Lassa virus is the causative agent of Lassa fever, an acute viral hemorrhagic illness. This disease was first identified in 1969 in Lassa, Nigeria, following the deaths of two missionary nurses. The virus belongs to the Arenaviridae family and represents a significant public health concern in West Africa.
Viral Transmission and Geographic Scope
The primary host for Lassa virus is the multimammate rat, Mastomys natalensis, a rodent prevalent throughout Sub-Saharan Africa. Infected rats do not show signs of illness, but they continuously shed the virus in their urine and droppings. Human infection occurs through direct or indirect contact with these contaminated excretions, often when food or household items are exposed to infected rodent waste.
People can also become infected by consuming food or water contaminated with the virus or by coming into contact with infected rats, such as during hunting or preparing them for consumption. Human-to-human transmission can also occur through direct contact with the blood, urine, feces, or other bodily fluids of an infected person. This type of spread is particularly relevant in healthcare settings or within households lacking appropriate infection control measures.
Lassa fever is endemic in several West African countries, including Nigeria, Sierra Leone, Liberia, and Guinea. Other nations like Benin, Ghana, Mali, and Togo also report cases, indicating a broader distribution. While most cases occur within these endemic areas, travel-related infections have been documented in countries outside West Africa.
Symptom Progression and Diagnosis
The incubation period for Lassa fever ranges from one to three weeks. About 80% of individuals infected with Lassa virus experience mild symptoms or no symptoms at all, making diagnosis difficult. For those who develop illness, symptoms begin gradually rather than suddenly.
Initial symptoms include fever, general weakness, fatigue, headache, and generalized body pain. As the illness progresses, more severe manifestations appear, such as sore throat, chest pain, vomiting, diarrhea, and abdominal pain. In some severe cases, patients develop facial swelling or bleeding from the gums, nose, or gastrointestinal tract.
A common complication of Lassa fever is sensorineural deafness, affecting about 25% to 30% of survivors. This hearing loss manifests during the acute phase of the disease or during recovery. Diagnosing Lassa fever clinically is challenging in endemic regions because its early symptoms resemble those of other common illnesses like malaria or typhoid fever.
Confirmation of Lassa virus infection relies on specific laboratory tests. Methods include reverse transcriptase polymerase chain reaction (RT-PCR) to detect viral genetic material, antibody enzyme-linked immunosorbent assay (ELISA) to identify specific antibodies, antigen detection tests, and virus isolation through cell culture. Samples from suspected patients pose a high biohazard risk and require handling under maximum biological containment conditions.
Treatment and Prognosis
The primary treatment for Lassa fever involves the antiviral drug ribavirin, which is most effective when administered early in the illness. Despite its common use, uncertainties exist regarding its optimal dosing and overall efficacy, and it is not specifically licensed for Lassa fever. Research continues to evaluate its role and potential alternatives.
Supportive care plays a significant role in managing the disease and improving patient outcomes. This care includes careful fluid management to maintain hydration, ensuring adequate oxygen levels, and treating any complicating infections. Patients with severe disease also require symptomatic relief for pain, fever, vomiting, diarrhea, and in some instances, blood transfusions, dialysis, or ventilation are necessary.
The overall case-fatality rate for Lassa fever is approximately 1%. However, for patients hospitalized with severe disease, the case-fatality rate is considerably higher, often reaching 15% or more. The prognosis is particularly unfavorable for pregnant women in their third trimester, with a high risk of fetal mortality, 90% to 95%.
Prevention and Control Measures
Preventing Lassa fever relies heavily on promoting good community hygiene to discourage rodents from entering human dwellings. Storing grains and other foodstuffs in rodent-proof containers helps prevent contamination. Maintaining clean households and properly disposing of garbage away from homes are additional effective measures to limit rodent access.
Avoiding contact with rodent excreta and thoroughly cooking all food items also reduces the risk of infection. In healthcare settings, strict adherence to standard infection control precautions is important to prevent person-to-person transmission. These precautions include consistent hand hygiene practices and respiratory hygiene.
Healthcare workers caring for patients with suspected or confirmed Lassa fever must use personal protective equipment, such as masks, gloves, gowns, and face shields. Careful sterilization of medical equipment and adherence to safe injection practices are also implemented. Avoiding direct physical contact with patient blood and body fluids, as well as contaminated surfaces and materials like clothing and bedding, further minimizes spread.