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Japanese encephalitis

Acute meningoencephalitis caused by infection with Japanese encephalitis virus involves the brain, spinal cord and meninges. The incubation period is 5-15 days. Most of the patients have no obvious symptoms. Only about 1% of the infected patients have clinical symptoms.

Fever, diarrhea, headache and vomiting are the initial symptoms. The mild symptoms are aseptic meningitis or fever of unknown origin. The severe symptoms include altered state of consciousness, general weakness, high fever, neurological disorders, confusion or even coma or death.

The majority of the patients in Taiwan are adults aged 40 to 60. At present, there are no antiviral drugs available. Once infected, only supportive therapy can relieve symptoms. The mortality rate is about 20% to 30%, and about 30% to 50% survival patients have neurological or psychiatric sequelae.

The main vectors of infection in Taiwan are Culex tritaeniorhynchus, Culex annulus and Culex fuscocephala. The epidemic season is from May to October, and the peak period is from June to July. It is a zoonotic disease, and pigs and water birds are the primary amplifying hosts. After the propagation of the virus in the host, if it is bitten by mosquito vectors, the mosquito vectors will be infectious and then transmit the disease to humans. The peak period of mosquito vector bites is around dawn and dusk. Because of the short duration and low concentration of the virus in humans, there will be no human-to-human transmission problems.

Prevention

• Receive a vaccine against Japanese encephalitis.
• Stay away from pigsties, animal barns, ponds and other areas at dawn and dusk.
• Wear light-colored long-sleeved shirts and pants and apply the mosquito repellent agent approved by the Ministry of Health and Welfare to the exposed skin.
• Pay attention to whether the accommodation environment is equipped with mosquito control measures such as window screens, mosquito nets and bug zappers.

Vaccination suggestions

At present, Japanese encephalitis vaccine is provided all year round. Since May 2017, Taiwan has completely switched to the live attenuated chimeric Japanese encephalitis vaccine made by cell culture process.

It is suggested that the following people receive a dose of Japanese encephalitis vaccine at their own expense:

• Those who have not received the vaccine, have not received the vaccine completely, and have lost the protection of the vaccine.
• Those who are scheduled to visit Japanese encephalitis-affected areas (covering the whole Asia, stretching from Siberia and Japan to Taiwan, the Philippines, Malaysia, Indonesia and Australia in the western Pacific islands, and east Asia from South Korea to China, Nepal, Indo-China peninsula, India and Sri Lanka).

Vaccination contraindications

Those with severe allergies to the components of the vaccine, congenital or acquired immunodeficiency (including receiving chemotherapy, using high-dose systemic corticosteroids for ≧ 14 days), infected with human immunodeficiency virus, pregnant women, lactating mothers are not fit for or are suitable for delaying the vaccination of live attenuated Japanese encephalitis vaccine.

Possible side effects and vaccine response after injection

• Pain, redness and swelling at the injection site. A few may develop mild or moderate general weakness, myalgia, irritability, loss of appetite, fever, headache and other symptoms 3 to 7 days after inoculation, which may go away within days.
• Severe allergies, lethargy or cramps are extremely rare. If the above symptoms remain unimproved, seek medical treatment as soon as possible and ask the physician to inform the health department.

Reminders

• After vaccination, please take a rest under observation for 30 minutes. If there is no discomfort, you can leave hospital.
• Women of childbearing age should avoid pregnancy within 1 month after receiving the Japanese encephalitis vaccine.
• Since the Japanese encephalitis vaccine is a live attenuated vaccine, other live attenuated vaccines to be administered (e.g. varicella vaccine) should be given simultaneously (at different sites) or at least four weeks apart.
• After vaccination, please drink more water and get plenty of rest to reduce discomfort. If you have any questions, please return to the hospital.