Gastroenteritis is inflammation of the stomach, small intestine and large intestine which develops due to an infection.

Uganda Wildlife Conservation Education Centre (UWEC) made the announcement with "deep sorrow and grief" saying the male chimpanzee suffered from chronic gastroenteritis and was "highly susceptible to opportunistic infections" due to old age.

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Zakayo has been living at UWEC since 1976 after he was rescued from Bundibugyo.

Chimpanzees can live for about 45 years in the wild and over 60 years in captivity.