A rapid entomological reconnaissance during the first Zika outbreak in Thiruvananthapuram city, Kerala, India

Abstract

There was an outbreak of Zika virus in Thiruvananthapuram city of Kerala state, India in July 2021. In order to ascertain the prevalence and breeding pattern of the potential vectors, a study was conducted from 22 July 2021 to 27 July 2021. Breeding habitat surveys were conducted in seven localities in the city from where Zika cases were reported. House to house searches were conducted from mosquito breeding in 35-40 houses in each locality. Fourth instar larvae were identified using larval keys and later confirmed their identities after emergence. Lower instar larvae were reared in the laboratory and were identified after emergence using adult keys. Larval indices were calculated using WHO methods. Of the 280 houses surveyed mosquito breeding was encountered in 38 houses. Three Aedes species viz., Ae. aegypti, Ae. albopictus and Ae. vittatus were detected. Ae. agypti and Ae. albopictus were breeding in 30.5% and 43.9% of the outdoor habitats and 56.0% and 16.0% of the indoor habitats respectively. The overall Container Index for (CI), Breteau Index (BI) and House Index (HI) for both species together were 56.07, 23.07 and 14.61 respectively. Two established urban Zika vectors viz., Ae. aegypti and Ae. albopictus were prevalent in the city with very high container indices. For the first time in the world, indoor flower vases used for money plant has been observed as an important breeding habitat of Aedes mosquitoes. Rapid elimination of the breeding habitats with community support is recommended to reduce the larval indices.