THE EBOLA VIRUS:Information on Ebola and the different variants and subtypes of the Ebola Virus

THE EBOLA VIRUS

The Ebola owes its name to the fact that it was discovered in Zaire near the river Ebola

Classification

The Ebola virus belongs to the family filoviridae, which is a group of negatively stranded RNA viruses. This group of viruses is thread like in structure, or string shaped and hence they are called filoviruses. The Ebola virus has a single RNA strand for its genetic code. This type of genetic coding is widely believed to be the most primitive coding mechanism for life. Thus it would be safe to suppose, given its genetic coding and structure, the Ebola virus is probably an extremely old life form probably dating back to the beginning of life on earth. However, this is conjecture. I received a mail from Ed Rybicki of the dept of molecular biology of the University of Cape town - it was a too technical for a layman to understand so I have provided the one link above and the other one here, detailing this.

Form

The Ebola virus when viewed through an electron microscope has been described in many ways - a worm, a thread, pigtails, bends like the letter U and even snakes. One of the descriptions that was made and was adopted was the similarity to a “shepherds crook”. The virus is pleomorphic, appearing as long filamentous (and sometimes branched) forms in a variety of shapes including U, 6-shaped, and circular. The virions have a uniform diameter of 80 nm, composed of a helical nucleocapsid and are enveloped with surface projections

Replication

The exact mechanism that the Ebola virus uses to make its entry into the host cell is still unknown. It is assumed that they use the same mechanism as rhabdoviruses which have similar genetic characteristics. The actual process of replication has been described in a later part of this report.

Image of the Virus

Fig. 1 is one of the first images taken of the Ebola virus taken in October 1976, right after the Sudan outbreak. The lumpy rope like braided features are seven unknown structural proteins. They surround a single strand of RNA, which is contains the genetic code information of the virus. The magnification is 112,000 X.

Reservoir Species

A reservoir species is a species that carries a virus with experiencing little or no side effects from carrying the virus. One of the major drawbacks so far in the isolation of the Ebola virus and the search for a cure, has been the inability to identify the reservoir species. During the outbreaks of Ebola, frantic attempts were made to isolate the reservoir species. The cotton factory where the virus was first recorded was scoured and every living thing within the factory was captured, including spiders, cockroaches and other insects and they were all tested. Even bat droppings were collected and analysed but the virus remained elusive. It was earlier thought that the virus was carried by primates but recent studies and evidence show that primates are as much a victim of the virus as human beings.

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.

It is evident that this reservoir species has its home somewhere within the rainforest and has only in recent times come into contact with man. This also indicates the possibility that the species is not yet a recorded one.

VARIATIONS OF THE VIRUS

Ebola Zaire

Ebola Zaire was the first recorded occurrence of the Ebola virus in man. Ebola Zaire is so far the most lethal of the Ebola strains with a fatality rate between 80 – 90 %. It was isolated after the Zaire outbreak in 1976.

Ebola Sudan

The Ebola Sudan outbreak occurred roughly the same time that the Ebola Zaire outbreak took place. The Sudan variation has a fatality rate of between 50 – 60 %.

Ebola Reston

This strain was identified and named after a batch of monkeys shipped to an experimental lab in Reston, Virginia in the United States. This batch of monkeys arrived from the Philippines indicating an Asian strain of the virus. This strain can be transmitted by air but fortunately has not yet been proved dangerous to Homo Sapiens.

Ebola Tai

This is the most recently identified of Ebola viruses (1995), though the discovery of the Tai strain has now sparked a debate as to what actually constitutes an Ebola strain. Several Chimpanzees were killed by this virus but the only known human infection was the non-fatal infection of a Swiss researcher in the Ivory Coast.

Marburg

The Marburg filovirus is not considered to be an Ebola strain but however very closely resembles the Ebola virus and also causes severe hemorrhagic fever. This virus was discovered in Marburg, Germany, in 1967. It happened when a worker at the Behring works vaccine factory who fed the monkeys and washed their cages broke out with the virus. In an advanced, developed country like Germany where the medical care system is excellent, the fatality rate was 25 %, compared to 5 % for a highly lethal virus like yellow fever.

Other Haemorrhagic fevers

Other well-known haemorrhagic fevers are:

· Lassa fever - first noticed in the 1960s after an outbreak in Nigeria, and is spread from rodents, the natural host

· Rift Valley fever - mainly found in sub-Saharan Africa, and spread by mosquitoes

Congo-Crimean haemorrhagic fever - found in many parts of Africa, the Middle East and even warmer parts of the former Soviet Union, in which an outbreak is ongoing. It is spread by ticks