Lassa fever is a common disease in West Africa with thousands to tens of thousands of cases a year. For hospitalized patients, case-fatality rate is as high as 15%. Transmission is through contact with infected rodents or infected patients (blood, urine, throat secretions, and sexual contact).
CASES/YEAR
1 (US); 75,000 (Global)
OTHER NAMES
Lassa virus infection; Lujo disease (Related Infection);
INCUBATION
6-21 days; [CCDM]
INITIAL SYMPTOMS
Flu-like illness with fever, myalgia, exudative pharyngitis, cervical adenopathy; conjunctivitis, vomiting, abdominal pain, chest pain, and cough; [CCDM]
PRECAUTIONS
Standard; "Single-patient room preferred. Emphasize: 1) use of sharps safety devices and safe work practices, 2) hand hygiene; 3) barrier protection against blood and body fluids upon entry into room (single gloves and fluid-resistant or impermeable gown, face/eye protection with masks, goggles or face shields); and 4) appropriate waste handling. Use N95 or higher respirators when performing aerosol-generating procedures. Largest viral load in final stages of illness when hemorrhage may occur; additional PPE, including double gloves, leg and shoe coverings may be used, especially in resource-limited settings where options for cleaning and laundry are limited. Notify public health officials immediately if Ebola is suspected. Also see Table 3 for Ebola as a bioterrorism agent." [CDC 2007 Guideline for Isolation Precautions] See recommendations for isolation and disinfection in CCDM.
COMMENTS
FINDINGS:
About 80% of infections are asymptomatic or mild. Findings of severe infections may include shock, pleural effusions, hemorrhages, seizures, encephalopathy, albuminuria, elevated liver enzymes, and nerve deafness (eighth cranial nerve). [CCDM, p. 50-4] The typical case starts as a flu-like illness with pharyngitis, cough, chest pain, conjunctivitis, and abdominal pain. Some patients then develop the severe form of the disease with neck swelling and mild bleeding from the conjunctiva, nose, mouth, gastrointestinal, and genitourinary tracts. Maculopapular or petechial rashes may be visible in patients with lighter skin complexions. Some patients deteriorate with delirium, respiratory distress, shock, coma, and death. [Guerrant, p. 456-7] By the end of the first week, patients are very ill with high fever. Common symptoms are conjunctivitis, stomatitis, pharyngitis, cervical lymphadenopathy, abdominal pain, myalgias, arthralgias, hypotension, and relative bradycardia. There is no typical rash. Most patients do not have evidence of neurological disease. Leukopenia is common early in the illness, and leukocytosis is seen later. Platelet counts are not depressed, but platelet function is impaired. [ID, p. 2136] Common symptoms are fever, pharyngitis, chest pain, and proteinuria. Other findings are mucosal bleeding, encephalitis, stiff neck, pulmonary edema, and pleural effusions. [PPID, p. 2181-2] Iridocyclitis and transient blindness are late complications. [Merck Manual., p. 1486] Patients with Lassa fever do not have jaundice. {Guerrant, p. 445t]
EPIDEMIOLOGY:
Lassa fever is a common disease in West Africa with thousands to tens of thousands of cases a year. [ID, p. 2133] For hospitalized patients, case-fatality rate is as high as 15%. Transmission occurs through contact with infected rodents or infected patients (blood, urine, throat secretions, and sexual contact). Patients excrete the virus in urine for several weeks and in the semen for up to 3 months. [CCDM, p. 50-2] Infection spreads from infected rodents (small particle aerosols) and infected people (close contact). [Harrison ID, p. 950t, 968]
RELATED INFECTIONS:
Lujo disease is similar to Lassa fever based on observations of 5 patients, 4 of whom died. The virus has been isolated from a patient in Zambia. [CCDM, p. 51-2]
DIAGNOSTIC
Antibody or antigen detection (PCR, ELISA, and IFA); Culture; [CCDM]
SCOPE
West Africa (Guinea, Liberia, parts of Nigeria, and Sierra Leone); [CCDM, p. 52]
SIGNS & SYMPTOMS
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>arthralgia
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>fatigue, weakness
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>fever
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>fever, biphasic or relapsing
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>myalgia
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>relative bradycardia
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E dysphagia
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E epistaxis
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E pharyngitis
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E stomatitis
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G abdominal pain
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G blood in stool
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G diarrhea
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G liver function test, abnormal
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G nausea, vomiting
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H leukocytosis
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H leukopenia
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H lymphadenopathy
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H thrombocytopenia
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N confusion, delirium
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N headache
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N lethargy
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N seizure
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N stiff neck
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O conjunctivitis, acute
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R chest pain
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R cough
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R dyspnea
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S papules or plaques
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S petechiae and ecchymoses
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S rash (exanthem)
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U hematuria
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X lung infiltrates
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X pleural effusions
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*bleeding tendency
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*blindness
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*cranial neuropathy
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*encephalitis
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*epididymo-orchitis
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*myocarditis
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*pericarditis
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*pulmonary edema
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*shock
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*stupor, coma
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*uveitis
ENTRY
Inhalation, Needle (Includes Drug Abuse), Scalpel or Transfusion, Sexual Contact
SOURCE
Person-to-Person, Animal Excreta
RISK FACTORS
- Care for patients (bloodborne pathogen)
- Care for patients (droplet/airborne)
- Handle infected rodents (not bite)
- Handle needles or surgical instruments
- Have a blood transfusion
- Raise dust of excreta from rodents
- Travel to endemic area
- Victim--air release of infectious agents
- Work in a medical or research lab
TREATMENT
Ribavirin, given intravenously, is most effective when started within 6 days of onset. [CCDM, p. 53]
REFERENCES FOR CASES/YEAR
1. (US) Assumption: about the same as in England & Wales = less than 1 case per year;
2. (Global) Cases reported in England & Wales: From 1970 through 2009, 13 cases imported from Africa (all but one from Nigeria and Sierra Leone) [Public Health England website] Extremely common in endemic areas in West Africa; Antibody prevalence ranged from 8-52% on one study in Sierra Leone; Annual incidence = 1000-10,000; Case fatality rate = 1% to 3% (20% in hospitalized patients); [ID, p. 2133-4] 50,000 to 100,000 annual cases; [Cecil, p. 2214]