Lassa virus

Lassa virus is a segmented, negative-sense, single-stranded RNA virus belonging to the Arenaviridae family (Old World arenavirus). It is endemic to West Africa (Nigeria, Sierra Leone, Liberia, Guinea) and is transmitted to humans primarily through inhalation or ingestion of food/materials contaminated with urine or feces from the multimammate rat (Mastomys natalensis), the natural reservoir. Human-to-human transmission occurs via direct contact with blood, secretions, or contaminated medical equipment, making it a concern in healthcare settings.

Pathophysiology: After entry, the virus targets antigen-presenting cells (macrophages, dendritic cells) and replicates, leading to widespread cytokine dysregulation, immune suppression, and increased vascular permeability without significant vessel destruction (unlike Ebola). This results in a viral hemorrhagic fever syndrome.

Clinical presentation: Most infections (~80%) are mild or asymptomatic. Symptomatic cases present with fever, malaise, headache, sore throat, and myalgias, progressing in severe cases to hemorrhage, pleural effusion, facial/neck swelling, hypotension, and shock. A hallmark complication is sensorineural hearing loss, occurring in up to 1/3 of survivors, which can be permanent. Lassa fever in pregnancy, particularly the third trimester, carries very high maternal and fetal mortality (up to 80% fetal loss); uterine evacuation may improve maternal survival.

Diagnosis: RT-PCR for viral RNA, ELISA for antigen/antibody detection, viral culture (requires BSL-4 containment).

Treatment: Ribavirin is effective, especially if given early in the course of illness. Supportive care (fluid/electrolyte management) is critical. No FDA-approved vaccine currently exists, though candidates are in development.

Board relevance: Distinguish from other viral hemorrhagic fevers (Ebola, Marburg - filoviruses; Crimean-Congo, Rift Valley - bunyaviruses). Key differentiators: Lassa's association with rodent reservoir, sensorineural hearing loss as sequela, and use of ribavirin as treatment (unlike Ebola/Marburg where ribavirin is ineffective).