Use of Temephos for Control of Field Population of Aedes aegypti in Americana São Paulo, Brazil+ by
Maria Rita Camargo Donalisio*#, Odair Ferreira Leite**, Renata Caporale Mayo**, Maria José Chinelatto Pinheiro Alves**, Amauri de Souza**, Osias Rangel**, Valmir Roberto Andrade**, Susely Salviano de Oliveira** and Vera Lúcia M Matias** *Department of Preventive and Social Medicine-FCM-UNICAMP (State University of Campinas), Caixa Postal 543, Botucatu, Cep: 18.618-970 São Paulo, Brazil **Department of Endemic Disease Control - Health State Secretary of São Paulo, SUCEN-Campinas Rua São Carlos, 546, Cep: 13035-420 Campinas São Paulo, Brazil
Abstract The control of Aedes aegypti with 1% granulated formulation of temephos has been widely used in field control programmes in Brazil. The impact of temephos application was evaluated in Americana São Paulo, where an Aedes control programme was in place since 1991. Two areas with similar conditions of Aedes infestivity were selected. In the experimental area, temephos application @ 1 ppm at a frequency of three-month intervals and source reduction by communities were the methods used for control, whereas in the control area only source reduction was attempted. Monthly surveillance of larval population was undertaken using the larval indicies, viz. Breteau Index (BI), Container Index (CI), and identification of Aedes aegypti types of breeding sites. Trends were also observed in relation to rainfall and minimum temperature. A covariance test was performed to compare the two different areas. Results indicated that the area subjected to temephos application presented similar levels of Aedes aegypti larval infestation as the untreated area. The larval infestation varied with the degree of rainfall but not with temperature. Positive breeding sites for Aedes aegypti more frequently encountered were plant vases, tanks and drums in the experimental area. A comprehensive operational research study is required to determine the causes of failure of temephos to suppress the Aedes aegypti population under an operational programme. Keywords: Dengue, Aedes aegypti, temephos, control programme, Americana SP.
+ Project financed by the Brazilian Ministry of Health/FUNSA/Plan to Eradicate Aedes ageypti, Pan American Health Organization (PAHO), and Dalmo Giacometti Foundation. # For correspondence: rita@fmb.unesp.br
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Introduction Brazil, which achieved the eradication of Aedes aegypti in the 1950s, was re-infested in the 1970s and, by 1976, an extensive infestation of Aedes aegypti began in the seaports of Rio de Janeiro and Salvador. The species spread to other regions and, by the year 2000, vectors were reported in all Brazilian states(1). In 1980, Aedes aegypti was identified in isolated focal points in the west of São Paulo state. Since then a combination of chemical and physical measures have been taken for its control(2,3). The main objective of this study was to evaluate the efficacy of temephos for the control of the larval population of Aedes aegypti as a part of a control programme’s routine field actions over a ten-month period during 2000 and 2001 in a medium sized city in São Paulo state. • Control area: 37,955 houses and 1775 blocks.
Control activities Experimental area • 1% temephos (1 ppm conc.) application in all “non-removable” wet containers, viz. drinking troughs, roof gutters, cement mixers, non-potable water cisterns and hollow trees at a frequency of three months. Source reduction of temporary water collection in “removable” containers, i.e. bottles, pots, cans, plastics, etc., by communities on a regular basis. Drinking water tanks were not treated. Health education by health staff.
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Materials and methods Study area Americana city (pop. 174,439) in São Paulo state, which reported occasional incidence of DF/DHF, led the local health authorities to intensify the Aedes control programme in 1991 based on source reduction and temephos application at three-month intervals, with community participation. Over the years the control programme stabilized. Two areas were randomly chosen from a total of five, with similar socio-economic and Aedes infestation characteristics: • Experimental area: 17,994 houses and 665 blocks
Control area • • Source reduction in removable containers by communities. Health education by health staff.
The whole city is visited by the ‘Health Department Vector Control Team’, comprising of 34 visitors and six supervisors, at three-month intervals.
