Discrepancies between Aedes aegypti identification in the field and in the laboratory after collection with a sticky trap

Currently, sticky traps are regularly employed to assist in the surveillance of Aedes aegypti infestation. We tested two alternative procedures for specimen identification performed by local health agents: directly in the field, as recommended by certain manufacturers, or after transportation to the laboratory. A total of 384 sticky traps (MosquiTRAP) were monitored monthly during one year in four geographically representative Brazilian municipalities. When the same samples were inspected in the field and in the laboratory, large differences were noted in the total number of mosquitoes recorded and in the number of specimens identified as Ae. aegypti by both procedures. Although field identification has the potential to speed vector surveillance, these results point to uncertainties in the evaluated protocol.

Estimation of Aedes aegypti (Diptera: Culicidae) population size and adult male survival in an urban area in Panama

Traditional mosquito control strategies rely heavily on the use of chemical insecticides. However, concerns about the efficiency of traditional control methods, environmental impact and emerging pesticide resistance have highlighted the necessity for developing innovative tools for mosquito control. Some novel strategies, including release of insects carrying a dominant lethal gene (RIDL®), rely on the sustained release of modified male mosquitoes and therefore benefit from a thorough understanding of the biology of the male of the species. In this report we present the results of a mark-release-recapture study aimed at: (i) establishing the survival in the field of laboratory-reared, wild-type male Aedes aegypti and (b) estimating the size of the local adult Ae. aegypti population. The study took place in Panama, a country where recent increases in the incidence and severity of dengue cases have prompted health authorities to evaluate alternative strategies for vector control. Results suggest a life expectancy of 2.3 days for released male mosquitoes (confidence interval: 1.78-2.86). Overall, the male mosquito population was estimated at 58 males/ha (range 12-81 males/ha), which can be extrapolated to an average of 0.64 pupae/person for the study area. The practical implications of these results are discussed.

Mass trapping with MosquiTRAPs does not reduce Aedes aegypti abundance

The objective of this study was to evaluate the effectiveness of Aedes aegyptimass trapping using the sticky trap MosquiTRAP (MQT) by performing a cluster randomised controlled trial in Manaus, state of Amazonas, Brazil. After an initial questionnaire and baseline monitoring of adultAe. aegyptiabundance with BG-Sentinel (BGS) traps in six clusters, three clusters were randomly assigned to the intervention arm where each participating household received three MQTs for mass trapping during 17 months. The remaining three clusters (control arm) did not receive traps. The effect of mass trapping on adult Ae. aegyptiabundance was monitored fortnightly with BGS traps. During the last two months of the study, a serological survey was conducted. After the study, a second questionnaire was applied in the intervention arm. Entomological monitoring indicated that MQT mass trapping did not reduce adult Ae. aegyptiabundance. The serological survey indicated that recent dengue infections were equally frequent in the intervention and the control arm. Most participants responded positively to questions concerning user satisfaction. According to the results, there is no evidence that mass trapping with MQTs can be used as a part of dengue control programs. The use of this sticky trap is only recommendable for dengue vector monitoring.

Evaluation of oviposition traps as an entomological surveillance method for Aedes aegypti (Diptera, Culicidae)

This study aimed to describe the behavior of oviposition traps for Aedes aegypti over time, to compare it with the larval survey and to investigate the association with climatic variables. It was conducted in S��o Jos�� do Rio Preto city, S��o Paulo. Daily climatic data and fortnightly measurements for oviposition traps and larval infestation were collected from October 2003 to September 2004. Three different periods were identified in the behavior of oviposition traps' positivity and mean number of eggs: increase, plateau and decrease in values. These measurements followed the variation of climatic data from the first and third periods. High correlation was obtained between the positivity and the mean number of eggs. The oviposition traps showed higher capacity to detect the vector than did larval survey. It was observed that the first (October to December) and third (May to September) periods were considered to be the most suitable to use oviposition traps than larval surveys.

