine fauna, we conducted a study of the biogeography and reports of these insects and a survey of patients with Chagas disease in the northwestern region of São Paulo State. Data collected from 1995 to 2009 indicated 700 individuals with Chagas disease, demonstrating a range of 0 to 40 years, which shows that the disease may be active in this region. Moreover, of the 1150 patients treated for cardiomyopathy, 44% were chagasic. Regarding the triatomines noted and captured in the period from 2004 to 2009, the species were Triatoma sordida and Rhodnius neglectus, with T. sordida being the most abundant. In addition, some triatomines were infected by T. cruzi in various developmental stages. We also analyzed the nucleolar cycle and fibrillarin nucleolar protein expression in CB of spermatogenic cells of T. infestans and T. sordida, using histological, ultrastructural and immunocytochemical techniques. The results revealed fibrillarin nucleolar protein expression in the nucleus and in some cytoplasmic spots of germ cells during spermatogenesis in triatomines. These data suggest that fibrillarin could be a constituent of CB, which was most likely derived from nucleolar fragmentation. This is the first time that fibrillarin protein expression has been shown in CB during spermatogenesis progression in triatomines. Knowledge about the biology of triatomines was deepened in this study and, in particular, the structural and ultrastructural aspects of spermatogenesis in triatomines. This study showed that the disease may be active in the northwestern region of São Paulo and expanded our knowledge of the biology of triatomines, the main vectors of Chagas disease. © FUNPEC-RP.