PUPAL SURVEY - AN EPIDEMIOLOGICALLY SIGNIFICANT SURVEILLANCE METHOD FOR AEDES-AEGYPTI - AN EXAMPLE USING DATA FROM TRINIDAD

This report documents the results of a country-wide pupal survey of Ae des aegypti (L.) conducted in Trinidad. The survey was designed to ide ntify the important Ae. aegypti-producing containers, importance being a function of a container's abundance and its productivity. Results a re summarized on a country-wide basis and by county: urban versus rura l comparisons are also made. Numerically, the most common water-filled containers positive for the larvae or pupae of Ae. aegypti (foci) wer e outdoor drums, water storage tanks and buckets, laundry tubs, discar ded tires, and small miscellaneous containers such as drink bottles an d cans. The island-wide average number of foci per hectare was 287 and ranged between 65 and 499. The average standing crop per container of Ae. aegypti pupae was 9.5 and ranged 12-fold, the most and least prod uctive being the flower pot (> 30) and the small indoor vase (< 3), re spectively. In terms of production by type of container, four of the 1 1 types, outdoor drums, tubs, buckets, and small containers, accounted for > 90% of all Ae. aegypti pupae: the remaining seven types were re sponsible for < 10%. If targeted source reduction programs were direct ed by how important various container types were in the production of Ae. aegypti, environmental sanitation efforts designed to actually eli minate the ubiquitous small receptacle and tires would reduce mosquito densities by 43%; the provision of an adequate water supply system pr ecluding the need for water storage in drums and buckets would have th e potential to eliminate an additional 38%. Combined, these two measur es have the potential to reduce the sources responsible for > 80% of A e. aegypti production in the country. In our survey, the traditional S tegomyia indices used to document the density of Ae. aegypti and predi ct the threat of dengue transmission, the House, Container, and Bretea u indices, were seen to have virtually no correspondence with the actu al number of pupae per hectare or per person. We conclude that pupal s urvey is more appropriate for assessing risk and directing control ope rations.