Lassa Fever

The incubation period for Lassa fever is 5 to 16 days.

Symptoms begin with gradually progressive fever, weakness, malaise, and gastrointestinal 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 first week; patches of white or yellow exudate may appear on the tonsils, often coalescing into a pseudomembrane.

In severe cases, facial swelling; fluid in the lung cavity; bleeding from the mouth, nose, vagina, or gastrointestinal tract; and low blood pressure may develop (1). Mucosal bleeding occurs in up to 40% of patients and is associated with a poor prognosis (2).

Occasionally, patients have tinnitus, epistaxis, maculopapular rash, cough, and dizziness.

Sensorineural hearing loss develops in 20 to 30% (3); it is often permanent.

Patients who recover defervesce in 4 to 7 days. Progression to severe illness results in shock, delirium, pulmonary crackles, pleural effusion, and, occasionally, generalized seizures. Pericarditis occasionally occurs. Degree of fever and aminotransferase levels correlate with disease severity.

Late sequelae include alopecia, iridocyclitis, and transient blindness.

• Polymerase chain reaction (PCR) or serologic testing

Lassa fever is suspected in patients with possible exposure if they have a viral prodrome followed by unexplained disease of any organ system.

Liver tests, urinalysis, serologic tests, and complete blood count should then be done. Proteinuria is common and may be massive. Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels rise (to 10 times normal), as do lactic dehydrogenase levels.

The most rapid diagnostic test is PCR, but demonstrating either Lassa IgM antibodies or a 4-fold rise in IgG antibody titer using an indirect fluorescent antibody technique is also diagnostic. Typically, both PCR and serology are used to confirm diagnosis.

Although the virus can be grown in cell culture, cultures are not routine. Because infection is a risk for laboratory personnel, particularly in specimens from patients with hemorrhagic fever, cultures must be handled only in a biosafety level 4 laboratory.

Chest radiographs, obtained if lung involvement is suspected, may show basilar pneumonitis and pleural effusions.

• RibavirinRibavirin

Ribavirin may be given.Ribavirin may be given.

Convalescent plasma from patients with Lassa fever has not been shown to be beneficial and is not recommended.

Supportive treatment, including correction of fluid and electrolyte imbalances, is imperative.

For infected pregnant women, abortion reduces risk of maternal death.

Recovery or death usually occurs 7 to 31 days (average 12 to 15 days) after symptoms begin. Approximately 15 to 20% of patients hospitalized for severe Lassa fever die from the illness (1).

Disease is severe during pregnancy, especially during the third trimester. Most infected pregnant women lose the fetus (1).

Universal precautions, including use of personal preventive equipment and other measures for airborne isolation (eg, use of goggles, high-efficiency masks, a negative-pressure room, positive-pressure filtered air respirators), and surveillance of contacts are recommended when treating patients with Lassa fever.

Primary transmission of the Lassa virus from its rodent host to humans can be prevented in endemic areas by avoiding food, water, and environment contaminated by infected rodents; however, the wide distribution of these rodent hosts in Africa makes complete control of these rodent reservoirs impractical. Guidelines for cleaning up after rodents and working in areas with potential rodent excreta are available from the Centers for Disease Control and Prevention (CDC) (1).

No vaccine for Lassa fever is available.