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Ebola Virus

Ebola Virus

In 1976, two large outbreaks of a mysterious disease occurred almost simultaneously in Sudan and in the Democratic Republic of the Congo (DRC) (then known as Zaire). Over 500 total cases of disease were reported, with death rates of 53 percent in Sudan, and 88 percent in the DRC. One doctor recording details of the outbreak in the DRC wrote, “the illness is characterized with a high temperature of about 39°C (102°F), hematemesis (vomiting of blood), diarrhea with blood . . . and rapid evolution death after a mean of three days.” This disease was later named Ebola hemorrhagic fever, after a river in the Congo near the outbreak location, and the causative virus was named Ebola virus.

Ebola virus is one of two members of the filovirus family. Filoviruses have RNA as their genetic material; a long, filament-like shape; and cause severe hemorrhagic disease primarily in primates. The other known filovirus is Marburg virus, first identified in Germany in 1967.

Despite extensive research efforts, the natural reservoir of Ebola virus has not been identified. Scientists believe the virus is zoonotic, or animal-borne, and that humans and other primates most likely contract the virus through contact with host animals. Some research has pointed to bats as carriers, but this has not yet been confirmed.

There are five strains, or subtypes, of Ebola virus, all named for the locations in which they first occurred. Ebola Bundibugyo was most recently identified in Uganda in 2007. Ebola Zaire, Ebola Sudan, and Ebola Bundibugyo subtypes cause severe disease in humans. Ebola Reston and Ebola Ivory Coast have not been known to cause disease in humans. Before last year, Ebola Reston and Ebola Ivory Coast had only been known to cause disease in nonhuman primates. However, in 2008, pigs in the Philippines were found to have died from Ebola Reston. As of January 2009, one farm worker has become infected with Ebola Reston through contact with infected pigs, but has not become ill. This constitutes the first known instance of pig-to-human transmission of the Ebola virus.

In humans, the onset of symptoms is usually rapid with Ebola infections following an incubation period of 2-21 days. Initial symptoms are nonspecific (fever, joint and muscle aches, weakness, etc.), and can be associated with other more common and less deadly diseases. Because of this, early diagnosis of Ebola is difficult. Symptoms progress to vomiting, diarrhea, impaired kidney and liver function, and internal and external bleeding. The virus causes damage to almost every organ in the body and the cause of death is usually shock due to blood and fluid loss. The mortality rate of Ebola outbreaks has been between 50-90 percent.

Once a person has become infected with Ebola, the virus can be transmitted from person to person through contact with infected body fluids or contaminated objects, such as needles. Because of the dangerous nature of the virus, research on Ebola virus must be conducted in a level-4 biocontainment facility. Healthcare workers should take strict precautions when treating Ebola patients, including using protective gloves, masks, and gowns. However, materials such as protective clothing and disposable needles are not always used, or available, in countries where Ebola outbreaks occur. This leads to high rates of infection in healthcare workers and family members caring for Ebola patients.

No specific treatment is available for Ebola hemorrhagic fever. An Ebola vaccine has been developed by the National Institutes of Health (NIH), and is currently being tested in clinical trials. The challenge in vaccine and treatment development for Ebola hemorrhagic fever is the rapid progress of the disease. Unless a vaccine or other form of supportive treatment is administered soon after the onset of symptoms, the virus causes too much physical damage to bodily organs to be repaired or overcome.

As a potential biological weapons agent, Ebola could be effective due to its high mortality rate and level of contagiousness, as well as its availability in nature.