Swine flu is a mild illness in most people.
That flu had a low pathogenic strain, meaning it caused a mild illness in the chickens.
Most often, infection with West Nile virus in people leads to a mild illness that feels like influenza.
In a statement, it said: "Chickenpox is usually a mild illness from which most children recover on their own.
Taiwan has reported that a different strain of avian influenza, A(H5N2), is causing mild illness among poultry.
Yang Guang, eight, has retreated from public view to his sick bed while he recovers from the mild illness.
Allen, a nursery manager in Cambridgeshire, spoke out after doctors said her son Jasper's chickenpox was the worst case of the usually mild illness they had ever seen.
Although the disease may cause only a mild illness in healthy people, it can be severe and even fatal in older people.
Zika is usually a mild illness, though it can be particularly dangerous in pregnant women because it can cause brain damage and developmental disorders in a baby's head.
The virus usually takes the form of a mild illness in healthy adults, which can result in fever, rashes and joint pain.
"I think there is perhaps a misperception that norovirus causes a mild illness," said Aron Hall, an epidemiologist at the disease centers.
