Ebola virus and Marburg virus

Definition

Ebola virus and Marburg virus are related viruses that cause severe, often fatal, disease. Ebola virus and Marburg virus originate primarily in the tropical forests of Africa and cause hemorrhagic fevers that can lead to extensive bleeding (hemorrhage), organ failure and shock. Ebola virus and Marburg virus initially move from animals to humans, then can spread from person to person through direct contact with blood and other body fluids.

The first reported cases of hemorrhagic fever caused by the Ebola virus were in Zaire (now Democratic Republic of Congo) and Sudan in 1976. Outbreaks in the 1990s and early 2000s also occurred in sub-Saharan Africa.

Public health officials identified the Marburg virus in 1967, when laboratory workers in Marburg, Germany, developed hemorrhagic fever after handling infected African green monkeys. Since then, limited outbreaks of Marburg infection have occurred sporadically in southern and eastern Africa.

No treatment or vaccines are available for hemorrhagic fevers caused by the Ebola virus and the Marburg virus. But for most people, the risk of infection is extremely low.

Symptoms

Signs and symptoms of hemorrhagic fevers caused by Ebola virus and Marburg virus start abruptly within a few days to a week or more following infection. Early signs and symptoms may include:

• Fever
• Severe headache
• Joint and muscle aches
• Chills
• Sore throat
• Weakness

Other signs and symptoms include:

• Nausea and vomiting
• Diarrhea (may be bloody)
• Red eyes
• Raised rash
• Chest pain and cough
• Hiccups (from Ebola virus)
• Stomach pain
• Bleeding
• Confusion, irritability or aggression
• Depression

Many, but not all, people with Ebola or Marburg hemorrhagic fever bleed from many sites, including their nose, mouth, rectum, eyes and ears.

Causes

The Marburg and Ebola viruses emerged from tropical rain forests in Africa and parts of the Western Pacific. The viruses live in an animal host or "reservoir." The natural hosts for Ebola and Marburg remain a mystery, though some scientists speculate that bats are the source. The viruses that cause hemorrhagic fevers jump from animals to humans when people encroach on a native habitat and encounter the viruses for the first time. Although humans have been infected with Ebola and Marburg through contact with monkeys, chimpanzees and other primates, these animals aren't the viruses' natural reservoir.

Once a person has been infected with Ebola or Marburg, the virus can spread to other people through contact with body fluids or through use of contaminated needles or syringes. Researchers believe that humans usually don't produce enough Ebola or Marburg virus in airborne droplets to infect others through casual contact.

Risk factors

For most people — including international travelers — the risk of getting Ebola or Marburg hemorrhagic fever is low. The risk increases for those who:

• Travel to or work in areas where Ebola or Marburg outbreaks have occurred, such as Democratic Republic of Congo (DRC), Sudan, Gabon, Cote d'Ivoire and Angola
• Conduct animal research, especially in tropical African forests, or handle primates infected with Ebola or Marburg
• Provide medical or personal care for people with Ebola or Marburg hemorrhagic fever
• Prepare people who died of Ebola or Marburg fever for burial

Public health officials also consider the Ebola and Marburg viruses potential bioterror weapons.

Tests and diagnosis

Ebola and Marburg hemorrhagic fevers are hard to diagnose initially because many of the early signs and symptoms resemble those of other infectious diseases, such as typhoid or malaria. But if doctors believe that someone may have been exposed to Ebola or Marburg, they can use specialized laboratory tests to identify the viruses within a few days.

Most people with Ebola or Marburg fever have high concentrations of the virus in their blood. Blood tests known as ELISA (enzyme-linked immunosorbent assay) and reverse transcriptase polymerase chain reaction (PCR) can detect antibodies to or specific genes of the viruses. Testing blood or tissue samples poses a high risk and must be done under controlled conditions at a "biosafety level 4" lab. Newer diagnostic techniques include testing saliva and urine samples or testing samples in which the virus has been inactivated.

Complications

Both Ebola and Marburg hemorrhagic fevers lead to death for a high percentage of people affected. As the illness progresses, it can cause organ failure, severe bleeding, jaundice, delirium, seizures, coma and shock. Death often occurs less than 10 days from the start of signs and symptoms.

The fatality rate for Ebola fever ranges from 50 percent to 90 percent. In most Marburg outbreaks, about 25 percent of people who got it died. But the fatality rate reached nearly 90 percent in recent large outbreaks in Angola and the Democratic Republic of Congo. One reason the viruses are so deadly is that they hamper the immune system's ability to mount a defense. But scientists don't understand why some people recover from Ebola and Marburg and others don't.

For people who survive, recovery is slow. It may take months to regain weight and strength. Studies show that the viruses remain in the body for many weeks after the illness. Survivors may experience hair loss, sensory changes, eye problems, liver inflammation (hepatitis), weakness, fatigue, headaches and testicular inflammation.

Treatments and drugs

No antiviral medications have proved effective in treating Ebola virus or Marburg virus infection. As a result, treatment consists of supportive care in a hospital. This includes providing fluids, maintaining adequate blood pressure, replacing blood loss and treating any other infections that develop. Some people receive transfusions of plasma to replace blood proteins that improve clotting.

Public health officials urge hospitals to keep people with Ebola or Marburg hemorrhagic fever isolated from others. Health care workers should follow strict infection-control precautions.

Prevention

Prevention efforts focus on avoiding contact with the viruses. The following precautions can help prevent infection and spread of Ebola and Marburg.

• Don't travel to areas of known outbreaks. Before traveling to Africa, find out about any current epidemics. To date, human cases of Ebola and Marburg have occurred in Democratic Republic of Congo, Angola, Uganda, Sudan and Gabon. One case of Ebola was reported in Cote d'Ivoire and one in Liberia. Two cases of Marburg occurred in Kenya (in people who had visited Kitum Cave in Mount Elgon National Park). Another person may have acquired the Marburg virus in Zimbabwe.
• Avoid all contact with dead primates in areas where infections have occurred. To meet the demand for exotic meats and "bush meat," some hunters enter remote forests and kill monkeys, chimpanzees and other primates. The hunters sometimes scavenge dead chimpanzees.
• Avoid close physical contact with someone infected with Ebola or Marburg. In particular, caregivers should avoid contact with the person's body fluids and tissues, including blood, semen, vaginal secretions and saliva.
• Health care workers should follow strict infection-control procedures. This includes wearing protective clothing, such as gloves, masks, gowns and leg and shoe coverings; and properly using, disinfecting and disposing of needles and other instruments. Injection needles and syringes should not be reused.
• Don't handle the remains of anyone suspected of dying of Ebola or Marburg fever. Specially organized and trained teams should bury the remains using appropriate safety equipment.

Vaccine development
Although no vaccines are available yet to prevent Ebola or Marburg diseases, several are in development. Recently the first clinical trial of a human DNA vaccine for Ebola virus showed that it was safe and produced an immune system response. This vaccine uses genetically engineered portions of the virus's DNA — proteins designed to trigger an immune system response to Ebola. Potential vaccines for Marburg virus have proved effective in nonhuman primates. Further studies are under way.

Advice for travelers
Most international travelers don't have to worry about exposure to Ebola or Marburg. But people who plan to travel to areas where outbreaks have occurred should stay up-to-date on current health advisories and epidemic information. Traveler's advisories about current disease outbreaks are posted on the Web sites of the Centers for Disease Control and Prevention and the World Health Organization.