WHO Priority Diseases: Lassa fever

As I had mentioned yesterday in this column, we will be covering about the priority diseases as revised by the World Health Organization (WHO). The first to be covered is Lassa fever.

Here are some salient facts about Lassa fever.

  • Lassa fever is an acute viral hemorrhagic illness caused by Lassa virus, a member of the Arenavirusfamily of viruses.
  • Lassa virus is endemic in Benin, Ghana, Guinea, Liberia, Mali, Sierra Leone, and Nigeria and other countries in West Africa.
  • It is a zoonotic disease. Rodents (multimammate rats) are the animal reservoirs and shed the virus in their urine and feces.
  • Humans acquire the infection from contact with infected rodents through rodent urine or feces, inhalation of aerosolized rodent excretions, or consumption of infected rodents as a food source.
  • Person-to-person transmission can occur through direct contact with infectious body fluids (e. g., blood, urine, pharyngeal secretions, vomitus, or other body secretions), unprotected contact with potentially infectious material (e.g., touching vomitus) and mucosal exposure from splashes of body fluids.
  • Infection does not spread via casual contact such as hugging, shaking hands, or sitting near someone.
  • Persons with Lassa fever infection are not believed to be contagious prior to symptom onset.
  • The incubation period of Lassa fever is about 10 days (range 6-21 days).
  • Clinical picture: Gradual onset of symptoms in most patients. Symptoms are mild to begin with viz. low-grade fever, general weakness, malaise and so may be ignored. These are followed by headache, sore throat, muscle pain, chest pain, nausea, vomiting, diarrhea, cough, and abdominal pain. In severe disease, facial swelling, fluid in the lung cavity, bleeding from the mouth, nose, vagina or gastrointestinal tract and low blood pressure are present. Later stage may be characterized by shock, seizures, tremor, disorientation and coma.
  • In fatal cases, death usually occurs within 14 days on onset of illness.
  • The most common complication of Lassa fever is deafness, which may occur following either mild or severe illness.
  • Lassa fever is difficult to distinguish from other febrile illnesses, including malaria, shigellosis, typhoid fever, yellow fever and other viral hemorrhagic fevers.
  • The overall case-fatality rate is 1%, while in hospitalized patients, the case-fatality rate is 15%.
  • Diagnosis is usually supported by a relevant history of exposure along with suggestive signs and symptoms.
  • Confirmatory test: ELISA to detect IgM and IgG antibodis and Lassa antigen. Serum IgM is detectable 10 to 21 days after symptom onset; serum IgG is detectable approximately 21 days after symptom onset. Serum reverse-transcription polymerase chain reaction is the preferred diagnostic tool but is expensive and requires technical expertise.
  • Early supportive care with rehydration and symptomatic treatment improves survival
  • Treatment in confirmed cases: IV ribavirin (Grade 1B); ribavirin may be administered orally, if IV ribavirin is not available.

o    IV ribavirin: 30 mg/kg (maximum 2 g) loading dose followed by 15 mg/kg (1 g max) IV 4-6 hourly x 4 days, followed by 7.5 mg/kg IV (500 mg max) 8 hourly x 6 days

o    Oral ribavirin: 35 mg/kg (2.5 g max), followed by 15 mg/kg (1 g max) orally 6 hourly x 4 days, followed by 15 mg/kg (1 g max) 8 hourly x 6 days

  • Prevention

o    Avoiding rodents (multimammate rats).

o    Consider all patients as infectious even if signs and symptoms are mild.

o    All standard, contact, and droplet precautions as well as correct use of appropriate personal protective equipment should be strictly adhered to.

o    Blood and body fluid specimens from patients with suspected Lassa fever infection should be considered highly infectious. Caution should be exercised when handling such material.

o    Postexposure prophylaxis with oral ribavirin for contacts with known or suspected Lassa fever infection with risk factors for transmission such as penetrating needle stick injury, exposure of mucous membranes or broken skin to blood or body fluids, and participation in procedures involving exposure to bodily fluids or respiratory secretions without use of personal protective equipment.

  • There is currently no vaccine that protects against Lassa fever

(Source: Uptodate, WHO)

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