Impact of small variations in temperature and humidity on the reproductive activity and survival of Aedes aegypti (Diptera, Culicidae)

In short space of time increase in temperature and rainfall can affect vector populations and, consequently, the diseases for them transmitted. The present study analyzed the effect of small temperature and humidity variations on the fecundity, fertility and survival of Aedes aegypti. These parameters were analyzed using individual females at temperatures ranging from 23 to 27 ��C (mean 25 ��C); 28 to 32 ��C (mean 30 ��C) and 33 to 37 ��C (mean 35 ��C) associated to 60��8% and 80��6% relative humidity. Females responded to an increase in temperature by reducing egg production, oviposition time and changing oviposition patterns. At 25 ��C and 80% relative humidity, females survived two-fold more and produced 40% more eggs when compared to those kept at 35 ��C and 80% relative humidity. However, in 45% of females kept at 35 ��C and 60% relative humidity oviposition was inhibited and only 15% females laid more than 100 eggs, suggesting that the intensity of the temperature effect was influenced by humidity. Gradual reductions in egg fertility at 60% relative humidity were observed with the increase in temperature, although such effect was not found in the 80% relative humidity at 25 �� C and 30 �� C. These results suggest that the reduction in population densities recorded in tropical areas during seasons when temperatures reach over 35 ��C is likely to be strongly influenced by temperature and humidity, with a negative effect on several aspects of mosquito biology.

Isolation of Bacillus thuringiensis from the state of Amazonas, in Brazil, and screening against Aedes aegypti (Diptera, Culicidae)

We investigated the use of Bacillus thuringiensis isolated in the state of Amazonas, in Brazil, for the biological control of the dengue vector Aedes aegypti. From 25 soil samples collected in nine municipalities, 484 bacterial colonies were obtained, 57 (11.78%) of which were identified as B. thuringiensis. Six isolates, IBt-03, IBt-06, IBt-07, IBt-28, IBt-30, and BtAM-27 showed insecticidal activity, and only BtAM-27 presents the five genes investigated cry4Aa, cry4Ba, cry10Aa, cry11Aa, and cry11Ba. The IBt-07 and IBt- 28, with lower LC50 values, showed equal toxicity compared to the standards. The isolates of B. thuringiensisfrom Amazonas constitute potential new means of biological control for A. aegypti, because of their larvicidal activity and the possibility that they may also contain new combinations of toxins.

The yellow fever 17D vaccine virus: molecular basis of viral attenuation and its use as an expression vector

The yellow fever (YF) virus is the prototype flavivirus. The use of molecular techniques has unraveled the basic mechanisms of viral genome structure and expression. Recent trends in flavivirus research include the use of infectious clone technology with which it is possible to recover virus from cloned cDNA. Using this technique, mutations can be introduced at any point of the viral genome and their resulting effect on virus phenotype can be assessed. This approach has opened new possibilities to study several biological viral features with special emphasis on the issue of virulence/attenuation of the YF virus. The feasibility of using YF virus 17D vaccine strain, for which infectious cDNA is available, as a vector for the expression of heterologous antigens is reviewed

Attenuation and immunogenicity of recombinant yellow fever 17D-dengue type 2 virus for rhesus monkeys

A chimeric yellow fever (YF)-dengue serotype 2 (dengue 2) virus was constructed by replacing the premembrane and envelope genes of the YF 17D virus with those from dengue 2 virus strains of Southeast Asian genotype. The virus grew to high titers in Vero cells and, after passage 2, was used for immunogenicity and attenuation studies in rhesus monkeys. Subcutaneous immunization of naive rhesus monkeys with the 17D-D2 chimeric virus induced a neutralizing antibody response associated with the protection of 6 of 7 monkeys against viremia by wild-type dengue 2 virus. Neutralizing antibody titers to dengue 2 were significantly lower in YF-immune animals than in YF-naive monkeys and protection against challenge with wild-type dengue 2 virus was observed in only 2 of 11 YF-immune monkeys. An anamnestic response to dengue 2, indicated by a sharp increase of neutralizing antibody titers, was observed in the majority of the monkeys after challenge with wild-type virus. Virus attenuation was demonstrated using the standard monkey neurovirulence test. The 17D-D2 chimera caused significantly fewer histological lesions than the YF 17DD virus. The attenuated phenotype could also be inferred from the limited viremias compared to the YF 17DD vaccine. Overall, these results provide further support for the use of chimeric viruses for the development of a new live tetravalent dengue vaccine.

Plano amostral para c��lculo de densidade larv��ria de Aedes aegypti e Aedes albopictus no Estado de S��o Paulo, Brasil

