Risk of Aedes aegypti (Linnaeus) Development of Breeding in Polluted Drainage Systems of Urban Cities of Sri Lanka

Abstract

Dengue Fever (DF) is a major public health problem at present in Sri Lanka. Drastic environmental changes due to rapid and unplanned development, extended rainfall during rainy seasons, and ambient relative humidity and temperature that favor for the breeding of Aedes aegypti (Linnaeus), the main vector of DF are the major factors contributing high incidence of dengue in the country. Dengue control programs mainly target the removal or treatment of fresh water holding artificial or natural breeding containers for controlling Ae. aegypti. Negligence of the polluted water drains during vector control programs has raised concerns and suggested the possibility of Ae. aegypti breeding. The present study was designed and conducted to evaluate the presence of Ae. aegypti in the polluted water drains in some urban areas in Sri Lanka. A preliminary entomological survey was carried out in urban areas from Chilaw to Galle to detect Ae. aegypti larvae. The drains that marked as the positive for Ae. aegypti larvae, were further surveyed for a period of three months from June to August in 2017. Ae. aegypti was recorded in drains containing polluted water in Galle city for the first time in Sri Lanka. From total of 26,949 mosquitoes, predominant species in the preliminary survey was Cx. quinquefasciatus (97.38%) followed by Cx. gelidus (0.98%), Ae. albopictus (0.62%) and Ae. aegypti (0.59%). Other species recorded were Armigeres sp., Cx. hutchinsoni and Ae. vittatus which accounted for only 0.4% of the specimens collected. Ae. aegypti was only recorded in polluted water drains with four other species during further studies carried out in the Galle district. Cx quinquefasciatus (97.2%) was predominately recorded from all the polluted drains sampled with a total of 9594 mosquitoes collected in Galle. This was followed by Ae. aegypti (1.58%) with 156 mosquitoes and Ae. vittatus (0.78%) with 77 mosquitoes. Highly deteriorated water quality characteristics were detected as low dissolved oxygen and high conductivity with visible organic pollutants at every study site. Destruction of breeding grounds during vector control programs and constant stress due to insecticidal control leads to adapt Ae. aegypti to new breeding environments. Therefore, further in-depth studies that are based on behavioral changes in the mosquitoes for selecting oviposition need to be carried out by which the control program can be well targeted to lower the disease burden.