Primary prevention
Vaccination:
There are no vaccines licensed for use in humans. Inactivated Lassa viral vaccine or live attenuated virus vaccines have shown promise in animal models, but safety concerns around the use of live vaccines for this and other viral haemorrhagic fevers have limited their development. Subunit vaccines have demonstrated insufficient protection in animal models so far.[1] Recombinant viral vector vaccines using vaccinia virus, vesicular stomatitis virus, or yellow fever virus vaccine strain have shown more promise, along with cross-protecting alpha-virus DNA or alpha-virus-derived virus-like particle vaccines.[1] A recombinant, live attenuated, measles virus vector-based vaccine called MV-LASV has been studied in one phase 1 trial to determine optimal dosing.[23] Another vaccine, using a recombinant vesicular stomatitis virus (rVSV) vector backbone, is being investigated in one phase 1 trial to evaluate its safety and immunogenicity in healthy adults.[24]
Preventing animal-to-human transmission:
In endemic areas, avoiding contact with the multimammate rat (Mastomys natalensis), the natural host of the Lassa virus, and its excreta is the main method for primary prevention. Infected rodents will shed the virus in excreta throughout their life.
The following measures are recommended for people living in endemic areas to help discourage rodents from entering the home:[2][9]
Store foodstuff, including water, in rodent-proof containers
Dispose of waste far from the home
Maintain a clean home
Place rat traps around the home and dispose of dead rodents using a plastic bag to avoid direct contact with the carcass
Keep cats.
All foods should be cooked thoroughly
Rodents should be avoided as a food source.
Secondary prevention
Preventing nosocomial transmission:
Human-to-human transmission can be prevented by avoiding direct contact with the blood or body fluids of an infected person. Nosocomial transmission is common in endemic areas. Lassa fever is a notifiable disease; thus, healthcare workers seeing a patient suspected of having Lassa fever should immediately contact the local health authority for reporting, advice, and to arrange for laboratory testing. If Lassa fever is suspected, extra infection control measures should be applied to prevent contact with blood, body fluids, and contaminated surfaces or materials (e.g., clothing and bedding), and the patient transferred to an isolation unit. Healthcare workers should apply standard infection prevention and control precautions, regardless of the presumed diagnosis of a patient. These should include:
Basic hand hygiene
Respiratory hygiene
Use of personal protective equipment (PPE) to block splashes or other contact with infected materials
Safe injection practices
Safe burial practices.
When in close contact (within 1 metre) of patients with Lassa fever, healthcare workers should wear face protection (e.g., face shield, face mask [N95 or above], or goggles), a clean non-sterile long-sleeved gown, and gloves.[2][9]
The World Health Organization (WHO), CDC, and UK Department of Health (DoH) have produced detailed guidance on PPE for viral haemorrhagic fevers, including Ebola, and these should be followed for Lassa fever:
Preventing transmission in the laboratory setting:
Laboratory workers handling samples containing Lassa virus should be fully trained in handling contagious agents, and all work should be carried out in a suitably equipped laboratory under maximum (biosafety level 4) biological containment conditions.
Samples should only be sent to a laboratory once a full risk assessment has been carried out and following discussions with the laboratory (i.e., to alert them of potentially biohazardous material).
Post-exposure prevention:
If exposure to body fluids from a patient with suspected infection has occurred, the person should immediately wash affected skin surfaces with soap and water, and irrigate mucous membranes with copious amounts of water. The patient’s home and any personal belongings that could have been contaminated (e.g., clothes, linens, eating utensils, medical material) should be appropriately disinfected (e.g., sprayed with 0.5% chlorine solution in epidemic areas) or disposed of (usually by incineration). Safe burial practices are essential but are not always culturally accepted, and this continues to be a challenge.
There is anecdotal evidence showing the antiviral drug ribavirin to be effective for post-exposure prophylaxis (PEP) if used early, but it has significant side effects, particularly at the dose required to achieve theoretical efficacy, which often leads to poor adherence with treatment.[38] The prophylactic dose is given orally and is different to the dose used for treatment.
There is also concern that the availability of PEP for Lassa fever might result in lapses in PPE use and care. Therefore, recommendations for the use of oral ribavirin as PEP are restricted to high-risk exposures, which include:[38][39]
Penetration of skin by a contaminated instrument (e.g., needlestick)
Contamination of mucous membranes or broken skin with blood or bodily secretions (e.g., blood splashing in the eyes or mouth)
Participation in emergency procedures (e.g., resuscitation after cardiac arrest, intubation, or suctioning) without use of appropriate PPE
Prolonged (i.e., for hours) and continuous contact in an enclosed space without use of appropriate PPE (e.g., a healthcare worker accompanying a patient during medical evacuation).
Antiviral drugs (including ribavirin) are not recommended for non-exposed close contacts due to the absence of evidence of proven effectiveness as prophylaxis. UK Department of Health: management of Hazard Group 4 viral haemorrhagic fevers and similar human infectious diseases of high consequence Opens in new window
Contact tracing:
Contact tracing of individuals, including those who have travelled with, lived with, or cared for an individual with Lassa fever within the last 21 days and who are asymptomatic, should be assessed and provided with post-exposure prophylaxis if they meet high-risk exposure criteria.[38] These individuals should be monitored for the duration of the incubation period in order to ensure rapid recognition of symptoms followed by immediate isolation.
The WHO has produced guidance on contact tracing for Ebola, and this can be followed for Lassa fever: WHO: implementation and management of contact tracing for Ebola virus disease Opens in new window
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