Japanese Encephalitis Outbreaks
Japanese Encephalitis Outbreaks 2024
According to the World Health Organization (WHO), on August 6, 2024, 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. A study estimated that in 2015, JEV infections globally caused 100,308 cases (95% CI: 61,720–157,522) and 25,125 deaths (95% CI: 14,550–46,031). 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 5, 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, primarily children, annually. 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 available 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
In 2024, the WHO reported various JEV outbreaks across four Australian states, including Queensland. In addition, Australia's government declared a JEV outbreak in Queensland a Communicable Disease Incident of National Significance in March 2022. 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 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 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.
