Instructions for users

• This slide presentation provides an overview of the epidemiology of JE.

• Below many of the slides, there are notes to explain the information in the slide.

• You should adapt the presentation for your own use.

Japanese Encephalitis:

Epidemiology of the Disease

Learning Objectives

Participants will:

• Understand the extent and severity of the JE problem worldwide

• Understand the means and patterns of transmission of JE

JE virus: Virology

• Japanese encephalitis (JE) serocomplex

— 10 viruses

— 6 human pathogens (JE, West Nile, Kunjin, Usutu, St. Louis encephalitis, Murray Valley encephalitis viruses)

— Most are amplified bird – mosquito – bird

• 4 genotypes in Asia (possibly 5)

JE virus: History of discovery

• 1871: “Summer encephalitis” epidemic in Japan

• 1924: Agent from human brain tissue isolated in rabbits

• 1934: Isolate of this virus produced experimental encephalitis in monkeys

• 1938: First isolate from Culex tritaeniorhynchus

• 1930s: First mouse brain-derived vaccines developed

• 1954: “Refined” mouse brain vaccine developed

Why is JE a problem?

• JE is the leading cause of viral neurological disease in Asia, now that poliomyelitis has nearly been eradicated.

• More than 3 billion people live in areas where JE is transmitted.

• Up to 50,000 cases of JE are reported to WHO each year.

• Up to 10,000 to 15,000 deaths are reported each year.

Cases are under-reported

• Cases are under-reported due to— Lack of good surveillance

systems.

— Lack of diagnostics.

• Actual number of cases is likely much higher.

Photo credit: Julie Jacobson

Clinical spectrum of JE disease

DieSevere

Moderate

Mild

Asymptomatic

Death and disability from JE

• Up to 30% of all patients with JE die.

• For those that survive the illness, 30% to 75% cases are left with disability.

• Disability is both physical and cognitive.

Photo credit: Julie Jacobson

Where does JE occur ?

Age groups affected by JE

• Children 1 to 15 years of age are mainly affected in endemic areas.

• But people of any age can be infected. Adult infection most often occurs in areas where the disease is newly introduced.

Photo credit: Carib Nelson, PATH

Distribution of encephalitis cases by age group Andhra Pradesh, India, 2000

6

136

201

00

50

100

150

200

250

Under 1 yr 2 to 5 yrs 6 to 15 yrs 16+ yrs

Num

ber

of C

ases

Distribution of encephalitis cases by age group Nepal, 2004

734

267356

170

150100200300400500600700800

Under 1 yr 1 to 4 yrs 5 to 9 yrs 10 to 14 yrs 15+ yrs

Num

ber

of C

ases

Data supplied by Government of Andhra Pradesh

Data supplied by WHO, Nepal

Different patterns of

age distribution

of cases

Two patterns of transmission of JE

1. Seasonal pattern, with a large increase in cases at a certain time of the year (e.g., southern China)

2. Year-round pattern (e.g., Bali, Indonesia)

JE may be spread:

Data supplied by International Vaccine Institute

Transmission of JE

• JE is spread by mosquitoes.

• Culex tritaeniorhynchus is the main vector in most of Asia, but other species that breed in rice paddies, ditches, and ground pools are also important.

Photo credit: Richard G. Weber

Culex mosquito laying eggs on water

JE Transmission Cycle

People at risk

• People living in rural areas have the highest risk of disease because the mosquitoes that spread JE breed in rice paddies and pools of water.

• Cases in urban areas also occur.

Photo credit: Julie Jacobson, PATH

Data from your country/region

• History of disease in your country.

• Incidence/case data.

• Map of JE distribution in your country.

• Age and sex distribution.

• Seasonal patterns.

• Local mosquito vectors and habitats.

You may want to include your local data here. For example:

Acknowledgements

Please include the following acknowledgement if you use this slide set:

This slide set was adapted from a slide set prepared by PATH’s Japanese Encephalitis Project.

For information: www.JEproject.org