What is the animal reservoir for Japanese Encephalitis (JE)?

Animal Reservoir for Japanese Encephalitis

The primary animal reservoirs for Japanese encephalitis virus are domestic pigs and wading birds (particularly herons and egrets), with pigs serving as the main amplifying host responsible for transmission to humans. 1

Primary Reservoirs

Domestic Pigs - The Critical Amplifying Host

• Pigs are the most important source of infection for mosquitoes that transmit JE virus to humans due to their rapid population turnover with numerous susceptible offspring and development of high-titer viremia 1
• The high-level viremia in pigs provides optimal conditions for mosquito infection, making them the principal amplifying host in the transmission cycle 1
• Pigs play a central role in maintaining the enzootic cycle, particularly in rural agricultural settings where they are raised in proximity to mosquito breeding sites 1

Wading Birds - The Natural Reservoir

• Ardeid wading birds, specifically herons and egrets, serve as the natural reservoir hosts for JE virus 1
• These birds maintain the virus in nature and contribute to the enzootic transmission cycle between mosquitoes and vertebrate hosts 2
• Birds are particularly important for geographic spread and maintenance of the virus in endemic areas 1

Transmission Cycle Dynamics

The Enzootic Cycle

• JE virus is transmitted in an enzootic cycle between Culex mosquitoes (especially Cx. tritaeniorhynchus) and these amplifying vertebrate hosts 1
• The cycle occurs primarily in rural agricultural areas associated with rice production and flooding irrigation, where mosquito vectors breed near animal reservoirs 1

Humans as Dead-End Hosts

• Humans do not develop sufficient viremia levels or duration to infect mosquitoes, making them dead-end hosts 1
• This means infected travelers returning to non-endemic areas pose minimal to no risk for subsequent virus transmission 1
• Horses are similarly dead-end hosts in the transmission cycle 1

Clinical Implications

Risk Assessment

• Proximity to pig farms and wading bird habitats significantly increases JE risk, particularly in rural agricultural settings 3, 4
• The disease occurs where large numbers of vector mosquitoes breed in close proximity to these animal reservoirs 1
• Understanding this reservoir pattern is essential for risk stratification when advising travelers to endemic areas 3

Geographic and Seasonal Patterns

• The presence of pigs and suitable wading bird habitats, combined with Culex mosquito breeding conditions, determines JE transmission risk 1
• Changes in agricultural practices, animal husbandry, or migratory bird patterns can alter geographic distribution and risk 1