LASSA FEVER, an acute viral hemorrhagic disease, is found mostly in West Africa.1 It's a zoonotic disease, meaning it can be passed between animals and humans.2 Though it's endemic to parts of five West African countries, Benin, Guinea, Liberia, Nigeria, and Sierra Leone, evidence suggests that Lassa virus is even more prevalent than previously thought.2-5 A handful of imported cases have been reported in the United States involving patients who worked or traveled in West Africa.5,6 The most recent imported case was diagnosed in the United States in May 2015 in a patient who'd traveled to Liberia.7 That patient died.
Bringing Lassa fever to light
A World Health Organization expert panel recently named Lassa fever one of eight emerging infectious diseases most likely to cause major epidemics.8 The panel prioritized the pathogens that are most threatening and for which little is available in terms of diagnostics, treatments, vaccinations, or control measures. The purpose of highlighting these pathogens was to spur research and develop interventions. Also included were other viruses such as Ebola virus and severe acute respiratory syndrome.8
The CDC classifies Lassa virus as a Biosafety Level 4 (BSL-4) lab microbe.9 This is the highest level of biosecurity required for labs working with “dangerous and exotic agents that pose a high individual risk of aerosol-transmitted laboratory infections and life-threatening disease.” No rapid point-of-care diagnostic tests, treatments, or vaccinations have yet been developed for BSL-4 agents.
Lassa fever is also a National Institute of Allergy and Infectious Diseases Biodefense Category A agent.10 Pathogens in this category pose the highest risk to national security and public health because they're easily transmitted person to person, disease manifestations are severe, mortality is significant, and outbreaks would have a major impact on public health. The Lassa virus also has potential as a biological weapon because it can cause extensive illness and death.11
Lassa virus is a single-stranded RNA virus that can quickly overwhelm the immune system. The incubation period for Lassa ranges from 6 days to 3 weeks.2,5,12 Eighty percent of patients with Lassa virus infection either have mild, nonspecific symptoms or are asymptomatic (further discussion of signs and symptoms follow). However, 20% of patients develop severe infection.
Although only 1% of Lassa fever cases result in mortality, up to 20% of all patients with Lassa fever hospitalized for severe infection will die within 2 weeks of illness onset.2 For pregnant patients in their third trimester, maternal and fetal mortality can exceed 80%.5
An estimated 100,000 to 300,000 cases of Lassa fever are reported annually in West Africa, with 5,000 resulting in death. These are crude estimates; many barriers exist to diagnostic testing and surveillance such as a lack of in-country expertise and training, as well as appropriate lab equipment and facilities.2 The virus affects both genders and all age groups, though children and pregnant women are disproportionately susceptible to illness.5,13
Etiology and transmission
The Mastomys natalensis, or the multimammate rat, a common rodent found in many parts of sub-Saharan Africa, is a natural reservoir for Lassa virus. A rodent infected with the virus remains asymptomatic, but can shed the virus in its saliva, urine, feces, respiratory secretions, and blood throughout its lifespan.12
The multimammate rat is rampant in rural areas, especially in substandard dwellings and food storage areas. This habitat potentiates frequent rodent-to-human interactions.2,11,14 Rodent-to-human transmission of Lassa virus occurs when humans ingest, inhale, or have direct contact with rat urine or feces. A household chore such as sweeping can aerosolize the secretions, which humans then inhale. Ingesting food stored where a rat has been burrowing can also result in transmission of virus, as can killing and eating an infected rat.2
Human-to-human transmission is possible in community and healthcare settings. Direct contact with an infected person's urine, feces, vomit, blood, semen, or saliva can transmit the virus.12 Lassa virus can be excreted in an infected human's urine for up to 2 months, and in the semen for 3 months.11 Healthcare-associated transmission of the virus has occurred between hospitalized patients where strict infection control practices and use of personal protective equipment are lacking.5 However, casual contact doesn't transmit disease among humans, and aerosolized transmission of the virus between humans has never been documented.5
Signs and symptoms
