91130
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 .
 Congo River
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Congo River