Lassa Fever

Lassa fever, first described in 1969 in Lassa, is an acute viral hemorrhagic fever. Clinical cases were known a decade before this but were not associated with this viral pathogen. It is endemic in West African countries and causes approximately 5,000 deaths.

The Natal Multimammate Mouse is the primary animal host. The rodent is a source of protein but the virus is usually transmitted by the contact with the feces and urine of animals accessing grain stores in residences. The lassa virus is a member of the Arenavirdae family and is a single-stranded, bisegmented RNA virus.

The Lassa virus replicates very quickly. The first step is making mRNA copies of the ““ sense genome. Lassa has four lineages, three were found in Nigeria and the fourth in Guinea, Liberia, and Sierra Leone.

It will infect nearly every tissue in the human body starting with the mucosa, intestine, lungs, and urinary system and then progressing to the vascular system. It is zoonotic. The rats that carry the virus have the infection in an asymptomatic state. The virus is then shed in excreta.

Human infection typically occurs via exposure to animal excrement usually through inhalation of tiny particles of infective material. It is possible to acquire the infection through broken skin or mucous membranes. It can be transmitted from human to human. Since it would be impossible to control the rodent population the best measures are to limit rodent access to homes and food supplies. Disease is not apparent in 80% of cases while the remaining 20% is more complicated. The virus is estimate to cause about 5,000 deaths annually.

Laboratory investigations are performed to diagnose the disease and assess its course and complications. Overall mortality rate is 1% however during epidemics it can climb up to 50%. Ribavirin treatment has helped to lower these rates. These treatments were started by Joe McCormick in 1979. It is nearly twice as effective when give intravenously than when taken by mouth.