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Ebola FAQ: Frequently Asked Questions

Compiled by David Ornstein and Kai Matthews

Last Updated 5/26/95


Please send your favorite Frequently Asked Question to us. Send the answer, too, if you can. Don't forget the references when possible.


This page is an ongoing attempt to fill in the blanks for those who may be coming across this Ebola site with little or no previous general knowledge of Ebola. This page is specifically not designed to be a complete collection of information about Ebola; it serves as an introduction to the subject.


A Note about Scientific Precision

There are some places in this FAQ which give only the basic answer to the question. This is not an attempt to exclude information, but an attempt to give a concise answer. The difference between 99% and 100% accuracy is often somewhere between multiple paragraphs and an advanced degree in virology (which I don't have, by the way). If you want the complete answer, study the subject in depth.


Table of Contents

What exactly is Ebola?
What varieties are known to exist?
How do these varieties differ?
How long is the incubation period/onset of symptoms?
What are the symptoms?
How does it damage (and usually kill) its victims?
How is it transmitted?
Is Ebola airborne?
Geographically, where does Ebola come from?
What is the natural reservoir for Ebola?
What is the probability of Ebola mutating and becoming airborne?
What has caused Ebola epidemics to end in past occurrences?
Can blood from survivors be used to make a serum?
How is the Ebola virus shipped to the CDC from Zaire?

Open Questions

This is a list of questions that people would like answered, but that I don't feel capable of answering. If you think you can provide a solid answer to one of these questions (no speculation, references preferred), please send some mail .

What are the short and long term effects on survivors of having had Ebola?
What happens to survivors of an Ebola infection?
Are survivors immune to Ebola? If yes, is it permanent?
Can Ebola be spread by mosquitoes?

Frequently Asked Questions and Answers

What exactly is Ebola?

Ebola (ee-BOH-luh) is a virus named after a river in Zaire, its first site of discovery. A usually fatal filovirus which affects monkeys and humans, it is a cause of viral hemorrhagic fever -- there are others. Filoviruses are string-shaped, often with a little hook or loop at one end. Another, somewhat less deadly filovirus is the Marburg virus.

What varieties are known to exist?

Ebola Sudan (EBOS), Ebola Zaire (EBOZ), and Ebola Reston (EBOR).

It is somewhat unclear to researchers to what extent EBOS, EBOZ and EBOR are really three different viruses (9).

Newsflash: It has just been announced that a fourth strain of Ebola, also affecting humans, has been identified: it was isolated from a blood sample taken from a Swiss zoologist who contracted it in Ivory Coast, West Africa last fall from an infected chimpanzee. [Fortunately, she survived, thanks to intensive medical care.] The announcement was made in the 20/5/95 issue of the Lancet. Ref.: V.O.A.

How do these varieties differ?

Clinically, they all produce similar effects. Ebola Sudan and Ebola Zaire affect humans as well as monkeys; Ebola Reston harms monkeys, but not humans. (The Ebola Reston incident is the main subject of Richard Preston's book The Hot Zone.) We are all very lucky that humans seem to be asymptomatic in response to Reston, since there were indications at the time of the incident that it was airborne, unlike (apparently) the other two.

How long is the incubation period/onset of symptoms?

Anywhere from 4 to 21 days.

What are the symptoms?

Quoting the CDC:

All forms of viral hemorrhagic fever begin with fever and muscle aches. Depending on the particular virus, the disease can progress until the patient becomes very ill with respiratory problems, severe bleeding, kidney problems, and shock. The severity of viral hemorrhagic fever can range from a relatively mild illness to death.

EBOZ seems to be fatal in about 90% of the cases. EBOS is fatal in about 60%. EBOR is not fatal to humans.

Is there any cure or vaccine?

No.

How does it damage (and usually kill) its victims?

By slowly "dissolving" their organs, blood cells and connective tissue, causing massive and usually fatal internal hemorrhaging. This apparent dissolving (from a macroscopic viewpoint) is caused by the multiplication of virus particles within the cells until the cells literally explode. What's left is a "mush" of blood and cell debris.

How is it transmitted?

Ebola virus is spread through close personal contact with a person who is very ill with the disease. In previous outbreaks, person-to-person spread frequently occurred among hospital care workers or family members who were caring for an ill person infected with Ebola virus. Transmission of the virus has also occurred as a result of hypodermic needles being reused in the treatment of patients. Reusing 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 reuse needles.

Ebola virus can also be spread from person to person through sexual contact. Close personal contact with persons who are infected but show no signs of active disease is very unlikely to result in infection. Patients who have recovered from an illness caused by Ebola virus do not pose a serious risk for spreading the infection. However, the virus may be present in the genital secretions of such persons for a brief period after their recovery, and therefore it is possible they can spread the virus through sexual contact.

