Resumo

A dengue ocorre no Timor-Leste desde 2005, porém não existe um programa de monitoramento e controle do "Aedes aegypti". O objetivo deste estudo foi de avaliar a armadilha ovitrampa iscada com atraente natural como uma possível ferramenta para monitorar o vetor das arboviroses: Dengue (DENV), Chikungunya (CHIKV) e Zika (ZIKV). O estudo foi realizado na cidade de Dili, capital do Timor-Leste, entre as semanas epidemiológicas 32 (02/08) a 48 (02/12) de 2016. Foram instaladas 70 armadilhas Ovitrampa, em residências de 15 sucos (ruas), de quatro Postos Administrativos (bairros) da cidade. Para as analises dos dados utilizou-se os indicadores entomológicos: Índice de Positividade de Ovitrampa (IPO), Índice de Densidade Vetorial (IDV) e Índice de Densidade de Ovos (IDO). Durante o experimento foram coletados 158.904 ovos de Aedes spp.. O IPO demonstrou que todas as áreas tiveram 98% a 100% de armadilhas contendo ovos de Aedes spp.. Os indicadores IDO e IPO apresentaram correlações positivas e significativa com a temperatura. A defasagem de duas e três semanas para precipitação indicou correlação positiva significativa para IDV e IDO. Portanto, a armadilha ovitrampa é uma ferramenta que pode integrar as ações de um programa de monitoramento e controle de Aedes spp. no Timor-Leste.

Palavras-chave
"Aedes" spp.; Armadilha de oviposição; Ovitrampa; Timor-Leste

Introduction

Aedes mosquitoes originate in the Old World, most likely in northeastern Africa, and were initially described in Egypt¹1 Eiras AE. Família Culicidae. In: Neves DP, Melo AL, Genaro O, Linardi PM, organizadores. Parasitologia Humana. São Paulo: Atheneu; 2015. p. 434-437.. They are considered cosmopolitan mosquitoes and are found in tropical and subtropical areas of the globe, always associated with human domicile and peridomicile²2 Forattini OP. Culicidologia Médica: identificação, biologia e epidemiologia. 2ª ed. São Paulo: Edusp; 2002.. Aedes spp. specimens are vectors of several arboviruses such as Dengue, Zika, Chikungunya, and Yellow Fever³3 Consoli RAGB, Oliveira RL. Principais mosquitos de importância no Brasil. Rio de Janeiro: Fiocruz; 1994..

Understanding the population dynamics of vectors of medical interest in a given geographic region through vector monitoring allows better planning of public health policies³3 Consoli RAGB, Oliveira RL. Principais mosquitos de importância no Brasil. Rio de Janeiro: Fiocruz; 1994.^,44 Brasil. Ministério da Saúde (MS), FUNASA. Programa Nacional de Controle da Dengue. Brasília: MS; 2002.. Strategies for monitoring and controlling these insects are necessary to slow down the viral circulation and ensure the population’s quality of life⁵5 Figueiredo MLG, Gomes AC, Amarilla AA, Leandro AS, Orrico AS, Araujo RF, SM Castro J, Durigon EL, Aquino VH, Figueiredo LT. Mosquitoes infected with dengue viruses in Brazil. Virol J 2010; 12(7):152-157..

In East Timor, dengue is considered a significant arbovirus transmitted by the Aedes aegypti, and studies mainly on vector monitoring⁶6 World Health Organization (WHO). Dengue Guidelines for Diagnosis, Treatment, Prevention and Control. New Edition. Genebra: WHO; 2009. are scarce. Given the consecutive cases of dengue in East Timor, from 2014, mainly in the municipality of Dili, it became essential to plan a vector monitoring program through oviposition traps (ovitraps)⁷7 Whelan P, Hapgoog GA. Mosquito Survey of Dili, East Timor, and Implications for Disease Control Department of Health and Community Services. Med. Entomol. 2000; 1(12):405-416..

The use of ovitraps is a safe, inexpensive, fast, efficient, and environmentally-friendly technique⁸8 Beserra EB, Ribeiro OS, Oliveira SA. Flutuação populacional e comparação de métodos de coleta de Aedes (Stegomyia) aegypti (Diptera, Culicidae). Iheringia, Sér. Zool. 2014; 5(4):418-425.. This tool allows determining the geographic dispersion, density, frequency, occupation, and seasonality of the vector⁹9 Roque RA. Avaliação de armadilhas iscadas com infusões de gramíneas como atraentes e/ou estimulantes de oviposição do mosquito Aedes (Stegomyia) sp. (Diptera: Culicidae) [dissertação]. Belo Horizonte: Universidade Federal Minas Gerais; 2002..