Data collection Data was collected monthly to construct infestation indicators by random sampling in each study area (N=300). Index confidence intervals were calculated for N=300 samples. Types of positive breeding sites were recorded in monthly larval collection Dengue Bulletin – Vol 26, 2002
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forms. The monthly average minimum temperature data provided by the local council. measured in millimetres of using standard collectors.
rainfall and (OC) were Rainfall was precipitation
assuming a significance level of 95% (α = 0.05).
Results The figure shows the Breteau Index (BI) and rainfall measurement in the study areas from September 2000 to June 2001. There were general similarities between both areas; however, larval density was slightly lower in the untreated area for most of the studied period. In December 2000, the Aedes aegypti infestation was substantially lower in the treated area. Data showed the seasonality of the infestation.
An analysis was made of ten months of larval infestation indices, viz. rainfall data and minimum temperature. The indicators obtained in the experimental and control areas were compared by covariance analysis, using Breteau Index (BI)* and Container Index (CI)** as the dependent variables; and larvicide use, minimum temperature, and rainfall as independent variables. The notifications of different types of breeding sites were compared by the Student t test,
Figure: Rainfall precipitation (mm) and Breteau Index (BI) in areas with and without temephos treatment in Americana, September 2000 to June 2001 9 8 7 6 BI 5 200 4 3 2 1 0 Feb May Sep Dec Mar Oct Nov Apr Jun Jan 150 100 50 0 400 350 300 250
Rainfall (mm)
W it h te m e p h o s W it h o u t te m e p h o s R a in fa ll
* BI = (number of positive larval containers/number of buildings investigated) X 100 ** CI = (number of positive larval containers/number of water containers investigated) X 100
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The Table gives estimates of the covariance analysis, demonstrating that larval infestation indices BI and CI did not vary with the use of temephos p=0.87 and p=0.62, respectively. On the other hand, rainfall precipitation showed a significant impact on larval infestation, p=0.001 for BI and p=0.02 for CI; minimum temperature did not interfere with the detection rates of Aedes aegypti in this study (p=0.36 for BI and p=0.19 for CI). Minimum temperatures varied between 11.8 and 21.1OC. Plant pot holders and vases were found to be the predominant breeding sites throughout this study. These positive types of Aedes aegypti containers were more frequent in the treated area (p=0.003). The Aedes aegypti larva-positive levels for permanent sites such as guttering, hollow trees, drinking troughs, bamboos, cement mixers, etc., were similar in both areas (p=0.13). Table: Covariance analysis of Breteau and Container Indicies with temephos use, minimum temperature and rainfall, American SP , September 2000 to June 2001 Independent Variables BI Temephos Rainfall Minimum Temperature CI Temephos Rainfall Minimum Temperature F value 0.03 16.11 0.89 0.26 6.42 1.93 P 0.87 0.001 0.36 0.62 0.02 0.19
Discussion It must be remembered that these analyses were referenced in time and space. The numbers and different types of breeding sites and their normal uses varied from area to area. The results of this study were contrary to the expectation that at least some residual effect of temephos was expected in the experimental area. However, the results suggested that there was no relevant impact of temephos application on Aedes larval prevalence. One hypothesis is that the false complacency created by the larvicidal treatment contributed to the increased negligence in the physical elimination of breeding sites by communities as reflected by the presence of a high number of removable containers. The transitory effectiveness of temephos (around 3 weeks) as well as eventual overflowing of water and consequent dilution factors in nonremovable containers added to the ineffectiveness of this treatment. Vector resistance to temephos has been observed in the Caribbean and neighbouring regions(4,5,6). Although there is no study available about temephos resistance status to Aedes aegypti, specifically in Americana, in the main regional city (Campinas) 40 km from the study area, bioassays showed 96.5% Aedes aegypti larval mortality after exposure to temephos(7,8). This is less than the WHO limit (> 98%) at a dose concentration of 0.012 mg/l (ppm). Potential temephos resistance alone in the Campinas region does not seem to sufficiently explain the lack of success in the field. Dengue Bulletin – Vol 26, 2002
F value: Best value; P: Significant value
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A comprehensive study of the field routine is essential to identify the operational difficulties in the management of Aedes aegypti control programmes, such as insufficient interaction between professionals
and the community, ineffective implementation of temephos application in the field and lack of professional training in health education.
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