What is a Filovirus?

A filovirus is a virus which is part of the family known as filoviridae. These viruses are so named because of their microscopic appearance: they are long and thin, resembling fibrous threads. Filoviruses cause a type of disease called a hemorrhagic fever, characterized by very high fever, excessive bleeding, and lack of blood coagulation. Often, infection with a filovirus is fatal, with mortality rates ranging between 50% and 90%.

There are two types of filoviruses, called Marburgvirus and Ebolavirus. In the Marburgvirus genus there is just one species, known as Lake Victoria marburgvirus. Within the Ebolavirus genus there are three species, called Ivory Coast ebolavirus, Reston ebolavirus, and Sudan ebolavirus. Each filovirus species is named for the region in which it was first discovered.

The first species of filoviridae to be discovered was Marburg, in a virology laboratory in Marburg, Germany in 1967. In this outbreak 31 people were infected with the virus and seven people died. The disease was contracted the virus through contact with infected monkeys. While there have been several small outbreaks of Marburgvirus in several African countries, this remains the only outbreak which has occurred on a continent other than Africa. The first reported outbreak of an Ebola species was in 1976, in Sudan and Zaire. A further outbreak occurred in Reston, Washington D.C. in 1989. A third Ebola outbreak occurred in the Philippines in 2009; this was again of the Reston variety.

Filoviruses are zoonotic viruses, meaning the natural hosts of these viruses are animals, but infection can be transmitted to humans. Although some species of filovirus have been found to infect monkeys and swine, the natural host of these viruses is not known. Some species of bat have been found which are naturally infected with Ebolavirus in the wild, without displaying disease symptoms. On the basis of this evidence it is currently suspected that bats are the natural hosts of filoviruses.

Filoviruses can be spread through contact with infected bodily fluids, including blood, saliva, vomit, and excrement. This is generally how the virus is spread from person to person during an outbreak. Most outbreaks start when the virus is transmitted from an animal to a human; however it is not known how this transmission occurs.

Initial symptoms of filovirus infection include severe headache, aching muscles, fatigue, sore throat, dizziness, nausea, and joint or muscle pain. These symptoms appear between two days and three weeks after first contact with the virus. As the infection progresses, more serious symptoms begin to develop, such as blood in vomit and feces, rash and hemorrhage in the skin, and internal bleeding. Treatment for hemorrhagic fever is supportive rather than curative, as there is no reliable cure for infection. Instead, treatment aims to reduce the impact of the infection by replacing lost blood and fluids, using medication to promote blood clotting, and preventing complications.