Japanese encephalitis is a rare but serious disease of the brain that is caused by the Japanese encephalitis virus. It is spread by infected mosquitos to humans and other animals, such as waterbirds, pigs and horses. Waterbirds and pigs are important in the Japanese encephalitis virus transmission cycle as they can pass the virus back to biting mosquitoes.
The annual incidence of clinical disease varies both across and within endemic countries, ranging from 10 per 100 000 population or higher during outbreaks. A literature review estimates nearly 68 000 clinical cases of JE globally each year, with approximately 13 600 to 20 400 deaths. JE primarily affects children. Most adults in endemic countries have natural immunity after childhood infection, but individuals of any age may be affected.
Also key facts from WHO:
- Japanese encephalitis virus (JEV) is a flavivirus related to dengue, yellow fever and West Nile viruses, and is spread by mosquitoes.
- JEV is the main cause of viral encephalitis in many countries of Asia with an estimated 68 000 clinical cases every year.
- Although symptomatic Japanese encephalitis (JE) is rare, the case-fatality rate among those with encephalitis can be as high as 30%. Permanent neurologic or psychiatric sequelae can occur in 30%–50% of those with encephalitis.
- 24 countries in the WHO South-East Asia and Western Pacific regions have endemic JEV transmission, exposing more than 3 billion people to risks of infection.
- There is no cure for the disease. Treatment is focused on relieving severe clinical signs and supporting the patient to overcome the infection.
- Safe and effective vaccines are available to prevent JE. WHO recommends that JE vaccination be integrated into national immunization schedules in all areas where JE disease is recognized as a public health issue.
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Symptoms of Japanese encephalitis
It’s rare to get symptoms from it. Less than 1% of infected people get sick. If you do get symptoms, they usually start about 4 to 15 days after you were bitten. Many people who develop symptoms get a mild headache and fever. A child may throw up or tell you their stomach hurts. In more severe cases, more serious symptoms can develop quickly.
The following are the possible symptoms of Japanese encephalitis:
- high fever
- a headache
- tremors
- nausea
- vomiting
- spastic paralysis
- stiff neck
You might also undergo changes to brain function, including:
- stupor
- disorientation
- coma
- convulsions in children
- The testicles can also swell
The brain symptoms can cause lifelong complications, such as deafness, uncontrollable emotions, and weakness on one body side.
The chances of survival varies, but children face the highest risk of fatal results.
You can also read about symptoms and causes of cholera.
Causes & transmission of Japanese encephalitis
Japanese encephalitis is a virus in the flavivirus family. The Culex mosquito passes it on. A host is the source of a virus, and the vector passes it on. Wild birds are likely to be the natural hosts of JEV, and mosquitoes are the vectors. A vector does not cause disease but passes it on. The mosquitoes then pass the virus to humans and animals. Only infected mosquitoes can pass it on.
It is more likely to affect children because adults in areas where the virus is endemic generally become immune as they get older.
People are at the highest risk in rural areas where the virus is common. It is common around towns and cities especially rural areas of Asia.
Risk factors and common area of Japanese encephalitis
Japanese encephalitis is most common throughout Southeast Asia.
China, Korea, Japan, Taiwan, and Thailand have had outbreaks in the past, but they have mainly controlled the disease through vaccination. Vietnam, Cambodia, Myanmar, India, Nepal, and Malaysia still experience occasional epidemics.
There have been cases in northern Australia, but health authorities in mainland Australia consider the disease to be low-risk.
The United States has seen a few reports of Japanese encephalitis in people who have traveled to places in which the disease is active.
Travelers to some parts of Asia and the Western Pacific can get infected if bitten by an infected mosquito. However, for most travelers the chance of getting infected with Japanese encephalitis virus is low.
Activities that can increase a traveler’s chance of getting Japanese encephalitis include:
- Spending a lot of time outdoors in rural areas
- Traveling during times of the year when mosquitoes are more common, such as during the summer
- Traveling for long periods of time in a place that has Japanese encephalitis
In places with four seasons, your chances of getting Japanese encephalitis are greatest in the summer and fall. In tropical and subtropical areas, mosquitoes spread the virus all year long.
Your chances of getting bitten by an infected mosquito are higher in rural agricultural areas, usually ones where rice production and irrigation by flooding happens. But sometimes the mosquitoes can show up near urban areas.
