in the total white cell count (particularly the lymphocytes), a decrease in the platelet count, an increase in the blood serum liver enzymes, and reduced blood clotting ability measured as an increase in both the prothrombin (PT) and activated partial thromboplastin times (PTT). The hematocrit may be elevated. The serum urea and creatine may be raised but this is dependent on the hydration status of the patient. The bleeding time tends to be prolonged. Prevention With the exception of yellow fever vaccine and Ebola vaccines, vaccines for VHF-associated viruses are generally not available. Post-exposure prophylactic (preventive) ribavirin may be effective for some bunyavirus and arenavirus infections. VHF isolation guidelines dictate that all VHF patients (with the exception of dengue patients) should be cared for using strict contact precautions, including hand hygiene, double gloves, gowns, shoe and leg coverings, and face shield or goggles. Lassa, CCHF, Ebola, and Marburg viruses may be particularly prone to nosocomial (hospital-based) spread. Airborne precautions should be utilized including, at a minimum, a fit-tested, HEPA filter-equipped respirator (such as an N-95 mask), a battery-powered, air-purifying respirator, or a positive pressure supplied air respirator to be worn by personnel coming within 1,8 meter (six feet) of a VHF patient. Groups of patients should be cohorted (sequestered) to a separate building or a ward with an isolated air-handling system. Environmental decontamination is typically accomplished with hypochlorite (e.g. bleach) or phenolic disinfectants. Management Medical management of VHF patients may require intensive supportive care. Antiviral therapy with intravenous ribavirin may be useful in Bunyaviridae and Arenaviridae infections (specifically Lassa fever, RVF, CCHF, and HFRS due to Old World Hantavirus infection) and can be used only under an experimental protocol as IND approved by the U.S. Food and Drug Administration (FDA). Interferon may be effective in Argentine or Bolivian hemorrhagic fevers (also available only as IND). Epidemiology Cocoliztli in Mexico 1545 and 1576. The Great Yellow Fever Epidemic of 1793 in Philadelphia, PA, US. Nearly 10% of the population of 50,000 died from the disease. Mékambo in Gabon is the site of several outbreaks of Ebola virus disease. Orientale Province, Democratic Republic of the Congo villages of Durba and Watsa were the epicenter of the 1998–2000 outbreak of Marburg virus disease. Uíge Province in Angola was the site of another outbreak of Marburg virus disease in 2005, the largest one to date of this disease. A VHF outbreak in the village