Lassa fever is a recently discovered viral infection found in the tropical regions of the world, especially West Africa. This fever is a major public health concern because it is highly contagious and can cause a severe or fatal illness. The rapid spread of the infection has been clearly identified in the case of hospital outbreaks. Treatment is symptomatic (treating the symptoms of high fever, etc.); there is no special 'cure'.
Native rats are the reservoir of the disease but the exact mode of transmission to humans is uncertain. The virus is present in all body fluids of an infected person and persists in the urine for several weeks after recovery.
The multimammate rat Mastomys natalensis was originally described as the reservoir for Lassa fever in West Africa. Subsequent taxonomic studies have shown that several morphologically similar animals in sub-Saharan Africa actually form a species complex. It will be years before the geographic distributions of each species can be mapped and used to interpret the restricted distribution of Lassa fever.
Epidemics have been recognized in Nigeria, Sierra Leone and Zaire.