Lassa Fever
Lassa fever is a severe and often fatal hemorrhagic illness caused by Lassa virus. Since its original discovery in 1969 in the village of Lassa in Borno State, Nigeria,
there have been countless outbreaks of various magnitude and severity across West Africa. Estimates of annual incidences of Lassa fever across this region reach as high as 300,000 infections and 5,000 deaths.
However due to scarce resources to diagnose the illness as well as inadequate surveillance, many cases remain unaccounted.
Lassa virus is a member of the Arenaviridae viru family. Humans contract the virus primarily through contact with the contaminated excreta of Mastomys
natalensis rodents (commonly known as the
Multimammate rat), which is the natural reservoir for the virus. Little is known regarding the transmission of the
virus from the rodent reservoir to the human host, although there is compelling evidence that Arenaviruses are stable and infectious by the aerosol route in
nonhuman primates. The rodents live in houses with humans and deposit excreta on floors, tables, beds and
food. Consequently the virus is transmitted to humans through cuts and scratches, or inhaled via dust particles in the air. In some regions Mastomys rodents are also
consumed as food. Secondary transmission of the virus between humans occurs through direct contact with infected blood or bodily secretions. This occurs mainly between individuals caring for sick patients although anyone who comes into close
contact with a person carrying the virus is at risk of infection. Nosocomial transmission (transmission that
occurs as a result of treatment in a hospital) and outbreaks in healthcare facilities in endemic areas represent a significant burden on the healthcare system.
In the early stages, Lassa fever is often misdiagnosed as influenza, typhoid or malaria, and as a result many
patients fail to receive appropriate medical treatment. Making a correct diagnosis of Lassa fever is made difficult by the wide spectrum of clinical effects that
manifest, ranging from asymptomatic to multi-organ system failure and death. The onset of the illness is typically indolent, with no specific symptoms that would
distinguish it from other febrile illnesses. Early signs include fever, headache and general malaise, followed by
a sore throat, nausea, vomiting, abdominal pain and diarrhea in some cases. After 4 to 7 days, many patients will start to feel better, but a small minority will
proceed to display symptoms such as edema,
hypertension, bleeding and shock. Death from Lassa
fever most commonly occurs 10 to 14 days after
symptom onset.
Because of its high case fatality rate, ability to spread
easily by human-to-human contact, and potential for
aerosol release, Lassa virus is classified as a Biosafety
Level 4 (BSL4) and NIAID Biodefense category A agent.
The potential use of Lassa virus as a biological weapon
directed against civilian or military targets necessitates
the development of counter-threat measures, such as
diagnostic assays, vaccines and therapeutics. Moreover,
the impact of the disease in endemic regions of West
Africa is immense, and therefore means to diagnose,
treat and prevent this viral hemorrhagic fever will provide
a significant public health benefit.
No vaccine for Lassa fever is currently available for use
in humans, and the only available drug, ribavirin , is only
effective if administered early in infection (within the first
6 days after disease onset). One of the hallmarks of
Lassa virus infection is the apparent absence of
functional antibodies during acute infection. A fundamental
understanding of the mechanisms of antibody-mediated
neutralization of Lassa virus may have significant
implications for the generation of antibody-based
therapeutics or epitope-targeted vaccines.

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