What is Japanese Encephalitis?
Japanese encephalitis, a type of brain swelling, is the main type of preventable illness spread by mosquitoes in Asia, Australia, and the western Pacific. This illness is transmitted through the bite of a particular mosquito species called ‘Culex.’ They are commonly found in agricultural settings like farms and rice fields, but can also occur in cities under certain conditions.
Although most people who get bitten by these mosquitoes don’t show any symptoms of the illness, for those who do, it can be a serious health condition leading to sickness and even death. The symptoms include high fever, headache, confusion, a state of unconsciousness, and trembling, all due to the inflammation in the brain. It can also cause issues with movement, nerve function, and seizures, especially in children.
About one in four people with symptoms end up dying from the disease. Children are most likely to be affected. However, most people who live in places where the virus is common usually become immune by the time they reach adulthood.
The best way to manage this situation is through prevention. There’s not a specific treatment for the disease itself, except for providing supportive care to manage the symptoms. That’s why there’s a highly recommended vaccine to prevent getting the infection, especially for those who are traveling to high-risk areas. Many of these high-risk regions have also started vaccination programs for youngsters. But the best defense is always to prevent mosquito bites in the first place.
What Causes Japanese Encephalitis?
Japanese encephalitis is a disease you can get from a mosquito bite. The bug responsible is a type of mosquito called “Culex,” with the Culex tritaeniorhynchus being the most common. It carries a virus related to the West Nile virus. This disease is most often found in and spread by pigs and wading birds. Humans can get the virus if bitten by a mosquito that has bitten one of these animals, but we don’t usually get sick enough to pass the virus back to other mosquitos.
People generally get Japanese encephalitis in rural areas like farms or rice fields because that’s where you’ll find the most pigs and wading birds. These places often have lots of water, which attract the birds. However, recent reports show that more people in suburbs in countries like South Korea, China, Singapore, and Taiwan are getting the disease, so it’s suggested that travellers to suburban regions should also get vaccinated.
While mosquitos are the main way this disease spreads, there is some worry people could catch the virus if they’re in really close contact with sick pigs, even without mosquitos.
Risk Factors and Frequency for Japanese Encephalitis
Every year, the world sees between 30,000 and 50,000 cases of Japanese encephalitis. Serious cases of the disease happen about once per 250 infections. The disease spreads more frequently in certain times and places. In climates with clear differences between seasons, more cases occur from May to October. However, in tropical climates where it’s always warm, there’s a risk of getting infected all year round.
The disease is most common during the rainy season and before the harvest in areas that grow rice because mosquitoes are more plentiful. Mosquitoes, which carry the disease, mostly bite between dawn and dusk. There are 24 countries in South-East Asia and the Western Pacific where Japanese encephalitis is constantly present. This puts over three billion people at risk of getting infected.
Major outbreaks of the disease happen every 2 to 15 years. For example, China reported over a million cases between 1965 and 1975. On the other hand, countries such as Japan, Korea, and Taiwan have nearly wiped out the disease among their own residents by making it routine for children to get vaccinated against it. Despite this, the disease is still present in animals and birds that live in these areas, which sometimes causes unvaccinated visitors to become infected.
Signs and Symptoms of Japanese Encephalitis
People who get infected mostly have a history of being bitten by a mosquito in an area where the disease is common. It usually takes around 6 to 8 days (but it can range from 4 to 15 days) for the disease to show symptoms after the person is bitten. Initially, the patient may experience various symptoms that are not very specific, such as:
- Fever
- Headache
- Nausea
- Vomiting
- Diarrhea
- Muscle ache
These symptoms can persist for several days. Afterwards symptoms common of serious brain inflammation, or ‘encephalitis’, start to show up. These symptoms may include:
- Change in mental state
- Agitation
- Confusion
- Psychosis
- Headache and signs of meningitis (mainly in adults)
- Seizures (mainly in children)
- Uncommon symptoms such as muteness and paralysis
As the disease progresses, patients may also develop:
- Muscle stiffness
- Movements that mimic the symptom of Parkinson’s disease.
Testing for Japanese Encephalitis
If you are experiencing symptoms that your doctor thinks could be encephalitis, they will likely recommend two types of tests – a brain scan using either MRI or CT, and a spinal tap, which is also known as a lumbar puncture.
The brain scans might show signs of fluid buildup or damage in specific parts of the brain called the thalamus. These signs could be swelling, lesions, or bleeding. The lumbar puncture involves collecting and examining a sample of your spinal fluid. The results could show high pressure or an increased amount of proteins, while the levels of sugar (glucose) remain normal.
You’ll also have some blood tests done which could show an increased number of white blood cells (a condition called leukocytosis) or low levels of sodium (hyponatremia). These findings are fairly common in many types of encephalitis or viral meningitis.
In some cases, based on your recent travel history, your doctor might suspect a specific type of encephalitis caused by the Japanese encephalitis virus. In such situations, they can use tests known as enzyme-linked immunoassays (ELISA) to check for a specific type of antibody (immunoglobulin M or IgM) in your blood or spinal fluid that your body might have produced in response to the virus.
Please note that in humans, this particular virus does not stay around for a long time nor does it multiply to high levels, which makes culturing or isolating the virus from samples challenging.
Treatment Options for Japanese Encephalitis
Unfortunately, there is no effective medicine that kills the virus causing Japanese encephalitis. Taking care of a person with this disease involves providing fluids through a drip (intravenous), and drugs to reduce fever (antipyretics). Medications to stop seizures (anticonvulsants) may also be needed. Sadly, many people who survive the disease are left with long-lasting, serious health problems affecting the brain and nervous system. This often results in needing continuous care. As many as 30% of survivors may have ongoing intellectual, behavioural, or neurological issues, including paralysis, constant seizures, being unable to speak, or having difficulties with common daily activities.
Because there’s no effective treatment, preventing the disease is key. The best way to prevent Japanese encephalitis is to avoid getting bitten by mosquitoes altogether. Even short moments outside can put you at risk of getting bitten. So, it’s crucial to wear protective clothing, including long sleeves, long pants, socks, and closed shoes whenever you’re outdoors. Tucking your pant legs into your socks can also protect your ankles from mosquito bites. Mosquitoes are most active and likely to transmit the disease during warm months and can even bite through thin clothing. To prevent this, consider treating your clothes with repellents that contain permethrin, DEET or other insect repellents approved by the Environmental Protection Agency (EPA). It’s also best to avoid being outdoors during early mornings and evenings when mosquitoes feed. To avoid mosquito bites while sleeping, sleep in air-conditioned spaces or use bed nets and screens.
Vaccination is another excellent preventive measure. There is a safe and effective vaccine that you can get within a short period. However, the vaccine is not used as often as it should be. As per the recommendations from the Centers for Disease Control and Prevention (CDC), you should consider getting the Japanese encephalitis vaccine if:
1. You plan to stay for a month or more in regions where the disease is common (endemic areas) during the mosquito season, even if you’re staying in city areas.
2. You’re going for a short-term trip (less than one month) and plan to spend lots of time outdoors in countryside or farming areas, take part in outdoor activities or stay in places without air conditioning, screens or bed nets. You should also consider getting vaccinated if you’re travelling to an area with an ongoing outbreak of the disease, or if you’re unsure about where you’ll be going, what activities you’ll be doing, and how long you’ll be staying.
The vaccine is currently not recommended if you’re only planning a short trip to city areas.
What else can Japanese Encephalitis be?
When a doctor is trying to diagnose Japanese encephalitis, they have to consider many other conditions that might look similar. Therefore, it’s critical to take a thorough travel history from the patient. Here are some of those conditions that doctors should keep in mind:
- Murray Valley encephalitis
- West Nile virus encephalitis
- St. Louis encephalitis
- Herpes simplex encephalitis
- Western and Eastern equine encephalitis
- Venezuelan Equine encephalitis
- Ehrlichiosis
- Enterovirus meningitis
- Mycoplasma meningitis
- Cytomegalovirus infection in patients with weak immune systems
- Typhoid fever
- Dengue fever
- Malaria
- Brain abscess
- Tuberculous meningitis
- Nipah virus infection
- Rocky Mountain spotted fever
- Fungal meningitis
- Leptospirosis
- Neurocysticercosis
- Amebic meningoencephalitis
- Lupus with central nervous system involvement
- Central nervous system (CNS) tumor
- Cerebrovascular accident (stroke)
What to expect with Japanese Encephalitis
Only 1% of patients infected with the virus will develop encephalitis, a serious condition where the brain becomes inflamed. Regrettably, the mortality rate for those who do develop encephalitis is quite high, ranging between 20% to 30%.
Most patients will begin to get better within 6 to 12 months. However, it’s important to note, many survivors are left with significant neurological and psychiatric consequences (30% to 50% of cases). This means they may experience long-term changes in their brain function or behavior as a result of the illness.
