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Lassa fever:essential data |
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Viral weapon acting on humans |
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Synopsis, Diagnosis, Symptoms,
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Safety Precautions for Lassa Fever Casualties |
Contact Precautions defined by the 1996 CDC guidelines should be adopted for handling patients.Biosafety level 4 practices should be adopted for handling of samples. |
| Causative organism: (Systematic name in 1997) | Lassa virus |
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| ICTV Acronym | LASV |
| Virus classification: | An Old World Arenavirus. An enveloped spherical
virus with two subgenomic single-stranded RNAs. Click here for a detailed description of Arenaviruses |
| Vector involvement: | The virus is carried by the multimammate rat Mastommys natalensis, but no intermediate vector is known. |
| Epidemiology of natural outbreaks: | The virus is spread throughout western Africa, although not all isolates have been associated with outbreaks of the disease. Infection is thought to occur by inhaling virus in dust after it has been deposited in the urine of a carrier animal. Person-to-person contact in hospitals(nosocomial infection) has been known but can be prevented by good practice of contact precautions. The virus may be secreted in the urine of patients for several weeks after infection. |
The initial physical findings are non-specific (fever, myalgia, prostration, headaches, diarrhea) until the development of hemorrhagic symptoms. Normal tests of blood clotting do not detect the effects that the virus has on platelets and the walls of blood vessels.
Differential DiagnosisOther disease or conditions that need to be eliminated |
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| Other infectious diseases | Other problems |
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Symptoms and effects.
After an incubation period of 7-21 days the disease begin to develop slowly and have been described as insidious. Symptoms first become severe enough to seek medical help at 4-9 days after their onset. The first symptoms are always a fever and general malaise. Chills, rigor and myalgia each occur in about 50% of cases. As the disease progresses pain develops in the chest, abdomen, and lower back. Nausea, vomiting and anorexia also develop along with a cough and sore throat. Hemorrhage and encephalopathy develop as the disease progresses, typically during the second week.
When hemorrhagic disease develops, patients die on the seventh to tenth day, usually of shock accompanied by lung problems and severe (grand mal) seizures..
In areas where the disease is endemic, 15-40% of the population have circulating antibodies to the virus that appear to be as a result of asymptomatic or low-grade infections.
Medical and Physical Countermeasures.
Vaccination (Immunoprophylaxis)
No vaccine is available.
Specific Therapy
Ribavirin is effective in severe, but not in acute cases. Convalescent serum has also been helpful in a limited number of tests.
Supportive care
Symptoms are treated. Minimize intrusive care to protect a weakened vascular bed. Attempt replacement therapy only in the case of severe hemorrhage. Fluid infusion to deal with dehydration is often counterproductive.
Decontamination
The virus is killed by common disinfectants, moist heat and drying.
Agent Properties and Potential Uses
Relatively little is known about the natural history of the virus. Its natural host is the multimammate rat Mastomys natalensis. This rat does not compete well with black rat that is dominant in towns of any size and it is unlikely that it could be used as a vector against conurbations.Like other arenaviruses it does not cause disease in the rat and is secreted in the urine with the most likely mode of infection being from aerosols of urine. The agent may therefore be deliverable as an aerosol if a suitable stabilizing medium can be found.
The mortality rate is about 40% when untreated. Treatment with ribavirin lowers this to 15%.
Spread of the disease, in the absence of the rat host, should be controllable by strict application of nursing practices with special care being taken to minimize spread of body fluids and desctruction of contaminated materials.
Terrorist Acquisition and Attempted Use.
| Disease | ICD-9-CM | ICD-10 |
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| Lassa fever | 078.8 |
A96.2 |
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