Lassa fever

Disease Description (Causes and Symptoms)

• Cause: Lassa virus (a member of the Arenaviridae family) is the cause. The main animal reservoirs are multimammate rats (Mastomys spp.) in West Africa, and the virus is transmitted to humans through rat excreta (urine and secretions). Person-to-person transmission can occur through contact with bodily fluids (blood, oral and respiratory secretions, urine, etc.), and transmission through sexual contact (semen) has also been reported.
• Pathophysiology: The virus enters through mucous membranes or damaged skin and causes systemic infection, affecting the vascular endothelium, immune system, central nervous system, and other systems. Some patients develop bleeding, hypotension, organ failure, and neurological complications.
• Main symptoms: After an incubation period of 6–21 days, the illness begins with nonspecific symptoms such as fever, headache, muscle pain, chest pain, sore throat, cough, vomiting, diarrhea, and abdominal pain. In severe cases, hypotension, shock, seizures, edema, kidney failure, mucosal bleeding, and encephalitis may occur. The most common sequela is hearing loss, which occurs in about one-third of recovered patients and may be permanent.

Treatment and Precautions

• Basic principles: Antiviral medication + intensive supportive care (fluid and electrolyte correction, oxygen supplementation, blood pressure maintenance, renal replacement therapy when necessary, etc.).
• Medication: Ribavirin is used as the standard antiviral medication during the acute phase (early in the course of symptoms). It is known to be more effective when administered as early as possible. The dose and route of administration of ribavirin are determined according to the patient's condition, and its risks in pregnant women require careful assessment.
• Supportive care: Control of fever and pain, fluid and electrolyte management, monitoring of blood pressure, respiration, and kidney function, and appropriate transfusion and hemostatic treatment if bleeding occurs. Intensive care unit management is required when intensive treatment is necessary.
• Infection control: Patients should be isolated, and personal protective equipment (PPE) should be worn for standard, contact, and droplet precautions (airborne precautions when necessary). Avoid direct contact with the patient's bodily fluids, and treat contaminated items with high heat or disinfect them with 0.5% hypochlorite (or a recommended disinfectant).
• Prevention and lifestyle precautions:
  • Do not consume food contaminated with rat excreta; prevent rodent access to homes and food storage areas and implement rodent control.
  • Wear gloves, a mask, and a gown when coming into contact with a patient, and follow biosafety precautions during invasive procedures.
  • Men are advised to abstain from sexual intercourse or use condoms while the virus may be detectable in semen (or for at least 3 months).
  • Because pregnant women have high rates of miscarriage and death if infected, prompt evaluation and treatment are necessary.
• Risk of complications: Permanent hearing loss, encephalitis, hemorrhagic complications, kidney failure, miscarriage and fetal injury during pregnancy, severe multiple-organ failure, and death.

Checklist Before an Outpatient Visit (Items to Bring and Example Questions)

• Items to bring:
  • A list of medications currently being taken (including prescription and nonprescription drugs, herbal medicines, and supplements)
  • Copies of recent test results (blood tests and imaging tests) or a medical certificate, if available
  • A record of when symptoms began (such as the date the fever started) and how the symptoms have progressed
  • Information about overseas travel (especially whether you recently visited West Africa), rodent exposure, and contact with patients
  • Pregnancy status (for women), sexual activity, and information about recent partners (including possible exposure to sexually transmitted infections)
• Examples of things to tell the doctor in advance during the outpatient visit:
  • The date symptoms began and the first symptoms (fever, vomiting, bleeding, etc.)
  • Whether you recently entered or departed West Africa and any rodent exposure
  • Whether there are signs of bleeding or hearing loss
  • Whether you are pregnant or could be pregnant

Examples of General Questions to Ask the Doctor

• What are the expected effects and side effects of this medication (for example, ribavirin)?
• Do I need inpatient treatment? Can I be monitored as an outpatient?
• Will the medications I am currently taking (or my existing conditions) affect ribavirin or the treatment?
• What is the prognosis? How likely are long-term sequelae, such as hearing loss?
• If infection is suspected or confirmed, how should I isolate at home and protect my family?

Examples of Disease-Specific Questions

• I recently visited West Africa. Until what point after the onset of symptoms is ribavirin treatment effective?
• If I am pregnant (or could be pregnant), what is the treatment approach when Lassa fever is suspected? (Treatment options, fetal risks, etc.)

If you need additional information, please tell us the date your symptoms began, your recent travel history, whether you are pregnant, and your current symptoms (such as bleeding or hearing loss) so that we can provide more specific guidance.