Ebola is the common term for a group of viruses belonging to genus Ebolavirus, family Filoviridae, and for the disease which they cause, Ebola hemorrhagic fever.

The viruses are characterised by a long, filamentous morphology surrounded by a lipid viral envelope. The Ebola virus first emerged in 1976 in simultaneous outbreaks in Sudan and Zaire.

It is known to be a zoonotic virus as it is currently devastating the populations of lowland gorillas in Central Africa.

Despite considerable effort by the World Health Organization, no animal reservoir capable of sustaining the virus between outbreaks has been identified.

However, it has been hypothesized that the most likely candidate is the fruit bat. Ebola hemorrhagic fever is potentially lethal and encompasses a range of symptoms including fever, vomiting, diarrhea, generalized pain or malaise, and sometimes internal and external bleeding.

Subtypes

Microbiologists have defined several subtypes of Ebola. The following list is not exclusive. A new strain of Ebola has been identified in Uganda during an outbreak. It does not match any of the four Ebola subtypes previously identified by scientists.

Zaïre ebolavirus

Known human cases and deaths during outbreaks of Zaïre Ebolavirus between 1976 and 2003The Zaïre Ebolavirus has the highest mortality rate, up to 90% in some epidemics, with an average of approximately 83% mortality over 27 years.

Others include:

Sudan Ebolavirus

Known human cases and deaths during outbreaks of Sudan Ebolavirus between 1976 and 2003Sudan Ebolavirus was the second strand of Ebola reported in 1976. It apparently originated amongst cotton factory workers in Nzara, Sudan.

Reston Ebolavirus

First discovered in November 1989 in a group of 100 Crab-eating macaques (Macaca fascicularis) imported from the Philippines to Reston, Virginia.

A parallel infected shipment was also sent to Philadelphia. This strain was highly lethal in monkeys, but did not cause any fatalities in humans. Six of the Reston primate handlers tested positive for the virus, two due to previous exposure. A novel is written of this incident called "The Hot Zone."

Tai (Ivory Coast) Ebolavirus

This subtype of Ebola was first discovered amongst chimpanzees of the Tai Forest in Côte d’Ivoire, Africa. On November 1, 1994, the corpses of two chimpanzees were found in the forest.

Necropsies showed blood within the heart to be liquid and brown, no obvious marks seen on the organs, and one presented lungs filled with liquid blood.
 
Bundibugyo Ebolavirus

On November 30, 2007, the Uganda Ministry of Health confirmed an outbreak of Ebola in the Bundibugyo District. After confirmation of samples tested by the United States National Reference Laboratories and the Centers for Disease Control the World.

Symptoms
 
1976 photograph of two nurses standing in front of Kinshasa case #3 (Nurse Mayinga) who was treated and later died in Ngaliema Hospital, in Kinshasa, ZaïreSymptoms are varied and often appear suddenly.

Initial symptoms include high fever (at least 38.8°C; 101.8°F), severe headache, muscle, joint, or abdominal pain, severe weakness and exhaustion, sore throat, nausea, and dizziness.

Before an outbreak is suspected, these early symptoms are easily mistaken for malaria, typhoid fever, dysentery, influenza, or various bacterial infections, which are all far more common and less reliably fatal.

Ebola may progress to cause more serious symptoms, such as diarrhea, dark or bloody feces, vomiting blood, red eyes due to distention and hemorrhage of sclerotic arterioles, petechia, maculopapular rash, and purpura.

Other secondary symptoms include hypotension (less than 90 mm Hg systolic /60 mm Hg diastolic), hypovolemia, tachycardia, organ damage (especially the kidneys, spleen, and liver) as a result of disseminated systemic necrosis, and proteinuria.

The interior bleeding is caused by a chemical reaction between the virus and the platelets which creates a chemical that will cut cell sized holes into the capillary walls.

After several days, the person will die literally of "a million cuts." Occasionally, Internal and external hemorrhage from orifices, such as the nose and mouth may also occur, as well as from incompletely healed injuries such as needle-puncture sites.

Ebola virus can infect platelets, disrupting clotting. [Citation needed] Fewer than 50 percent of patients will develop any hemorrhaging at all.

The span of time from onset of symptoms to death is usually between 7 and 14 days. By the second week of infection, patients will either defervesce (the fever will lessen) or undergo systemic multi-organ failure.