Methods

Area of study

The municipality of Dili, the capital of East Timor, is located on the north coast of the island, and its bordering municipalities are Manatuto to the east, Aileu to the south, Liquiçá to the west, and the Savu Sea to the north, which also includes the island of Ataúro. The municipality is located at Latitude 8º33’31" S and Longitude 125º34’25" E. The climate is tropical humid with annual mean temperature ranging from 26ºC to 32ºC and relative air humidity between 60% to 74%.

According to the 2010 census, Dili had a population of 252,884 inhabitants and 39,310 households and an area of 372 km². The municipality of Dili is divided into six Administrative Posts: Dom Aleixo, Vera Cruz, Nain Feto, Cristo Rei, Metinaro, and the island of Atauro¹⁰10 Deen J, Matos LC, Temple B, Su JY, da Silva J, Liberato S, Silva V, Soares AI, Joshi V, Moon S, Tulloch J, Martins J, Mulholland K. Identifying national health research priorities in Timor-Leste through a scoping review of existing health data. Health Res Policy Syst 2013; 11(1):8-10..

Preparation of natural infusion as an attractant of oviposition

The infusion used in the ovitraps was prepared with 350 grams of green leaves of Acacia (Leucaena leucocephala) placed in a 15L bucket containing 2L of water. The bucket remained closed for 48 hours to ferment the leaves. After this fermentation period, the infusion was filtered through a clean cloth, and 100 mL of infusion and 400 mL of water were used, totaling 500 mL per oviposition device.

Oviposition Substrate (Palette)

As a substrate for egg-laying, we used fabric (80% cotton and 20% polyester, made in China), light brown, and measuring 12 cm long by 6 cm wide. The tissue had a smooth side and a rough side, and the rough side was exposed for oviposition of female Aedes spp. The palettes were placed vertically and attached by a clip inside the device.

Installation of ovitraps

Seventy ovitraps were installed in 15 streets from four Dili Administrative Posts. The selection of Administrative Posts for the study took into consideration the availability of human resources, and we selected the Administrative Posts of Dom Aleixo (36 ovitraps), Cristo Rei (8 ovitraps), Nain Feto (11ovitraps) and Vera Cruz (15 ovitraps). The traps were allocated by convenience in the buildings, with 64 devices installed in the intra-domicile area (47 in the bedroom, 12 in the kitchen, 5 in the bathroom), and six in the peridomicile of the property (on the balcony). The facilities and surveys of the devices were handled by the students of the National University of Timor Lorosa’e.

The ovitraps were regularly inspected every seven days for palette change and infusion during the 17 weeks of study. The structure of the laboratory of the Department of Biology of the Faculty of Education, Arts, and Humanities of the National University of Timor Lorosa’e was used for counting eggs of Aedes spp. in the palettes.

Meteorological data

Meteorological data for mean, minimum, maximum temperature, rainfall, and relative humidity of the municipality of Dili were provided by the Ministry of Public Works of East Timor.

Data analysis

The eggs collected in the ovitraps allowed to calculate the total eggs of Aedes spp., the Ovitrap Positivity Index (OPI = Aedes spp. egg trap percentage and installed traps), Egg Density Index (EDI = Aedes spp. eggs and positive traps) and the Vector Density Index (VDI = Aedes spp. eggs and the traps inspected)¹¹11 Gomes ADC. Medidas dos níveis de infestação urbana para Aedes (Stegomyia) aegypti e Aedes (Stegomyia) albopictus em programa de vigilância entomológica. Info. Epid. do SUS 1998; 17(7):49-57..

The OPI, VDI, EDI, and total egg data of Aedes spp. were correlated with abiotic factors (maximum, mean, minimum temperature, rainfall, and relative humidity) using Pearson’s test. The VDI per Epidemiological Week was submitted to the Shapiro-Wilks normality test at 5% probability, showed a normal distribution, and underwent analysis of variance (Anova). The entomological means were compared a posteriori by the Tukey test at the significance level of p < 0.05.

