Beat the bite

Dr Dipankara Devebrata

(drdipdev@gmail.com)

Japanese Encephalitis (JE) is an inflammation of the brain caused by the JE virus, which is transmitted to humans by mosquitoes. JE is a disease of major public health importance worldwide due to its high epidemic potential, high case fatality rate (CFR) and neurologic sequelae among survivors as well as considerable economic costs. According to World Health Organization (WHO), approximately 3 billion people are living in countries which are at risk of JE in Southeast Asia and the Western Pacific. The first case of JE was documented in 1871 in Japan. It was first reported in India in 1955. It is endemic in states such as Assam, Bihar, Uttar Pradesh, Andhra Pradesh, West Bengal and Manipur. JE can present in forms of mild severity that heals spontaneously or in aggressive forms with a poor prognosis and severe neurological sequelae in survivors. There is no cure for JE.

Japanese Encephalitis Virus (JEV) is an RNA virus and belongs to the family Flaviviridae and genus Flavivirus. The virus is maintained in a cycle between mosquitoes and vertebrate hosts, primarily pigs and wading birds (herons, egrets). Humans are considered dead-end hosts because they usually do not develop high enough concentrations of JE virus in their blood to infect feeding mosquitoes. JEV is transmitted to humans through bites from infected mosquitoes, primarily of the Culex species. The most important vector Culex tritaeniorhynchus, prefers low-lying water bodies with abundant plants, so paddy fields are a major habitat of the larvae. Domestic pigs serve as key virus-amplifying hosts as they develop high and long-lasting viral load in their blood. The disease is predominantly found in rural and peri-urban areas and transmission is principally associated with the rainy season.

Most infections are asymptomatic or paucisymptomatic, with fever and headache. Approximately 1 in 250 infected people develops a severe neuroinvasive illness that is characterised by rapid onset of high fever, headache, neck stiffness, disorientation, coma, seizures and paralysis, which can lead to death. The case fatality rate in severe diseases is up to 30% and up to 50% of patients who survive severe illnesses have significant neurologic or psychiatric sequelae. The incubation period (time from infection until illness) is usually 5-15 days. All ages can be affected in a population without previous exposure. In endemic areas, the paediatric population are usually affected as most people develop immunity by the time they reach adulthood. JE cannot be transmitted from human to human.

Diagnosis is established by detecting JEV-specific IgM antibodies in Cerebrospinal fluid or serum. There is no antiviral and treatment is supportive. The best way to prevent JE is through vaccination and avoiding mosquito bites. Use mosquito nets (preferably insecticide-treated) while sleeping even during the daytime, use insecticide (vapour dispensing units) inside the house in the evening, avoid outdoors at dawn and dusk, wearing full-sleeve shirts and long trousers that are loose and light coloured along with closed shoes when outdoors, using mosquito repellent on the skin, covering windows and doors with insect screens are advisable. Furtherused cans and bottles should be put into covered dustbins, all drains should be kept free from blockage, water storage tanks should be tightly covered and water for plants should be changed at least once a week, leaving no water in the saucers underneath flower pots. Swimming pools should be well maintained especially those in schools that may be neglected when not in use during summer vacation. Piggeries should be kept away from human dwellings as also cattle as they are 'mosquito attractants'.

Climatic conditions, an abundance of mosquitoes and pigs, agricultural practices and floods together provide ideal conditions for JE in our state. Most cases are seen in June, July and August. The annual flood situation has been worsened by climate change and also by man-made factors like deforestation, hill cutting and encroachment of wetlands. Although considered a rural disease, the emergence of JE in urban areas is a possibility as increased population density, unplanned expansion, poor sanitation, artificial floods, increased temperature and urban pig farming are all favourable to mosquitoes.