Epidemiological studies suggest the disease was transferred between humans ( which happens rarely with Yersinia pestis and very rarely for Bacillus anthracis ) .
Some genes that determine immunity to Ebola - like viruses are much more widespread in Europe than in other parts of the world .
Epidemiological studies suggest the disease was transferred between humans ( which happens rarely with Yersinia pestis and very rarely for Bacillus anthracis ) , and some genes that determine immunity to Ebola - like viruses are much more widespread in Europe than in other parts of the world .