Japanese Encephalitis Outbreaks

Japanese Encephalitis Outbreaks 2024

According to the World Health Organization (WHO), the Japanese encephalitis virus (JEV) is a flavivirus spread by mosquitoes, primarily Culex tritaeniorhynchus. JEV is the leading cause of viral encephalitis in many Asian and western Pacific Ocean countries. Twenty-four 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. The WHO reports Japanese encephalitis by region in 2022. Pigs play an essential role in the natural cycle and serve as an amplifier host since they allow virus multiplication manifold without suffering from disease. Man is a dead-end host in the transmission cycle, and there is no human-to-human transmission of JE.

As of October 6, 2024, the U.S. Centers for Disease Control and Prevention (CDC) identified countries reporting JEV cases. JE infections cause approximately 13,600–20,400 deaths in people annually, primarily children. JE survivors are estimated to live normally, but 49% of JE patients report neurological sequelae. The CDC states that the risk for JE varies based on destination, accommodations, activities, trip duration, and travel season. One Japanese encephalitis vaccine (IXIARO) is U.S. FDA-approved, and the CDC recommends it for travelers in 2024. 

Japanese Encephalitis in the United States

JEV was confirmed in the United States in the 1980s when the exotic mosquito species and secondary JEV vector, Aedes albopictus, was introduced into the country. A risk assessment conducted in 2019 considered the potential mechanisms of introducing JEV into the U.S.. It concluded that an infected adult mosquito had a high risk of introduction on passenger aircraft. Geographically, the risk of JE introduction into the U.S. may be highest in California due to the frequency of international arrivals (670,845, Aug. 2024) from Asia (LA County) and the abundance of Culex vectors and avian hosts. In July 2005, one JE case was reported to LA County regarding a California resident who traveled to the Philippines and became ill upon return to CA and subsequently recovered.

Japanese Encephalitis in Australia

Since January 2021, 45 people in Australia have been infected with JEV, resulting in seven deaths. In 2024, the WHO reported various JEV across Australia, including Queensland, New South Wales, South Australia, Victoria, Australian Capital Territory, Tasmania, Western Australia, and the Northern Territory. JEV is endemic to parts of the Torres Strait region of Australia. Australia's government declared a JEV outbreak of National Significance in March 2022. QIMR Berghofer senior researchers reported in May 2024 that the new JEV virus strain (genotype 4) impact on the brain is consistent with the seven human fatalities during the 2022 outbreak, which involved 44 confirmed human cases across Victoria, New South Wales, South Australia, Northern Territory, and Queensland. The findings of the two studies (May 2024), taken together with the broad geographic spread of human infections and infected piggeries over a relatively short period, have shown that the 2022 JEV outbreak was more extensive than first thought. The health department says JE vaccination is recommended for travelers spending one month or more in endemic areas in Asia and Papua New Guinea during the virus transmission season. And JE vaccination is recommended for residents of the outer islands in Torres Strait and non-residents living or working on the outer islands of Torres Strait for 30 days or more during the wet season. People who are at ongoing risk of acquiring JE may need booster doses.

The U.S. CDC updated an Alert - Level 2, Practice Enhanced Precautions in December 2022 regarding the JE outbreak in eastern and southeastern Australia.

Japanese Encephalitis in Canada

The Canadian government says the JEV risk to most travelers is low, especially for those visiting cities. However, there is a higher risk of infection if they visit rural areas for longer periods and participate in outdoor activities.

Japanese Encephalitis in Europe

The European CDC published a study in 2023 that concluded that the environmental conditions in the European Union are expected to be suitable for autochthonous Japanese encephalitis virus circulation; therefore, there is a high likelihood of virus transmission in the region after virus introduction in environmentally adequate areas.

Japanese Encephalitis in India

The first evidence of the JE virus's presence in India dates back to 1952, when the first case was reported and continues to pose a significant public health problem in 2024. India's National Center for Vector Borne Diseases Control (NCVBDC) confirmed that adult JE vaccinations started in 42 districts of three states with high JE incidence: Assam (9 districts), Uttar Pradesh (7 districts), and West Bengal (26 districts). In September 2024, media reported a child in Jabalpur reportedly died due to JE infection.

Japanese Encephalitis in Indonesia

The U.S. CDC reports JE cases from many Indonesian islands, including Bali, Java, Kalimantan, Nusa Tenggara, Papua, and Sumatra. The WHO has actively supported Indonesia's Ministry of Health with interventions to control JEV infection, such as preparing to introduce JEV vaccination in new endemic provinces, focusing on West Kalimantan.

Japanese Encephalitis in Japan

Sporadic JE cases are reported from all of Japan's islands except Hokkaido.

Japanese Encephalitis in Papua New Guinea

The surveillance and detection of Japanese encephalitis in Papua New Guinea (PNG) has been confirmed. The U.S. CDC recommends considering JE vaccination for travelers spending less than a month in areas with Japanese encephalitis but who will be doing activities that increase the risk of infection, such as visiting rural areas, hiking or camping, or staying in places without air conditioning, screens, or bed nets.

Japanese Encephalitis in the Philippines 

Human, animal, and mosquito studies indicate transmission in 32 Philippines provinces.

Japanese Encephalitis in Nepal

About 12.5 million people in Nepal are at high risk of JE infection. As of September 2024, twenty-nine districts in Nepal, including those in the Kathmandu Valley, have reported infection from the deadly virus, while eight districts, Kailali, Kapilvastu, Palpa, Chitwan, Rautahat, Sarlahi, Siraha, and Sunsari, have reported deaths from the infection. In September 2024, the Kathmandu Post reported that 12 people had died, and 59 others had been infected with the JE virus since June 2024. In 2005, JE infections killed nearly 2,000 people in Nepal's Tarai region.

Japanese Encephalitis South Korea

The U.S. CDC says Japanese encephalitis was a significant public health concern in South Korea until the late 1960s, with several thousand cases reported annually. The KCDC reported that in 2018, JE surveillance data showed an average of 20 JE cases per year, which is the highest number in the past ten years. In August 2024, the Korea Disease Control and Prevention Agency (KDCA) reported two older unvaccinated patients were diagnosed with the JEV as of Week 40, 2024 (October 10, 2024).

Japanese Encephalitis in Thailand

The most significant rates of JE disease have been reported from Thailand's Chiang Mai Valley. Several traveler cases have been reported in recent years from southern Thailand's resort and coastal areas.

Japanese Encephalitis in Taiwan

In Taiwan, JE has been categorized as a mandatory notifiable infectious disease since 1955. As of May 2024, CNA reported Taiwan recorded two cases of JE in Kaohsiung, including one death, the first in 2024, according to the Centers for Disease Control.