Simultaneous external and internal marking of Triatoma sordida nymphs: trace element efficacy and microgeographic dispersal in a peridomestic Brazilian Cerrado rural household.

BACKGROUND: Chagas disease (American trypanosomiasis) is an important neglected tropical illness, which has the flagellate protozoan Trypanosoma cruzi as etiological agent and blood-feeding insects of the Triatominae subfamily as vectors. Despite its importance for disease epidemiology, field studies targeting microgeographic dispersal of triatomines in endemic areas are rare. The ability wingless nymphs have to move (crawl) within peridomestic settings is a key component regarding the design and development of rational control strategies. METHODS: We double-marked Triatoma sordida fourth-instar nymphs (N4) with a reliable fluorescent dye and a trace element. This new methodology allowed us to simultaneously evaluate (i) nymph dispersal and (ii) the effectiveness of copper (Cu), chromium (Cr), and cadmium (Cd) trace elements as potential new markers. In the mark-release-recapture (MRR) experiment, 390 T. sordida N4 were released in the peridomicile of a single rural household, 130 individuals at each of three release points, at distances of 2, 5, and 10 m from the chicken coop (CC) and 27, 32, and 35 m away from the horse corral (HC). All specimens were double marked (Cu/blue, Cr/orange, Cd/green). Recaptures occurred in two intervals: 1-3 days and 15-17 days after release. RESULTS: Specimens were successfully recaptured at all distances up to 10 m. A total of 19, 23, and 10 specimens were able to disperse 2, 5, and 10 m, respectively, to reach the CC. No insects were recaptured at the HC. Of the three analyte/paint combinations tested, Cr/orange gave the most promising results; Cu/blue marker and Cd/green marker performed very poorly with only 4/19 and 0/10 analyte/paint ratios, respectively. CONCLUSIONS: Triatoma sordida N4 could cover a distance of 10 m in 17 days. This indicates that nymphs seem to have a reduced dispersal capability compared to adults. Ninety-one percent of the 22 recaptured orange-marked nymphs were still Cr positive after the 17-day period evaluated. This makes this analyte a good candidate for future investigations that will apply this marking method in MRR studies.

Should I stay or should I go? Movement of adult Triatoma sordida within the peridomestic area of a typical Brazilian Cerrado rural household.

BACKGROUND: Chagas disease, or American trypanosomiasis, is an important neglected tropical illness caused by the flagellate protozoan Trypanosoma cruzi, which is primarily transmitted to humans by hematophagous insects of the subfamily Triatominae. Although knowledge on triatomine movement capabilities at the micro-geographical scale is of fundamental importance concerning the development of effective vector control strategies, it remains a poorly understood subject. Furthermore, survival rates and size estimates of natural populations are important topics to consider when evaluating transmission intensity. RESULTS: The movement of adult Triatoma sordida within the peridomestic area of a rural Brazilian household was evaluated via mark-release-recapture assays. A total of 210 insects had their pronota marked with fluorescent dyes and were released at different distances from the chicken coop (two, five, ten and 20 m), and from the horse corral (27, 32, 35, 46 and 56 m). Recaptures occurred in three consecutive 15-day intervals. Specimens were successfully recaptured at all distances up to 32 m. Bayesian models were used to estimate recapture probability, survival rates (males vs females) and population size. Although recapture probability was inversely proportional to distance for both sexes, females were more affected by increased distance. On the other hand, no significant difference was detected in the survival rates between males and females in a 15-day period. Fisher-Ford and Bayesian models gave more accurate population size estimates than Lincoln method. CONCLUSIONS: Triatoma sordida adults were able to cover a distance of 32 m in 45 days. Recapture data modelling reveals that male dispersal was more effective suggesting that T. sordida males are more likely to contribute as potential colonizers of the peridomestic environment. Increasing the distance between the peridomestic structures and the sylvatic environment as much as possible appears to be a simple and feasible recommendation to reduce the contact rate between humans and infected bugs and ultimately Chagas disease transmission.

Avaliação da influência de algumas características do criadouro e da água na freqüência de formas imaturas e no tamanho e peso de adultos do mosquito aedes aegypti (díptera: culicidae) no Rio de Janeiro / Evaluation of the influence of some characteristics of livestock and water in the frequency of immature and adult size and weight of the mosquito Aedes aegypti (Diptera: Culicidae) in Rio de Janeiro

Aedes aegypti é uma espécie sinantrópica que utiliza essencialmente criadouros artificiais como locais de desenvolvimento das formas imaturas, localizados dentro e ao redor das casas. Sabe-se que a produtividade dos criadouros, assim como o tamanho dos mosquitos adultos neles gerados dependem de uma série de fatores bióticos e abióticos, como disponibilidade de alimentos, competição larval inter e intraespecífica, temperatura, características físico-químicas da água, entre outras. Mosquitos de diferentes tamanhos podem ter capacidade vetorial diferente: podem se dispersar, sobreviver, alimentar-se e se infectar diferentemente. No presente estudo buscamos avaliar o potencial papel dos nutrientes (encontrados na água e no sedimento do criadouro), assim como de parâmetros físico-químicos na determinação do peso corporal e do tamanho das asas de A. aegypti. Também procuramos avaliar os efeitos da competição interespecífica entre A. aegypti e A. albopictus sobre o peso e tamanho das asas dessas duas espécies de mosquitos quando as mesmas foram encontradas simultaneamente no mesmo criadouro. Para tal, de abril a agosto de 2010, foram examinados 240 criadouros em quatro bairros da área metropolitana do Rio de Janeiro com características sócio-econômicas e ambientais distintas, sendo 50 criadouros positivos e 10 negativos em cada bairro. Avaliamos características físico-químicas da água (nitratos, fosfatos, carbono dissolvido, carbono no sedimento, O2 dissolvido, pH, condutividade, temperatura e volume de água), além da temperatura ambiente, velocidade do vento, exposição ao sol, área do criadouro, presença de predadores e de outros mosquitos co-ocorrendo com A. aegypti. As caixas d’água e outros recipientes usados para armazenamento de água foram os mais freqüentemente positivos para mosquitos nas localidades onde as condições sócio-econômicas e ambientais são mais precárias (Prainha e Tubiacanga), ao passo que, nas localidades com melhores condições socioeconômicas, os focos mais freqüentes foram vasos de plantas (Curicica), ralos e bromélias (Vila Valqueire). Observou-se um menor tamanho das asas e peso corporal em A. aegypti quando encontrados co-ocorrendo nos mesmos que A. albopictus, apesar de não significativo estatisticamente, sugere que uma espécie interfere no desenvolvimento da outra, produzindo mosquitos menores. O volume de água e a área do criadouro se mostraram como fatores importantes para a colonização por A. aegypti e parecem ser limitantes para o número de formas imaturas. A temperatura ambiente mostrou-se associada ao número de imaturos. O teor per capita de carbono orgânico no sedimento per capita não se mostrou associado ao número de imaturos presentes no criadouro, mas, tal como o oxigênio dissolvido, condutividade e incidência de luz, parece influenciar positivamente o tamanho das asas e o peso dos A. aegypti adultos emergidos.