Lassa fever
Lassa fever is a viral hemorrhagic fever first identified in 1969, primarily affecting regions in West Africa, particularly Nigeria, Sierra Leone, Guinea, and Liberia. Caused by the Lassa virus, a member of the Arenaviridae family, the disease is transmitted primarily through contact with the African rodent species Mastomys natalensis, which carries the virus. Human infection can also occur through direct contact with bodily fluids of infected individuals, especially in healthcare settings with inadequate infection control. Symptoms of Lassa fever can range from mild febrile illness to severe hemorrhagic conditions, with notable complications including sensorineural deafness and various neuropsychiatric issues.
Diagnosis of Lassa fever requires laboratory testing, as initial symptoms are often nonspecific. Common diagnostic methods include enzyme-linked immunosorbent assays and polymerase chain reaction techniques. The antiviral drug ribavirin can significantly reduce mortality if administered early, although it has limited efficacy against later neurologic complications. Prevention focuses on enhancing infection control measures and regional surveillance efforts, particularly in areas affected by political instability and limited resources, which hinder vaccine development. Overall, combined public health initiatives aim to address the threat posed by Lassa fever in endemic regions.
Lassa fever
- ANATOMY OR SYSTEM AFFECTED: All
Definition
First described in 1969, Lassa fever is a viral hemorrhagic fever endemic to West Africa, principally Nigeria, Sierra Leone, Guinea, and Liberia.
Causes
Lassa fever is caused by a strain of Lassa virus, a single-stranded ribonucleic acid (RNA) arenavirus and a member of the family Arenaviridae. The viral reservoir and disease vector is Mastomys natalensis, a species of ubiquitous African rodent.
Risk Factors
Contact with Mastomys rodents in the human settlements they frequent is the primary infection source. Mud-walled huts built directly on the ground offer the rodents easy entry. Once a dwelling is infested with rats, the inhabitants come into contact with the virus-laden excretions of those rats.
Human-to-human contact is also a major risk factor, documented by hospital-based Lassa fever outbreaks. Largely responsible to these outbreaks is poor attention to infection-control measures, such as not reusing syringes. Hospitalized persons represent the severe end of the clinical spectrum, and outbreaks of this kind generally confer high mortality. Household contact with a symptomatic person is also a significant risk factor.
Symptoms
The clinical course of Lassa fever varies from mild illness to severe hemorrhagic disorder, with blood loss too profuse to sustain life. Initially, however, symptoms mirror those of other febrile illnesses, such as influenza. According to the World Health Organization, roughly 80 percent of the people infected with Lassa fever display no symptoms. The remaining twenty percent of infections tend to result in severe symptoms.
The striking clinical features of Lassa fever are poorly understood neurologic complications. Sensorineural deafness frequently occurs, most often during convalescence. Hearing may become distorted or characterized by tinnitus, chronic ringing in the ears. Other neurologic symptoms can include involuntary eye movements (nystagmus) and loss of consciousness. Lassa fever also causes neuropsychiatric complications: among them psychosis, hallucinations, and dementia.
Screening and Diagnosis
Given the lack of definitive initial symptoms, Lassa fever requires a laboratory-based diagnosis. Several techniques are available. The indirect fluorescent-antibody (IFA) test, long a mainstay, identifies antibodies in a person’s blood serum specific to Lassa virus infection. Diagnosis through IFA is not dependably rapid, however. Enzyme-linked immunosorbent assays have been developed that quantify Lassa virus antigens in the serum of infected persons. This method is rapid and reliable, early in the disease course.
A molecular technique, polymerase chain reaction (PCR), directly identifies Lassa virus RNA in infected cells and in urine. Viral RNA is first transcribed to deoxyribonucleic acid (DNA) by a process called reverse transcription PCR.
Treatment and Therapy
Ribavirin is a broad-spectrum antiviral drug that significantly reduces the case-fatality rate when given early in the disease course. It is less effective, however, in limiting late-onset neurologic complications. Researchers are looking at potential treatments using alternative antiviral strategies.
Prevention and Outcomes
Political instability and sparse economic resources are among the factors that have stood in the way of vaccine development. Meanwhile, instituting standard infection-control measures would help prevent hospital outbreaks. To the extent possible, quarantine would impede the spread of Lassa fever in local areas.
To meet the public health threat that Lassa fever raises in West Africa, the Mano River Union has been established in Sierra Leone, Liberia, and Guinea to provide national and regional surveillance, control, and prevention.
Bibliography
"About Lassa Fever." Centers for Disease Control, 31 Jan. 2025, www.cdc.gov/lassa-fever/about/index.html. Accessed 4 Feb. 2025.
Crawford, Dorothy. The Invisible Enemy: A Natural History of Viruses. New York: Oxford University Press, 2000.
Donaldson, Ross I. The Lassa Ward: One Man’s Fight Against One of the World’s Deadliest Diseases. New York: St. Martin’s Press, 2009.
Howard, Colin R., ed. Viral Haemorrhagic Fevers. Boston: Elsevier, 2005.
"Lassa Fever." World Health Organization, www.who.int/health-topics/lassa-fever#tab=tab‗1. Accessed 4 Feb. 2025.
Oldstone, Michael B. A. Viruses, Plagues, and History: Past, Present, and Future. New York: Oxford University Press, 2010.