Lassa fever is an acute
viral illness that occurs in west Africa. The illness was discovered in 1969
when two missionary nurses died in Nigeria. The virus is named after the town
in Nigeria where the first cases occurred. The virus, a member of the virus family Arenaviridae,
is a single-stranded RNA virus and is zoonotic, or animal-borne.
Lassa fever is endemic
in parts of west Africa including Sierra Leone, Liberia, Guinea and Nigeria;
however, other neighboring countries are also at risk, as the animal vector for
Lassa virus, the "multimammate rat" (Mastomys natalensis) is
distributed throughout the region. In 2009, the first case from Mali was
reported in a traveler living in southern Mali; Ghana reported its first cases
in late 2011. Isolated cases have also been reported in Côte d’Ivoire and
Burkina Faso and there is serologic evidence of Lassa virus infection in Togo
and Benin.
The number of Lassa
virus infections per year in west Africa is estimated at 100,000 to 300,000,
with approximately 5,000 deaths. Unfortunately, such estimates are crude,
because surveillance for cases of the disease is not uniformly performed. In
some areas of Sierra Leone and Liberia, it is known that 10%-16% of people
admitted to hospitals every year have Lassa fever, which indicates the serious
impact of the disease on the population of this region.
CDC and the New Jersey Department of Health have confirmed a death from Lassa fever that
was diagnosed May 25 in a person returning to the United States from Liberia.
CDC is working with public health officials to identify people who had contact
with the patient. Those identified as close contacts of the patient will be
monitored for 21 days to see if symptoms occur. Updates will be provided as the
investigation continues.
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