Signs and symptoms typically begin abruptly within five to 10 days of infection with Ebola or Marburg virus. Early signs and symptoms include:

• Fever
• Severe headache
• Joint and muscle aches
• Chills
• 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
• Sore throat
• Stomach pain
• Severe weight loss
• Bruising
• Bleeding, usually from the eyes, and when close to death, possible bleeding from the ears, nose and rectum
• Internal bleeding

Ebola virus has been found in African monkeys, chimps and other nonhuman primates. A milder strain of Ebola has been discovered in monkeys and pigs in the Philippines.

Marburg virus has been found in monkeys, chimps and fruit bats in Africa.

Transmission from animals to humans

Experts suspect that both viruses are transmitted to humans through an infected animal's bodily fluids. Examples include:

• Blood. Butchering or eating infected animals can spread the viruses. Scientists who have operated on infected animals as part of their research have also contracted the virus.
• Waste products. Tourists in certain African caves and some underground mine workers have been infected with the Marburg virus, possibly through contact with the feces or urine of infected bats.

Transmission from person to person

Infected people typically don't become contagious until they develop symptoms. Family members are often infected as they care for sick relatives or prepare the dead for burial.

Medical personnel can be infected if they don't use protective gear, such as surgical masks and gloves.

There's no evidence that Ebola virus or Marburg virus can be spread via insect bites.

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

• Travel to Africa. You're at increased risk if you visit or work in areas where Ebola virus or Marburg virus outbreaks have occurred.
• Conduct animal research. People are more likely to contract the Ebola or Marburg virus if they conduct animal research with monkeys imported from Africa or the Philippines.
• Provide medical or personal care. Family members are often infected as they care for sick relatives. Medical personnel also can be infected if they don't use protective gear, such as surgical masks and gloves.
• Prepare people for burial. The bodies of people who have died of Ebola or Marburg hemorrhagic fever are still contagious. Helping prepare these bodies for burial can increase your risk of developing the disease.

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

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 weeks. People may experience:

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