A restricted, hospital-centred outbreak of Lassa fever involving 28 persons occurred early in 1970 in Jos, Nigeria. 24 patients were in hospital. Every patient, save the index, could be traced to some prior known human source of infection. Complement-fixing antibody to Lassa virus was detected in the sera of only 4 of 172 family and hospital contacts bled. These 4 persons had all been ill. Animal studies have so far failed to reveal a non-human host.
Reference: Carey DE, Kemp GE, White HA, Pinneo L, Addy RF, Fom AL, Stroh G, Casals J, Henderson BE, 1972. Lassa fever. Epidemiological aspects of the 1970 epidemic, Jos, Nigeria. Trans R Soc Trop Med Hyg 66: 402 –408