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Lassa Virus

Lassa virus



NAME: Lassa virus.

SYNONYM OR CROSS REFERENCE: Lassa fever, Lassa fever virus, viral haemorrhagic fever (VHF)(1,2,3).

CHARACTERISTICS: Double-segmented, single-stranded RNA virus, belonging to the genus Arenavirus , family Arenaviridae . The viral fragment may occupy several distinct shapes (pleomorphic) measuring 80 to 150nm in diameter(1,4). The surface of the virion lipid envelope is studded with glycoproteins that consist of tetrameric complexes of the viral glycoproteins GP1 and GP2(4).


PATHOGENICITY/TOXICITY: Acute viral illness of 1 to 4 weeks duration(3). Disease may be asymptomatic to mild (80 % of cases), severe, or fatal(1,3,5,6,7). Early symptoms include gradual onset of fever, nausea, abdominal pain, severe sore throat, cough, conjunctivitis, ulceration of buccal mucosa, exudative pharyngitis, and cervical lymphadenopathy(1,3,5,7,8). Late symptoms include severe swelling of head and neck, pleural and pericardial effusions(8,9). Twenty-five percent of cases result in deafness and/or (transient) alopecia(1,3,5,7,10). The disease is severe in pregnancy, resulting in foetal loss in 80 % of cases(3,10). Death as a result of infection with Lassa virus is usually due to cardiac arrest(1). Fatality rate is 15 to 20 % of hospitalized patients and 1 to 2 % of infected individuals in general(1,3,7).

EPIDEMIOLOGY: Endemic in West Africa. Between 10,000 and 300,000 infections occur annually with 5,000 deaths(1,3,6,10). Outbreaks have occurred in Guinea, Liberia (1972), Sierra Leone (1970-72, 1973-75, and 1996-97), areas of Nigeria (first cases in 1969, further outbreaks in 1970, 1974, and 1975), Central African Republic, Democratic Republic of Congo, Mali, Senegal, Benin, Burkina Faso, Cameroon, Ghana, Ivory Coast and Sudan(1,3). Approximately 20 cases of imported Lassa fever have been recorded worldwide(11,12).

HOST RANGE: Mastomys natalensis (an African rodent also known as the multimammate mouse or multimammate rat) and humans(1,3,4,7,10,3,4,7,10,13,14).

INFECTIOUS DOSE: One to 10 aerosolized organisms(13).

MODE OF TRANSMISSION: Transmission from the multimammate rat to humans occurs via aerosols; or by direct contact with rat excretions, or with food and water contaminated with excretions(1,3,6). Infection may occur through cuts and sores or when infected rats are prepared as food(1,4,6). Person-to-person transmission can cause epidemics with a high mortality rate, or be achieved by nosocomial outbreaks involving blood (contaminated needles), pharyngeal secretions and urine or contaminated medical equipment(1,2,3,6,7,15). Lassa virus can also be transmitted via sexual contact or via contact with skin lesions.

INCUBATION PERIOD: Five to 21 days(1,3,7,8).

COMMUNICABILITY: Person-to-person spread may occur during the acute febrile phase when the virus is present in the throat(3). Lassa virus can be excreted in urine for 3-9 weeks from the onset of illness. Male patients should refrain from unprotected sex until the semen is virus- free for 3 months(2,9).


RESERVOIR: The primary reservoir is the multimammate rat ( Mastomys natalensis )(1,2,3,7).

ZOONOSIS: Yes, transmission from the multimammate rat to humans(1,3,7).

VECTORS: Rodents(9).


DRUG SUSCEPTIBILITY: Ribavirin(1,3,10,16).

SUSCEPTIBILITY TO DISINFECTANTS: Lassa virus is susceptible to 0.5 % sodium hypochlorite, phenolic compounds, 3 % acetic acid (pH 2.5), lipid solvents and detergents such as SDS, formaldehyde and paraformaldehyde fixation, formaldehyde fumigation, and β- propiolactone(1,3,4,17,18,19).

PHYSICAL INACTIVATION: Lassa virus can be inactivated by heating serum for 1 hour at 60oC, gamma irradiation (1.2 x106 rads to 1.27 x106 rads), UV irradiation, autoclaving, incineration, and/or boiling(3,4,7,17,19).

