The virus belongs to Arenaviridae[?] family; it is single-stranded RNA virus. It has been determined that the virus is zoonotic (transmitted from animals), and that it spreads to man from rodents (Mastomys[?] natalensis) in which it causes a persistent asymptomatic infection that is well tolerated by the animals.
The route of infection to humans is by respiratory tract[?] or by gastrointestinal tract when someone comes in contact with excrement of an infected rodent or eats some food contaminated with animal excrement. Inhalation of tiny particles of infective material (aerosol) is believed to be the most significant. It is also possible to acquire the infection through broken skin or mucous membranes that are directly exposed to infective material. Another route of transmission is man-to-man transmission when someone comes in close contact with an disease-stricken person. Similarly healthcare personnel can contract the disease while caring for Lassa fever patients.
In 80% of cases the disease is inapparent but in the remaining 20% it takes a complicated course. It is estimated (no definitive data exist) that the virus is responsible for about 5000 deaths annually.
After an incubation period of 5-21 days, an acute illness with multiorgan involvement develops. Nonspecific symptoms include fever, facial swelling, and muscle fatigue as well as conjunctivitis and mucosal bleeding. The other symptoms arising from the affected organs are:
Control of the Mastomys rodent population is impractical, so measures are limited to keeping rodents out of homes and general food and personal hygiene. Gloves, masks, white coats, and goggles are advised while in contact with or caring for a sick person. No vaccine is available yet, although it is being worked on. Another virus (Mozambique virus[?]) that highly resembles the deadly Lassa virus but without it lethal effects can act as a form of vaccine.
Symptomatic and supportive therapy is crucial but recently a new drug--ribavirin--has been used in Lassa fever infection with success. The drug interferes with the virus metabolism, decreasing its replication. It is important to administer the drug early in the course of the disease. However the cost of the drug can be a setback especially in poverty-stricken West African states. Fluid replacement and fighting hypotension is usually required.
About 15%-20% of hospitalized patients with the illness will die. It is guessed that the overall mortality is 1%, however during epidemics mortality can be as high as 50%. Thanks to new treatment with ribavirin there are great prospects for improvement. Needless to say that the vaccine would be the best option.
You may want to consult Center for Disease Control Site (http://www.cdc.gov/travel/diseases/lassa.htm) for additional information.