Ebola virus and Marburg virus are related viruses that cause hemorrhagic fevers — illnesses marked by severe bleeding (hemorrhage), organ failure and, in many cases, death. Both Ebola virus and Marburg virus are native to Africa, where sporadic outbreaks have occurred for decades. No human cases of Ebola virus have been reported in the United States.

Ebola and Marburg viruses live in one or more animal hosts, and humans can contract the viruses from infected animals. After the initial transmission, the viruses can spread from person-to-person through contact with body fluids or contaminated needles.

No effective therapy exists for the hemorrhagic fevers caused by Ebola virus and Marburg virus. People diagnosed with Ebola virus or Marburg virus receive supportive care and treatment for complications.

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

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

Over time, symptoms become increasingly severe and may include:

• Nausea and vomiting
• Diarrhea (may be bloody)
• Red eyes
• Raised rash
• Chest pain and cough
• Stomach pain
• Severe weight loss
• Confusion, irritability or aggression
• Massive hemorrhaging from many sites, including nose, mouth, rectum, eyes and ears

The Marburg and Ebola viruses emerged from tropical rain forests in Africa in the mid-20th century. The viruses live in an animal host or "reservoir." Humans most likely became infected when they encroached on native habitat and encountered the viruses for the first time. Exactly how this initial infection occurred isn't known.

Scientists have identified one species of African fruit bat as a source of the virus. Although humans have been infected with Ebola and Marburg through contact with monkeys, chimpanzees and other nonhuman primates, these animals aren't the viruses' natural reservoir. Instead, they are one link in the chain of infection.

Once a person has been infected with Ebola or Marburg, the virus can spread to others through contact with that person's body fluids or through use of contaminated needles or syringes.

Researchers don't think that humans produce enough Ebola or Marburg virus in airborne droplets to cause infection through casual contact.

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

• Travel to or work in areas where Ebola virus or Marburg virus 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 virus or Marburg virus
• Provide medical or personal care for people with Ebola hemorrhagic fever or Marburg hemorrhagic fever
• Prepare people who have died of Ebola hemorrhagic fever or Marburg hemorrhagic fever for burial

Both Ebola and Marburg hemorrhagic fevers lead to death for a high percentage of people who are affected. As the illness progresses, it can cause:

• Multiple organ failure
• Severe bleeding
• Jaundice
• Delirium
• Seizures
• Coma
• Shock

Death often occurs less than 10 days from the start of signs and symptoms.

One reason the viruses are so deadly is that they interfere with 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, and the viruses remain in the body for many weeks. People may experience:

• Hair loss
• Sensory changes
• Liver inflammation (hepatitis)
• Weakness
• Fatigue
• Headaches
• Eye inflammation
• Testicular inflammation

The possibility of contracting Marburg or Ebola virus is extremely low unless you've had direct contact with the body fluids of an infected person or animal or with contaminated objects. If you think that you or a family member may have been exposed to one of the viruses, call your doctor or go to the nearest emergency room immediately. If you're not referred to an infectious disease specialist, ask to see one.

If you're traveling or working abroad, the nearest U.S. Embassy can help you find a healthcare provider. Be sure to tell your doctor or hospital about your symptoms before your visit so that precautions can be taken to prevent transmission of the virus to others.

To help your doctor find the cause of your symptoms as quickly as possible:

• Write down all the symptoms you're experiencing, including any that seem unrelated to Ebola virus or Marburg virus infection.
• Write down key personal information. Have you recently worked or traveled in a part of the world where outbreaks of Ebola or Marburg have occurred? Do you do animal research? Is there any other way you might have been exposed to one of the viruses?
• Make a list of all medications, vitamins and supplements that you're taking.
• If possible, take a family member or friend with you. Sometimes it can be difficult to absorb all the information provided to you in the hospital or during an appointment. Someone who accompanies you may remember something that you missed or forgot.
• Write down questions to ask your doctor. For instance, if you're found to have Ebola or Marburg infection, you'll want to clearly understand available treatments, the complications of the disease and the outlook for your recovery.

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

Most people with Ebola or Marburg hemorrhagic fever have high concentrations of the virus in their blood. Blood tests known as enzyme-linked immunosorbent assay (ELISA) and reverse transcriptase polymerase chain reaction (PCR) can detect specific genes or the virus or antibodies to them.

No antiviral medications have proved effective in treating Ebola virus or Marburg virus infection. As a result, treatment consists of supportive hospital care. 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 replenish blood proteins that improve clotting.

Public health officials urge hospitals to keep people with Ebola or Marburg hemorrhagic fever isolated from others in negative-pressure rooms, which maintain the flow of air into, rather than out of, enclosed spaces. Health care workers should follow strict infection-control precautions.

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

• Avoid traveling to areas of known outbreaks. Before traveling to Africa, find out about any current epidemics by checking the Centers for Disease Control and Prevention (CDC) Web site. To date, human cases of Ebola and Marburg have been reported in Democratic Republic of Congo, Angola, Uganda, Sudan, Gabon, Cote d'Ivoire, Liberia and Kenya.
• Wash your hands frequently. As with other infectious diseases, one of the most important preventive measures for Ebola virus and Marburg virus is frequent hand washing. Use soap and water or use alcohol-based hand rubs containing at least 60 percent alcohol when soap and water aren't available.
• Avoid bush meat. In developing countries, wild animals, including nonhuman primates, are sold in local markets. Avoid buying or eating any of these animals.
• Avoid close physical contact with anyone 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. People with Ebola or Marburg are most contagious in the later stages of the disease. No one has been known to contract the disease from a person who is infected but hasn't yet developed symptoms.
• Follow strict infection-control procedures if you're a health care worker. This includes wearing protective clothing, such as gloves, masks, gowns and eye shields; keeping infected people isolated from other patients; and carefully 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 hemorrhagic fever. Specially organized and trained teams should bury the remains, using appropriate safety equipment.

Vaccine development
Although no vaccines are available to prevent Ebola or Marburg diseases, several are under study.

Advice for travelers
Most international travelers don't need to worry about exposure to Ebola virus or Marburg virus. But if you're planning to travel to areas where outbreaks have occurred, stay up to date on health advisories and epidemic information. Advisories for travelers about current disease outbreaks are posted on the Web sites of the Centers for Disease Control and Prevention and the World Health Organization.