SURVIVAL OUTSIDE HOST: The virus is stable as an aerosol, particularly at low relative humidity (30 % RH). The biological half-live at both 24°C and 32°C ranges from 10.1 to 54.6 minutes(20).


SURVEILLANCE: Definitive diagnosis is reached mainly upon laboratory testing (i.e. RT-PCR or serological testing) of virus isolation from blood samples, pharyngeal washings, pharyngeal swabs, and/or urine(1,2,3,7).

Note: All diagnostic methods are not necessarily available in all countries.

FIRST AID/TREATMENT: Ribavirin, which is most effective within the first 6 to 7 days of illness, and supportive care(1,3,7,9,13,15,16).

IMMUNIZATION: None(7,9,13).

PROPHYLAXIS: Ribavirin may reduce mortality after infection(1,9,16).


LABORATORY-ACQUIRED INFECTIONS: Two cases, one fatal, occurred among staff at a research institute in the United States(1,21). Laboratory infections have also occurred in hospital environments(3)

SOURCES/SPECIMENS: Blood, respiratory and pharyngeal secretions, urine, semen, tissues from human or animal hosts, and rodent excreta(3,7,21).

PRIMARY HAZARDS: Respiratory exposure to infectious aerosols, mucous membrane exposure to infectious droplets, and accidental parenteral inoculation are the primary hazards(15,21).

SPECIAL HAZARDS: Work with, or exposure to rodents that are naturally or experimentally infected represents a risk of human infection.



CONTAINMENT REQUIREMENTS: Containment Level 4 facilities, equipment, and operational practices for work involving infectious or potentially infectious materials, animals, and cultures.

PROTECTIVE CLOTHING: Personnel entering the laboratory must remove street clothing, including undergarments, and jewellery, and change into dedicated laboratory clothing and shoes, or don full coverage protective clothing (i.e., completely covering all street clothing). Additional protection may be worn over laboratory clothing when infectious materials are directly handled, such as solid-front gowns with tight fitting wrists, gloves, and respiratory protection. Eye protection must be used where there is a known or potential risk of exposure to splashes(23).

OTHER PRECAUTIONS: All activities with infectious material should be conducted in a biological safety cabinet (BSC) in combination with a positive pressure suit, or within a class III BSC line. Centrifugation of infected materials must be carried out in closed containers placed in sealed safety cups, or in rotors that are loaded or unloaded in a biological safety cabinet. The integrity of positive pressure suits must be routinely checked for leaks. The use of needles, syringes, and other sharp objects should be strictly limited. Open wounds, cuts, scratches, and grazes should be covered with waterproof dressings. Additional precautions should be considered with work involving animal activities(23).


SPILLS: Allow aerosols to settle and, wearing protective clothing, gently cover spill with paper towels and apply suitable disinfectant, starting at the perimeter and working towards the centre. Allow sufficient contact time before clean up (30 min)(23).

DISPOSAL: Patient excreta, sputum, blood and all objects with which a patient has had contact with, including laboratory equipment used for testing, should be disinfected with 0.5 % sodium hypochlorite solution or 0.5 % phenol with detergent, followed by autoclaving, incineration or boiling(3). Decontaminate all materials for disposal from the containment laboratory by steam sterilization, chemical disinfection, incineration or by gaseous methods. Contaminated materials include both liquid and solid wastes(23).

STORAGE: In sealed leak-proof containers that are appropriately labelled and locked in a Containment Level 4 laboratory(23).


REGULATORY INFORMATION: The import, transport, and use of pathogens in Canada is regulated under many regulatory bodies, including the Public Health Agency of Canada, Health Canada, Canadian Food Inspection Agency, Environment Canada, and Transport Canada. Users are responsible for ensuring they are compliant with all relevant acts, regulations, guidelines, and standards.

UPDATED: September 2010.

PREPARED BY: Pathogen Regulation Directorate, Public Health Agency of Canada.

Although the information, opinions and recommendations contained in this Pathogen Safety Data Sheet are compiled from sources believed to be reliable, we accept no responsibility for the accuracy, sufficiency, or reliability or for any loss or injury resulting from the use of the information. Newly discovered hazards are frequent and this information may not be completely up to date.

Copyright © Public Health Agency of Canada, 2010 Canada

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