Because Lassa fever is a generalized viral infection, it can be difficult to recognize, especially early in the course of the disease. Lassa has no distinguishing characteristics and can present as many other diseases endemic to West Africa. In the early stages of Lassa fever, signs and symptoms can mimic malaria, typhoid fever, and yellow fever, as well as Ebola virus disease.5,12 Mild signs and symptoms include low-grade fever, headache, malaise, weakness, and myalgia in the early stages. If the infection progresses, signs and symptoms can include nausea, vomiting, abdominal pain, and mucosal bleeding. The infection can spread throughout the body and affect multiple organs, including the liver, kidneys, and the brain. Shock and multiorgan dysfunction can result, leading to death.2
Diagnosing Lassa fever
Definitive diagnosis must occur in specialized labs with specially trained personnel due to the potential for virus transmission when handling and testing BSL-4 pathogens.2,5,12 Few such labs exist in resource-limited areas such as West Africa. A rapid, point-of-care test to distinguish between the presence or absence of malaria, Ebola virus disease, and Lassa fever is in the development phase.15
Labs utilize several different testing methods for Lassa fever, including an enzyme-linked immunosorbent serologic assay to detect Lassa antigen and immunoglobulin (Ig)M and IgG antibodies, a reverse transcription-polymerase chain reaction, and viral culture.2
Treatment of severe signs and symptoms includes early I.V. administration of the antiviral drug ribavirin, with continued administration for up to 10 days.3,12 Ideally, the drug is administered within 6 days of symptom onset for optimal effectiveness.3,12 However, I.V. ribavirin isn't readily available in West Africa.
Additional supportive care includes fluid and electrolyte management, antipyretics, broad-spectrum antibiotics if indicated, and management of organ failure.2,12
No vaccine is currently available to prevent Lassa virus infection.16 Prevention efforts in West Africa focus on community education to reduce human exposure to rodent secretions. This is difficult due to the wide geographic distribution of the multimammate rat and the poor quality housing typical of many rural areas.12,14 Improved infection control practices (such as barrier precautions) among healthcare personnel in regions where Lassa is common are also a focus of transmission reduction. Public health interventions such as surveillance, contact tracing, and patient monitoring are essential preventive measures.12
Many challenges impede the prevention, reduction, and eradication of Lassa virus infection. These challenges include a lack of an effective vaccine, rapid diagnostics, approved therapeutics, and limited resources and expertise. Civil conflict and the recent Ebola virus disease epidemic have also hindered the ability of international partners to eradicate Lassa fever in West Africa.
Globalization, international travel and immigration, fluid national borders, and climate change make Lassa fever an international concern. It's essential that nurses keep abreast of this rapidly emerging infectious disease. Informed nurses with current knowledge of Lassa fever are essential to safe patient care on a global scale.
3. Branco LM, Boisen ML, Andersen KG, et al. Lassa hemorrhagic fever in a late term pregnancy from northern Sierra Leone with a positive maternal outcome: case report. Virol J
4. Sogoba N, Feldmann H, Safronetz D. Lassa fever in West Africa: evidence for an expanded region of endemicity. Zoonoses Public Health
. 2012;59(suppl 2):43–47.
6. Kyei NN, Abilba MM, Kwawu FK, et al. Imported Lassa fever: a report of 2 cases in Ghana. BMC Infect Dis
12. Ogbu O, Ajuluchukwu E, Uneke CJ. Lassa fever in West African sub-region: an overview. J Vector Borne Dis
13. Shaffer JG, Grant DS, Schieffelin JS, et al. Lassa fever in post-conflict Sierra Leone. PLoS Negl Trop Dis
14. Kelly JD, Barrie MB, Ross RA, Temple BA, Moses LM, Bausch DG. Housing equity for health equity: a rights-based approach to the control of Lassa fever in post-war Sierra Leone. BMC Int Health Hum Rights
15. Nelson D, McCormick S, Boisen M, et al.Prototype multi-agent lateral flow immunoassay (LFI) for the detection of Lassa virus, malaria, and Ebola virus (EBOV) for point of care detection of endemic infections. Poster session presented at the American Society of Tropical Medicine and Hygiene meeting. 2015. http://vhfc.org/sites/default/files/blogimages/Multiplex_poster.pdf
16. Lukashevich IS. The search for animal models for Lassa fever vaccine development. Expert Rev Vaccines