Japanese encephalitis

Japanese encephalitis virus (JEV) is an arthropod-borne flavivirus, which has a wide distribution in many countries of Asia, Western Pacific and in northern Australia

It is transmitted by mosquitoes (Culex tritaeniorhynchus is the principal vector) in humans causing inflammation of the membranes around the brain. 

Disease recognised in Japan since 1871- virus isolated during an epidemic in Japan in 1935

Japanese encephalitis is a leading cause of viral encephalitis in Asia

An incubation period of 5 to 15 days- Majority of infections are asymptomatic i.e. only 1 in 200 infections develop into encephalitis

The disease has an abrupt onset with fever, vomiting and headache, it can also be mild or without apparent symptoms- 1 in 200 infections can result in severe disease characterized by rapid onset of high grade fever, headache, neck stiffness, disorientation, coma, seizures, spastic paralysis and death.

Mortality rate in some epidemics has been upto 50 percent- recovery may take many weeks- residual neurological damage persist in upto 50 percent survivors.

Large majority of infections are asymptomatic however, it is calculated that 500-1000 inapparent infections occur for every clinical case of disease

In India, Japanese encephalitis was first recognized in 1955, from Vellore, during an epidemic in Tamil Nadu. First confined to South India, now it is a major public health problem of national importance in India, cases being reported from West Bengal, UP, Assam, Haryana, Goa, Maharshtra, Andhra Pradesh, Pondicherry, Kerala etc

Transmission

Japanese encephalitis virus can affect both animals and humans. 

No person to person transmission

The virus is passed on to humans from animals through an infected mosquito. Birds such as herons act as reservoir hosts and pigs act as amplifier hosts. Other birds such as ducks, pigeons, sparrows and vertebrate hosts such as cattle and buffaloes may be involved

The major vector Culex tritaeniorhynchus preferentially infects cattle, but since they do not develop viremia, they do not spread the virus

The high cattle-pig ratio in India is suggested as a factor which reduces human infections

Diagnosis 

Blood tests: For antibodies present in the blood.

Lumbar puncture: It is also done to check for antibodies in CSF and spinal fluid.

CT or MRI Scans: In case of brain encephalitis

Treatment

There is no specific treatment for Japanese encephalitis, supportive treatment is provided- to control symptoms and prevent complications from developing.

Prevention and control measures 

• Vector control- mosquito control
• Locate piggeries away from human dwellings
• Vaccination of pigs
• Personal protection measures against mosquito bites.
• Use of insecticides
•  Screening of the houses with wire mesh
•  Japanese encephalitis (JE) vaccination –
• 1.      Formaline inactivated mouse brain vaccine using Nakayama strain-two doses followed by a booster dose - vaccine can prevent Japanese encephalitis (JE) for a number of years.   
• 2.      Live attenuated vaccine of IE strain SA14-14-2 produced in baby hamster kidney cells