Bệnh viêm não Nhật Bản

Cúm là gì?

Bệnh viêm não Nhật Bản (JE) là a rare but potentially serious disease caused by infection with Japanese encephalitis virus (JEV). JEV is a flavivirus (other flaviviruses cause diseases including sốt vàng, dengue and Murray Valley encephalitis). Spread to humans through mosquito bites, JEV is a leading cause of vaccine-preventable encephalitis (brain inflammation) in Asia and the Western Pacific.

Bạn cần tìm gì?

Most people infected with JEV do not develop symptoms or develop mild symptoms only. However, approximately 1 in 250 people infected will experience severe clinical illness. If symptoms develop, they will occur 5 to 15 days after exposure Và can include fever, diarrhoea and rigors (episodes of shivering and feeling cold). FeMộttures of severe illness with encephalitis include headache, confusion, vomiting, paralysis, seizures, neck stiffness, disorientation and coma. JE has Một mortality rate of 20 to 30%, with permanent neurological disability occurring in 30 to 50% of survivors.

Bệnh lây truyền qua đường nào

JE is a zoonotic disease and can spread to humans when a mosquito bites an infected animal (mostly water birds or pigs) and then bites a human. It cannot be transmitted from person to person, or through eating pork or pig products. Horses can be infected with JEV; however, they cannot transmit the disease further.

When JE occurs during pregnancy, infection can be transmitted to the unborn baby.

In most temperate areas of Asia and Australia, JEV is transmitted mainly during the warmer months. In the tropics and subtropics, transmission can occur year-round but often intensifies during the rainy season when mosquito numbers are greater.

Dịch tễ học

There are an estimated 100,000 clinical cases of JE globally each year, resulting in approximately 25,000 deaths. JE is most common across Asia and the Western Pacific. In the 1990s, cases were reported in the Torres Strait Islands and in Cape York (mainland Australia).  In 2022 and 2023, cases occurred in the Murray and Riverina regions of south-eastern Australian states.

Where JEV is present, people with increased exposure to mosquitoes are at higher risk of infection, particularly those spending time outdoors or working with pigs. Children under 5 years of age and older people who are infected with JEV are at higher risk of more severe illness, including encephalitis.

Phòng ngừa

Rào cản vật lý

Preventing mosquito bites with physical barriers is the most effective way to avoid infection with JEV. Exposure to mosquito bites can be prevented by: 

• mặc quần áo dài, rộng rãi khi ở ngoài trời
• sử dụng thuốc chống muỗi có chứa picaridin hoặc DEET
• hạn chế hoạt động ngoài trời nếu có nhiều muỗi
• sử dụng thuốc xịt ruồi, nhang muỗi và các thiết bị đuổi muỗi cắm vào
• ngủ trong màn chống muỗi được xử lý bằng thuốc diệt côn trùng nếu bạn không có lưới chắn ruồi trên cửa sổ hoặc đang ngủ trong lều/lều không được xử lý ở ngoài trời.

Vắc-xin

Vaccines are also available to prevent the development of bệnh. There are currently two JE vaccines available in Australia: imojev Và JEspect.  Vaccination is recommended for:

• all research laboratory workers at risk of exposure to JEV
• travellers spending 1 month or more in areas outside of Australia with endemic JEV transmission
• people who live or work in the outer islands in the Torres Strait (for a cumulative total of 30 days or more) during the wet season (December to May).

Other individuals with specific risk factors are prioritised and funded to receive vaccines through state-led programs:

• Victoria
• News South Wales
• Queensland

Table 1: Vaccine brands and dose recommendations

shaded boxes indicate live-attenuated vaccines, which are contraindicated for phụ nữ có thai and people who are suy giảm miễn dịch.
* Intradermal (ID) administration of Imojev (single dose of 0.1 mL) may be used as a dose-sparing strategy for heatlhy adults (non-pregnant, non-breastfeeding, no immunocompromise) aged ≥ 18 years in circumstances where public health benefits outweigh potential risk as determined by State/Territory health authorities.
^JEspect is an inactivated vaccine and is therefore suitable for administration in pregnant women or immunocompromised individuals.
# The interval between doses of JEspect can be shortened to 7 days for those aged ≥ 18 years, if the individual is at imminent risk of JEV exposure.
Ω Where possible the same brand of vaccine should be used for the booster dose as the primary course. Based on first prinicples, use of the alternate brand should provide a satisfactory immune response however there are no studies confirming this.

Phản ứng phụ

Expected side effects following either vaccine are usually mild and short lived. They can include injection site pain, redness and swelling, as well fever, headaches and muscle aches.

Tài liệu

• Bộ Y tế Victoria: Bệnh viêm não Nhật Bản ở Victoria
• Cẩm nang Tiêm chủng Úc: Viêm não Nhật Bản
• ATAGI statement on the intradermal use of Imojev Japanese encephalitis vaccine
• Bộ Y tế và Chăm sóc Người cao tuổi của Chính phủ Úc: Tình hình vi rút viêm não Nhật Bản được tuyên bố là Sự cố Bệnh Truyền nhiễm có Ý nghĩa Quốc gia
• Lời khuyên của CDNA về việc tiêm vắc-xin phòng vi-rút viêm não Nhật Bản