Lassa virus has been classified by the CDC as a Category A bioterrorism agent due to its ease of aerosol dissemination and ability to infect with very few organisms. One or more of the arenaviruses are known to have been weaponized by the Russians; therefore, any outbreak should be highly suspect for bioterrorism. The most likely method of dispersal of Lassa virus would be by aerosol release, but it is also contagious by contact with infected body fluids and tissues. The mortality rate is 15% in hospitalized patients (1% overall), although it can be up to 50% during occasional epidemics.

About Lassa fever: Lassa fever refers to systemic infection with the Lassa virus from the genus Arenavirus of the Arenaviridae family. This genus is divided into two groups based on the location of the rodent reservoir: Old World (Eastern hemisphere) or New World (Western hemisphere). The diseases all share a common feature of most commonly being transmitted to humans by contact with food or household items contaminated with native rodent urine or excreta. Person-to-person transmission is possible through direct contact with infected tissues and body fluids or by aerosol inhalation. Transmission may also occur from contaminated medical equipment.

The Old World Arenaviridae include Lassa virus (from West Africa) and lymphocytic choriomeningitis virus (found in Europe, Asia, and the Americas) as well as Lujo virus (isolated in South Africa; patients develop Lujo-associated hemorrhagic fever, which has a high case fatality rate [80%], after inhalation of dust containing the virus, by ingestion of contaminated foods, or by inoculation with infected body materials). Lassa virus is enzootic in the West African multimammate mouse Mastomys natalensis. Outbreaks have been reported in several countries of West Africa. It is endemic in Nigeria, Sierra Leone, Guinea and Liberia, where outbreaks occur annually, often during the dry season. Rarely, imported cases occur outside of endemic regions. It is rarely seen in the United States or Europe; bioterrorism should be suspected in any case outside of Western Africa.

Clinical presentation: Whether acquired naturally or as a result of a bioterrorist attack, the symptoms of Lassa fever may be mild or subclinical in up to 80% of cases, although symptomatic cases would likely be higher following a bioterrorist attack due to the higher initial level of exposure. Symptoms for the more severe cases, which appear gradually after an incubation period of approximately 7-14 days, include fever, malaise, dizziness, headache, sore throat, cough, nausea, vomiting, diarrhea, myalgia, chest pain, abdominal pain, back pain, cervical adenopathy, proteinuria, flushing of the face and trunk, and conjunctivitis. Small axillary petechiae may be noted. In some cases, the disease progresses to facial edema, neck swelling, pleural effusion, hemorrhages, seizures, encephalopathy, hypotension, and shock. Additionally, hair and hearing loss may occur. Spontaneous abortion occurs in 80% of cases involving pregnant patients.

Precautions: Use airborne and contact precautions such as gloves, gown, hand washing, splash precautions, and HEPA or equivalent mask when cleaning rodent nests or treating patients with suspected Lassa virus infection. Isolate confirmed cases of Lassa fever. Lassa fever must be reported immediately to the local department of health and/or the CDC.