Japanese Encephalitis: A Concern for Adults Too

Japanese encephalitis, a viral infection affecting the central nervous system, is commonly associated with children under 15 years old. However, it's essential to recognize that this disease can also afflict adults.

1. Japanese Encephalitis in Adults

Back in 1933, Japanese scientists identified the Japanese encephalitis virus, a member of the Flavivirus genus in the Togaviridae family, as the causative agent of this condition. The primary sources of infection are wild birds and livestock. Birds and pigs serve as reservoirs for the virus in the natural environment. Mosquitoes play a pivotal role in transmitting the virus to humans, as they feed on infected birds and pigs and subsequently transmit the virus to humans through their bites. So far, there has been no documented human-to-human transmission of the disease.

While Japanese encephalitis primarily affects children, it's worth noting that adults can still contract the disease, albeit less frequently due to acquired immunity. Nonetheless, cases among adults do occur, underscoring the importance of awareness.

Outbreaks tend to be concentrated in areas where wet rice cultivation coexists with pig farming or in semi-mountainous regions where fruit cultivation and pig rearing are prevalent. Japanese encephalitis can manifest throughout the year but typically peaks from May to July.

2. Symptoms of Japanese Encephalitis in Adults

In adults, Japanese encephalitis has an average incubation period of one week (ranging from 5 to 14 days). The onset is sudden, marked by high fever (39-40 degrees Celsius), severe headaches, nausea, and vomiting. The progression of symptoms is rapid, evolving from high fever to vomiting, stiff neck, increased muscle tone, seizures, confusion, lethargy, and eventually coma within the initial 1-3 days.

The full-blown phase in adults resembles that seen in children, persisting from day 3-4 to day 6-7 of the illness. The virus invades the cerebrospinal parenchyma, leading to nerve cell damage. Symptoms continue to intensify without remission during this stage, often accompanied by signs of brain and focal nerve damage. These can include consciousness disorders, confusion, deep coma, limb paralysis (partial or complete), epilepsy, muscle coordination problems, autonomic nervous system dysfunction (characterized by profuse sweating, fluctuating skin color, breathing difficulties, increased tracheal secretions, rapid pulse, and low blood pressure), all of which severely affect life functions. Unfortunately, many patients who reach this stage do not survive, while those who do face a better prognosis.

The remission period typically begins around the second week, with fever symptoms gradually diminishing and disappearing around the 10th day, provided there are no secondary bacterial infections. Comatose patients may gradually regain consciousness, with a cessation of spasms, vomiting, and headaches.

3. The Dangers of Japanese Encephalitis in Adults

Japanese encephalitis in adults carries a high mortality rate and frequently results in severe long-term complications. These may include pneumonia, bronchitis, bronchopneumonia (due to bacterial superinfections), urinary tract infections (linked to catheterization or catheter drainage), pressure ulcers, thrombophlebitis (resulting from prolonged immobility), and other nutritional disorders.

Possible sequelae in adults encompass limb paralysis, loss of speech, chorea, parkinsonism, epilepsy, coordination difficulties, severe memory impairment, mental or emotional disturbances, metabolic disorders, hearing loss, or deafness.

4. Vaccination for Adults against Japanese Encephalitis

The Central Institute of Hygiene and Epidemiology recommends immediate vaccination for adults who have never received the Japanese encephalitis vaccine, following a basic three-shot vaccination schedule. If you have previously received the basic dose, a single booster shot suffices.

Vaccination should ideally occur approximately one month before the disease season, as protective antibodies develop roughly three weeks after the second vaccine dose, with full protection manifesting about a week after the third dose.

This vaccine is recommended for individuals residing in areas where the disease is endemic, as well as for tourists, workers, and immigrants from non-immune areas planning to stay for extended periods in regions with Japanese encephalitis outbreaks.

However, individuals with hypersensitivity to vaccine components, a history of allergic reactions to the vaccine, high fever, progressive infections, severe chronic illnesses, leukemia, malignant diseases, advanced HIV/AIDS, or pregnant women should not receive the Japanese encephalitis vaccine.

A complete vaccination regimen comprises three doses, each consisting of 0.5 mL. The second dose follows one week after the first, while the third dose is administered one year after the second. Subsequently, individuals should receive a booster dose every three years to maintain lasting immunity.