Lassa virus: Infectious substances pathogen safety data sheet

Section I – Infectious agent

Name

Lassa virus

Agent type

Virus

Taxonomy

Family

Arenaviridae

Genus

Mammarenavirus

Species

Mammarenavirus lassaense

Synonym or cross-reference

Formerly Lassa mammarenavirus^{Footnote 1Footnote 2}. Also known as LASV, Lassa fever virus, viral haemorrhagic fever (VHF), Lassa hemorrhagic fever (LHF)^{Footnote 3Footnote 4Footnote 5}. Causative agent of Lassa fever^{Footnote 2}.

Characteristics

Brief description

Lassa virus (LASV) is a member of the genus Mammarenavirus within the family Arenaviridae^{Footnote 1Footnote 2}. Enveloped virions of LASV may occupy several distinct shapes (pleomorphic), with diameters ranging from 50-300 nm, and contain a single-stranded, double-segmented, single-stranded ambisense RNA genome of ~10.5 kb^{Footnote 2}. The large segment encodes the zinc-binding matrix protein, which regulates transcription and replication, and the RNA polymerase^{Footnote 2}. The small segment encodes the nucleoprotein (NP) and the viral glycoprotein precursor protein (GPC)^{Footnote 2Footnote 6}.

Properties

The life cycle of LASV is similar to other Old World arenaviruses, which use an unknown endocytotic pathway to enter the host cell^{Footnote 6}. The receptor used for cell entry is α-dystroglycan (α-DG), a highly conserved and ubiquitously expressed cell surface receptor for extracellular (ECM) proteins^{Footnote 6}. Virus internalization is reportedly sensitive to cholesterol depletion^{Footnote 6}. Upon receptor binding, the virus is internalized by endocytosis into a low-pH environment which triggers pH-dependent membrane fusion and release of viral ribonucleoprotein (RNP) complex into the cytoplasm, followed by initiation of replication and transcription. After translation of GPC, it is proteolytically cleaved into the mature virion glycoproteins GP1 and GP2, which are incorporated into the virion envelope where viral budding and release occur^{Footnote 6Footnote 7}.

While NP is essential in viral replication and transcription, it also exhibits double-stranded RNA (dsRNA)-specific exonuclease activity, resulting in suppression of host innate immune response by inhibiting translocation of interferon regulatory factor 3 (IRF-3)^{Footnote 8}.

Section II – Hazard identification

Pathogenicity and toxicity

Lassa fever is an acute viral hemorrhagic illness lasting 1 to 4 weeks^{Footnote 5}. Symptoms of infection occur within 1 to 3 weeks following exposure^{Footnote 9Footnote 10}. Disease presents as asymptomatic to mild in an estimated 80% of the affected population, based on seroprevalence of LASV antibodies and geographical location^{Footnote 5Footnote 11Footnote 12Footnote 13}. Mild symptoms of infection include fever, nausea, sore throat, general malaise, and weakness^{Footnote 9Footnote 14}. Infection may progress to more serious symptoms, including abdominal pain, gastrointestinal symptoms, swelling of the head/neck/brain, respiratory distress, seizures, hemorrhage, prolonged bleeding or shock, and neurological effects^{Footnote 5Footnote 10Footnote 15Footnote 16}. Approximately 25% of infections result in hearing loss, with half of patients recovering some hearing function after 1-3 months, and the remaining patients experiencing permanent hearing loss^{Footnote 5Footnote 17}.

Some infections may cause deaths as a result of multiple organ failure within 2 weeks after onset of symptoms^{Footnote 9}. The fatality rate is estimated to be 1-2% in endemic areas, with higher rates noted in women than in men, women in the third trimester of pregnancy (30%), and hospitalized individuals (15-20%)^{Footnote 5Footnote 9Footnote 18Footnote 19Footnote 20}. Infection during pregnancy results in fetal loss in more than 80% of cases^{Footnote 19}.

Animals are not known to display symptoms of disease associated with infection through natural exposure.

