Japanese Encephalitis is a mosquito-borne viral infection that primarily affects children below 15 years of age. It is a severe disease that involves inflammation of the brain and is a major public health problem endemic in parts of China, Russian Federation’s South East and South and South East Asia. Major outbreaks of JE occur every 2-15 years. Its transmission intensifies during the rainy season, during which vector populations increase. The spread of JE in new areas has been correlated with agricultural development and intensive rice cultivation supported by irrigation programmes.
In Asia, JE is the leading cause of acute encephalitis and causes 68,000 cases (and 20,400 deaths) annually. The annual incidence of clinical disease varies both across and within countries, ranging from <10 to >100 per 100 000 population. It primarily affects children since most adults in endemic countries have natural immunity after childhood infection. However, individuals of any age may be affected.24 countries in the WHO South-East Asia and Western Pacific regions have JE transmission risk, which includes more than 3 billion people.
JE in India
The disease was first recognised in India in 1955 when cases of encephalitis from Tamil Nadu and neighbouring districts of Andhra Pradesh admitted to Christian Medical College hospital, Vellore, were serologically diagnosed as JE. Since 1992, it has further spread to newer areas and epidemics/outbreaks have been reported from West Bengal, Uttar Pradesh, Assam, Manipur, Bihar, Andhra Pradesh, Pondicherry, Karnataka, Goa, Kerala and Maharashtra. In India, it is endemic in 171 districts in 19 states with outbreaks being reported from across the country.
Challenges of JE prevention and control
In addition to the known endemic foci of JE, recent emergence of JE has occurred in areas of the world where it was previously unknown. A considerable percentage of JEV outbreaks occur in developing countries. This tests the health systems that are already struggling with different operational challenges. There is also considerable variation throughout the world in the intensity and quality of JE surveillance and availability of diagnostic laboratory testing. This adversely affects understanding of the nature and magnitude of the problem. From an intervention perspective, there are still countries in the endemic belts that less developed vaccination programmes, and still others have no programmes at all. Finally, from an evidence-for-policy perspective, the focus of the research community biomedical in nature; several knowledge gaps related to the health system and policy issues remain largely unaddressed and are left for the program managers to manage.
Success stories in JE control
Human vaccination has been the mainstay of JE prevention and control. Countries that have implemented high-quality childhood JE vaccination programmes have seen dramatic decline in JE incidence. In the pre-JE-vaccination era, tens of thousands of JE cases were often reported annually in Asia. During 1965–1975, more than 1 million cases were reported in China alone. However, in Japan, the Republic of Korea and Taiwan (China) the introduction of routine childhood vaccination programmes against JE beginning 40 to 50 years ago, combined with increased urbanisation and evolving agricultural practices, resulted in the virtual elimination of JE, despite continued enzootic JEV transmission because of expenses and difficult logistics.
References and additional reading
http://zoonoses.phfi.org/Japanese_encephalitis.html Bulletin of WHO, October 2011
JE outbreaks are being reported from previously unknown foci. Further, encephalitis outbreaks of other aetiologies in endemic areas have only added to their complexity. For programme managers, researchers and community health professionals, access to accurate and updated information is key to planning interventions and other relief measures.read more