Lassa virus or Lassa viral haemorrhagic fever is an acute illness of 1-4 weeks duration that occurs in West Africa. Though first described in the 1950s, the virus causing the disease was not identified until 1969. The virus is a single-stranded RNA virus belonging to the virus family Arenaviridae. 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.
Endemic in Western African countries, Lassa virus is transmitted to humans through food or household items that are contaminated with the urine or faeces of Mastomys rats.
Scientists have demonstrated that a large class of viruses, such as the influenza viruses, expand their genomes by stealing genetic signals from their hosts.