"brought cholera with them"
Cholera
Public DomainCholera - Credit: Folcrum

Cholera is a disease caused by the bacterium Vibrio cholerae and can be transmitted to humans through contaminated food or water.  The symptoms of cholera include vomiting, diarrhoea, cramps and dehydration.  If untreated, cholera can be fatal and was a serious illness in the 19th century.  In developed countries it is no longer a major health threat, but is still common in poorer parts of the world.

Cholera factsheet