A study on outbreak of dengue from Bihar, India- establishing new foci, attributable to climatic changes

Dengue fever (DF) is a mosquito-borne viral infection which is emerging fast in terms of mortality and morbidity in humans worldwide, particularly in tropical and subtropical countries. DF is characterized clinically by headache, retro-orbital pain, myalgia, arthralgia, integumentary rashes, and sometimes with haemorrhagic manifestations. Aedes aegypti , the main vector species of dengue fever/dengue haemorrhagic fever (DHF) is commonly found in urban areas which can be attributed to the availability of breeding sites such as water storage containers due to poor management of water and limited supply of drinking water, non degradable tyres, long lasting plastic containers and ineffective community participation in eliminating the breeding places. However, new foci are a major concern for public health by affecting the epidemiology of this disease such as rural and semi-urban areas, which may be linked to climate change. Climate change has led to unusual rainfall pattern leading to excess rain in some parts and deficient rainfall in other parts. This is accompanied by overall rise in average temperature which favors fast circulation of the vector and consequently of dengue virus in the environment. Thus, epidemiological, environmental and entomological observations were made to confirm the aetiology of a focal outbreak of dengue fever in rural and semi-urban areas providing breeding sites for larval growth. The present research aimed to record outbreak of dengue from new foci from Bihar, India, and correlates it with climate change. Bihar was said to be free from dengue but in September, 2010, outbreaks have been reported specially from three districts: Patna, Munger and Begusarai. The epidemiological investigation of probable cases showed clustered distribution of cases in adjacent houses and streets and absence of travellers to dengue endemic regions, though many cases of migration was also noted during early phase of outbreak. Cases reported from Patna were mostly related to migration from different areas in order to get better treatment facilities. Entomological investigations were carried out in 60, 94 and 75 houses in the districts of Patna, Munger and Begusarai respectively. The index of House, Container and Breteau from Patna, Munger and Begusarai found were 20, 40 and 29, 11.11, 43 and 31, and 26, 91.48 and 56, respectively, thereby indicating the high receptivity of Munger to DF/DHF transmission which can subsequently be confirmed with the number of cases reported from there. The environmental investigations included in this study were average temperature, humidity and rainfall of three affected districts. The averages temperatures during the outbreak from Patna were 32.21 (maximum) and 25.09 (minimum), from Munger were 32.39 (maximum) and 25.19 (minimum) and from Begusarai were 32.33 (maximum) and 25.43 (minimum). The rate of humidity from Patna were 86.29 (morning) and 82.43 (evening), from Munger were 84.97 (morning) and 82.86 (evening) and from Begusarai were 84.12 (morning) and 83.43 (evening). The rate of rainfall in the year 2010 was 226.9, 220.00 and 224.45 mm for Patna, Munger and Begusarai respectively. The reasons for death may be attributed to absence of herd immunity in new foci.