Mortality rates are generally high, ranging from 50% - 90%.[9] The cause of death is usually due to hypovolemic shock or organ failure.

Transmission

This section needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (August 2007)

Among humans, the virus is transmitted by direct contact with infected body fluids, or to a lesser extent, skin or mucus membrane contact. The incubation period can be anywhere from 2 to 21 days, but is generally between 5 and 10 days.

Although airborne transmission between monkeys has been demonstrated by an accidental outbreak in a laboratory located in Virginia, USA, there is very limited evidence for human-to-human airborne transmission in any reported epidemics.

Nurse Mayinga might represent the only possible case. The means by which she contracted the virus remain uncertain.
The infection of human cases with Ebola virus has been documented through the handling of infected chimpanzees, gorillas, and forest antelopes--both dead and alive--as was documented in Côte d'Ivoire, the Republic of Congo and Gabon.

The transmission of the Ebola Reston strain through the handling of cynomolgus monkeys has also been reported.
In the early stages, Ebola may not be highly contagious. Contact with someone in early stages may not even transmit the disease.

As the illness progresses, bodily fluids from diarrhea, vomiting, and bleeding represent an extreme biohazard. Due to lack of proper equipment and hygienic practices, large scale epidemics occur mostly in poor, isolated areas without modern hospitals or well-educated medical staff. Many areas where the infectious reservoir exists have just these characteristics.

In such environments, all that can be done is to immediately cease all needle-sharing or use without adequate sterilization procedures, to isolate patients, and to observe strict barrier nursing procedures with the use of a medical rated disposable face mask, gloves, goggles, and a gown at all times. This should be strictly enforced for all medical personnel and visitors.

Treatments

Treatment is primarily supportive and includes minimizing invasive procedures, balancing electrolytes, replacing lost coagulation factors to help stop bleeding, maintaining oxygen and blood levels, and treating any complicating infections.

Despite some initial anecdotal evidence, blood serum from Ebola survivors has been shown to be ineffective in treating the virus. Interferon is also thought to be ineffective. Ribavirin is ineffective.

In monkeys, administration of an inhibitor of coagulation (rNAPc2) has shown some benefit, protecting 33% of infected animals from a usually 100% (for monkeys) lethal infection (unfortunately this inoculation does not work on humans).

In early 2006, scientists at USAMRIID announced a 75% recovery rate after infecting four rhesus monkeys with Ebola virus and administering antisense drugs.

Vaccines

Vaccines have been produced for both Ebola and Marburg that were 100% effective in protecting a group of monkeys from the disease.

These vaccines are based on either a recombinant Vesicular stomatitis virus or a recombinant Adenovirus carrying the Ebola spike protein on its surface. Early human vaccine efforts, like the one at NIAID in 2003, have so far not reported any successes.

Recent outbreaks

As of August 30, 2007, 103 people (100 adults and three children) had died due to a suspected hemorrhagic fever outbreak in the village of Mweka, Democratic Republic of the Congo (DRC).

The outbreak started after the funerals of two village chiefs, and 217 people in four villages have fallen ill due to the disease.

The World Health Organization sent a team to take blood samples for analysis and confirmed that many of the cases are the result of the Ebola virus.

The Congo's last major Ebola epidemic killed 245 people in 1995 in Kikwit, about 200 miles from the source of the current outbreak.

On November 30, 2007, the Uganda Ministry of Health confirmed an outbreak of Ebola in the Bundibugyo District. After confirmation of samples tested by the United States National Reference Laboratories and the Centers for Disease Control, the World Health Organization has confirmed the presence of a new species of the Ebola virus.

Whether this species is the same as that from the outbreak in the DRC has yet to be announced. On December 8, 2007, the number of Ugandans infected by a new strain of the Ebola virus had risen to 104. This has increased fears, the death toll of 25 will also increase.

Rwanda

There are no cases for Ebola in the country yet, health officials including the State Minister for HIV/Aids and other Infectious Diseases, Dr Innocent Nyaruhirira, have confirmed.

Addressing a press conference recently, Nyaruhirira said Rwanda has not yet registered any Ebola case within her borders but urged medical doctors and the general public to remain on high alert.

Rwanda maintains an Ebola screening exercise on both the Ugandan and Congolese borders, to prevent a spill over.

Ends