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Lassa Fever


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.

Diagnostic Tests

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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3. F Charatan BMJ 2000 Oct 21;321(7267):980.

4. The Merck Manual, 7th edition, by M. H. Beers et al., Whitehouse   Station, N.J., 1999. Chapter 43.

5. JR Zunt and CM Marra  Neurol Clinics Vol.17, No.4,1999: 675-689.

6. The Merck Manual, 7th edition, by M. H. Beers et al., Whitehouse   Station, N.J., 1999. Chapter 162.

7. LE Chapman : Antivir Ther 1999; 4(4): 211-19.

8. HW Cho: Vaccine 1999 Jun 4; 17(20-21): 2569-2575.

9. DO Freedman et al. Med Clinics N. Amer. Vol.83, No 4 (July 1999):     865-883.

10. SP Fisher-Hoch et al. J Virol 2000 Aug; 74(15): 6777-6783.

11. Mandell: Principles and Practice of Infectious Diseases, 5th ed., ©   2000 Churchill Livingstone, Inc.

12. Goldman: Cecil Textbook of Medicine, 21st ed., Copyright © 2000   W. B. Saunders Company

13. PE Sax: Infect DisClinics of N America Vol.15, No 2 (June 2001):   433-455.

14. David Heymann, MD, Editor: Control of Communicable Diseases Manual, 18th Edition, 2004, American Public Health Association.

Last modified: April 16, 2021

This outline is only a teaching aid to patients and should stimulate you to ask the right questions when seeing your doctor. However, the responsibility of treatment stays in the hands of your doctor and you.