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Lassa fever is a viral hemorrhagic fever caused by an RNA virus of the arenavirus family. It is most common in a large region of West Africa, and is named after the Nigerian town where it was first discovered by Western medical professionals. It is animal-borne, and the vector is a species of rat named Mastomys natalensis. Besides Nigeria it is endemic in Guinea, Liberia, and Sierra Leone. It is also found sporadically in neighboring countries due to the distribution of the rat’s habitat over the whole region.
The mortality due to Lassa fever is about 5000 deaths a year, out of 100,000 to 300,000 cases. The death rate depends on the severity of illness. Up to 20% of hospitalized patients die of the infection, but the mortality shoots up to 50% during an epidemic. In contrast, about 1% of all infected cases die.
The virus is shed in the urine and feces of infected rats for possibly the whole lifetime of the animal. This rat is widespread throughout the forests and grasslands of West and Central Africa. It is also common inside homes and food storage areas, leading to a high frequency of transmission to humans.
The infection may be acquired through:
The symptoms take up to 3 weeks to manifest, and are so mild as to be ignored in about 80% of cases. They start with a low fever, tiredness, malaise, body aches, a sore throat and headache. There may be nausea and vomiting, or diarrhea.
In more serious cases, high fever develops, along with symptoms such as:
Death occurs within 2 weeks in seriously sick patients, and is due to the failure of multiple organs. Death is preceded by the occurrence of widespread bleeding into the skin, the mucosa and internal organs.
Complications of the disease include:
Diagnosis is by:
Treatment with Ribavirin is quite effective, but needs to be given in the earlier stages of infection, in the first 6 days.
Supportive treatment with oxygen, intravenous fluids, antibiotics for other complicating infections and respiratory support are all vital in maximizing the chances of recovery.
Exposure to a large population of infected rats or humans is an effective means of virus transmission.
To prevent rat-human transmission, contact between the rats and humans should be minimized:
The infected person sheds the virus in their urine for up to 9 weeks following infection, and in semen for up to 3 months. Sexual contact of any sort should be avoided during this period.
In the healthcare system, the use of barrier nursing precautions is very effective in limiting the spread of infection: