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In 1962 in the Bukoba district of Tanganyika, Africa, an isolated fit of laughter in a group of 12- to 18-year-old schoolgirls rapidly rose to epidemic proportions. Contagious laughter propagated from one individual to the next, eventually infecting adjacent communities, becoming so severe that schools were forced to close.

At the mission school in Kashasha, 95 out of 159 pupils were affected over a period of about seven weeks. The school closed in March, and a few days later, the epidemic of laughter broke out in some of the villages to which the girls from the school had been transferred. It was clear that the laughter spread from person to person, but no evidence of any infectious agent, toxic substance in food, or physical abnormality in the patients was ever found. However some victims had symptoms such as fever and headache.

This is an extreme example of pathological laughter - fits of abnormal laughter, producing an inappropriate, unrestrained, uncontrollable laughter dissociated from any stimulus. To observers, the laughter often appears childish or violent.

The case of Tanganyika, laboratory searches for abnormalities in the blood such as viruses or bacteria came up empty and all the investigating doctors could conclude was that it was a case of mass hysteria.

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