Effect of Environment and Elevation on Seasonal Prevalence of Culicoides in West Bengal

Abstract

Background: Culicoides, popularly known as ‘biting midges’ is a group of vector insects causing transmission of pathogens to livestock and other closely related mammals leading to animal health deterioration. They are among the smallest and most abundant hematophagous vectors of Blue tongue virus (BTV), Epizootic haemorrhagic disease virus (EHDV), African horse sickness virus (AHSV), Equine encephalitis virus (EEV), protozoans, filarial nematodes throughout the world. They are known to spread livestock diseases in India in the states of Andhra Pradesh, Assam, Gujarat, Haryana, Himachal Pradesh, Jammu and Kashmir, Jharkhand, Karnataka, Kerala, Madhya Pradesh, Maharashtra, Nagaland, Punjab, Rajasthan, Sikkim, Tamil Nadu, Tripura, Uttar Pradesh and West Bengal. 30 Culicoides vectors are reported worldwide, 13 of them from India, of which 11 are found in West Bengal. In the Indian subcontinent, biting midges live throughout the year, with two distinct peaks - one in the monsoon (August-September) and another peak during post-monsoon or beginning of winter (November) and there is a steady decrease during the summer months (May). Adults thrive best at low-temperature range (19-32oC) and rainfall plays an important role in Culicoides breeding and life-cycle. But a detailed account on the ecology, breeding sites, biology and bionomics of immature and adults have been poorly understood with very scanty literature. The present research is aimed to provide an exhaustive detail on the ecological behavior of Culicoides and their prevalence pattern based on the effect of meteorological parameter and elevation across different regions of West Bengal. Methods: Insect samples were collected using sweep nets in the early morning, afternoon and just before sunset for a period of four years from January 2014 to December 2017 in six agro-climatic regions of West Bengal. After collection, they were transferred in 70% ethanol, kept in a cool place, sorted and different parts of the specimen were mounted on glass slides in the phenol-balsam mixture and identified through Leica DFC 295 binocular light microscope. Ecological graph analysis were generated using software PAST 3.0 and MS-EXCEL 2016. Maps on sampling sites was generated using software ARC GIS 10.5). Result: Five Culicoides species-Culicoides oxystoma, C. actoni, C. peregrinus,C. orientalis and C. anophelis were collected. The results show highest prevalence in post-monsoon months at the coastal-saline region, at an of elevation 5-15m with ideal temperature of 14-35oC and rainfall of 1100-2000mm in West Bengal, with the highest dominance of Culicoides oxystoma throughout the year.