Lassa fever is an acute viral hemorrhagic illness caused by the Lassa virus, a member of the Arenaviridae family of viruses. This animal-borne, or zoonotic, infection was first identified in 1969 in Lassa, a town in Nigeria, from which the disease derives its name.
Lassa fever can range from mild or asymptomatic cases to severe, life-threatening manifestations. The virus is considered an emerging threat, particularly in regions where its animal host is common.
Geographic Distribution and Transmission
The primary animal host for Lassa virus is the multimammate rat, Mastomys natalensis. These rodents are widespread in sub-Saharan Africa, often inhabiting areas in and around human settlements where food is stored. Lassa fever is endemic in several West African countries, including Sierra Leone, Liberia, Guinea, Nigeria, Benin, Ghana, and Mali.
Human infection occurs through direct or indirect contact with the urine or feces of infected Mastomys rats. This contamination happens when rodent excreta are deposited on food items, household surfaces, or water. Inhalation of dried rat urine or droppings can also lead to human infection. Exposure through broken skin or mucous membranes after contact with infected materials is another possible route.
Person-to-person transmission can also occur, primarily through direct contact with the blood, urine, feces, or other bodily fluids of an infected individual. This secondary spread is common in healthcare settings that lack adequate infection prevention and control measures. Contaminated medical equipment, such as reused needles, can also facilitate transmission. Sexual transmission of the Lassa virus has been reported.
Symptoms and Progression of the Disease
The incubation period for Lassa fever ranges from 2 to 21 days. Approximately 80% of individuals infected with the Lassa virus experience mild or no symptoms, and these cases often go undiagnosed or are mistaken for other common febrile illnesses like malaria or typhoid fever. Mild symptoms can include a slight fever, general weakness, and a headache. Many mild cases resolve within one to three weeks.
In the remaining 20% of cases, the disease can progress to a severe form, affecting multiple organs such as the liver, spleen, and kidneys. Symptoms in these severe cases may include hemorrhaging from the gums, eyes, or nose, along with respiratory distress, repeated vomiting, and facial swelling. Patients might also experience chest and back pain, abdominal pain, and in later stages, shock, seizures, tremors, or disorientation. Protein in the urine may also be observed.
A long-term complication of Lassa fever is sensorineural hearing loss, which affects about 25% of recovered patients. This hearing loss can be temporary or permanent, sometimes appearing 5 to 12 days after the fever subsides. Transient hair loss and gait disturbance are other issues that may occur during recovery.
Diagnosis and Medical Treatment
Diagnosing Lassa fever can be challenging because its symptoms are varied and often resemble those of other common infectious diseases like malaria, typhoid fever, or other viral hemorrhagic fevers. Laboratory testing is required to confirm a Lassa virus infection.
Specific diagnostic methods include reverse transcriptase polymerase chain reaction (RT-PCR) assays, which detect the virus’s genetic material, and antibody tests like enzyme-linked immunosorbent assay (ELISA), which identify IgM and IgG antibodies. Antigen detection tests and virus isolation by cell culture are also used for confirmation. Early detection through these specialized tests is important for effective treatment and outbreak control.
The antiviral drug ribavirin is the primary treatment for Lassa fever. It is most effective when administered early in the illness, ideally within the first six days of symptom onset. Supportive care forms a major part of treatment, focusing on managing symptoms and maintaining bodily functions. This includes ensuring adequate hydration, maintaining oxygen levels, and treating any complicating infections that may arise.
Prevention and Control Measures
Prevention of Lassa fever involves promoting good community hygiene to discourage rodents from entering homes. Measures include storing grain and other foodstuffs in rodent-proof containers to prevent contamination. It is also important to dispose of garbage far from residential areas and maintain clean households to reduce rodent attraction. Keeping domestic animals like cats can also help control rodent populations.
Individual prevention strategies involve avoiding contact with rodents and their excretions. People should refrain from consuming rats as a food source. Consistent handwashing with soap and water is also important, especially after potential contact with contaminated surfaces or items. If soap and water are not available, an alcohol-based hand sanitizer can be used.
In healthcare settings, strict infection control measures are applied to prevent person-to-person transmission. Healthcare workers caring for suspected or confirmed Lassa fever patients should use personal protective equipment, including masks, face shields or goggles, clean non-sterile long-sleeved gowns, and gloves. Regular hand hygiene, safe injection practices, and proper disinfection of surfaces and equipment are also important to limit spread within facilities.