O Programa de Controle de Vetores de Febre Amarela e Dengue, desenvolvido pela Superintend��ncia de Controle de Endemias do Estado de S��o Paulo, Brasil, prev�� a realiza����o de pesquisa para avalia����o da densidade larv��ria de Aedes aegypti e Aedes albopictus em edifica����es de munic��pios com infesta����o domiciliar. Descreve-se o plano amostral que vem sendo aplicado, desde outubro de 1987, nos munic��pios da Regi��o de Presidente Prudente. Para acompanhamento da densidade est�� sendo utilizado o ��ndice de Breteau. S��o sorteados, nos munic��pios infestados, mensalmente e de forma independente, amostras de edifica����es para a obten����o das estimativas do ��ndice. O plano amostral prev�� a sele����o de conglomerados em 2 est��gios: quadras e edifica����es. O tamanho da amostra foi definido estimando-se o coeficiente da correla����o intraconglomerado e vari��ncia relativa por elemento atrav��s de pesquisas realizadas anteriormente em munic��pios do Servi��o Regional de S��o Jos�� do Rio Preto. O plano prop��e que os valores relativos ao tamanho da amostra sejam atualizados periodicamente em fun����o dos valores obtidos para o estimador do ��ndice de Breteau e sua vari��ncia, em meses anteriores.

Microhabitats de Aedes albopictus (Skuse) na regi��o do Vale do Para��ba, Estado de S��o Paulo, Brasil

Objetivou-se determinar o n��vel de dissemina����o de Ae. albopictus na regi��o do Vale do Para��ba, Estado de S��o Paulo, Brasil. Foram realizadas coletas de larvas e pupas em seis locais distintos, segundo transecto com 10 km de extens��o. O alvo principal foi oco de ��rvores, tendo sido tamb��m inclu��dos artefatos antr��picos. As esp��cies Ae. terrens e Ae. albopictus foram as ��nicas do g��nero Aedes presentes e, algumas vezes, coexistiram no mesmo microhabitat natural. A segrega����o de sete esp��cies da comunidade de oco variou de acordo com os macro e microhabitats examinados. Assim, a distribui����o de Ae. albopictus envolveu as zonas rural, rural-urbana e urbana, por��m a segunda ��rea foi a mais preferida. Como fator favor��vel �� infesta����o de Ae. albopictus na regi��o, destacou-se a vac��ncia de nichos ecol��gicos naturais resultante da influ��ncia antr��pica. As chuvas foram relevantes no "input" de larvas e pupas e os ocos, com volumes superiores a 600 ml, foram os mais produtivos. A abund��ncia desses dois est��dios ocorreu nas esta����es ver��o-outono, sendo o pico m��ximo alcan��ado nos meses de mar��o-abril. Essa sazonalidade foi comum em bambu experimental e recipientes artificiais. Os dados de temperatura m��dia sugeriram a faixa de 23 a 17°C como o per��odo mais favor��vel ao desenvolvimento larv��rio. Face a isso, a cepa de Ae. albopictus estudada parece ser oriunda da ��sia tropical e, portanto, se reveste de elevada import��ncia epidemiol��gica pela possibilidade dessa esp��cie vir a exercer, al��m do dengue, papel vetorial para a febre amarela no Brasil.

Estudo comparativo de efic��cia de larvitrampas e ovitrampas para vigil��ncia de vetores de dengue e febre amarela

Com a finalidade de aprimorar a vigil��ncia entomol��gica dos vetores de Dengue e Febre Amarela - Aedes aegypti e Aedes albopictus - no Estado de S��o Paulo, Brasil, realizou-se estudo comparativo de efic��cia de larvitrampas (armadilhas de larvas), e ovitrampas (armadilhas de ovos). A regi��o estudada �� infestada somente pelo Aedes albopictus, esp��cie que conserva h��bitos silvestres, mas tamb��m coloniza criadouros artificiais. A primeira parte do estudo foi realizada em ��rea periurbana de Trememb��-SP, onde foram comparados tr��s ocos de ��rvore, 23 ovitrampas e 5 larvitrampas. A segunda parte dos experimentos desenvolveu-se no Munic��pio de Lavrinhas-SP, no distrito de Pinheiros, onde 20 ovitrampas foram instaladas (uma por quadra) e 5 larvitrampas foram localizadas em pontos estrat��gicos (com��rcios, dep��sitos e postos). Os resultados obtidos mostraram que a ovitrampa, al��m da capacidade de positivar-se mesmo em presen��a de criadouros naturais, possui efici��ncia superior �� larvitrampa. Constatou-se que para avalia����o de efeitos da termonebuliza����o as ovitrampas apresentaram uma significativa redu����o na m��dia de ovos, o que n��o se verificou em rela����o ao ��ndice de Breteau.

Encontro de Aedes scapularis (Diptera: Culicidae) em criadouro artificial em localidade da regi��o Sul do Brasil

Duas larvas de Aedes scapularis foram encontradas em um criadouro artificial, no Munic��pio de Sertaneja, Norte do Estado do Paran��, Brasil, durante atividade de rotina para o controle de vetores da dengue.

