Ebola, Marburg and Lassa viruses are commonly called emerging diseases, but virus experts note that they have existed for centuries.
In an article published in the November issue of the journal Science, a group of researchers assert that the rise in hemorrhagic fevers caused by these viruses over the last 40 years possibly reflects emerging diagnoses instead.
The emerging character of the diseases may primarily be a matter of improved detection. The pathogens seemed to appear from nowhere around the middle of the 20th century - first Marburg virus in 1967, then Lassa virus in 1969 and Ebola virus in 1976, according to Science
Epidemiologic and genetic studies conducted recently on Lassa and Ebola fevers, however, point towards ancient origins.
"The infectious agents were identified around the middle of the twentieth century but that does not mean that they were new," Dr. Joseph McCormick from the University of Texas said, HomelandSecurityNewswire.com
reports. "Some of the viruses, including Lassa and Ebola, have been around for thousands of years."
Most of the viruses thrive in animal populations, but people can still become infected if they have close contact with infected fluids or tissues. Viral hemorrhagic fevers are epidemic in some areas of Africa. Ebola viruses are endemic in other parts of the world.
"The Arenavirus family of viruses that occur on many continents, of which the African Lassa virus is a member, is an ancient family of viruses that have likely evolved along with their rodent hosts over millions of years," McCormick said, according to HomelandSecurityNewswire.com
. "Now that we understand more about their ecological niches and geographical distribution, we know more about how to avoid them. We also know more about how they cause disease and we may be able to improve treatment and seek vaccines."