Epidemiology

LASV was first described in Sierra Leone in the 1950s but was not identified until 1969 in Nigeria^{Footnote 19}. The virus is endemic in West Africa (Sierra Leone, Liberia, Guinea, Nigeria, Ghana, Mali, Senegal), with infrequent reports of imported cases outside the area of endemicity^{Footnote 10Footnote 19Footnote 21Footnote 22}. LASV has four established lineages, I–IV, and three additional lineages (V–VII) recently discovered based on phylogenetic analysis of human and rodent samples^{Footnote 23}. These lineages are distributed in geographically determined clusters, with lineages I–III found in Nigeria and lineage IV present in Sierra Leone, Guinea, and Liberia. The proposed additional lineages include lineage V from Mali and Côte d'Ivoire, lineage VI from Nigeria, and lineage VII from Benin, Ghana, and Togo^{Footnote 23Footnote 24}. Due to limitations in accurate diagnosis^{Footnote 22}, limited testing for the virus, and under-reporting of infections, the annual number of infections and fatalities is difficult to determine^{Footnote 22Footnote 25}. An estimated 300,000 to 500,000 infections resulting in 5,000 to 10,000 deaths are presumed to occur annually^{Footnote 26Footnote 27Footnote 28}. The case fatality rate is approximately 1-2%, but reach 15% among hospitalized patients, or higher during outbreaks^{Footnote 5Footnote 9}.

The largest recorded outbreak of Lassa fever occurred in Nigeria in 2018, with 1,849 suspected cases reported on April 15, 2018^{Footnote 29}. Among 413 confirmed and 9 probable Lassa fever cases, 114 deaths were reported, with a case fatality rate of ~25% for confirmed cases^{Footnote 29}. Another outbreak was reported in Nigeria between January 3 and 30, 2022, with 211 laboratory-confirmed cases, including 40 deaths, for a case fatality rate of 19%^{Footnote 30}.

LASV infection may occur in any demographic group; however, individuals at greatest risk are those living in or visiting endemic regions, including Sierra Leone, Liberia, Guinea, and Nigeria, and those who have exposure to the multimammate rat^{Footnote 31}. The majority of cases are reported in individuals between 30 and 39 years of age and in rural areas, due to increased likelihood of exposure with Mastomys rodents, poor sanitation, or crowded living conditions^{Footnote 9Footnote 18Footnote 19Footnote 32}.

Disease is more severe during pregnancy; fetal loss occurs in the majority of cases, likely a result of the viral affinity for placental tissue, and maternal death is frequent^{Footnote 5Footnote 19}. The mortality rate for fetuses in early pregnancy is 92%, 75% for fetuses in the third trimester and 100% for full-term babies in the neonatal period^{Footnote 19}.

Host range

Natural host(s)

Humans and rodents are the natural hosts for LASV^{Footnote 28Footnote 33Footnote 34}. Mastomys natalensis, a rodent commonly referred to as the multimammate rat, is the main natural animal host for LASV^{Footnote 33Footnote 35}. Other rodents, including Hylomyscus pamfi and Mastomys erythroleucus, have been suggested as possible secondary hosts.

Other host(s)

Experimentally infected animals susceptible to LASV include guinea pigs (particularly the strain 13 breed), mice, and non-human primates (macaques and marmosets)^{Footnote 36Footnote 37Footnote 38Footnote 39}.

Infectious dose

Viral hemorrhagic fevers have an infectious dose of 1-10 organisms for aerosol infection in non-human primates^{Footnote 40}. The prototypic Josiah strain is the most commonly used LASV strain in experimental studies and is known to induce severe disease in non-human primate models^{Footnote 41}, with 100% lethality reported in macaques administered an inoculum of 200 to 300 plaque forming units (PFU) in aerosol format using a head-only chamber^{Footnote 42}. The median infectious dose for LASV for guinea pigs is 15 PFU by full-body chamber exposure^{Footnote 43}.

Incubation period

The incubation period spans 3-21 days (average 10 days)^{Footnote 5Footnote 9Footnote 14Footnote 19}. The virus is shed in urine for 3-9 weeks and in semen for up to 3 months post-infection^{Footnote 35}.

