Causes

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 spread to humans through an infected animal's bodily fluids. Examples include:

• Blood. Killing or eating infected animals can spread the viruses. Scientists who have operated on infected animals as part of their research have also caught 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

People who have Ebola virus or Marburg virus typically don't become contagious until they develop symptoms. The viruses can spread through blood, body fluids, or contaminated items such as bedding, clothing or needles. Family members can be infected as they care for sick relatives or prepare the dead for burial.

Medical personnel can be infected if they don't use specialized personal protective equipment that covers them from head to toe.

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