Ebola Ebola hemorrhagic fever is one of the most virulent diseases known. After a 2-to 21-day incubation period, victims develop a fever, followed by chest and abdominal pain, diarrhea, and reduced liver and kidney function. Its pathogenic reputation is a result of the extensive internal and external bleeding in the late stage of the disease as the body tissues break down. Its natural host is unknown. For more information on Ebola, use the search engine on the World Health Organization WWW Home Page.

Four Corners (FC) This virus is one of several that cause Hanta Pulmonary Syndrome (HPS). Initial symptoms include fever, chills, and muscle pain, which are followed by severe problems with the respiratory, circulatory, and immune systems. The natural host of FC is the deer mouse. The virus's unusual name comes from the place where it was first identified in 1993, the Four Corners region of the United States (where the corners of Utah, Arizona, Colorado, and New Mexico meet). By January 1995, 122 cases of FC-caused HPS had been reported throughout 21 U.S. states, Brazil, and Canada. FC is one of several in the Hantavirus genus.

Human Immunodeficiency Virus (HIV) This virus causes Acquired Immune Deficiency Syndrome (AIDS), which is an infectious disease characterized by a breakdown of the body's immune system. HIV is spread through direct contact with infected bodily fluids. At least 13 million people have been infected worldwide. By the year 2000, it is projected that number will triple.

Human T-cell Lymphotropic Virus Type 1 (HTLV-1) This virus is transmitted through infected bodily fluids and has spread to all continents. In less than 5% of infected people, it causes adult T-cell leukemia and lymphoma, which are often fatal. HTLV and HIV are the only known human retroviruses.

Lassa This virus, which has been distributed over much of West Africa, is carried by a mouse that has a strong inclination to invade homes and an expert ability to avoid traps. Symptoms include fever and hemorrhage. Infections in Africans have resulted in less than 1% mortality or serious illness; mortality rates in people of non-African descent is much higher.

Marburg This virus causes a hemorrhagic fever similar to that caused by Ebola virus. Marburg was identified in 1967, when African green monkeys from Uganda infected 25 laboratory workers in Marburg, Germany. Six secondary infections also occurred among medical personnel and family members. The natural host of the virus is unknown. Marburg virus became the first member of the filovirus family (Filorviridae), which includes Ebola virus.

Oropouche This virus causes a serious, though non-fatal illness. Symptoms include fever, headache, muscle pains, and meningitis. Its natural host is a tiny fly called the biting midge. An outbreak occurred in 1991 in Belem, Brazil, where more than 11,000 residents became infected.

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