The natural reservoirs for Japanese encephalitis are wild wading birds (3) and the amplifying reservoirs are pigs (1). The disease can be transmitted to animal hosts, including humans through a mosquito vector. Japanese encephalitis is considered to be a zoonotic disease since it can be passed between animals and humans. Animals that can be infected include pigs, horses, and donkeys (10). Other animals that may become infected but are usually asymptomatic include cattle, sheep, goats, dogs, cats, wild mammals, reptiles, amphibians, and birds (10). In the case of this disease, humans are considered to be a ‘dead end host’ since they do not develop high concentrations of the disease in their bloodstream and therefore cannot pass JE to mosquitoes (1). Japanese encephalitis has an incubation period of 6-16 days after the bite of an infected mosquito (5). Most people bitten by a mosquito infected with JE are asymptomatic and never show and signs of symptoms of being exposed to the disease (5).
In recent years, scientists are beginning to speculate that pigs could potentially pass Japanese encephalitis to each other without a mosquito vector. Generally, disease prevalence is more common during warm, rainy seasons because this is when mosquitoes are more active and more likely to breed and pass the disease. However, scientists are finding in some regions of Asia, that the JE virus seems to be surviving the winter months, even though there are no mosquitoes around to spread the disease (4). Since this is a very new idea, studies are still being conducted to see if this is something pig farmers need to worry about in the future. The risk of contracting Japanese encephalitis is very low for people traveling to southeast Asia and the Pacific Islands. Risks do vary based on season, where is Asia the traveler is visiting, how long the traveler will visit the area, and activities (3). Vaccinations are available for people traveling to this area of the world but is only recommended to those that will be camping, hiking, or working in areas where flooding irrigation is used (3). |
Image from: http://outbreaknewstoday.com/philippines-doh-no-outbreak-japanese-encephalitis-72310/
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