Ecology and Biology of Culex quinquefasciatus Say, 1823, in Two Physiographically Different Ecosystems with Special Reference to Human Lymphatic Filariasis in West Bengal, India

Abstract

Lymphatic filariasis (LF) is a major cause of public health concern worldwide especially in a tropical country like India. About 1254 million people worldwide, inhabiting 83 countries including 554.2 million people in India, are at the threshold of the filarial infection. The nematode Wuchereria bancrofti accounts for an estimated 95 % of these infections worldwide. The other two nematodes Brugia malayi and B. timori are minor agents of filariasis. The periodic (nocturnal) form of W. bancrofti is prevalent in the Indian mainland transmitted by Culex quinquefasciatus, a member of Culex pipiens species complex. Recent studies have indicated that Cx. pipiens and Cx. quinquefasciatus are two distinct species. The complete genome sequencing studies of Culex quinquefasciatus reveal that the number of their protein-coding genes (18,883) is 22 % greater than that of Aedes aegypti and 52% greater than that of Anopheles gambiae. In addition to this, the species exhibit multiple gene family expansion which includes olfactory and gustatory receptors, salivary gland genes and genes associated with xenobiotic detoxification. The mosquito species is a nocturnal biter and has been predominantly recorded from human baits in Calcutta. Culex quinquefasciatus is considered as an opportunistic feeder in rural Bengal as it feeds on 26.45 % humans only, with mostly on ruminants (46.25 %), followed by pigs (14.19 %) and birds (6.45 %). This mosquito species is found in domestic collections of water, places like flooded open cement drains, flooded latrines, overflow water from roof-top tanks, kitchens as well as in ground pools, ditches and shallow wells. This species usually selects organically rich and polluted surface waters and artificial containers for breeding. The post-monsoon season (September, October, November) records the highest per man-hour density of the vector, Cx. quinquefasciatus, followed by the monsoon (June, July, August) and winter (December, January, February). The summer months have the lowest per man-hour density of the vector population in the studied areas. The overall per man-hour density of Cx. quinquefasciatus in the urban area (72.23 %) is markedly higher than that of the rural areas (37.03 %). In West Bengal, urban areas were more endemic for bancroftian filariasis than the rural area. Urban developments such as road, flyover, building, metro rail construction, etc. are the contributing factors in creating a complex mosquitogenic and filariogenic situations in urban areas. Global warming and globalization are likely to reshape the ecology of vector mosquitoes, especially ubiquitous Cx. quinquefasciatus. This will have wide-ranging consequences on the epidemiology of vector-borne diseases like lymphatic filariasis.