Filoviridae

The first filovirus was discovered in 1967 when a number of laboratory workers in Germany and Yugoslavia handling vervet monkey tissues developed haemorrhagic fever. A total of 31 cases and 7 deaths were associated with these outbreaks. The virus was named after Marburg, Germany, the site of one of the outbreaks. In addition to the 31 reported cases, one additional primary case was retrospectively diagnosed serologically. After this initial outbreak, the virus disappeared. It did not reappear until 1975, when a traveler, most likely exposed in Zimbabwe, became ill in Johannesburg, South Africa. The virus was transmitted there to his travel companion and a nurse. Since then, a few sporadic cases and 2 major epidemics (Democratic Republic of Congo in 1999 and Angola in 2005) of Marburg hemorrhagic fever (Marburg HF) have been reported. For information on known Marburg HF cases and outbreaks, see the chronological list.

Ebola virus was first identified in 1976, when two outbreaks of Ebola hemorrhagic fever (Ebola HF) occurred in northern Zaire (now the Democratic Republic of Congo) and southern Sudan. The outbreaks involved two different types of Ebola virus, named after the countries in which they were discovered. Both viruses proved highly lethal, with 90% of Zairean cases and 50% of Sudanese cases resulting in death.

Ebola viruses have occurred sporadically in Africa since 1976, with small to medium-sized outbreaks confirmed between 1976 and 1979. Large Ebola HF epidemics occurred in Kikwit, DRC, in 1995; Gulu, Uganda, in 2000; Bundibugyo, Uganda, in 2008; and Issiro, DRC, in 2012. Smaller outbreaks have been detected in Gabon, DRC, and Uganda. For information on known Ebola HF cases and outbreaks, see the chronological list.

During outbreaks, isolation of patients and use of protective clothing and disinfection procedures (collectively referred to as viral hemorrhagic fever isolation measures or barrier care) have been shown to be sufficient to interrupt further transmission of Marburg virus or Ebola virus, thereby controlling and ending the outbreak. Because there is no known effective treatment for the hemorrhagic fevers caused by filoviruses, prevention of transmission through the use of isolation measures for viral hemorrhagic fever is currently the centerpiece of filovirus control.

Animal hosts: It appears that filoviruses are zoonotic, that is, they are transmitted to humans through ongoing life cycles in animals other than humans. Despite numerous attempts to locate the natural reservoir or reservoirs of Ebolavirus and Marburgvirus species, their origin was undetermined until recently when Marburgvirus and Ebolavirus were detected in fruit bats in Africa. Marburg virus has been isolated in several cases from Rousettus bats in Uganda.

Spread of filovirus infections: In an outbreak or isolated case among humans, it is not known how the virus is transmitted from the natural reservoir to humans. However, once a human is infected, human-to-human transmission is possible. Transmission occurs through close personal contact between an infected person or their body fluids and another person. During recorded outbreaks of hemorrhagic fever caused by filovirus infection, persons who cared for (nursing, medical treatment) or worked very closely with infected persons were at particular risk of becoming infected themselves. Nosocomial transmission is also an important factor in the spread of the disease. When close contact between uninfected and infected persons is minimized, the number of new filovirus infections in humans usually decreases. Although the viruses have shown some ability to infect through small particle aerosols in the laboratory, airborne spread among humans has not been clearly demonstrated.

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