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Sleeping sickness ravaged the country and must also be taken into account for the dramatic decrease in population ; it has been estimated that sleeping sickness and smallpox killed nearly half the population in the areas surrounding the lower Congo River .
 disease: Sleeping sickness; disease: smallpox; location: Congo River
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: media, plant, vehicle, astronomical object, time, disease, animal, location, person, organization, mythical figure, food, biology, geographical phenomenon, instrument, event 
Text: {0} 
Answer:
 disease: Sleeping sickness; disease: smallpox; location: Congo River