Definition of Lassa fever

Lassa fever: An acute viral infection found in the tropics, especially in West Africa. Epidemics of Lassa fever have occurred in countries such as Sierra Leone, Congo (formerly Zaire), Liberia and Nigeria.

The disease was discovered in 1969 when two missionary nurses died of it in the village of Lassa, Nigeria. The virus is an arenavirus, a single-stranded RNA virus that is animal-borne (zoonotic).

Lassa fever is a grave health concern because it can cause a very severe potentially fatal illness, is highly contagious and can spread like wildfire. The number of Lassa virus infections per year in West Africa has been roughly estimated at 100,000 to 300,000, with at least 5,000 deaths yearly.

The Lassa virus has been found in a rodent known as the "multimammate rat" of the genus Mastomys. People can become infected by eating this infected rat or by eating food contaminated by rat excretions. Person-to-person transmission also occurs by direct contact, contamination of skin breaks with infected blood, and aerosol spreads (virus particles moving through the air).

The first symptoms of the disease typically occur 1-3 weeks after the patient comes into contact with the virus and can include increasingly high fever, sore throat, cough, eye inflammation (conjunctivitis), facial swelling, retrosternal pain (behind the breastbone), back pain, abdominal pain, vomiting, diarrhea and general weakness lasting for several days. Neurological symptoms have also been described, including hearing loss, tremors, and encephalitis (brain inflammation). The most common long-term complication of Lassa fever is deafness.

Because the symptoms are so varied and nonspecific, clinical diagnosis is often difficult. If the person has traveled to West Africa and has a severe fever within 3 weeks after returning (the incubation period of lassa virus is 1 to 3 weeks), the illness should be reported to a doctor.

The key agent for treatment is Ribavirin (Rebetron, Virazole), an antiviral drug, which is most effective when given early in the course of the disease. Patients are also given supportive care with fluid balance, oxygen as needed, treatment of any other complicating infections, etc.

Medical isolation procedures should be followed, due to the highly contagious nature of Lassa fever. These procedures are termed VHF isolation precautions or barrier nursing methods and include protective clothing such as masks, gloves, gowns, and goggles; infection control measures such as complete equipment sterilization; and isolating infected patients from contact with unprotected persons until the disease has run its course. Patients may excrete the virus weeks after recovery. Their bodily fluids should therefore be monitored for the virus before they leave the hospital.

Cases of Lassa fever in such areas as the US, Canada, and Europe tend to make the news because of the fearsome and seemingly exotic nature of the disease. For example, in January, 2000 it was reported that a 23-year-old woman died of Lassa fever in Wuerzburg, Germany. An art student, she had been traveling in Africa where she contracted a new and especially aggressive strain of the Lassa virus. She died of massive internal bleeding. Cases in West Africa rarely, if ever, make news.

Lassa virus was discovered in 1969 by a team led by Dr. Jordi Casals-Ariet.

See also: Lassa virus; and Casals-Ariet, Jordi.

Common Misspellings: lassa feaver