Dengue and chikungunya in India - High temperatures, humidity, rainfall and local practices to blame?

High temperatures, humidity, rainfall and local practices favour breeding and abundance of Aedes mosquito species increasing the risk of dengue and chikungunya
Aedes aegypti mosquito (Source: Wikimedia Commons)
Aedes aegypti mosquito (Source: Wikimedia Commons)

Climate change has been predicted to have a tremendous impact on the health of populations leading to deaths as well as increase in the incidence of diseases such as dengue and chikungunya. Dengue and chikungunya have emerged as major public health problems making headlines in many states in India following the erratic monsoons. Both are caused because of mosquito bites and transmitted by the Aedes genus (Aedes aegypti or Ae. Albopictus) vector or carrier mosquitoes.

Recent trends in the incidence of dengue and chikungunya epidemics

The paper titled 'Current status of dengue and chikungunya in India' published in the journal WHO South-East Asia Journal of Public Health discusses the details on the recent distribution of dengue and chikungunya epidemics in the country.

The chikungunya epidemic: The chikungunya virus has found to have re-emerged since 2006 after a gap of 32 years and caused a massive outbreak affecting 13 states. In 2008, almost 100,000 people in different villages of Kasargode district, Kerala were affected by it. This was followed by a large outbreak in Tirunelveli district, Tamil Nadu in 2009–2010 and also cases were reported from Maharashtra. In subsequent years, it spread to Goa,Orissa, Rajasthan, West Bengal, Andaman & Nicobar Islands and Puducherry. In the year 2011, cases were reported from all states except Punjab, Dadra and Nagar Haveli and Lakshadweep.

The dengue epidemic: Between 2006 and 2012, India reported an annual average of 20,474 dengue cases.  DF / Dengue Haemorrhagic Fever (DHF), a serious form of dengue, was reported from 13 states in the country. Recently, wide-spread outbreak of dengue was reported from Manipur in NE India. It has been reported that there are two types of the dengue virus circulating in the country and there have also been reports of co-infection with malaria, chikungunya, and leptospirosis as well.

Rainfall, humidity, high temperatures, local practices linked with dengue and chikungunya

Recent studies that have looked at the determinants of dengue and chikungunya have found an association between environmental factors and incidence of both the epidemics. This paper titled 'The environmental aspects of dengue and chikungunya outbreaks in India: GIS for epidemic control' published in the International Journal of Mosquito Research presents the findings of a study that used GIS to map the prevalence of dengue and chickungunya and analysed the environmental determinants for both the diseases.

Findings of the study

The spatial analysis of climatic variables with the epidemic cases found that:

  • Temperatures in the range of 22 to 31 degrees C, relative humidity of 70% to 90%, and rainfall, provided a suitable environment for breeding and abundance of Aedes mosquito species increasing the risk of dengue and chikungunya.
  • Chikungunya epidemics in major metropolitan cities across the country, and rural areas in Maharashtra, Haryana, Uttar Pradesh, Pondicherry and Tamil Nadu were associated with the presence of a large number of containers of damaged household materials in the coastal areas making it suitable for mosquito breeding.
  • Irregular water supply made people store water in huge plastic container vessels and cement containers, which provided ideal breeding sites for mosquitoes. Chikungunya in Kerala was mostly associated with massive number of coconut shells used for collection of rubber milk in the rubber plantations and the massive pineapple cultivation in the state.

Thus, climate, landscape, environment and local practices were found to play an important role and influence the dengue and chickungunya epidemic transmission across the country. The paper concluded that the application of remote sensing and GIS was a potentially useful method for the control of dengue and chikungunya epidemics and their management in the country.

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