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Ebola Hemorrhagic Fever
Ebola hemorrhagic fever (Ebola HF) is a severe, often-fatal disease in humans and nonhuman primates (monkeys, gorillas, and chimpanzees) that has appeared sporadically since its initial recognition in 1976. The disease is caused by infection with Ebola virus, named after a river in the Democratic Republic of the Congo (formerly Zaire) in Africa, where it was first recognized. The virus is one of two members of a family of RNA viruses called the Filoviridae. There are four identified subtypes of Ebola virus. Three of the four have caused disease in humans: Ebola-Zaire, Ebola-Sudan, and Ebola-Ivory Coast. The fourth, Ebola-Reston, has caused disease in nonhuman primates, but not in humans.
The exact origin, locations, and natural habitat (known as the "natural reservoir") of Ebola virus remain unknown. However, on the basis of available evidence and the nature of similar viruses, researchers believe that the virus is zoonotic (animal-borne) and is normally maintained in an animal host that is native to the African continent. A similar host is probably associated with Ebola-Reston which was isolated from infected cynomolgous monkeys that were imported to the United States and Italy from the Philippines. The virus is not known to be native to other continents, such as North America.
Confirmed cases of Ebola HF have been reported in the Democratic Republic of the Congo, Gabon, Sudan, the Ivory Coast, Uganda, and the Republic of the Congo. An individual with serologic evidence of infection but showing no apparent illness has been reported in Liberia, and a laboratory worker in England became ill as a result of an accidental needle-stick. No case of the disease in humans has ever been reported in the United States. Ebola-Reston virus caused severe illness and death in monkeys imported to research facilities in the United States and Italy from the Philippines; during these outbreaks, several research workers became infected with the virus, but did not become ill. Ebola HF typically appears in sporadic outbreaks, usually spread within a health-care setting (a situation known as amplification). It is likely that sporadic, isolated cases occur as well, but go unrecognized. A table showing a chronological list of known cases and outbreaks is available.
Infections with Ebola virus are acute. There is no carrier state. Because the natural reservoir of the virus is unknown, the manner in which the virus first appears in a human at the start of an outbreak has not been determined. However, researchers have hypothesized that the first patient becomes infected through contact with an infected animal.
After the first case-patient in an outbreak setting is infected, the virus can be transmitted in several ways. People can be exposed to Ebola virus from direct contact with the blood and/or secretions of an infected person. Thus, the virus is often spread through families and friends because they come in close contact with such secretions when caring for infected persons. People can also be exposed to Ebola virus through contact with objects, such as needles, that have been contaminated with infected secretions. Nosocomial transmission refers to the spread of a disease within a health-care setting, such as a clinic or hospital. It occurs frequently during Ebola HF outbreaks. It includes both types of transmission described above. In African health-care facilities, patients are often cared for without the use of a mask, gown, or gloves. Exposure to the virus has occurred when health care workers treated individuals with Ebola HF without wearing these types of protective clothing. In addition, when needles or syringes are used, they may not be of the disposable type, or may not have been sterilized, but only rinsed before reinsertion into multi-use vials of medicine. If needles or syringes become contaminated with virus and are then reused, numerous people can become infected. Ebola-Reston appeared in a primate research facility in Virginia, where it may have been transmitted from monkey to monkey through the air. While all Ebola virus species have displayed the ability to be spread through airborne particles (aerosols) under research conditions, this type of spread has not been documented among humans in a real-world setting, such as a hospital or household.
What is Ebola hemorrhagic fever is one of the deadliest of a group of diseases called viral hemorrhagic fevers. They range in seriousness from relatively mild illnesses to severe and potentially fatal diseases. All forms of viral hemorrhagic fever begin with fever and muscle aches. Depending on the virus, the disease can get worse until the patient becomes very ill with breathing problems, severe bleeding (hemorrhage), kidney problems, and shock. Viral hemorrhagic fevers are caused by viruses from four families: filoviruses, arenaviruses, flaviviruses, and bunyaviruses. The usual hosts for most of these viruses are rodents or arthropods (such as ticks and mosquitoes). In some cases, the natural host for the virus is not known. What is the infectious agent that causes Ebola hemorrhagic fever is caused by several Ebola viruses. Ebola viruses are members of the filovirus family; when magnified several thousand times by an electron microscope, these viruses look like threads (filaments). Ebola virus was discovered in 1976 and named for a river in Zaire, Africa, where it was first detected. Where is Ebola hemorrhagic fever found are found in Central Africa. The source of the viruses in nature remains unknown. Monkeys, like humans, appear to be susceptible to infection and might serve as a source of virus if infected. How do people get Ebola hemorrhagic fever by direct contact with virus-infected blood, body fluids, organs, or semen. The disease is spread mainly by close person-to-person contact with severely ill patients. This happens most often to hospital-care workers and family members who care for an ill person infected with Ebola virus. Close personal contact with persons who are infected but show no signs of active disease is very unlikely to result in infection. Transmission of the virus has also been linked to the re-use of hypodermic needles in the treatment of patients. Re-using needles is a common practice in developing countries, such as Zaire and Sudan, where the health-care system is underfinanced. Medical facilities in the United States do not re-use needles. Ebola virus can be spread from person to person through sexual contact. Persons who have recuperated from an illness caused by Ebola virus can still have the virus in their genital secretions for a short time after recovery and can spread the virus through sexual activity. Who is at risk for Ebola hemorrhagic fever Hospital staff and family members who care for patients with Ebola hemorrhagic fever Central African residents of rural areas and small towns Until recently, only three outbreaks of Ebola hemorrhagic fever in humans had been reported. The first two, in 1976 in Zaire and in western Sudan, were large outbreaks that resulted in more than 550 cases and 340 deaths. The third outbreak, in 1979 in Sudan, was smaller, with 34 cases and 22 deaths. In each of these outbreaks, most cases occurred in hospitals where medical supplies were inadequate and where needles and syringes were re-used. The outbreaks were quickly controlled by isolating sick patients in a place requiring the wearing of mask, gown, and gloves; sterilizing needles and syringes; and disposing of wastes and corpses in a sanitary way. In 1995, an outbreak in Kikwit and surrounding areas in Bandundu Province, Zaire, caused 316 deaths. The outbreak was amplified in a hospital by staff who became infected through poor nursing techniques. At the request of health officials in Zaire, medical teams from CDC and the World Health Organization, and from Belgium, France, and South Africa, collaborated to investigate and control the outbreak. Two isolated cases of Ebola hemorrhagic fever were identified in Cote d'Ivoire in 1994-1995. The most recent outbreaks were in rural Gabon in 1994 and in 1996. A patient from the 1996 Gabon outbreak traveled to Johannesburg, South Africa, and fatally infected a health-worker there as well.
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