Way Forward for Seasonal Planning of Vector Control of Aedes aegypti and Aedes albopictus in a Highly Dengue Endemic Area in India

Special Article - Dengue Fever

Austin J Infect Dis. 2016; 3(1): 1022.

Way Forward for Seasonal Planning of Vector Control of Aedes aegypti and Aedes albopictus in a Highly Dengue Endemic Area in India

Roop K*, Priya S, Sunita P, Mujib M, Kanhekar LJ and Venkatesh S

National Centre for Disease Control, India

*Corresponding author: Kumari Roop, Joint Director, Centre for Medical Entomology & Vector Management, National Centre for Disease Control, Delhi, India

Received: May 09, 2016; Accepted: June 16, 2016; Published: June 17, 2016

Abstract

Aedes aegypti and Aedes albopictus have acquired an international importance in view of recent spurt in zika cases in Brazil as these mosquitoes are the vectors of dengue, chikungunya, yellow fever as well as for Zika fever. Although yellow fever and Zika fever are not reported from India, but both mosquitoes are well prevalent in the country. Ae. aegypti is most prevalent Aedes mosquitoes recorded that preferred to breed in artificial containers in and around the houses and adaptation of Ae. albopictus in man-made containers was also reported from India. Therefore, the objective of present study is to find out season wise key containers for larvae and pupae production of Ae. aegypti and Ae. albopictus in a highly endemic area for dengue in the capital city of India. Delhi has so far witnessed several outbreaks of dengue fever since 1967. Besides larvae survey, pupae survey was also conducted during 2013 and 2014 as pupal production is a better proxy for adult mosquito reproduction than traditional breeding indices and are more appropriate for directing dengue control programs. All pupae were counted and reared for species identification. Total 16168 houses and 48713 containers were checked. Four key containers such as plastic containers, cement tanks, coolers and syntax tanks harboured 89% of Ae. aegypti pupae. Among them Plastic Water Storage Containers (PWSC) are recorded as perennial source of Aedes infestation that contributed 41% of the immature breeding and about half of pupal production. It was observed that Aedes breeding preference has been shifted toward PWSC as compare to previous studies, therefore, public health attention is required to control breeding in such containers. Present study indicates there is aseasonal variation of breeding preference of Ae. aegypti and Ae. albopictus in different containers in Delhi, so it is important for a target and effective planning of seasonwise control measures. The containers that produced the larger proportion of pupae, vector control intervention should be targeted to maximize their intact.

Keywords: Dengue; Aedes aegypti; Aedes albopictus; Key containers; Pupal survey; Breeding; India

Abbreviations

PWSC: Plastic water storage container; HI: House Index; CI: Container Index; BI: Breteau Index; DF: Dengue Fever; DHF: Dengue Haemorrhagic Fever; NCT: National Capital Territory; MCD: Municipal Corporation of Delhi; NDMC: North Delhi Municipal Corporation; ID: Indoor; PD: Peri-Domestic; OD: Outdoor; PPC: Pupae per Container; PI: Pupal Index

Introduction

Dengue Fever (DF) is one of the most rapidly rising mosquito transmitted infections in the world. The maximum burden is contributed by countries of the Asia Pacific Region. Dengue outbreaks are occurring with increasing frequency and intensity. In India, the first outbreak of dengue was reported from Calcutta in 1963 and after that disease has been reported from other States also. So far in India, outbreaks of DF/ Dengue Haemorrhagic Fever (DHF) have been recorded in almost all parts of the country including the NCT of Delhi. The first epidemic of dengue fever was recorded in 1967 [1] after that many outbreaks were recorded from Delhi [2-6]. Among them, the first major outbreak occurred in 1996 with 10252 cases and 423 deaths [7] and during the year 2015, DF/DHF resurged in Delhi and total of 15836 cases and 46 deaths were reported [8]. It is important to study seasonal breeding preference of Aedes aegypti as it is also a vector of yellow fever and Zika fever, although these diseases are not reported from India.

Ae. aegypti is most prevalent dengue vector species recorded that preferred to breed in artificial containers in and around the houses and adaptation of Ae. albopictus in man-made containers was also reported from Delhi [9]. Dengue virus was also detected in both mosquitoes from Delhi [10]. For planning and implementation of control measures for dengue, it is necessary to know the most preferable breeding habitats for larvae and pupae.

Pupal survey is based on the assumption that pupal production is a better proxy for adult mosquito reproduction than traditional indices House Index (HI), Container Index (CI) and Breteau Index (BI) [11]. However, pupal surveys are more appropriate for assessing risk and directing dengue control programs because traditional larval indices correspond poorly with the actual number of pupae per person. Approximately 80% of Ae. aegypti pupae emerge into adult mosquitoes, allowing them to be used as a proxy measure for local adult mosquito abundance [12,13]. The containers that produced the larger proportion of pupae, vector control intervention should be targeted to maximize their intact. This consideration caused us to explore the hypothesis: 1) most pupae of Ae. aegypti are produce in a few types containers, 2) seasonal breeding preference of Aedes mosquitoes in different containers.

Therefore, proposed study was undertaken to detect most productive breeding sites for immature as well as for pupae of Aedes in Delhi and further to identify the key containers for pupal production. It is important to know the seasonal variation for breeding preference of Ae. aegypti and Ae. albopictus in different types of habitats/containers so that season wise planning can be done. In view of this seasonal preference of breeding of Aedes mosquitos in all the five seasons’ of Delhi were studied and presented in the paper. This is useful for season wise planning of vector control measures to be focussed in the key containers.

Materials and Methods

NCT of Delhi is the largest metropolis by area and the secondlargest metropolis by population in India. It is situated at 77o.15' E and 26o.15' N. It occupies 1,485 km2 area of which 900 km2 is classified as urban. Delhi has a population of 16.7 million (2011 Census). The city has three local bodies- New Delhi Municipal Council (NDMC), Delhi Cantonment Board and Municipal Corporation of Delhi (MCD). MCD covers nearly 97% of the total area of the city. The NCT of Delhi receives 611 mm of rainfall on an average annually mainly from July to September. The highest monthly average high temperature is 41oC in May and the lowest monthly average low temperature is 7oC in January. The average annual relative humidity is 49.2% and average monthly relative humidity ranges from 25% in April-May to 73% in August [14]. Delhi has five distinct seasons, viz. summer, rainy, autumn, winter and spring and details are given at (Table 1).