What are the risks of Lassa?

Individuals at greatest risk of Lassa virus infection are those who live in or visit endemic regions, including Sierra Leone, Liberia, Guinea, and Nigeria and have exposure to the multimammate rat.  Risk of exposure may also exist in other west African countries where Mastomys rodents exist. Hospital staff are not at great risk for infection as long as protective measures and proper sterilization methods are used.

Source: http://www.cdc.gov