Dengue: inqu��rito sorol��gico p��s-epid��mico em zona urbana do Estado de S��o Paulo (Brasil)

OBJETIVO: Avaliar o tamanho real da epidemia sobre dengue ocorrida na zona urbana do Munic��pio de Santa B��rbara D'Oeste, SP, Brasil, de abril a junho de 1995. M��TODOS: Foi realizado um inqu��rito soroepidemiol��gico p��s-epid��mico 5 meses ap��s o final da epidemia da dengue. Foram processados 1.113 soros atrav��s de amostragem aleat��ria domiciliar da popula����o da cidade pesquisada. As taxas de infec����o em diferentes partes da cidade foram relacionadas com os graus de infesta����o por Aedes aegipty e com a quantidade de casos notificados durante a epidemia. RESULTADOS E CONCLUS��ES: Foi encontrada varia����o concomitante e diretamente proporcional entre as taxas de infec����o pelo v��rus da dengue, em diferentes partes da cidade, e os graus de infesta����o domiciliar por Aedes aegipty, bem como em rela����o ao n��mero de casos notificados durante a epidemia. Encontrou-se preval��ncia de 630 por 100 mil habitantes, representando valor 15 vezes superior ao de incid��ncia de casos confirmados laboratorialmente durante a epidemia. Atrav��s de compara����o retrospectiva com dados de notifica����o compuls��ria, observou-se que a vigil��ncia epidemiol��gica n��o detectou a maioria das pessoas soro-reativas. Apesar disso, notificou grande quantidade de casos que n��o eram de indiv��duos com dengue, tipificando um valor preditivo positivo baixo (15,6%) para o diagn��stico cl��nico de dengue quando o resultado laboratorial (HAI) �� tomado como padr��o-ouro.

Primeiro registro de Aedes albopictus em ��rea da Mata Atl��ntica, Recife, PE, Brasil

Pela primeira vez �� registrada a presen��a do Aedes albopictus em remanescentes de Mata Atl��ntica, localizada em ��rea urbana em Recife (Pernambuco, Brasil). As coletas foram realizadas em isca humana e em criadouros de formas jovens (ocos de ��rvores, bambus, brom��lias e pneu). A presen��a de Ae. albopictus na regi��o metropolitana do Recife representa um risco potencial do inter-relacionamento dessa esp��cie de mosquito com a popula����o.

Freq����ncia de larvas e pupas de Aedes aegypti e Aedes albopictus em armadilhas, Brasil

OBJETIVO: Avaliar a freq����ncia mensal de larvas e pupas de Ae. albopictus, Ae. aegypti e de outras esp��cies de mosquitos e verificar a influ��ncia de fatores ambientais dessas esp��cies em pneus. M��TODOS: A pesquisa foi desenvolvida no munic��pio de Nova Igua��u, Estado do Rio de Janeiro, Brasil. Efetuaram-se coletas mensais de formas imaturas, em quatro pneus, no per��odo de novembro de 1997 a outubro de 1998. Os pneus foram numerados e dispostos em forma de pir��mide, um na base (pneu 1) e os tr��s restantes (2, 3 e 4) inclinados sobre o primeiro. Os pneus 1 e 4 eram mais sombreados, e 2 e 3 eram expostos ao sol, j�� que n��o eram alcan��ados, como os demais, pela sombra de ��rvores e de um galinheiro pr��ximos a esses pneus. Foram estudadas as vari��veis: pluviosidade; temperatura ambiente; volume; pH da ��gua; e condi����es de isolamento de ��gua em pneus. RESULTADOS: Coletaram-se 10.310 larvas e 612 pupas. Ae. albopictus foi a esp��cie predominante tanto na fase larvar quanto na de pupa; Ae. aegypti e Ae. albopictus foram coletados em todos os meses, sendo mais freq��entes naqueles de maior pluviosidade. A temperatura, a pluviosidade e o volume de ��gua apresentaram diferen��as significativas, quando correlacionados ao n��mero de larvas de Ae. aegypti. N��o houve diferen��a significativa na freq����ncia de larvas quanto ao pH da ��gua. Registrou-se maior n��mero de larvas de Ae. albopictus em pneus mais sombreados. CONCLUS��ES: Ae. albopictus instala-se muito mais freq��entemente em pneus do que Ae. aegypti. Pneus descartados parecem representar importantes focos de manuten����o de ambos os Aedes, durante todo o ano. Mesmo pr��ximo uns ao outros, os pneus podem oferecer diferentes condi����es para a coloniza����o desses mosquitos, de acordo com o volume d'��gua e a exposi����o ao sol.