Japanese Encephalitis
Ø Japanese Encephalitis is an arthropod-borne viral disease transmitted by mosquitoes.
Ø Causes serious inflammation of the brain.
Ø May lead to permanent brain damage.
Ø Carries a high mortality rate.
Ø Human Encephalitis in JAPAN recognized as early as 1871.
Ø JE in epidemic form has been known since 1924.
Ø 4000 human deaths recorded in JAPAN.
Global scenario
Major public health problem in Asia.
Virus first isolated in Japan in 1935.
As per WHO estimates 50 thousand serious cases and 10 thousand deaths each year.
Disease is prevalent in Indian Sub-continent: Nepal, India Sri Lanka and some areas in Bangladesh.
Other SE Asian countries reporting cases include:
Ø Myanmar, Thailand, Cambodia, China,
Indonesia, Laos, Vietnam, Malaysia, Philippines, Taiwan,
Hong Kong and Korea
DISTRIBUTION OF JAPANESE ENCEPHALITIS
• Japanese encephalitis is endemic in India, China, Japan, and all of South East Asia.
• Japanese encephalitis is the leading cause of viral encephalitis in Asia, with 30,000–50,000 cases reported annually.
JAPANESE ENCEPHALITIS IN INDIA
« 1952 - First evidence of JE viral activity by
VRC (NIV) during sero-surveys for arbo-viruses.
« 1955 - First human case of JE.
« 1958 - First viral isolation from JE case.
« 1973 - First outbreak- Bankura and Burdwan in West Bengal.
« 1976 - Repeat outbreak in Burdwan.
« 1978
• Widespread occurrence of suspected JE cases.
• National level monitoring initiated by NMEP in 1978.
Initiation of immunization using inactivated mouse brain vaccine
JE affected areas
v Andhra Pradesh
v Assam
v Bihar
v Goa
v Haryana
v Karnataka
v Kerala
v Maharashtra
v Manipur
v Tamil Nadu
v Uttarakhand
v Uttar Pradesh
v West Bengal
v Nagaland
EPIDEMIOLOGY
Japanese encephalitis is a flavivirus that is transmitted by the mosquito Culex tritaeniorhynchus.
The mosquitoes that transmit the virus breed in rice fields, and standing water
Majority of infections occur in rural areas and occur during July and October coinciding with monsoon and postmonsoon period.
The virus can also infect other vertebrates like birds and pigs.
Japanese encephalitis is primarily a childhood disease because people develop immunity through exposure.
The majority of cases occur in people under the age of 15.
CLINICAL FEATURES
Incubation Period - 5 to 15 days
only 1 in 250 infections develop into encephalitis, rest asymptomatic
Fever with severe rigor, headache and malaise
Acute encephalitic stage include
– neck rigidity
– hemiparesis
– convulsions
– Coma
CFR: Around 20% (in India), higher in children
30% of the people that survive the infection develop paralysis, brain damage, or other serious permanent sequelae
JE vectors
Major JE vectors:
Cx. tritaeniorynchus
Cx. pseudovishnui
Cx. vishnui
Ecology of vectors
Prolific breeders in rice fields, irrigation channels, other small water collections with vegetation
Majority rest outdoors
Primarily zoophilic
High densities in monsoons & post monsoons
Clinical spectrum of JE infection
Ø For every symptomatic JE case, there are likely to be about 300 – 1000 people infected with JE virus but without any clinical manifestation
Ø Children between 1 to 15 years of age are mainly affected in endemic areas.
Ø But people of any age can be infected. Adult infection most often occurs in areas where the disease is newly introduced.
Prognosis
Depends on cause and severity of illness and patient’s age.
Mild cases recover in 2 to 4 weeks with supportive care.
Severe encephalitis can lead to numerous complications.
– Hearing and/or speech loss, blindness, permanent brain and nerve damage, behavioral changes, cognitive disabilities, lack of muscle control, seizures, memory loss.
Seasonality
Almost all the states exhibit uniform seasonality
Assam shows a different pattern
Sometimes two peaks recorded in some states like Tamil Nadu due to two monsoon peaks
STRATEGIESFOR PREVENTION AND CONTROL
Surveillance for cases of encephalitis
For surveillance purposes, JE is also commonly reported under the heading of
“acute encephalitis”.
In WHO’s guidelines for JE surveillance, syndromic surveillance for JE is recommended. This means all cases of acute encephalitis syndrome (AES) should be reported.
Laboratory confirmation of suspected cases is done where feasible.
