This is a potentially devastating viral illness (due to an arenavirus), which can be incubated from 1 day to 3 weeks and takes about 2 weeks to clear, if the patient survives.
It was originally described in Lassa, Nigeria, where in 1969 there was an epidemic. It has a mortality rate of 20% to 40% (Ref. 6, p.1309), but with modern methods of the antiviral drug ribavirin, given intravenously in a hospital setting, the mortality rate is typically now around 15%.
The illness is transmitted through an African mouse strain (“Mastomys natalensis“), which spreads urine and feces. The dust particles that contain the virus are inhaled and infect humans mostly by this route.
Signs and Symptoms
Lassa fever starts as a cold and flu like illness with relatively mild symptoms in the beginning. After a sore throat, chills, muscle aches and a fever chest pains and upper abdominal pains develop, which suddenly turn into an acute abdominal pain after about 4 or 5 days. The throat disease does not clear up, but gets excruciatingly painful with pseudomembranes developing on the tonsils. At the same time the abdominal pain gets worse and localizes in the lower abdomen. Vomiting occurs and becomes intractable necessitating intravenous fluid replacement or the patient would die in dehydration. A generalized lymph gland swelling occurs all over the body from this viral illness.
Other less common symptoms are swelling of face and neck, dizziness, hearing loss, bleeding from nose and gums. Skin rashes can occur, and also fluid on the lungs (pulmonary edema), which usually is a bad prognostic sign. The blood pressure is low in the acute state. Grand mal seizures are an indication that the central nervous system is infected and this is associated with a higher mortality rate.
There are nonspecific tests such as elevated liver enzymes, elevated CK and LDH enzymes and protein in the urine.
The other test is a disease specific test, which consists of a fourfold increase of Lassa IgM antibody titer using an immunofluorescent technique. Chest X-rays show fluid accumulation on both lung bases (pleural effusions) and lines in the lung tissue on both bases (called “viral pneumonitis”).
Mortality has been reduced up to 10-fold with the use of intravenous ribavirin treatment, an antiviral antibiotic. At the same time it is important that fluid losses are carefully monitored in a hospital setting where the patient is treated in an isolation room with a high-tech negative pressure setup and the supervision of a tropical disease or infection specialist. There are attempts to develop an effective human Lassa vaccine after it has been successfully tested in a mouse model (Ref. 10). In this mouse model there was a 90% protection through the vaccine.
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