Aedes aegypti (Diptera: Culicidae) production from non-residential sites in the Amazonian city of Iquitos, Peru.

Programmes for the surveillance of Aedes aegypti (L.) often focus on residential areas, ignoring non-residential sites. Between November 2003 and October 2004, pupal/demographic surveys were therefore conducted in non-residential sites in the Peruvian city of Iquitos. The sampled sites included schools, factories, ports, public markets, petrol stations, commercial zones, airports, government buildings, animal-production areas, and recreational areas. Compared with the residential sites that had been surveyed a few years earlier, the non-residential sites generally had fewer pupae/ha, even though pupae were found in a high percentage of the sites investigated. Nonetheless, although <56 pupae/ha were observed in the industrial, commercial, recreational and school sites, the river boats in the ports and the areas in and around public markets sometimes had pupal abundances (of 122-213 pupae/ha) that were comparable with those previously recorded in the residential sites. When the relative production of Ae. aegypti was calculated by container type and characteristic (lidded/lidless, indoors/outdoors, and water-use patterns), no single container category was found to be a major producer of Ae. aegypti, with the exception of flower vases in cemeteries. In general, almost all (97%) of the pupae collected in the non-residential sites came from unlidded containers, although 91% of those collected in river boats came from lidded storage areas. With the exception of lumber mills, plant nurseries and markets (where only 39%-60% of the pupae were collected outdoors), >70% of pupal production was outdoors. In commercial areas, 41% of the pupae came from manually-filled containers, compared with <12% in residential sites. These results indicate that non-residential sites can be highly productive for Ae. aegypti and that the role of such sites in dengue transmission requires further investigation.

Evaluation of a sampling methodology for rapid assessment of Aedes aegypti infestation levels in Iquitos, Peru.

An epidemic of dengue during 2001 in Northwestern Peru reemphasized the need for efficient, accurate, and economical vector surveillance. Between November 1998 and January 1999, we carried out extensive entomological surveys in two neighborhoods of approximately 600 contiguous houses located in the Amazonian city of Iquitos, providing a unique opportunity to evaluate the Aedes aegypti (L.) rapid assessment survey strategy. Based on Pan American Health Organization recommendations, this strategy is used by the Peruvian Ministry of Health (MOH). In our analysis all household locations, including closed and unoccupied houses, were georeferenced and displayed in a geographic information system, which facilitated simulations of MOH surveys based on hypothetical systematic sampling transects. Larval, pupal, and adult mosquito indices were calculated for each simulation (n = 10) and compared with the indices calculated from the complete data set (n = 4). The range of indices calculated from simulations was moderately high, but included actual indices. For example, simulation ranges for house indices (HI, percentage of infested houses from complete survey) were 38-56% (45%), 36-42% (38%), 21-34% (30%), and 13-33% (27%) in four surveys. HI, Breteau index, pupae per hectare, adult index, and adults per hectare were more robust entomological indicators (coefficient of variation [CV]/mean = 0.1-2.9) than the container index, pupae per person, pupae per house, adults per person, and adults per house (CV/mean >20). Our results demonstrate that the MOH's Ae. aegypti risk assessment program provides reasonable estimates of indices based on samples from every house. However, it is critical that future studies investigate the association of these indices with rates of virus transmission to determine whether sampling variability will negatively impact the application of indices in a public health context.

Evaluation of a sampling methodology for the Rapid Assessment of Aedes aegypti infestation levels in Iquitos, Perú

An epidemic of dengue during 2001 in Northwestern Peru has re-emphasized the need for efficient, accurate, and economical vector surveillance methods. Between November 1998 and January 1999 we carried out extensive entomological surveys in two neighborhoods (Maynas and Tupac) of 600 contiguous houses (14-20 blocks) each located in the Amazonian city of Iquitos, which has provided a unique opportunity to evaluate the Aedes aegypti rapid assessment survey strategy. This strategy is based on PAHO recommendations employed by the Peruvian Ministry of Health (MOH). All household locations from 4 surveys (2/neighborhood), including closed and unoccupied houses were georeferenced and displayed in a Geographic Information System (GIS), facilitating simulations of 10 MOH surveys based on hypothetical systematic sampling transects for 3 work groups (15-25 houses per group starting from randomly selected blocks). Larval, pupal and adult mosquito indices were calculated for each simulation and compared to the indices calculated from the complete data set. Infestation rates were highest in Maynas where House Indices (HI: proportion of houses positive for larvae) were 45% and 38% in surveys 1 and 2, respectively. In Tupac Amaru the HI was 30% in survey 1 and 27% survey 2. The observed range in simulated House indices in Maynas survey 1 and 2 were 38-56% and 36-42%; whereas in Tupac they were 21-34% and 13-33%. Index stability was evaluated by comparing the coefficient of variation to the mean of the simulation results. HI, Breteau index, pupae/ha, adult index, and adults/ha were more robust entomological indicators (CV/mean=0.1-2.9), than the container index, pupae/person, pupae/house, adults/person, and adults/house (CV/mean>20). Results demonstrate that the MOH's Aedes aegypti risk assessment program provides reasonable estimates of actual indices; however, the further understanding of the association of these indices with rates of virus transmission...