Lassa Fever

  • Medical Author:

    Sandra Gonzalez Gompf, MD, FACP is a U.S. board-certified Infectious Disease subspecialist. Dr. Gompf received a Bachelor of Science from the University of Miami, and a Medical Degree from the University of South Florida. Dr. Gompf completed residency training in Internal Medicine at the University of South Florida followed by subspecialty fellowship training there in Infectious Diseases under the directorship of Dr. John T. Sinnott, IV.

  • Medical Editor: Charles Patrick Davis, MD, PhD
    Charles Patrick Davis, MD, PhD

    Charles Patrick Davis, MD, PhD

    Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.

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Lassa fever facts

  • Lassa fever is one of the hemorrhagic fever viruses, like Ebola virus, Marburg virus, and others.
  • Like Ebola virus, Lassa fever occurs primarily in West Africa.
  • Unlike Ebola virus, Lassa fever is not as contagious person to person, nor as deadly.
  • Lassa virus is transmitted from rodents to humans.

What is Lassa fever?

Lassa fever is a hemorrhagic fever virus from the family Arenaviridae. It is an acute viral illness lasting one to four weeks, and it occurs in West Africa and some areas beyond.

What is the history of Lassa fever?

Lassa fever was first described in the 1950s, and the viral particle was identified in 1969 from three missionary nurses who died in Lassa, Nigeria, after caring for an infected obstetrical patient. Lassa fever is one of the hemorrhagic fever viruses, occurring in West Africa in similar areas as Ebola virus. There are 100,000-300,000 cases of Lassa fever each year in the world, causing an estimated 5,000 deaths and about 10%-15% of admissions to hospitals in Sierra Leone and Liberia. Deaths are especially common in children. Case fatality is 1% in general, although severe cases have a case fatality of 15%.

Lassa fever has rarely been diagnosed in the U.S. each year, largely as a result of international travel or immigration. A case was diagnosed in May 2015 in New Jersey in a patient traveling from Liberia, the sixth active case documented in returning travelers to the U.S. since 1969.

What are causes and risk factors for Lassa fever?

Lassa fever virus is an Arenavirus that is mainly a zoonosis (a disease spread to humans from animals). It is spread to people through contact with household items or food contaminated with the rodent droppings or urine of infected multimammate rats (Mastomys natalensis). These rodents live throughout West Africa in homes, and they can shed this virus without being ill. People most become infected through inhaling aerosols in air contaminated with rodent excretions, swallowing the virus in food or contaminated utensils (or multimammate rats eaten as food), or through open wounds. Lassa fever virus is believed to be endemic (always present) in Benin, Guinea, Sierra Leone, Liberia, and some parts of Nigeria. It has also been detected in the Ivory Coast, Ghana, Burkina Faso, Mali, Senegal, Gambia, and Central African Republic.

Travelers to West Africa, especially those staying in homes or areas of poor sanitation or crowding, or health-care and laboratory professionals serving in affected areas, are most at risk.

Those at highest risk for serious complications and death are pregnant women in their third trimester. Stillbirth or fetal loss occurs in 95% of pregnancies.

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Lassa Fever Treatment & Medication

Ribavirin (Rebetol, Copegus, Ribasphere, RibaPak, Moderiba)

Ribavirin is an antiviral drug. It is used in combination with interferon for the treatment of chronic hepatitis C. Although the exact mechanism of its action is unknown, it is thought to interfere with the production and/or action of viral DNA and RNA which are critical to the survival and multiplication of the virus.

Is Lassa fever contagious? If so, what is the contagious period for Lassa fever?

Person-to-person spread is possible but is not as frequent as with Ebola virus. It can rarely occur upon direct contact with saliva, blood, and bodily fluids and mucous membrane or sexual contact. Contact of intact skin with intact skin does not transmit the virus. Laboratory workers and health-care professionals can become infected through improper infection-control precautions, and patients in rural hospitals have acquired it through reuse of disposable needles.

No person-to-person spread has been documented in the U.S. from returning travelers.