Communicability

Human-to-human transmission may occur following intimate contact with infected individuals, or contact with tissues or bodily secretions (e.g., blood, urine, feces) from infected individuals^{Footnote 9Footnote 10Footnote 15}. Sexual transmission of LASV has also been reported^{Footnote 35}. Risk of person-to-person transmission persists after recovery as the virus is shed in urine for 3-9 weeks and in semen for up to 3 months post-infection^{Footnote 35}. Casual contact has not been identified as a route of transmission.

Aerosol transmission may also occur when individuals come into contact with aerosol secretions in the form of sneezing or airborne droplets from contaminated urine^{Footnote 10Footnote 14Footnote 20}. Evidence of aerosol transmission is derived from epidemiological studies as well as experimental studies in guinea pigs and non-human primates, wherein susceptible guinea pigs (whole body chamber) and non-human primates (head-only chamber) were exposed to aerosolized LASV produced by a nebulizer under controlled temperature (24°C or 32°C) and humidity (30%)^{Footnote 42Footnote 43}.

Section III – Dissemination

Reservoir

The primary reservoir is the multimammate rat (Mastomys natalensis) which remains a carrier throughout its lifespan without displaying clinical symptoms^{Footnote 3Footnote 19Footnote 28Footnote 33}. Hylomyscus pamfi and Mastomys erythroleucus are also possible alternative host reservoirs^{Footnote 34}.

Zoonosis

Zoonotic transmission may occur from the multimammate rat to humans^{Footnote 20Footnote 32Footnote 44} through direct contact with infected rodents or their excretions, inhalation of infectious aerosols derived from rodent body fluids, urine or feces, or upon rodent consumption^{Footnote 10Footnote 32}. Contact via the fecal-oral route or respiratory tract can lead to infection in humans^{Footnote 19Footnote 20Footnote 32}.

Vectors

None.

Section IV – Stability and viability

Drug susceptibility/resistance

Ribavirin has been shown to reduce mortality (from about 55% to 5%) when administered within the first 6 days upon the onset of fever^{Footnote 9Footnote 15Footnote 18Footnote 19}. As diagnosis is often delayed or not determined, ribavirin is not always provided^{Footnote 18}. Drug resistance is unknown.

Susceptibility to disinfectants

LASV is susceptible to 0.5% sodium hypochlorite, phenolic compounds with detergent (0.5% phenol), 10% formalin, and 3% acetic acid (15-minute exposure)^{Footnote 19Footnote 45}.

Physical inactivation

LASV is labile to heat from 56-100°C and pH range between 5.5 and 8.5, or 1 hour at 60°C^{Footnote 5Footnote 19Footnote 45}, autoclaving, incineration, boiling^{Footnote 5}, gamma irradiation^{Footnote 19Footnote 46}, and UV-C irradiation^{Footnote 47}.

Survival outside host

LASV contained within biological samples and specimens can remain viable for 30 days or longer^{Footnote 19}. The biological half-life of the Josiah strain in aerosol maintained at 30% relative humidity was experimentally determined to be 10.1 and 54.6 minutes at 38°C and 24°C, respectively^{Footnote 43}. Viral solutions that were allowed to desiccate on a glass surface maintained 10% viability after 58.2 hours when maintained at 20-25°C and 30-40% relative humidity in covered dishes, which prevented exposure to light^{Footnote 48}. When incubated in rat blood at room temperature (19-22°C), LASV was experimentally determined to survive between 24 and 48 hours in an open tube, while incubation in a sealed tube yielded survival times of 48 hours or longer^{Footnote 49}.

Section V – First aid/medical

Surveillance

LASV can be diagnosed from viral isolates from excretions, blood, serum, or other tissues^{Footnote 4Footnote 22Footnote 50Footnote 51Footnote 52}. The preferred test for diagnosis is viral isolation in cell culture. LASV can also be identified using conventional reverse transcriptase (RT)-PCR, real-time RT-PCR, indirect ELISA, or an indirect fluorescent antibody test.

