In some cases, a young child can develop mental retardation after being sick with a serious infection or other illness, or after suffering a bad injury.

一些情况下，儿童在患了严重的传染病或者是其他疾病，或者是头部严重受伤之后，都会成为智力迟钝。

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"Less than 1% develop a serious neurologic illness such as encephalitis or meningitis (inflammation of the brain or surrounding tissues), " it said.

CNN: West Nile virus on the rise in the U.S., health officials say

"Less than 1% develop a serious neurologic illness such as encephalitis or meningitis (inflammation of the brain or surrounding tissues), " the CDC said.

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