Data were processed using the following programs: IBM SPSS version 2.4, and Microsoft® Office 365™ Excel and Word programs.

Results

During the 17 weeks of study, a total of 158,904 eggs of Aedes spp. in the four Administrative Posts of Dom Aleixo, Cristo Rei, Nain Feto, and Vera Cruz from the Dili capital of East Timor.

The largest proportion of Aedes spp. eggs (62.5%; 99,317 eggs) was recorded in Dom Aleixo, followed by Cristo Rei (16%; 25,396 eggs), Nain Feto (12%; 19,056 eggs) and Vera Cruz had the lowest proportion (9.2%; 14,585 eggs).

The mean number of Aedes spp. eggs showed no significant difference by oviposition installation environment in Dili residences (Anova F_{(4, 289)} = 0.678; p > 0.05) where in the intra-domicile environment represented by the bedroom collected on average 129 eggs, in the kitchen, 141 eggs; in the bathroom, 146 eggs; and in the peridomicile environment represented by the balcony, 134 eggs of Aedes spp.

The indicators provided by ovitraps evidenced that the VDI and EDI showed similar behavior in the four evaluated Administrative Posts, where Dom Aleixo ranged from 109.6 to 199.3; Cristo Rei, from 93 to 134.4; Nain Feto ranged from 73.4 to 143.4; and Vera Cruz ranged from 85.5 to 129.4. Noteworthy is the Dom Aleixo Administrative Post, with EDI above 100 eggs of Aedes spp. throughout the experimental period and peaking at 199 eggs at Epidemiological Week 43 (Table 1).

The VDI in the municipality did not observe a significant difference during the experimental period (Anova, F _(17,68) = 1.03; p > 0.05) (Figure 1).

The OPI at Dom Aleixo, Nain Feto, and Vera Cruz Administrative Posts ranged from 98.03 to 100%, and the Cristo Rei Administrative Post presented 100% of the positive egg traps of Aedes spp. During the study, mean, minimum, and maximum temperatures ranged from 26 to 32ºC, 16 and 24ºC, and 28 and 35ºC, respectively. Large fluctuations were observed for weekly rainfall, between August and September (EW 32 to 39) of 2016, a mean rainfall of 0.21mm occurred, while during the remaining epidemiological weeks, a mean of 1.53mm of rainfall representing the rainy season from October to December (Figure 2). The mean weekly relative air humidity ranged from 58% to 72%.

Pearson’s correlation analysis indicated a positive and significant relationship between total eggs, VDI, and EDI with the maximum, mean, and minimum temperature variables for the study period. No significant correlation was observed in the entomological variables provided by ovitrap and correlated with relative air humidity and precipitation in the same week. Relative humidity was negatively correlated with VDI, OPI and EDI, and rainfall for total eggs and OPI (Table 2).

However, the entomological indicators provided by ovitrap, when correlated with rainfall, under the effect of one, two, three and four weeks’ lag, observed that the action of delaying in two (r² = 0.518, p = 0.0332) and three weeks (r² = 0.5034, p = 0.0394) showed a significant positive correlation for the VDI and EDI variables (Table 3).

Discussion

The ovitrap has been used in several countries to monitor Aedes spp.⁸8 Beserra EB, Ribeiro OS, Oliveira SA. Flutuação populacional e comparação de métodos de coleta de Aedes (Stegomyia) aegypti (Diptera, Culicidae). Iheringia, Sér. Zool. 2014; 5(4):418-425.^,99 Roque RA. Avaliação de armadilhas iscadas com infusões de gramíneas como atraentes e/ou estimulantes de oviposição do mosquito Aedes (Stegomyia) sp. (Diptera: Culicidae) [dissertação]. Belo Horizonte: Universidade Federal Minas Gerais; 2002.^,1111 Gomes ADC. Medidas dos níveis de infestação urbana para Aedes (Stegomyia) aegypti e Aedes (Stegomyia) albopictus em programa de vigilância entomológica. Info. Epid. do SUS 1998; 17(7):49-57.. In the municipality of Dili, the ovitrap proved to be a highly sensitive tool for monitoring Aedes infestation, providing data at short (weekly) intervals and continuously.

