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A look at how the Japanese encephalitis virus is spread


Japanese encephalitis life cycle | Sanofi

The Japanese encephalitis mosquito

Culex Tritaeniorhynchus | Michael Wunderli

Japanese encephalitis is primarily spread by the Culex mosquito genus, specifically Culex tritaeniorhynchus and Culex vishnui. These mosquitoes breed in rice paddies and are active at night. They are responsible for the majority of Japanese encephalitis transmission in Asia. Culex mosquitoes also spread West Nile virus and a few other viral diseases. Culex mosquitoes can be found all over the wold but Japanese encephalitis is only endemic to the Asia/Oceania area in the eastern hemisphere.


Mosquitoes transmit disease by biting an infected animal or human and then biting another animal or human. When a mosquito bites an infected host, it picks up the pathogen and carries it in its gut. When it then bites another host, it can transfer the pathogen from its gut into the new host's bloodstream through its saliva. This is also how diseases such as malaria, dengue fever and yellow fever are spread.


The role of pigs and water fowl

Pigs and waterfowl play an important role in the transmission of Japanese encephalitis. These animals are considered to be amplifying hosts for the virus, meaning that they can become infected with the virus and develop high levels of the virus in their blood without showing any signs of illness. This allows the virus to multiply and spread to other mosquitoes that feed on their blood.


When a mosquito bites an infected pig or waterfowl, it picks up the virus and can then spread it to other animals or humans when it bites them. This amplifying role of pigs and waterfowl is believed to be a major factor in the persistence of the virus in certain areas, such as rural Asia, where there is a lot of interaction between these animals and humans.


Humans are "dead-end hosts" for Japanese encephalitis

Humans and horses are considered "dead-end hosts" for Japanese encephalitis because they do not develop high enough levels of the virus in their blood to be able to infect mosquitoes that bite them. This means that the virus cannot continue to multiply and spread through the mosquito population when it bites humans and horses.


The role of seasonality and weather in Japanese encephalitis transmission

Seasonality and weather can play a significant role in the transmission of Japanese encephalitis. The virus is primarily transmitted by mosquitoes of the Culex genus, which breed in rice paddies and other types of standing water. Mosquito populations, and therefore the risk of transmission, tend to be highest during the rainy season when there is more standing water available for mosquitoes to breed in.


In addition, high temperatures and high humidity can also contribute to increased mosquito populations and increased transmission of the virus.


Also, the transmission of Japanese encephalitis is often associated with rice-growing areas, where the mosquito vectors breed in abundance in flooded rice fields. In many areas, the transmission of the virus is seasonal and peaks during the rice-growing season, which is typically June through September.


Overall, weather conditions such as temperature, humidity, and rainfall can affect the transmission of Japanese encephalitis by impacting the abundance of mosquitoes and their breeding sites.


Stopping transmission of the Japanese encephalitis virus

Several things can be done to stop the transmission of the Japanese encephalitis virus:

  1. The Japanese encephalitis vaccine: The most effective way to prevent Japanese encephalitis is to get vaccinated. A vaccine is available and is particularly recommended for people living in or traveling to areas where the disease is prevalent. The Japanese encephalitis vaccine is very effective and safe.

  2. Mosquito control: Reducing the number of mosquitoes can help to stop the transmission of the virus. This can be done by eliminating standing water where mosquitoes breed, using mosquito nets and screens, and using insect repellents.

  3. Vector control: Vector control aims to reduce the mosquito population and includes the use of pesticides, such as larvicides, that target mosquitoes at different life stages. This can be done by treating areas where mosquitoes breed, such as rice paddies, and by using genetically modified mosquitoes that do not transmit the virus.

  4. Education: Education and awareness programs can help to educate people about the risks of Japanese encephalitis and how to protect themselves.

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