Ebola has been ravaging parts of West Africa for months. While it's long been an important international news story, American and European interest only spiked in September and early October, when two patients were diagnosed in the US and Spain.
This map shows the number of tweets mentioning Ebola, with a dramatic explosion in activity on September 30 and October 1, when the first case of Ebola was diagnosed in the US:
Here are the spikes in chart form:
The rise in tweets doesn't necessarily represent the risk of Ebola to Americans and Europeans. Up to this point, the disease's terrible damage has been largely contained to West Africa. In America, the biggest imminent health threat may be, in fact, the common flu.