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Lassa Fever

Last update 11/2001

Primary Distribution: West Africa (including Nigeria).

Agent and Vector: The Lassa virus (Arenavirus) is carried by several species of the multimammate rat (Mastomys) and is transmitted to humans via ingestion or inhalation of food, dust, and other materials contaminated with infectious droppings or urine. The virus is also spread from human to human via body fluids, including the aerosol route. The viral HFs are are considered by the CDC to be Category A biological warfare (BW) agents (CDC, 2000). See bioterror box below.

Incubation: 1-3 weeks.

Clinical Findings and Treatment

Signs and Symptoms: Presentation of Lassa fever varies. Common early symptoms are gradual onset of fever, malaise, headache, and abdominal pain. Other symptoms are conjunctivitis, facial swelling, sore throat, non-productive cough, retrosternal pain, nausea, vomiting, diarrhea, back pain, and myalgia. Respiratory rate, temperature, pulse rate are increased and blood pressure decreased. Neurological symptoms may also occur, including hearing loss, tremors, and encephalitis. Hemorrhagic manifestations (not usually evident) may include mucosal bleeding and, less frequently, conjunctival, gastrointestinal, or vaginal bleeding.

Bioterror Considerations

The viral HFs (Lassa, Junin and related) are considered by the CDC to be Category A biological warfare agents, thus posing a risk to national security because they "can be easily disseminated or transmitted from person to person; cause high mortality, with potential for major public health impact; might cause public panic and social disruption; and require special action for public health preparedness" (CDC, 2000, p. 5). Though Iraq is not known to have produced weaponized viral HFs (Shoham, 2000), "all are potentially infectious by the aerosol route and most are stable as respirable aerosols (Cieslak & Eitzen, 2000, p. 28). Treatment is supportive, hence large numbers of casualties would overwhelm health care systems.

Complications: Severe infections produce hemorrhagic manifestations, pleural effusions, and shock. Pregnant women are more likely to die than are others. Some degree of deafness occurs in about 30% of patients

Laboratory Findings: Leukopenia, albuminuria, and increased hematocrit.

Diagnosis: Living or traveling in or from an endemic area (or health care personnel exposure) increases suspicion. ELISA detects IgM and IgG antibodies and Lassa antigen. Laboratory animals may be intracerebrally inoculated with acute phase blood or throat washings.

Differential Diagnosis: Mild cases are similar to a variety of self-limited febrile illnesses. Other possibilities are typhoid fever, typhus, leptospirosis, rickettsial spotted fever, and meningococcemia.

Treatment: In more severe infections, basic hemorrhagic fever treatment principles apply: Reversal of hemorrhage, hemoconcentration, renal failure; and correction of protein, electrolyte, or blood loss. Whole blood and platelet transfusions may be given. Lassa fever responds to early treatment with IV ribavarin 33 mg/kg as a loading dose followed by 16 mg/kg every 6 hours for 4 days, then 8 mg/kg every 8 hours for 3 days.



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