Note: The specific recommendations for surveillance in the laboratory should come from the medical surveillance program, which is based on a local risk assessment of the pathogens and activities being undertaken, as well as an overarching risk assessment of the biosafety program as a whole. More information on medical surveillance is available in the Canadian Biosafety Handbook (CBH).

First aid/treatment

Ribavirin has been shown to improve patient prognosis when provided within 7 days following infection^{Footnote 9Footnote 15Footnote 18}. Favipiravir has also proven successful at treating cynomolgus macaques and guinea pigs infected with LASV but has not yet been approved for use in humans^{Footnote 53}. The novel antiviral drug LHF-535 has been suggested for a Phase 1a human clinical trial^{Footnote 54}. Supportive care, including fluid replacement, electrolyte balancing, and oxygen supplementation as well as dialysis, when indicated, are considered primary medical interventions for Lassa fever cases^{Footnote 55}.

Note: The specific recommendations for first aid/treatment in the laboratory should come from the post-exposure response plan, which is developed as part of the medical surveillance program. More information on the post-exposure response plan can be found in the CBH.

Immunization

No vaccine currently available. However, several candidate vaccines have been developed. Replication-competent vaccines include a vesicular stomatitis virus (VSV)-based LASV vaccine (the same VSV vaccine platform used to produce the Ebolavirus vaccine), Vaccinia virus-based vaccines (Lister, NYBH), ML29 and YFV17D^{Footnote 56}. Other vaccines include inactivated LASV, Alphavirus replicon and DNA/electroporation. An inactivated recombinant LASV and rabies vaccine candidate (LASSARAB) has proven effective in both mouse and guinea pig models^{Footnote 57}.

Note: More information on the medical surveillance program can be found in the CBH, and by consulting the Canadian Immunization Guide.

Prophylaxis

Ribavirin may reduce mortality after infection when administered within 7 days following infection^{Footnote 9Footnote 15Footnote 18}.

Note: More information on prophylaxis as part of the medical surveillance program can be found in the CBH.

Section VI – Laboratory hazard

Laboratory-acquired infections

A few laboratory-acquired infections have been suggested, but there is only one documented case of an investigator who became infected after working with tissue cultures and mice infected with LASV in 1970, with prodromal symptoms including malaise, shivering, and severe pain in the lower portion of both thighs, followed by severe, systemic, and febrile disease characterized by myositis, myocarditis, and thrombocytopenia^{Footnote 58Footnote 59Footnote 60Footnote 61Footnote 62}. Other infections have been reported in hospital environments^{Footnote 5Footnote 61}.

Note: Please consult the Canadian Biosafety Standard (CBS) and CBH for additional details on requirements for reporting exposure incidents. A Canadian biosafety guideline describing notification and reporting procedures is also available.

Sources/specimens

Blood, feces, respiratory and pharyngeal secretions, urine, semen, throat swab, vomit, saliva, tissues from human or animal hosts, and rodent excreta^{Footnote 5Footnote 44}.

Primary hazards

Respiratory exposure to infectious aerosols, mucous membrane exposure to infectious droplets, and accidental parenteral inoculation are the primary hazards associated with exposure to LASV^{Footnote 5Footnote 43Footnote 63}.

Special hazards

Work with, or exposure to, rodents that are naturally or experimentally infected represents a risk of human infection^{Footnote 3Footnote 34Footnote 64}.

Section VII – Exposure controls/personal protection

Risk group classification

LASV is a Risk Group 4 Human Pathogen and Risk Group 4 Animal Pathogen^{Footnote 65} as well as a Security Sensitive Biological Agent (SSBA).

Containment requirements

Containment Level 4 facilities, equipment, and operational practices outlined in the CBS for work involving infectious or potentially infectious materials, animals, or cultures.

Note that there are additional security requirements, such as obtaining a Human Pathogens and Toxins Act Security Clearance for work involving SSBAs.

Protective clothing

The applicable Containment Level 4 requirements for personal protective equipment and clothing outlined in the CBS to be followed. The use of a positive-pressure suit or use of a Class III biological safety cabinet (BSC) line is required for all work with RG4 pathogens.