You can also read about risk factors and prevention of typhoid fever.
Prevention of Japanese encephalitis
Beside getting the Japanese encephalitis vaccine, your best defense against the virus is to avoid mosquito bites. These following tips will help.
1. Use insect repellent. Choose one that’s registered by the EPA and has one of these active ingredients:
- DEET
- Picaridin (known as KBR 3023 and icaridin outside the U.S.)
- IR3535
- Oil of lemon eucalyptus (OLE)
- Para-menthane-diol (PMD)
- 2-undecanone
When you use EPA-registered bug repellents as directed, they’re safe and effective even if you’re pregnant or breastfeeding.
Also, If you’re putting insect repellent on a child, take extra care to follow the instructions on the label exactly. Don’t use products that have oil of lemon eucalyptus (OLE) or para-menthane-diol (PMD) on a child under 3 years old. Also, don’t put repellent on a child’s hands, eyes, or mouth, or on cuts or irritated skin. Spray repellent on your hands, then gently rub it on your little one’s face.
2. Wear long-sleeved clothes. If your child is traveling with you, dress them in long-sleeved pants and shirts, too.
You could consider treating your clothes and gear (like tents) with an insecticide called permethrin. You’d need to use a 0.5% solution of it and follow the product’s instructions exactly. Never put permethrin directly on your skin.
3. Keep bad bugs at bay. To help keep mosquitoes away, make sure the place where you’re staying has screens for its windows and doors. Get any holes in the screens fixed.
If you use a stroller or baby carriage for your little one, cover it with mosquito netting.
Use air conditioning if you can, rather than keeping windows and doors open.
Also, keep mosquitoes from laying their eggs in or near water. Once each week, empty and scrub, turn over, cover, or toss out any items that hold water (like tires, buckets, flowerpots, and outdoor trash cans). Also, look around indoors and outdoors for any containers where water could collect.
Vaccination of Japanese encephalitis
A safe and effective vaccine is available to prevent infection. A healthcare provider will give this as an injection over two doses.
The second dose will occur 28 days after the first. An accelerated schedule is also possible, in which only 7 days pass between the two doses. The accelerated schedule is only safe and suitable for people between 18 and 65 years old.
Be sure to complete either course at least 7 days before traveling to the prevalent region.
Doctors recommend the vaccine for the following people:
- those traveling to areas where the disease is endemic
- those on short-term trips lasting less than a month
- people visiting areas where there is an outbreak or after a recent outbreak
- those participating in outdoor activities while in an endemic area
A person who fits any of these categories should speak to a doctor 6 to 8 weeks before traveling to the region.
The Japanese encephalitis vaccine can cause some short-term side effects, including:
- red, swollen, and sore skin at the site of injection
- a headache
- muscle pain
- hives and breathing difficulties, in rare instances
Some people are allergic to certain ingredients in the vaccine. Speak to a primary care physician to confirm that the vaccine will not trigger any allergies.
The doctor may postpone the injection for people who are pregnant or breastfeeding, as well as people who have a fever.
Infants who are younger than 2 months old or people with severe allergies to any of the components of the vaccine should not receive this injection.
Diagnosis of Japanese encephalitis
To be able to diagnose the disease, healthcare provider will examine the symptoms, verify where the individual lives, and ask about the destinations of any recent visits from which the infection could have emerged.
- If a doctor suspects encephalitis, the patient will undergo tests, such as a CT or MRI scan of the brain.
- The physician might use a lumbar puncture or spinal tap to draw fluid from the spine. The results can show which virus is causing the encephalitis.
- Immunofluorescence tests can detect human antibodies. The antibodies show up after the doctor tags them with a fluorescent chemical.
You can also read about diagnosis and treatment of liver cirrhosis.
Treatment of Japanese encephalitis
Japanese encephalitis can sometimes cause long-term complications such as paralysis, seizures, and loss of speech.
No specific treatments have been found to benefit patients with JE. Treatment is symptomatic. However vaccine is available to help prevent disease.
You’ll need to be treated in hospital if you’re seriously unwell because the disease can be life-threatening.
Treatments for Japanese encephalitis include medicines to help relieve the symptoms, such as painkillers and steroids.
You should get medical advice quickly if you have Japanese encephalitis symptoms while you’re travelling.
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