• Japanese encephalitis is a potentially severe viral disease that is spread by infected mosquitoes in the agricultural regions of Asia.

 
• It is one of several mosquito-borne virus diseases that can affect the central nervous system and cause severe complications and death.

 
• Japanese encephalitis can be a risk to travelers to rural areas where the disease is common.

 
• There is no specific treatment for Japanese encephalitis.

• What is Japanese Encephalitis?
• How is Japanese Encephalitis Transmitted?
• Signs and Symptoms of Japanese Encephalitis
• How soon after Exposure do Symptoms Appear?
• How is Japanese encephalitis Diagnosed?
• Who is at Risk for Japanese Encephalitis?
• How common is Japanese Encephalitis?
• Habits of Mosquitoes Carrying Japanese Encephalitis
• Ways of Preventing Japanese Encephalitis
• Who Requires the Vaccination against Japanese Encephalitis 

• Introduction
• Types of Vaccines
• Contraindications
• Population at Risk and Dosage for Vaccination
• Payment for Vaccination

1.  Introduction

WHO (World Health Organisation) reports as many as 50,000 cases and 10,000 deaths due to Japanese encephalitis (JE) every year.  JE is endemic in many Asian countries like China, Japan, Taiwan, Korea, Philippines, Thailand, Indonesia, Bangladesh, Sri Lanka, Vietnam and Cambodia.

JE is also endemic in Malaysia and occurs sporadically throughout the country all year round. Although there has been no significant increase in JE in the last few decades, outbreaks were reported.

2.  What You Really Need to Know

What is Japanese Encephalitis?

JE is a disease caused by virus transmitted through the bites of Culex mosquitoes.

• JE cannot be spread from human to human.
• Eating pork cannot transmit the disease.
• The JE virus multiplies in the pig's body.  When the female Culex mosquito sucks the blood of pig, she picks up the JE virus.
• After an incubation period of 14 days, the Culex mosquito is able to transmit the JE virus to a new host usually the pig.

 

 

The JE virus can infect human and horses if the infectious Culex mosquitoes bit them. Human and horses are the dead end hosts since there are no transmission from man to man or from horse to  horse.

Most infected persons develop mild symptoms or no symptoms at all. In people who develop a more severe disease, JE usually starts as a flu-like illness, with fever, chills, tiredness, headache, nausea, and vomiting. Confusion and agitation can also occur in the early stage. The illness can progress to a serious infection of the brain (encephalitis) and can be fatal in 30% of cases. Among the survivors, another 30% will have serous brain damage, including paralysis.

Symptoms usually appear 6-8 days after the bite of an infected mosquito.

Diagnosis is based on tests of blood or spinal fluid.

Anyone can get Japanese encephalitis, but some people are at an increased risk:

• People living in rural areas where the disease is common
• Travelers to rural areas where the disease is common

Japanese encephalitis is the leading cause of viral encephalitis in Asia.
The disease is very rare, however, in U.S. travelers to Asia.

The chance that a traveler to Asia will get Japanese encephalitis is very small:

• Only certain mosquito species can spread Japanese encephalitis
• In areas infested with mosquitoes, only a small portion of the mosquitoes are usually infected with Japanese encephalitis virus
• Among persons who are infected by a mosquito bite, only 1 in 50 to 1 in 1,000 will develop an illness. As a result, fewer than 1 case per year is reported in U.S. civilians and military personnel traveling to and living in Asia.
• Only 5 cases among Americans traveling or working in Asia have been reported since 1981.

• Only the Culex mosquitoes can transmit the JE virus.
• The Culex mosquitoes breed in dirty polluted water such ponds, pools, ditches, puddles, drains and rice fields.
• Culex mosquitoes bite between dawn and dusk (6.30pm - 6.30am).
• Culex mosquitoes prefer pig rather than human blood.

• Avoid being bitten by mosquito
• Sleep in mosquito net
• Using insecticides to prevent insect bites (e.g. mosquito coil, repellent, aerosol spray and cream)
• Fixing wire netting at all windows
• Wear long sleeved clothes / trousers
• Eliminating all Culex breeding places
• Providing good and proper drainage system
• Drain or fill up all pools and puddles with sand
• Maintain cleanliness in the piggeries
• Conduct regular fogging exercise in and around the pig farms.

• Workers in the pig farms
• People staying in or near the pig farms up to a radius of 2 km, especially children.

3.    Vaccination against Japanese Encephalitis

Introduction

JE is the leading cause of viral encephalitis in Asia. In endemic areas, annual incidence of clinical disease ranges from 10-100 per 100,000 population.  Case fatality average 30% and a very high percentage of the survivors are left with permanent neuropsychiatric sequelae.

There is no efficient drug treatment for this disease. In recent decades the JE virus has caused epidemics in previously unaffected countries, including India, Myanmar, Nepal, Sri Lanka, Thailand and Vietnam.

No effective method of environmental control of JE transmission is known.  Although socioeconomic improvement and changes in agricultural practices are likely to reduce viral transmission in some places, large - scale vaccination of affected populations with effective and affordable vaccines appears to be the logical control measures, at least in the short term.

The impact of large-scale JE vaccination is clearly documented in some regions of China, and systematic vaccination has also contributed significantly to the declining incidence rates in Japan, Republic of Korea and Thailand.

Three types of JE vaccine are currently in large - scale production and use, namely:

• Mouse brain - derived inactivated vaccine
• Cell culture - derived inactivated vaccine and
• Cell culture - derived live attenuated vaccine

The mouse brain - derived and inactivated vaccine based on the Nagayama strain (or Beijing - 1 strain) is currently the only vaccine available on the international market. China produces two JE vaccines for domestic use, an inactivated JE as well as a live attenuated vaccine, both grown in primary hamster kidney cells.

Controlled studies have shown that the commercially available mouse brain-derived vaccine is efficacious and without serious side effects for childhood vaccination.  Local reactions such as tenderness, redness and swelling occur in 20% of vaccines. A similar percentage may experience mild systemic symptoms, including headache, myalgia, gastro-intestinal symptoms and fever.

The mouse brain - derived vaccine is given subcutaneously in doses of 0.5ml or 1ml, the lower dose being for children aged 1-3. The manufactures recommended that 2 injections be given at an interval of 1-2 weeks in primary immunization followed by a booster after 1 year, with subsequent boosters every 3-4 years to maintain immunity.

In several Asian trials, primary immunization has been a disease-preventing efficacy of 95%; 91% efficacy was achieved in a placebo - controlled trial.

No serious permanent side effects are known to be associated with the vaccine. Fever and local reactions such as redness, swelling and pain are reported in fewer than 10% of those vaccinated.

There are some contraindications to the vaccine. The manufacturer recommends that the vaccine not be administered to the following persons:

• Those acutely ill or with active infections
• Persons with heart, kidney, or liver disorders
• Persons with generalized cancerous malignancies such as leukemia, lymphoma
• Persons with a history of hypersensitivities
• Pregnant women.

Very high risk population

• Pig farmers and their families staying on the farm
• Dose: Day 0, Day 7, Day 30, Year 1
• Booster: after every 3 years

High risk group

• All those staying within 2 km from the pig farms and below 15 years of age
• Dose: Day 0, Day 7, 1 Year
• Booster: after every 3 years

The Ministry of Health will bear the cost incurred to vaccinate high-risk group.

Viral Encephalitis BattleGround
 

Kuala Lumpur, March 17, 1999

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