[1] When symptoms occur they typically include fever, weakness, headaches, vomiting, and muscle pains.

[1] Other efforts to control the spread of disease include having a cat to hunt vermin, and storing food in sealed containers.

[1][9] Lassa fever is relatively common in West Africa including the countries of Nigeria, Liberia, Sierra Leone, Guinea, and Ghana.

[11] In 20% of people more severe symptoms such as bleeding gums, breathing problems, vomiting, chest pain, or dangerously low blood pressure may occur.

[11] A "Swollen baby syndrome" may occur in newborns, infants and toddlers with pitting edema, abdominal distension and bleeding.

[19][20] The multimammate mouse can quickly produce a large number of offspring, tends to colonize human settlements, increasing the risk of rodent-human contact, and is found throughout the west, central and eastern parts of the African continent.

[21] Once the mouse has become a carrier, it will excrete the virus throughout the rest of its lifetime through feces and urine creating ample opportunity for exposure.

[21] The virus is probably transmitted by contact with the feces or urine of animals accessing grain stores in residences.

[13] Individuals who are at a higher risk of contracting the infection are those who live in rural areas where Mastomys are discovered, and where sanitation is not prevalent.

Infection typically occurs by direct or indirect exposure to animal excrement through the respiratory or gastrointestinal tracts.

[24] In West Africa, where Lassa is most common, it is difficult to diagnose due to the absence of proper equipment to perform testing.

[14] An ELISA test for antigen and Immunoglobulin M antibodies give 88% sensitivity and 90% specificity for the presence of the infection.

[26] Control of the Mastomys rodent population is impractical, so measures focus on keeping rodents out of homes and food supplies, encouraging effective personal hygiene, storing grain and other foodstuffs in rodent-proof containers, and disposing of garbage far from the home to help sustain clean households.

After a single intramuscular injection, test primates have survived lethal challenge, while showing no clinical symptoms.

[34][35] A potential novel treatment, the NMT inhibitor, has been shown to completely inhibit lassa infection in cells based assays by targeting Z protein and SSP for degradation.

[36] Favipiravir, a nucleoside analogue, has be shown to be effectiveat treating Lassa fever in immunocompetent mouse, guinea pigs and macaques.

[37][38][39] A case report showed combination favipiravir with ribavirin is effective for lassa fever, with two patients survived.

[40] In vivo, the EC50 of favipiravir is 2.89 μg.mL−1and doses larger than 1200 mg twice a day should have the capability to strongly reduce the production infectious virus.

[41] When Lassa fever infects pregnant women late in their third trimester, inducing delivery is necessary for the mother to have a good chance of survival.

The fetus has only a one in ten chance of survival no matter what course of action is taken; hence, the focus is always on saving the life of the mother.

[citation needed] The high risk areas cannot be well defined by any known biogeographical or environmental breaks except for the multimammate rat, particularly Guinea (Kindia, Faranah and Nzérékoré regions), Liberia (mostly in Lofa, Bong, and Nimba counties), Nigeria (in about 10 of 36 states) and Sierra Leone (typically from Kenema and Kailahun districts).

[52] Health officials indicate the person likely contracted Lassa fever—transmissible through contact with infected body fluids or, potentially, with rodents while abroad, according to guidance from the Centers for Disease Control and Prevention.

[59] On the 8th of December 2021, the Nigeria Centre for Disease Control (NCDC) was notified of the death of two persons from Lassa fever.

[62] In October 2024, a resident of Iowa, United States, died from Lassa fever after traveling to West Africa.

This case, confirmed by the Iowa Department of Health and Human Services, underscores the risk of international spread.

The individual likely contracted the virus abroad, as Lassa fever spreads through infected rodent excreta or bodily fluids.