It is not clear when infected humans are contagious or for how long they are contagious. The presence of virus in the blood is known to peak four to nine days after symptoms begin. The virus can be transmitted in semen for up to three months.

Lassa fever is one of the hemorrhagic fevers and may present with signs and symptoms like Ebola or Marburg hemorrhagic fever viruses. Until these viruses are ruled out, suspected cases must be managed with appropriate infection-control precautions to prevent contact with blood, body, fluid, and contaminated surfaces like clothing and bedding. These include basic hand washing or sanitizing between patients, and when working within 3 feet of an affected patient, use of additional barrier personal protective equipment. In between patients, health-care workers must put on a clean long-sleeved gown, gloves, and face mask with eye protection. Safe injection practices, safe laboratory handling, and safe mortuary procedures are also important.

When is Lassa fever no longer contagious?

It is not clear when infected humans are contagious or for how long, but the virus is cleared from the blood during recovery about three weeks after onset of symptoms.

What is the incubation period for Lassa fever?

The incubation period for Lassa fever is variable, from six days to three weeks. Most people have mild or no symptoms. British researchers suggest the incubation period varies from seven to 10 days and in some people, up to about 21 days.

What are Lassa fever symptoms and signs?

In those who have symptoms, Lassa fever begins with a flu-like illness and includes symptoms such as fever, malaise, generalized weakness, sore throat (appearing very similar to strep throat and without runny nose), severe headache, chest pain (especially behind the breastbone), back pain, and ringing ears. Nausea, vomiting, abdominal pain, and diarrhea also occur. Hemorrhage is not common in less serious disease, but loss of fluid from blood vessels into tissue may occur; this causes facial swelling, reddened whites of the eyes, and fluid accumulation around the lungs and heart. Dry cough and respiratory distress may occur if illness involves fluid in the lungs. Severe disease may cause encephalitis with confusion, tremors, seizures, and coma; organ failure and shock are often end-stage events. Fair-skinned individuals may have a faint rash of the upper body, which is not seen in dark-skinned individuals. Some bleeding from mucous membranes occurs in severe illness. Lassa virus infects all tissues, but the liver is especially typical. Hepatitis may be mild or severe, and laboratory tests may not correlate with the level of injury.

Lassa fever virus often causes deafness, and this complication may be noted in late-stage disease and during recovery periods.

How do physicians diagnose Lassa fever?

Without laboratory tests, Lassa fever is difficult to differentiate from other infections common to West Africa; however, this requires specialized laboratories and precautions for handling specimens.

Laboratory tests include enzyme-linked immunosorbent serologic assays (ELISA) for Lassa IgM and IgG antibodies and Lassa antigen. For definitive testing, virus can be grown in culture in seven to 10 days; reverse transcriptase polymerase chain reaction (RT-PCR) assay is also available but often limited to research.

Immunohistochemistry stains performed on tissue specimens can also be used to make a postmortem diagnosis.

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What is the treatment for Lassa fever?

Ribavirin (Copegus, Rebetol, Virazole, Ribasphere) given intravenously and early in the course of illness is an effective treatment, in addition to support of fluid and electrolytes, oxygenation, and blood pressure. This treatment reduces mortality from 50% to 5% when given early in serious illness in the only study to evaluate it in 1986. Adverse effects include hemolytic anemia (rupture of red blood cells) if the drug is infused too quickly.

What are complications for Lassa fever?

Other than acute illness, the commonest complication or after-effect of Lassa fever is hearing loss, which has been observed during recovery in 20%-30% of cases. Because most Lassa fever infections cause no symptoms, and because people with acute deafness have been shown to have high antibody levels to Lassa virus, suggesting recent infection, it believed to be a common cause of sudden deafness in affected areas.

Pregnant women, especially in the third trimester, are at risk for serious disease. Spontaneous abortion occurs in 95% of infections with Lassa fever.

What is the prognosis of Lassa fever?

Prognosis of Lassa fever is generally good, considering that many individuals in affected areas have antibodies to Lassa fever and do not recall illness. Most illness is mild and does not require hospitalization. Of those hospitalized from the community with Lassa fever, up to 15% die. Mortality may be up to 65% in cases of hospital-associated transmission, perhaps because patients are already compromised.