The weekly monitoring highlighted the Dom Aleixo Administrative Post with 62.5% of the eggs collected compared to the Cristo Rei, Nain Feto, and Vera Cruz Administrative Posts. The high percentage of eggs collected at Dom Aleixo Administrative Post can be attributed to the fact that it is a more urbanized area of the city of Dili with disordered growth and irregular water supply system, probably contributed to the higher prevalence of Aedes spp. in this area¹²12 Forattini OP, Brito M. Reservatórios domiciliares de água e controle do Aedes aegypti. Rev Saude Publica 2003; 29 (5):676-677..

When analyzing the environments for the installation of ovitraps, no significant differences were found in Aedes spp. collected in the ovitraps, installed in the intra-domicile environment (bedroom, kitchen, and bathroom) or the home (balcony). Despite not observing a difference between the analyzed environments, the high proportion of female Aedes spp. that do posture on breeding grounds within buildings. The event is due to poor housing conditions in Dili, houses built with openings in the walls allowing free movement of Aedes mosquitoes⁷7 Whelan P, Hapgoog GA. Mosquito Survey of Dili, East Timor, and Implications for Disease Control Department of Health and Community Services. Med. Entomol. 2000; 1(12):405-416.. These results differ from the Brazilian findings, where most of Aedes spp. are found in the peridomicile area¹²12 Forattini OP, Brito M. Reservatórios domiciliares de água e controle do Aedes aegypti. Rev Saude Publica 2003; 29 (5):676-677.^,1313 Domingos MDF. Aspectos da ecologia de Aedes aegypti (Linnaeus) em Santos, São Paulo, Brasil [tese]. São Paulo: Escola de Saúde Pública; 2005..

The weekly VDI of Aedes spp. provided by the ovitrap in Dili (East Timor) did not show significant differences, with a higher and lower infestation, during the experimental period.

The ovitrap’s OPI allowed the qualitative assessment of the presence of Aedes spp., showing that the Dom Aleixo, Cristo Rei, Nain Feto, and Vera Cruz Administrative Posts were similar and ranged from 98 to 100%. Despite not having the highest EDI and VDI, the Cristo Rei Administrative Post traps remained positive throughout the experiment. This positivity may be associated with the female Aedes spp. behavior, which does not lay all its eggs in a single breeding place, distributing them in different containers¹³13 Domingos MDF. Aspectos da ecologia de Aedes aegypti (Linnaeus) em Santos, São Paulo, Brasil [tese]. São Paulo: Escola de Saúde Pública; 2005.. This behavior, called "skip oviposition", allowed the same female to lay eggs in more than one trap¹⁴14 Micieli MV, Campos RE. Oviposition activity and seasonal pattern of a population of Aedes (Stegomyia) aegypti (L.)(Diptera: Culicidae) in subtropical Argentina. Mem Inst Oswaldo Cruz 2003; 18(7):659-663..

The OPI data in the administrative posts of the city of Dili allowed indicating that the studied areas are at high risk for the transmission of dengue and other arboviruses by Aedes aegypti and Aedes albopictus. According to the literature, the OPI indicator equal to or greater than 40% of positivity indicates the risk of arbovirus transmission¹¹11 Gomes ADC. Medidas dos níveis de infestação urbana para Aedes (Stegomyia) aegypti e Aedes (Stegomyia) albopictus em programa de vigilância entomológica. Info. Epid. do SUS 1998; 17(7):49-57..

Aedes spp. EDI and VDI by Dili Administrative Post varied similarly, and in most epidemiological weeks, were higher than 100 eggs of Aedes spp. collected by positive and inspected ovitraps, respectively. This behavior of EDI and VDI indicators is attributed to the high rate of Aedes spp.¹³13 Domingos MDF. Aspectos da ecologia de Aedes aegypti (Linnaeus) em Santos, São Paulo, Brasil [tese]. São Paulo: Escola de Saúde Pública; 2005.^,1414 Micieli MV, Campos RE. Oviposition activity and seasonal pattern of a population of Aedes (Stegomyia) aegypti (L.)(Diptera: Culicidae) in subtropical Argentina. Mem Inst Oswaldo Cruz 2003; 18(7):659-663. population infestation found in the evaluated Administrative Posts.

