Japanese Encephalitis (JE) is a serious mosquito-borne viral infection caused by a flavivirus. It primarily affects children and can lead to severe brain inflammation (encephalitis). JE is most common in rural parts of Southeast Asia and the Western Pacific region.
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Japanese Encephalitis was first clinically described in Japan in 1871, leading to its name. The causative virus was isolated in 1935, clarifying its viral nature. It has since been recognized as a major public health concern across Asia, prompting the development of effective vaccines.
JE is transmitted to humans through the bite of infected mosquitoes, primarily *Culex tritaeniorhynchus*. Mosquitoes become infected by feeding on amplifying hosts like wading birds and pigs. Humans are accidental 'dead-end' hosts, meaning the virus does not spread directly from person to person.
Contagious Period: Varies by disease
Local health department information and state-specific prevention guidance
Our AI-powered surveillance continuously monitors JE activity across Colorado. We track data from state health departments, local hospitals, CDC reports, and 50+ global health sources to provide early warning of emerging threats.
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For official state health alerts, vaccination locations, and public health guidance specific to Colorado, visit your state health department's website.
Whether you live in Colorado or are traveling there, knowing the symptoms, timeline, and when to seek care helps you act quickly if exposure occurs.
Seek care if you experience severe dehydration, bloody stools, high fever, or symptoms lasting more than 3 days. Children under 5, adults over 65, and immunocompromised individuals should seek care earlier.
Emergency symptoms: Severe dehydration, inability to keep fluids down for 12 or more hours, or neurological symptoms require emergency care.
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Trusted information from leading health organizations
Global disease surveillance and guidelines from the World Health Organization
View WHO Resources →Disease information on Virus Watcher is reviewed by our Chief Epidemiologist, a former CDC lead analyst for FluSight forecasting. Outbreak data is aggregated from verified sources including BEACON, ProMED, WHO, CDC, and 50+ national health agencies. This information is for educational purposes and should not replace professional medical advice.
Last reviewed: 2026-07-18
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