Is it possible to prevent Lassa fever? Is there a vaccine for Lassa fever?

There is no vaccine available as yet against Lassa fever.

Oral ribavirin given as prophylaxis or preventive treatment has been studied in a limited fashion during an outbreak, with no evidence of transmission; however, only 40% of the small number of participants completed treatment due to side effects from ribavirin that included weakness, dizziness, headache, and nausea.

There is no clear-cut data to support routine use of oral ribavirin as prophylaxis at this time, and suitable large trials have not been feasible, thus this use will have to rely on experience in the field over time.

What research is being done on Lassa fever?

Civil unrest and inadequate health-care resources has limited research on prevention and control of Lassa fever in West Africa. The Mano River Union Lassa Fever Network (MRU LFN) was established in 2004 to assist in developing national and regional surveillance, diagnosis, treatment, control, and prevention. This network includes local governments, the World Health Organization, Tulane University, the United Nations, the United States' Office of Foreign Disaster Assistance (OFDA), and the U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID).

In 2010, Tulane University was awarded a five-year $15 million grant by the National Institute of Health toward developing prevention, treatments, and a vaccine for Lassa and other hemorrhagic fevers. The Viral Hemorrhagic Fever Consortium was established from this contract, and brings together Tulane, Scripps Research Institute, Broad Institute, Harvard University, University of California at San Diego, University of Texas Medical Branch, Autoimmune Technologies LLC, Corgenix Medical Corporation, Kenema Government Hospital in Nigeria, and Irrua Specialist Teaching Hospital in Nigeria.

Where can people find more information on Lassa fever?

More information about Lassa fever may be found at the web sites for the World Health Organization (http://www.who.int/mediacentre/factsheets/fs179/en/) and the Centers for Disease Control and Prevention (http://www.cdc.gov/vhf/lassa/index.html).

Medically reviewed by Robert Cox, MD; American Board of Internal Medicine with subspecialty in Infectious Disease

REFERENCES:

Cummins, D., J.B. McCormick, D. Bennett, et al. "Acute sensorineural deafness in Lassa fever." JAMA. 264 (1990): 2093-2096.

Khan, S.H., A. Goba, M. Chu, et al. "New opportunities for field research on the pathogenesis and treatment of Lassa fever." Antiviral Res 78.1 (2008): 103-115.

Switzerland. World Health Organization. "Lassa Fever." Mar. 13, 2015. <http://www.cdc.gov/vhf/lassa/index.html>.

United States. Centers for Disease Control and Prevention. "Lassa Fever." June 2, 2015. <http://www.cdc.gov/vhf/lassa/index.html>.

Viral Hemorrhagic Fever Consortium. <http://vhfc.org/consortium>.

Yun, N.E., and D.H. Walker. "Pathogenesis of Lassa Fever." Viruses 4.10 (2012): 2031-2048.

Last Editorial Review: 10/27/2016

Reviewed on 10/27/2016
References
Medically reviewed by Robert Cox, MD; American Board of Internal Medicine with subspecialty in Infectious Disease

REFERENCES:

Cummins, D., J.B. McCormick, D. Bennett, et al. "Acute sensorineural deafness in Lassa fever." JAMA. 264 (1990): 2093-2096.

Khan, S.H., A. Goba, M. Chu, et al. "New opportunities for field research on the pathogenesis and treatment of Lassa fever." Antiviral Res 78.1 (2008): 103-115.

Switzerland. World Health Organization. "Lassa Fever." Mar. 13, 2015. <http://www.cdc.gov/vhf/lassa/index.html>.

United States. Centers for Disease Control and Prevention. "Lassa Fever." June 2, 2015. <http://www.cdc.gov/vhf/lassa/index.html>.

Viral Hemorrhagic Fever Consortium. <http://vhfc.org/consortium>.

Yun, N.E., and D.H. Walker. "Pathogenesis of Lassa Fever." Viruses 4.10 (2012): 2031-2048.

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