Dengue in Assam: A Public Health Challenge

Dr Dharmakanta Kumbhakar

(The author can be reached at drkdharmakanta@yahoo.com)

Dengue fever (DF) and its severe forms ‘dengue hemorrhagic fever’ (DHF) and ‘dengue shock syndrome’ (DSS) have become major international public health concerns. Over the past three decades, there has been dramatic increase in the dengue cases globally. Approximately 2.5 billion people live in dengue-risk regions with about 100 million new cases each year worldwide. Dengue is endemic in India, with reported disease outbreaks in large metropolises. However, with increased urbanization and population movement, the disease is reportedly spreading to other metropolitan areas or cities that were hitherto free from the disease.

Dengue is spreading rapidly and becoming established in Assam, owing to socio-economic and developmental changes, with a dramatic increase in unplanned urbanization, population movement, lack of proper waste management and inadequate vector-control measures. It has come to affect a large populace in the State for the past eight years. Assam reported 237 confirmed cases of dengue and two deaths for the first time in 2010. In 2011, it was recorded as nil. Subsequently, there was a significant increase in 2012 and 2013 with 1058 and 4526 cases recorded, five and two deaths respectively. But, it decreased in 2014 with 85 cases recorded and no death. Again there was a significant increase in 2015, 2016 and 2017 with 1076, 6157 and 5016 cases recorded respectively. Of the total confirmed cases for each year in Assam, the majority (70–90%) were recorded in Guwahati. In 2013, 91% (4121/4526) of the total reported dengue cases were recorded in Guwahati alone. The cases were, however, unevenly distributed in different zones of Guwahati, with large concentrations in the East zone and Capital zone. A few confirmed cases have also been reported from other district towns (Dibrugarh, Tinisukia, Lakhimpur, etc.) supported by serological evidence for circulating strains of dengue virus. Cases were reported mostly from those places where people harvest rain water and often leave tyres, drums and canisters out in the open. The actual disease burden is estimated to be much higher, with many cases undiagnosed and additional cases reported in public/private sectors.

Dengue infection is caused by any one of four types of distinct but closely-related viruses – DV1, DV2, DV3 and DV4 of the genus Flavivirus – that spread by the bite of infected Aedes mosquito. The virus causes self-resolving dengue fever in the majority of cases, characterized by severe body ache, retro-orbital pain, headache and at times rash, abdominal pain and nausea. In a small proportion of cases, the disease develops into the life-threatening DHF resulting in bleeding, low levels of blood platelet and blood plasma leakage or into DSS where dangerously low blood pressure occurs. The WHO 2009 classification divides dengue fever into two groups: uncomplicated and severe. The diagnosis of dengue infection is routinely done by demonstration of anti DV IgM antibodies or by NS1 antigen in patients’ serum depending upon the days of illness using ELISA kits. Molecular methods like RT-PCR and DV isolation in tissue culture cells and its sequencing is also done. The treatment of acute dengue is supportive, using either oral or intravenous rehydration for mild or moderate disease, and intravenous fluid and blood transfusion for more severe cases. In the absence of a vaccine, vector control is the primary means of controlling dengue infection.

In Assam, dengue cases are reported during the post monsoon period every year with a peak between mid-September and November. During 2013, a rise in trend was seen early owing to an early monsoon. Initially restricted to urban areas, the occurrence of dengue infections has now spread to the semi-urban and rural areas in Assam. The Kamrup (Metro) district and districts bordering Arunachal Pradesh are places mostly affected by dengue in Assam. Aedes aegypti and Aedes albopictus mosquito which are the vectors of dengue are reportedly prevalent in Assam and widely abundant in urban areas like Guwahati and suburbs, breeding in a wide variety of containers like empty car batteries, drums and tyres where water can accumulate easily and are especially found in abundance in Guwahati. Open dumping of solid waste materials is common in the city and this helps in breeding of mosquitoes. Aedes aegypti is the most common species in Guwahati. The seasonal prevalence of both mosquito species occurs from the onset of rains in April until December. The transmission patterns of dengue are influenced by temperature and precipitation. Temperature affects the egg viability, larval development, adult longevity and dispersal, whereas rainfall affects the abundance and productivity of the breeding habitats of Aedes mosquitoes. A temperature range of 18-33.2°C is considered to be ideal for the transmission of dengue fever. The favourable environment, high humidity (60–90%), warmer climates (22–33 degree C) for most of the year, excessive and prolonged rainfall in the State offer ideal conditions for proliferation of these mosquito vectors and the spread of disease.

With the increasing distribution range of Aedes aegypti and evidence of virus activity, it is projected that dengue will emerge as a major public health issue in Assam. There is a need of identification of high-risk areas, vector incrimination and seasonal infectivity of dengue so that future outbreaks could be avoided by targeted interventions. Surveillance for probable detection of dengue infections, monitoring of vector activity and initiation of vector control measures should be ensured so as to prevent disease transmission in the high risk zones. The control of Aedes mosquitoes in Assam is very challenging and requires community involvement. Destroying the breeding grounds of mosquitoes through an intense public campaign, proper solid waste disposal, improved water storage practices, including covering containers, to prevent access to egg-laying female mosquitoes, supplying medicated mosquito nets in affected areas, protecting oneself from mosquito bites using clothes with long sleeve and mosquito repellent, educating the people on the basics of health and hygiene are a simple yet very effective way of minimizing the impact of dengue in Assam.

Dengue is taking a turn in Assam this year also. The positive cases of dengue have been reported from Guwahati and different districts of the State. Though it has not reached epidemic scale in Assam, but there is chance of more dengue cases this year as nationally, there is a rise in the occurrence of the disease so far. This needs urgent attention of the government authorities. The authorities should launch a publicity campaign through different media to keep the people well-informed, proper information should reach the people on the dos and don’ts on dengue, improve its overall preparedness to meet any deterioration in the situation. Any laxity on the part of the authorities can easily lead to an epidemic-like situation in Assam, especially in Guwahati.