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Lassa fever
is an often fatal arenavirus infection that occurs mostly
in Africa. It may involve multiple organ systems but spares the
CNS. Diagnosis is with serologic tests and PCR. Treatment includes
IV ribavirin.
Lassa fever outbreaks have occurred in Nigeria, Liberia, and Sierra Leone. Cases have been imported to the US and the United Kingdom. The reservoir is Mastomys
natalensis, a rat that commonly inhabits houses in Africa. Most human cases probably result from contamination of food with rodent urine, but human-to-human transmission can occur via urine, feces, saliva, vomitus, or blood.
Symptoms and Signs
The incubation period is 5 to 16 days. Symptoms begin with gradually progressive fever, weakness, malaise, and GI symptoms (eg, nausea, vomiting, diarrhea, dysphagia, stomach ache); symptoms and signs of hepatitis may occur. Over the subsequent 4 to 5 days, symptoms progress to prostration with sore throat, cough, chest pain, and vomiting. The sore throat becomes more severe during the 1st wk; patches of white or yellow exudate may appear on the tonsils, often coalescing into a pseudomembrane. Sixty to 80% of patients have systolic BPs of < 90 mm Hg with pulse pressures of < 20 mm Hg, and relative bradycardia is possible. Facial and neck swelling and conjunctival edema occur in 10 to 30%. Occasionally, patients have tinnitus, epistaxis, bleeding from the gums and venipuncture sites, maculopapular rash, cough, and dizziness. Twenty percent of patients develop sensorineural hearing loss, often permanent. In patients who will recover, defervescence occurs; fatally ill patients often develop shock, delirium, rales, pleural effusion, and, occasionally, generalized seizures. Pericarditis occasionally occurs. The degree of fever and the aminotransferase levels correlate with disease severity. Late sequelae include alopecia, iridocyclitis, and transient blindness.
Diagnosis
Lassa fever is suspected in patients with possible exposure who have a viral prodrome followed by unexplained disease of any organ system except the CNS. If suspected, liver function tests, urinalysis, serologic tests, and possibly CBC should be obtained. Proteinuria is common and may be massive. AST and ALT levels rise (10× normal), as do LDH levels. The most rapid diagnostic test is PCR, although demonstrating either Lassa IgM antibodies or a 4-fold rise in IgG antibody titer using an indirect fluorescent antibody technique is also diagnostic. Although the virus can be grown in cell culture, cultures are not routine. Due to the risk of infection, particularly in patients with hemorrhagic fever, cultures must be handled only in a biosafety level 4 laboratory. Chest x-rays, obtained if lung involvement is suspected, may show basilar pneumonitis and pleural effusions.
Prognosis,
Treatment, and Prevention
Recovery or death generally occurs 7 to 31 days (average 12 to 15 days) after symptoms begin. Mortality occurs in 16 to 45%. Disease is severe during pregnancy. Mortality is 50 to 92% in women who are pregnant or who have delivered within 1 mo. Most pregnant women lose the fetus.
Ribavirin may reduce mortality up to 10-fold if begun within the first 6 days. All patients with AST levels ≥ 150 U/mL should be treated with IV ribavirin 30 mg/kg once followed by 16 mg/kg qid for 4 days followed by 8 mg/kg tid for an additional 7 days. Anti–Lassa fever plasma may be used as adjunctive therapy in very ill patients. Supportive treatment, including correction of fluid and electrolyte imbalances, is imperative. For infected pregnant women, particularly during the 3rd trimester, uterine evacuation appears to reduce maternal mortality.
Universal precautions, airborne isolation (including use of goggles, high-efficiency masks, a negative-pressure room, and positive-pressure filtered air respirators), and surveillance of contacts are recommended.
Last full review/revision November 2005
Content last modified November 2005
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