The arenavirus Lassa causes a severe illness called Lassa fever.

Lassa fever was first recognized in herdsmen’s village in Nigeria in 1969. Lassa fever is known to be endemic in Guinea (Conakry), Liberia, Sierra Leone and parts of Nigeria, but probably exists in other West African countries as well. Lassa fever has been seldom investigated outside of a few hyperendemic regions, where the described epidemiology may differ from that in areas of low or moderate incidence of disease.

Lassa fever is a serious, highly infectious, viral, hemorrhagic disease characterized by high fever, prostration, generalized hemorrhages, abdominal pain, vomiting, diarrhea, severe pharyngitis, dyspnea, serous effusions, facial edema, and shock.

It is fatal in almost half the cases. Some studies indicate that 300 000 to 500 000 cases of Lassa fever and 5000 deaths occur yearly across West Africa.

The lassa virus emerged suddenly and may be a virulent mutant of the lymphocytic choriomeningitis virus.

The lassa virus appears to have a natural cycle of transmission in rodents and has been isolated repeatedly from a rat, Mastomys natalensis (commonly known as the “multimammate rat”). Mastomys infected with Lassa virus can shed the virus in their excreta (urine and faeces).

According to a study, Mastomys natalensis, the reservoir of Lassa virus, constituted 50%-60% of the rodents captured in houses but only 10%-20% of those captured in surrounding agriculture and bush areas, a finding suggesting that houses are the most-important location for transmission of Lassa virus.

Lassa fever is difficult to distinguish from many other diseases which cause fever, including malaria , shigellosis , typhoid fever , yellow fever and other viral haemorrhagic fevers. Visit: Ebola Virus Infection ; Marburg Virus Disease .