The high rates provided by ovitraps in the city of Dili may be associated with disordered population growth as a consequence of the civil war that brought imbalances in urbanization¹⁰10 Deen J, Matos LC, Temple B, Su JY, da Silva J, Liberato S, Silva V, Soares AI, Joshi V, Moon S, Tulloch J, Martins J, Mulholland K. Identifying national health research priorities in Timor-Leste through a scoping review of existing health data. Health Res Policy Syst 2013; 11(1):8-10.. It is observed that the water supply in the city is irregular and the absence of a sewage collection system, where residential cloacal waste remains in the open, characteristics of occupation of the urban area that stimulate the proliferation and dispersion of Aedes spp. and other culicides¹²12 Forattini OP, Brito M. Reservatórios domiciliares de água e controle do Aedes aegypti. Rev Saude Publica 2003; 29 (5):676-677.^,1313 Domingos MDF. Aspectos da ecologia de Aedes aegypti (Linnaeus) em Santos, São Paulo, Brasil [tese]. São Paulo: Escola de Saúde Pública; 2005..

Regarding abiotic variables and infestation indices of Aedes spp. in Dili, a significant correlation was found between the VDI, EDI indicators, and the total number of Aedes spp. eggs collected with the temperature. No positive association was observed between rainfall in the same epidemiological week and relative air humidity. Rainfall was positively correlated with VDI and EDI indicators only when data were lagged at two and three weeks. This time lag probably allowed adjusting the rainfall variable as per the biological cycle of Aedes aegypti and Aedes albopictus. This time of two and three weeks is related to the appearance of potential breeding after the rainy season¹⁴14 Micieli MV, Campos RE. Oviposition activity and seasonal pattern of a population of Aedes (Stegomyia) aegypti (L.)(Diptera: Culicidae) in subtropical Argentina. Mem Inst Oswaldo Cruz 2003; 18(7):659-663..

The positive correlation data with the temperature that acts as a model factor for the Aedes spp. infestation process is in agreement with the results of the specific literature¹⁵15 Ajuz LC, Vestena LR. Influence of Rainfall and Temperature Ambient on Longevity and Fertility of Aedes aegypti and Aedes albopictus in the City of Guarapuava-PR and the Possibility of Superinfestation. Revista Brasileira de Geografia Médica e da Saúde 2013; 10(7):1-18.^,1616 Calado DC, Navarro-Silva MA. Exigências térmicas de Aedes (Stegomyia) albopictus Skuse, 1894 (Diptera, Culicidae) em condições de laboratório. Rev. Bras. Entomol.. 2002; 27(7):547-555., which emphasized the importance of temperature on the distribution of Aedes spp. East Timor climatic seasons can be divided into two periods, the dry season that occurs between May and October, and the rainy season that occurs between November and April.

Climatic conditions are determining factors for the existence and maintenance of Aedes aegypti in the environment¹⁶16 Calado DC, Navarro-Silva MA. Exigências térmicas de Aedes (Stegomyia) albopictus Skuse, 1894 (Diptera, Culicidae) em condições de laboratório. Rev. Bras. Entomol.. 2002; 27(7):547-555.. Thus, the ideal temperature for the proliferation of the Aedes aegypti mosquito would be between 24ºC and 28ºC, and the ideal relative air humidity above 70%. Under these conditions, the Aedes aegypti reproduces with higher intensity, increases its survival, oviposition, hematophagic activity, and the efficiency of virus reproduction in its environment¹⁵15 Ajuz LC, Vestena LR. Influence of Rainfall and Temperature Ambient on Longevity and Fertility of Aedes aegypti and Aedes albopictus in the City of Guarapuava-PR and the Possibility of Superinfestation. Revista Brasileira de Geografia Médica e da Saúde 2013; 10(7):1-18.. These weather patterns are found to have occurred throughout the experimental period in Dili.

Therefore, this study suggests the use of ovitraps in Dili, East Timor, as an appropriate method for detecting the presence and population density variation of Aedes aegypti in different environments. Therefore, the Ministry of Health of East Timor will be able to use the indicators provided by the ovitrap to direct Aedes spp. control activities, enabling it to act more effectively in the positive trap coverage areas and areas with EDI and VDI values indicating the risk of arbovirus transmission by Aedes spp.

References

Acknowledgments

Alvaro Eduardo Eiras thanks to The Brazilian National Council for Scientific and Technological Development (CNPq).

Publication Dates

History