Ref: CDC

Is Ebola airborne?

The Zaire and Sudan strains are not airborne. The Reston strain appears to have been transmittable by airborne means, but that strain is not harmful to humans.

Geographically, where does Ebola come from?

The Sudan and Zaire strains may come from the rainforests of northeastern Zaire and/or somewhere nearby in the bordering nations of Sudan, Uganda, and Kenya. The Marburg filovirus was circumstantially linked to the Mt. Elgon region near the Kenya-Uganda border. The Reston variety occured in monkeys imported from the Philipines, so there may be reservoirs in Asia as well. Preston speculates that an Ebola strain may have been introduced into the Phillipines from Africa by the rumored illegal importing of African game animals to remote areas of the Philipines by rich Filipino "sportsmen".

What is the natural reservoir for Ebola?

Attempts to find the source of the Ebola virus have been unsuccessful despite collection and analysis of ecologic samples from bats, monkeys, spiders and ticks. This question is currently the subject of ongoing speculation. See, for example, discussions going on in the bionet.virology USENET news group.

What is the probability of Ebola mutating and becoming airborne?

RNA viruses are known to undergo rapid genetic changes (1). The Ebola virus is subject to some (but not all) of these mutation processes. To become "airborne", the Ebola genome (RNA) would have to mutate in such a way that its outer protective coating of proteins (capsid) could resist the forces to which they are subjected in air (e.g., dryness). There are no exact measures of the rate of mutation in Ebola, but the probability of the required mutation(s) happening is very low.

What has caused Ebola epidemics to end in past occurrences?

Previous outbreaks of Ebola appear to have continued only as long as a steady supply of victims came in contact with body fluids from the infected. The epidemics were resolved by teaching the local population about how to avoid spreading the disease and improving conditions at hospitals in impacted areas (unsterilized needles and syringes were a major factor in the 1976 outbreak in Zaire). Ebola's virulence may also serve to limit its spread: it's victims die so quickly that they don't have a chance to spread infection very far.

Can blood from survivors be used to make a serum?

No. Normally, one can mix serum from a patient recovering from an infection with a test tube containing the involved virus and then inject a test animal with the mixture and expect that the convalescent serum 'killed' the virus. This is not the case with Ebola (7). This also means that the serum is ineffective in treating someone else who is infected.

How is the Ebola virus shipped to the CDC from Zaire?

A virus such as Ebola is packaged and shipped by air, using a courier such as Federal Express. Packaging and shipping procedures are strictly governed by the U.S. Department of Transportation, the Public Health Service and the International Air Transport Association's Dangerous Goods Regulations for Infectious Substances.

The substance is first placed in watertight primary containers such as test tubes, which are wrapped in shock-resistant material and placed in a watertight secondary container. That package is placed in a durable outer container, which is then packaged further and labeled with an international biohazard symbol. Packages are tracked continuously to ensure that they arrive intact and on time.

See reference (10)


Notes

  1. The three most common mechanisms are: (a) nucleotide substitutions resulting from purportedly high error rates during RNA synthesis (2,3); (b) reassortment of the RNA segments of multipartite genomic viruses (4,5); (c) RNA-RNA recombination between non-segmented RNAs. Ebola virus can use only the first and the third mechanisms as it has only one segment of RNA by capsid.
  2. Holland, J. et al. 1982 Rapid evolution of RNA genomes. Science 215: 1577-1585.
  3. Steinhauer, D.A. and J. Holland. 1986. Direct method for quantitation of extreme polymerase error frequencies at selected single base sites in viral RNA. J. Virol. 57: 219-228.
  4. Fields, B.N. 1981. Genetics of Reovirus. Curr. Top. Microbiol. Immunol. 91: 1-24.
  5. Palese, P. 1977. The genes of Influenza virus. Cell 10: 1-10.
  6. Lai, M.M.C. 1992. RNA recombination in animal and plant viruses. Microb. Rev. 56: 61-79.
  7. Many infections create an immune response that includes antibodies that will bind to and inactivate the virus when exposed in vitro. The antibodies raised by people or animals after Ebola infection apparently lack the ability to neutralize viruses experimentally (8).
  8. Peters, C.J. et al (1993). Filoviruses (p. 161) in Emerging Viruses, edited by Stephen S. Morse. Oxford Univ. Press.
  9. Peters, C.J. et al (1993). Filoviruses (p. 163) in Emerging Viruses, edited by Stephen S. Morse. Oxford Univ. Press.
  10. Atlanta Journal-Constitution. Weekly Q&A column by Colin Bessonette. Q&A on the News, Box 4689, Atlanta 30302. Week of 5/24/95.

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