Lassa fever

Lassa fever is an acute viral hemorrhagic fever caused by the Lassa virus, a member of the Arenaviridae family. The disease is endemic in parts of West Africa, where it is a significant public health concern, causing substantial morbidity and mortality. It was first described in the 1950s and identified in 1969 following an outbreak in the town of Lassa, Nigeria.

Overview

The Lassa virus is a single-stranded RNA virus belonging to the Old World complex of the Arenaviridae family. Its natural reservoir is the multimammate rat, a rodent commonly found in sub-Saharan Africa. The disease presents a spectrum of illness, from mild or asymptomatic infection to severe multi-organ failure and death. Management focuses on early diagnosis, supportive care, and the antiviral drug ribavirin, which is most effective when administered early in the course of the illness.

Signs and symptoms

The incubation period ranges from 6 to 21 days. Onset is typically gradual, beginning with non-specific symptoms such as fever, general weakness, and malaise. After a few days, headache, sore throat, muscle pain, chest pain, nausea, vomiting, diarrhea, cough, and abdominal pain may develop. Severe cases may progress to facial swelling, fluid in the lung cavity, bleeding from the mouth, nose, vagina or gastrointestinal tract, and low blood pressure. Proteinuria is a common finding. Approximately one-quarter of patients who survive the acute illness develop sensorineural hearing loss, which may be permanent. Infection during pregnancy, particularly in the third trimester, is especially severe and often results in maternal death or fetal loss.

Transmission

Humans usually become infected through exposure to aerosols or direct contact with the excreta of infected multimammate rats. The virus can also be transmitted through direct contact with the blood, secretions, organs, or other bodily fluids of infected persons, particularly in healthcare settings without adequate infection control measures. This nosocomial transmission has been responsible for several major outbreaks. There is no evidence for airborne transmission between humans under normal circumstances. The virus may be present in urine or semen for several weeks after recovery.

Diagnosis and treatment

Definitive diagnosis requires laboratory testing, typically through detection of Lassa virus antigens, anti-Lassa virus IgM antibodies, or viral RNA by reverse transcription polymerase chain reaction (RT-PCR). The mainstay of treatment is the early administration of the antiviral drug ribavirin. Supportive care, including management of fluid balance, electrolyte levels, oxygenation, and treatment of complicating infections, is critical. The World Health Organization maintains guidelines for case management and infection control. Convalescent plasma from recovered patients has been used experimentally but is not standard practice.

Epidemiology

Lassa fever is endemic in several West African countries, including Nigeria, Sierra Leone, Liberia, Guinea, and Ghana, with sporadic cases reported in Mali, Togo, and Benin. The multimammate rat is widespread in the region. Estimates suggest there are between 100,000 to 300,000 infections annually, with approximately 5,000 deaths. The peak incidence often occurs during the dry season. Major outbreaks have been documented, such as those in Sierra Leone in the 1970s and recurrent annual outbreaks in Nigeria since 2016. Imported cases have been reported in the United States, the United Kingdom, Germany, Sweden, and Japan.

Prevention and control

Primary prevention focuses on community education to promote rodent-proofing of homes, safe food storage, and avoiding contact with rats. In healthcare settings, strict standard precautions, contact precautions, and isolation of suspected cases are essential to prevent nosocomial transmission. There is currently no licensed vaccine for humans, although several candidates, such as those based on recombinant vesicular stomatitis virus technology, are in various stages of clinical trials. International surveillance and reporting are coordinated by agencies like the World Health Organization and the Africa Centres for Disease Control and Prevention.