Japanese Encephalitis Risks for Infants: Key Questions Answered

Questions about Japanese Encephalitis?

Dear Dr.
Hsiao,
On the evening of August 1st, my baby, who is under one year old, was bitten by a mosquito at home.
There are also a large number of pigeons near our residence, and I am very concerned about the issue of Japanese encephalitis, especially since my baby has not yet received the vaccine.
I researched the symptoms online and found the following text: "Most infections of Japanese encephalitis are asymptomatic, while a minority present symptoms including headache, fever, nausea, vomiting, agitation, altered consciousness, seizures, and even coma." I would like to ask you:
1.
What does "asymptomatic infection" mean? Does it refer to "having an infection but not causing harm to the body, hence no symptoms," or does it mean "the virus silently harms the body but there are no symptoms"?
2.
What should I be vigilant about regarding my baby, and what actions should I take? How can I determine if my baby has been infected?
Thank you!

Ms. Li, 30~39 year old female. Ask Date: 2019/08/02

Dr. Xiao Kaiwen reply Pediatrics

The main vectors for Japanese encephalitis are the Culex tritaeniorhynchus, Culex pipiens, and Culex quinquefasciatus mosquitoes, which prefer to breed in relatively clean water, primarily found in rice paddies in Taiwan.
Although pigeons are hosts for the Japanese encephalitis virus, the primary host in Taiwan is still pigs, with over 90% of infections being asymptomatic (meaning your immune system can immediately eliminate the virus without causing harm to the body, and often without noticeable symptoms).
Even when symptoms do occur, they are mostly mild, and there are typically no neurological sequelae afterward.
Only a very small number of severe cases may experience neurological complications.
Therefore, overall, if there are no rice paddies, pig farms, or reported cases near your residence, the likelihood of contracting Japanese encephalitis is extremely low, and there is no need for excessive concern.

Reply Date: 2019/08/02

More Info

Japanese Encephalitis (JE) is a viral infection that can pose serious health risks, particularly to infants and young children. Your concerns about your baby being bitten by a mosquito in an area with a high population of pigeons, which can be a vector for the virus, are valid. Let’s address your questions and provide some additional context regarding JE.

1. Understanding "Asymptomatic Infection": When we refer to "asymptomatic infection," it means that the individual has been infected with the virus but does not exhibit any noticeable symptoms. This does not imply that the virus is harmless; rather, it indicates that the immune system is managing the infection effectively without triggering the symptoms typically associated with illness. In some cases, the virus can still cause damage to the body without showing overt signs, but many people may never know they were infected. This is particularly common with JE, where the majority of infections are asymptomatic. However, in a small percentage of cases, the infection can progress to more severe neurological symptoms.

2. Monitoring Your Baby: Given that your baby has not yet received the JE vaccine, it is crucial to monitor for any signs of illness. Symptoms of JE can develop anywhere from 5 to 15 days after infection. You should be vigilant for the following signs:
- Fever
- Headache
- Vomiting
- Confusion or agitation
- Seizures
- Loss of consciousness
If you notice any of these symptoms, it is essential to seek medical attention immediately.
3. Preventive Measures: Since your baby is at risk due to the mosquito bite, consider the following preventive measures:
- Vaccination: The JE vaccine is recommended for children living in or traveling to areas where the virus is prevalent. Consult your pediatrician about the appropriate timing for vaccination.

- Mosquito Protection: Use mosquito nets, insect repellents safe for infants, and ensure that windows and doors are screened to minimize mosquito exposure.

- Environmental Control: Reduce standing water around your home where mosquitoes breed, and keep your living area clean to deter pests.

4. Testing for Infection: If you suspect that your baby may have been infected, a healthcare provider can perform tests to confirm the presence of the virus. This may include blood tests or a lumbar puncture (spinal tap) to analyze cerebrospinal fluid if neurological symptoms are present. However, these tests are typically only performed if there are clear signs of illness.

In summary, while the risk of JE is a concern, especially in areas with high mosquito populations, the majority of infections are asymptomatic. Monitoring your baby for any symptoms and taking preventive measures is essential. If you have any further concerns or if your baby shows any signs of illness, do not hesitate to contact your healthcare provider for guidance and potential testing.

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