- Japanese Encephalitis is a viral disease
- It 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
- JE virus is primarily zoonotic in its natural cycle and man is an accidental host.
- JE virus is neurotorpic and arbovirus and primarily affects central nervous system
- JE virus infection presents classical symptoms similar to any other virus causing encephalitis
- 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 subacute (2-5 days)
- In acute encephalitic stage, symptoms noted in prodromal phase convulsions, alteration of sensorium, behavioural changes, motor paralysis and involuntary movement supervene 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.
- Japanese encephalitis is a vector borne disease.
- Several species of mosquitoes are capable of transmitting JE virus.
- JE is a zoonotic infection. Natural hosts of JE virus include water birds of Ardeidae family (mainly pond herons and cattle egrets). Pigs play an important role in the natural cycle and serve as an amplifier host since they allow manifold virus multiplication without suffering from disease and maintain prolonged viraemia.
- Due to prolonged viraemia, mosquitoes get opportunity to pick up infection from pigs easily.
- Man is a dead end in transmission cycle due to low and short-lived viraemia. Mosquitoes do not get infection from JE patient.
- Japanese encephalitis virus isolation has been made from a variety of mosquito species.
- Culicine mosquitoes mainly Culex vishnui group (Culex tritaeniorhynchus, Culex vishnui and Culex pseudovishnui) are the chief vectors of JE in different parts of India.
- Life cycle consists of egg, four instars of larvae, pupa and adult. The whole cycle takes more than a month, however, duration depends on temperature and other ecological conditions.
- Culex vishnui subgroup is very common, widespread and breed in water with luxuriant vegetation mainly in paddy fields and the abundance is related to rice cultivation, shallow ditches and pools.
- These vectors are primarily outdoor resting in vegetation and other shaded places but in summer may also rest in indoors.
- They are in principally cattle feeders, though human and pig feeding are also recorded in some areas.
Clinical:
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. Symptoms can include headache, fever, meningeal signs, stupor, disorientation, coma, tremors, paralysis (generalized), hypertonia , loss of coordination.
Laboratory:
Several laboratory tests are available for JE virus detection which include;
- Antibody detection: Heamagglutination Inhibition Test (HI), Compliment Fixation Test (CF), Enzyme Linked Immuno-Sorbant Assay (ELISA) for IgG (paired) and IgM (MAC) antibodies, etc.
- Antigen Detection: RPHA, IFA, Immunoperoxidase etc.
- Genome Detection – RTPCR
- Isolation – Tissue culture, Infant mice, etc
- 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.
Clinical Suspect
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.
(Patient with fever, altered sensorium lasting more than 6 hours, no skin rash and other known causes of encephalitis excluded)
Probable
A suspected case with presumptive laboratory results: Detection of an acute phase anti-viral antibody response through IgM in serum/ elevated and stable JE antibody titres in serum through ELISA/HI/Neutralising assay.
Confirmed
A suspect case with confirmed laboratory result : JE IgM in CSF or 4 fold or greater rise in paired sera (acute & Convalescent) through IgM/IgG ELISA, HI, Neutralisation test or detection of virus, antigen or genome in tissue, blood or other body fluid by immuno-chemistry, immunoflourescence or PCR.
Treatment of Japanese Encephalitis
There is no specific anti-viral medicine available against JE virus. The cases are managed symptomatologically. Clinical management of JE is supportive and in the acute phase is directed at maintaining fluid and electrolyte balance and control of convulsions, if present. Maintenance of airway is crucial.
Is there a vaccine for Japanese Encephalitis?
- Central Research Institute, Kasuali,India has developed Japanese encephalitis vaccine indigenously.
- It is a mouse brain killed vaccine and 3 doses are required to produce primary immunization. Two doses are administered sub-cutaneously within a gap of 7-14 days followed by third dose any time after one month and before one year of the second dose. A booster is required after 3 years.
- Mouse brain technology has limitations in huge production beyond a few million.
- Tissue culture vaccines with feasibility of mass production are under various phases of development, standardization and/or commercialization.
- 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 mosquito breeding requires eco-management, as the role of insecticides is limited.
- JE vaccine is produced in limited quantities at the Central Research Institute, Kasauli. Three doses of the vaccine provide immunity lasting a few years. The vaccine is procured directly by the state health authorities. 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.
There is no specific treatment of JE. Clinical management is supportive and in the acute phase is directed at maintaining fluid and electrolyte balance and control of convulsions, if present. Maintenance of airway is crucial. The state governments have been advised that in the endemic districts, anticipatory preparations should be made for timely availability of medicines, equipment and accessories as well as sufficient number of trained medical, nursing and paramedical personnel. The Government of India supports training programmes.
Technical support is provided, on request by the state health authorities, for outbreak investigations and control. Factors that make the prevention and control of JE challenging are: - Outdoor habit of the vector
- Scattered distribution of cases spread over relatively large areas
- Role of different reservoir hosts
- Specific vectors for different geographical and ecological areas
- Immune status of various population groups is not known making it difficult to delineate vulnerable population groups.
- Piggeries may be kept away (4-5 kms) from human dwellings.
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