Pupal survey: an epidemiologically significant surveillance method for Aedes aegypti: an example using data from Trinidad
Focks, D.A.; Chadee, D.D.
American Journal of Tropical Medicine and Hygiene 56(2): 159-167
1997
ISSN/ISBN: 0002-9637 PMID: 9080874 Document Number: 471613
This report documents the results of a country-wide pupal survey of A. aegypti conducted in Trinidad between 27 May and 22 June 1994, designed to identify the important A. aegypti-producing containers, importance being a function of a container's abundance and its productivity. Results are summarized on a country-wide basis and by county; urban versus rural comparisons are also made. Numerically, the most common water-filled containers positive for the larvae or pupae of A. aegypti (foci) were outdoor drums, water storage tanks and buckets, laundry tubs, discarded tyres, and small miscellaneous containers such as drink bottles and cans. The island-wide average number of foci per ha was 287 and ranged between 65 and 499. The average standing crop per container of A. aegypti pupae was 9.5 and ranged 12-fold, the most and least productive being the flower pot (>30) and the small indoor vase (<3), respectively. In terms of production by type of container, 4 of the 11 types, outdoor drums, tubs, buckets and small containers, accounted for >90% of all A. aegypti pupae; the remaining 7 types were responsible for <10%. If targeted source reduction programmes were directed by how important various container types were in the production of A. aegypti, environmental sanitation efforts designed to actually eliminate the ubiquitous small receptacle and tyres would reduce mosquito densities by 43%; the provision of an adequate water supply system precluding the need for water storage in drums and buckets would have the potential to eliminate an additional 38%. Combined, these 2 measures have the potential to reduce the sources responsible for >80% of A. aegypti production in the country. In this survey, the traditional Stegomyia indices used to document the density of A. aegypti and predict the threat of dengue transmission, the House, Container and Breteau indices, were seen to have virtually no correspondence with the actual number of pupae per ha or per person. It was concluded that pupal survey is more appropriate for assessing risk and directing control operations.