Japanese Encephalitis (JE) is a deadly viral disease that kills several thousand people each year. The diseases is common in South East Asia including India, however, cases are also reported as far as the Pacific Islands and Australia. This virus is an important cause of endemic encephalitis in Japan, China, Russia, South-East Asia, India and Pakistan. There are 10,000–20,000 cases reported to the WHO annually. The first evidence of presence of JE virus dates back to 1952 and first case was reported in 1955. Outbreaks have been reported from different parts of the country. Pigs and other domestic animals are important source of infection
The disease is transmitted by infective bites of female mosquitoes mainly belonging to Culex tritaeniorhynchus, Culex vishnui and Culex pseudovishnui group. However, some other mosquito species also play a role in transmission under specific conditions. Japanese Encephalitis virus is primarily zoonotic (disease is a disease that can be passed between animals and humans) in its natural cycle and man is an accidental host.
The incubation period is typically 5-15 days. Initial symptoms often include fever, headache, and vomiting. Most JE virus infections are mild (fever and headache) or without apparent symptoms, but approximately 1 in 250 infections results in severe disease characterized by rapid onset of high fever, headache, neck stiffness, disorientation, coma, seizures, spastic paralysis and death.
The case-fatality rate can be as high as 30% among those with disease symptoms. Of those who survive, 20%–30% suffer permanent intellectual, behavioural or neurological problems such as paralysis, recurrent seizures or the inability to speak.
Most infections are subclinical in childhood and 1% or less of infections lead to encephalitis. Initial systemic illness with fever, malaise and anorexia is followed by photophobia, vomiting, headache and changes in brainstem function. JE virus infection may result in febrile illness of variable severity associated with neurological symptoms ranging from headache to meningitis or encephalitis. Symptoms can include headache, fever, meningeal signs, stupor, disorientation, coma, tremors, paralysis (generalized), hypertonia, loss of coordination, etc. Prodromal stage may be abrupt (1-6 hours), acute (6-24 hours) or more commonly sub acute (2-5 days). In acute encephalitic stage, symptoms noted in prodromal phase are convulsions, alteration of sensorium, behavioural changes, motor paralysis and involuntary movement and focal neurological deficit is common. Usually lasts for a week but may prolong due to complications. Amongst patients who survive, some lead to full recovery through steady improvement and some suffer with stabilization of neurological deficit. Convalescent phase is prolonged and vary from a few weeks to several months. Clinically it is difficult to differentiate between JE and other viral encephalitis JE virus infection presents classical symptoms similar to any other virus causing encephalitis.
Neurological features other than encephalitis include meningitis, seizures, cranial nerve palsies, flaccid or spastic paralysis, and extra pyramidal features. Mortality with neurological disease is 25%. Most children die from respiratory failure with infection of brainstem nuclei.
Diagnosis is based on a combination of clinical signs and symptoms and specialized laboratory tests of blood or spinal fluid. These tests typically detect antibodies that the immune system makes against the viral infection.
Clinically JE cases present signs and symptoms similar to encephalitis of viral origin and cannot be distinguished for confirmation. However, JE can be suspected as the cause of encephalitis as a febrile illness of variable severity associated with neurological symptoms ranging from headache to meningitis or encephalitis.
Several laboratory tests are available for JE virus detection which includes Antibody detection: Heamagglutination Inhibition Test (HI), Compliment Fixation Test (CF), Enzyme Linked Immuno-Sorbant Assay (ELISA) for IgG (paired) and IgM (MAC) antibodies.
In view of the limitations associated with various tests, IgM ELISA is the method of choice provided samples are collected 3-5 days after the infection.
Other infectious causes of encephalitis should be excluded. There is neutrophilia and often hyponatraemia. CSF analysis reveals lymphocytosis and elevated protein. Serological testing may be helpful and there is a CSF antigen test.
The preventive measures are directed at reducing the vector density and in taking personal protection against mosquito bites using insecticide treated mosquito nets. The reduction in vector mosquitoes breeding places requires eco-management, as the role of insecticides is limited. Piggeries may be kept away (4-5 kms) from human dwellings.
Factors that make the prevention and control of JE challenging are:
Ø Outdoor habit of the vector
Ø Scattered distribution of cases spread over relatively large areas
Ø Role of different reservoir hosts
Ø Specific vectors for different geographical and ecological areas
Ø Immune status of various population groups is not known making it difficult to delineate vulnerable population groups
Safe and effective JE vaccines are available to prevent disease. JE vaccine is produced i at the Central Research Institute, Kasauli. Three doses of the vaccine provide immunity lasting a few years. Vaccination is not recommended as an outbreak control measure as it takes at least one month after second dose to develop antibodies at protective levels and the outbreaks are usually short lived. Clinical management is supportive and in the acute phase is directed at maintaining fluid and electrolyte balance and control of convulsions, if present.
WHO recommends having strong prevention and control activities, including JE immunization in all regions where the disease is a recognized public health problem, along with strengthening surveillance and reporting mechanisms. Other control measures such as mosquito control or amplifying pig control have shown to be less reliable.
There are four main types of JE vaccines currently in use: inactivated mouse brain-based vaccines, inactivated cell-based vaccines, live attenuated vaccines, and live chimeric vaccines. Traditionally, the most widely used vaccine was a purified inactivated product made from either Nakayama or Beijing strains propagated in mouse brain tissue. It is still produced and used in several countries.
All travellers to Japanese encephalitis-endemic areas should take precautions to avoid mosquito bites to reduce the risk for JE. Personal preventive measures include the use of repellents, long-sleeved clothes, coils and vaporizers.
· Use insect repellent. When you go outdoors, use insect repellents or oil of lemon eucalyptus. Even a short time outdoors can be long enough to get a mosquito bite.
· Wear proper clothing to reduce mosquito bites. When weather permits, wear long-sleeves, long pants and socks when outdoors. Mosquitoes may bite through thin clothing, so treating clothes with repellent containing permethrin or repellents will give extra protection. Don't apply repellents containing permethrin directly to skin.
· Reduce exposure to mosquitoes during peak biting hours. The mosquitoes that transmit JE virus feed mainly outside during the cooler hours from dusk to dawn. Travellers to high risk areas should consider minimizing outdoor activities at these times if possible. To reduce the risk of JE and other vector-borne diseases, travellers should stay in air-conditioned or well-screened rooms, or use a bed net and aerosol room insecticides.
Treatment is supportive, anticipating and treating complications. Vaccination for travellers to endemic areas during the monsoon period is effective prophylaxis. Some endemic countries include this vaccination in their childhood schedules.
Complications of the JE is based on the fact that the virus primarily affects central nervous system. A significant number of survivors are left with neurological problems such as impaired cognative function, mental disorders, seizures and poor coordination. JE is the main cause of viral encephalitis in many countries of Asia.