Ebola virus was discovered in 1976 and has since, swept across
Research comparing recent samples from six gorillas and a chimpanzee revealed that the virus from all animals have similar genes. The genes are also homologous to Ebola virus obtained from human samples in the region. However, when compared to a broader range of Ebola virus samples, the virus sequences map to two separate strains. Gene sequences of Ebola virus in human samples taken before 1996 are all more similar to each other than to viral sequences from human and ape samples since then.
This in itself suggests mutation of the virus, but what is truly frightening is that some human patients carry a copy of one gene specific to each strain suggesting that the virus has recombined. This is rarely seen in RNA viruses, and has never been characterized in Ebola’s broader family of filoviruses to date.
The obvious consequence of recombination capable viruses is that vaccines developed to target specific protein on the Ebola may become ineffective once the protein profile changes.
Mackenzie, Debora. “Ebola evolves deadly new trick”. New Scientist October 13-19, 2007, 12.
Proceedings of the
8 comments:
Regarding the 90% that were infected by Ebola, and experienced fever, hemorrhage, and death, what was different in the remaining 10%?
How does one come across this virus? Is this 90% only in Africa?
Erin, I was looking at the history of the Ebola Virus on the CDC website and there are numerous cases of infected monkeys being imported into countries such as the US and Italy. A few humans developed antibodies to the virus but none became ill. Do you know if there are any distinct differences in signs and/or symptoms between humans and primates that are infected with Ebola? Also do the symptoms caused by the mutated virus differ at all from those caused by the strain that was originally discovered?
According to MayoClinic.com, there is no solid understanding of why some survive infection of Ebola virus, but some in fact do. Since there remains no effective antiviral treatments, treatment is purely supportive of fluid replacement, blood loss, organ system support, and addressing other opportunistic infections.
The virus is still believed to be transmitted mostly through blood particles and needles or syringe exposure. Casual contact is not believed to be enough to transmit the virus, but those most at risk for contracting Ebola are people who are exposed to other infected persons or their body's after death.
It can still largely be avoided by staying away from known outbreak regions, i.e. the Democratic Republic of the Congo, and not working with primates or people known or suspected of being infected.
I would venture a guess that those who are immune-impaired from the start, the very young and very old, are all at increased risk of fatality if infected with Ebola virus.
Because early symptoms resemble multiple other viruses (fever, chills, muscles aches, sore throat), suspicion of exposure based on travel and work experience play a large role in determining testing for this kind of lethal virus.
I do know there is a related virus called the Marburg virus and I was wondering if the article discussed mentions eliminating this virus as what is believed to be a new strain or if Marburg may potentially also be a mutated strain of the original Ebola virus? How similar or different are all of these viruses?
A fun, informative, and very dramatic book about hemorrhagic fevers is "The Hot Zone," if anyone is interested!
The Hot Zone is a GREAT book, but don't read it if you're planning to take a trip by plane any time soon
First of all, thanks for the great comments! I apologize for taking so long to get back to these comments. Virus/cold season is certainly taking it’s toll!
Jan, Ebola virus infects the key initiators of the innate immune system: blood monocytes, macrophages and dendritic cells. Once inside DCs, the virus not only replicates but interferes with cytokine and chemokine secretion. This results in poor mobilization of the adaptive cells (T&B) and also NK cells. So what's happening in the people who survive? Studies have shown that robust, EARLY innate responses which produce pro-inflammatory cytokines are critically linked to the host's survival. http://www.jem.org/cgi/content/full/jem.20032141v1#BIB1
Desiree, Ebola is found mostly in equatorial Africa where an unknown natural animal host population exists. The incidence of cases outside of Africa is likely due to import of infected animals.
Katie, since very little data is available about the non-human outbreaks, I don’t know if there are subtle differences in the initial symptoms between the groups infected with Ebola but primates still experience internal bleeding and shock, which can be determined by autopsy. In my search, there do not appear to be gross differences in the symptoms between the recombined Zaire and original Zaire Ebola. Much more research is needed in that area.
Jessica, Marburg virus is processed into unique antigenic determinants compared to Ebola, thus the host generates different antibodies (detected by IgG ELISA). The researchers could also distinguish Marburg from Ebola by PCR during early infection before antibodies are produced.
This article: http://vir.sgmjournals.org/cgi/content/full/83/1/67 shows that there is high genetic diversity between the 4 subtypes of Ebola virus (Zaire, Sudan, Côte d'Ivoire and Reston) but within a subtype, the mutation rate is very low. They attribute this to high fidelity of the RNA polymerase, sparse natural hosts, decreased replication once inside a natural host, and little pressure from the immune system to mutate.
Marburg and Ebola virus are genetically quite different, so the evidence suggests that evolution from Ebola to Marburg is unlikely.
Does anyone know the natural host for the Ebola virus- its seems that is able to infect multiple species- not unlike the bird flu- making its ability to recombine all that more dangerous to new hosts or to hosts that have been exposed to a recombined virus. How is the disease transmitted when not in the original host species? H
You know, the disease that the pig-brain-breathers got is rare, only 2 cases/100,000 in the US; but that adds up to about 6000 cases. And no one's ever heard of it. For Ebola, which everyone's heard of, there have been 1850 cases and 1200 deaths. Perception outweighs reality?
Here's what the WHO says in a FactSheet about Ebola's natural reservoir:
* The natural reservoir of the Ebola virus is unknown despite extensive studies, but seems to reside in the rain forests on the African continent and in the Western Pacific.
* Although non-human primates have been a source of infection for humans, they are not thought to be the reservoir. They, like humans, are believed to be infected directly from the natural reservoir or through a chain of transmission from the natural reservoir.
* On the African continent, Ebola infections of human cases have been linked to direct contact with gorillas, chimpanzees, monkeys, forest antelope and porcupines found dead in the rainforest. So far, the Ebola virus has been detected in the wild in carcasses of chimpanzees (in Cote-d’Ivoire and Republic of Congo), gorillas (Gabon and Republic of Congo) and duikers (Republic of Congo).
* Different hypotheses have been developed to try to explain the origin of Ebola outbreaks. Laboratory observation has shown that bats experimentally infected with Ebola do not die, and this has raised speculation that these mammals may play a role in maintaining the virus in the tropical forest.
* Extensive ecological studies are underway in the Republic of Congo and Gabon to identify the Ebola's natural reservoir.
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