The thought of Ebola hemorrhagic fever should scare any rational person. It is a severe viral illness, with no cure or vaccine to prevent it. Outbreaks appear at random. Images of health care workers in bio-hazard suits treating Ebola patients call to mind every pandemic movie made in the last thirty years.
Ebola was first identified as an illness in 1976, when two separate outbreaks of the illness were seen in remote areas of the Congo and the Sudan. There are five sub-species of Ebolavirus and four of those are infectious to humans. The Centers for Disease Control list these as "Ebola virus (Zaire ebolavirus); Sudan virus (Sudan ebolavirus); Taï Forest virus (Taï Forest ebolavirus, formerly Côte d’Ivoire ebolavirus); Bundibugyo virus (Bundibugyo ebolavirus) ... Reston virus (Reston ebolavirus)". Ebola takes its name from the Ebola River near where the the first cases were identified. The various sub-species take their names from the locations where they were identified as the cause of an outbreak.
Only the Reston virus is not infectious to humans. Sort of. Stanford University describes two outbreaks of Reston Ebola viral illness in monkeys. The first outbreak was in a monkey quarantine facility in Reston, Virginia. The Philippine government investigated the sources of the monkeys that were infected in Reston and discovered signs of exposure to the virus in a breeding farm in that nation.
In both locations, human handlers were found to have evidence of Ebola antibodies in their blood. None seem to have exhibited symptoms but they were clearly exposed, and their immune systems reacted to the exposure to the Reston virus. The belief that Reston does not infect humans is far from certain.
Ebola viruses infect a variety of other species in the tropical rain forest. The World Health Organization (WHO) notes that Ebola infections in Africa have been traced to human exposures to "infected chimpanzees, gorillas, fruit bats, monkeys, forest antelope and porcupines found ill or dead or in the rainforest."
Symptoms of Ebola, from the WHO, are:
... sudden onset of fever, intense weakness, muscle pain, headache and sore throat. This is followed by vomiting, diarrhea, rash, impaired kidney and liver function, and in some cases, both internal and external bleeding. Laboratory findings include low white blood cell and platelet counts and elevated liver enzymes.
Health care workers and family members may become infected with Ebola though contact with the bodily fluids of infected patients. This is the reason that bio-hazard suits are used by physicians and other medical personnel. The fatality rate for patients with Ebola varies with the sub-species of virus and the amount of supportive care that the patient receives. Mortality rates range from 25 to 80 percent.
All Ebola illnesses in humans have occurred in Africa other than a handful of lab accidents. All Ebola fatalities have been in Africa. Until the latest outbreak, all of the African illnesses have been in rural, remote areas of their respective nations.
The CDC reports a total of 34 Ebola outbreaks from 1976 to May 2014. The list includes three lab accidents which resulted in one fatality. It also includes three instances where humans have tested positive for Reston Ebola antibodies with no illnesses. The list also notes at least four instances of Reston Ebola in monkeys and pigs.
The largest Ebola outbreak on record is still underway as of this writing. In West Africa, Zaire Ebola appeared in March 2014. As of the June 24 WHO Ebola outbreak update, there have been 599 confirmed, probable or suspected cases of Ebola in three countries. A total of 341 Ebola-related fatalities have been recorded for a patient death rate of 56.9 percent. This is the first Ebola outbreak to have moved into densely populated urban areas.