Note: A local risk assessment will identify the appropriate hand, foot, head, body, eye/face, and respiratory protection, and the personal protective equipment requirements for the containment zone must be documented.

Other precautions

All activities involving open vessels of regulated materials are to be performed in a certified BSC or other appropriate primary containment device. Centrifugation of infected materials must be carried out in closed containers placed in sealed safety cups, or in rotors that are unloaded in a BSC. The integrity of positive pressure suits must be routinely checked for leaks. The use of needles, syringes, and other sharp objects to be strictly limited. Open wounds, cuts, scratches, and grazes are to be covered with waterproof dressings Additional precautions must be considered with work involving animal activities.

Section VIII – Handling and storage

Spills

The spill area is to be evacuated and secured. Aerosols must be allowed to settle for a minimum of 30 minutes. For spills outside of a BSC, air supply to positive-pressure suits must be ensured. Positive-pressure suits that have been in contact with the regulated materials must be completely decontaminated by following procedures for gross decontamination of a positive-pressure suit. Plastics to be transferred to a dishpan, which should be moved to the BSC. Spills of potentially contaminated material to be covered with absorbent paper-based material (e.g., paper towels), liberally covered with an effective disinfectant (e.g., 5% MicroChem), and left to soak for at least 5 minutes before being wiped up. Following the removal of the initial material, the disinfection process are to be repeated. After disinfection, inform the appropriate internal authority (e.g., containment zone supervisor, BSO) of the incident.

Disposal

All materials/substances that have come in contact with the regulated materials must be completely decontaminated before they are removed from the containment zone. This can be achieved by using decontamination technologies and processes that have been demonstrated to be effective against the regulated materials, such as chemical disinfectants, autoclaving, irradiation, incineration, an effluent treatment system, or gaseous decontamination (CBH).

Storage

The applicable Containment Level 4 requirements for storage outlined in the CBS are to be followed. Pathogens, toxins, and other regulated materials to be stored inside the containment zone.

Inventory of Risk Group 4 (RG4) pathogens and SSBAs in long-term storage to be maintained and to include:

• specific identification of the pathogens, toxins, and other regulated materials
• a means to allow for the detection of a missing or stolen sample in a timely manner

Section IX – Regulatory and other information

Canadian regulatory information

Controlled activities with Lassa virus require a Human Pathogen and Toxin Licence issued by the Public Health Agency of Canada. It is also a Emerging animal disease; therefore, importation of Lassa virus requires an import permit under the authority of the Health of Animals Regulations, issued by the Canadian Food Inspection Agency.

Note that there are additional security requirements, such as obtaining a Human Pathogens and Toxins Act Security Clearance, for work involving SSBAs.

The following is a non-exhaustive list of applicable designations, regulations, or legislations:

• Human Pathogen and Toxins Act and Human Pathogens and Toxins Regulations
• Health of Animals Act and Health of Animals Regulations
• Quarantine Act
• Transportation of Dangerous Goods Regulations
• National Notifiable Disease (human)

Last file update

March 2023

Prepared by

Centre for Biosecurity, Public Health Agency of Canada.

Disclaimer

The scientific information, opinions, and recommendations contained in this Pathogen Safety Data Sheet have been developed based on or compiled from trusted sources available at the time of publication. Newly discovered hazards are frequent and this information may not be completely up to date. The Government of Canada accepts no responsibility for the accuracy, sufficiency, or reliability or for any loss or injury resulting from the use of the information.

Persons in Canada are responsible for complying with the relevant laws, including regulations, guidelines and standards applicable to the import, transport, and use of pathogens in Canada set by relevant regulatory authorities, including the Public Health Agency of Canada, Health Canada, Canadian Food Inspection Agency, Environment and Climate Change Canada, and Transport Canada. The risk classification and related regulatory requirements referenced in this Pathogen Safety Data Sheet, such as those found in the Canadian Biosafety Standard, may be incomplete and are specific to the Canadian context. Other jurisdictions will have their own requirements.

Copyright ^© Public Health Agency of Canada, 2023, Canada