The Ebola, Marburg and Lassa viruses are commonly referred to as emerging diseases, but leading scientists say these life-threatening viruses have been around for centuries.

In a perspective in the Nov. 9 issue of the journal Science, researchers including a professor at The University of Texas Health Science Center at Houston (UTHealth) say it would be more appropriate to refer to these viruses as emerging diagnoses.

"The infectious agents were identified around the middle of the 20th century but that does not mean that they were new," said Joseph McCormick, M.D., one of the authors of the perspective and regional dean of The University of Texas School of Public Health Brownsville Regional Campus, which is part of UTHealth. "Some of the viruses, including Lassa and Ebola, have been around for thousands of years."

The viruses burst onto the scene in the 1960s when outbreaks decimated areas of west and central Africa. The viruses can lead to hemorrhagic fever, a condition characterized by bleeding, shock, vomiting and diarrhea. In severe cases, the death rate may reach 90 percent.

These viruses thrive in animals -- not humans. But people can get the viruses if they come in contact with infected animals or are exposed to virus-infected fluids or tissues. Infected people are moderately contagious with person-to-person transmission only through direct contact with infectious fluids such as blood or urine. Patients with Lassa virus can be successfully treated by antiviral medications.

With the aid of epidemiologic, ecologic and genetic studies, researchers have learned that these viral hemorrhagic fevers are endemic in several areas of Africa. And, the Ebola viruses are endemic in other parts of the globe.

"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," said McCormick, former chief of the Special Pathogens Branch of the Centers for Disease Control and Prevention.

So what would designating the viruses as emerging diagnoses mean?

"It means that these viruses have lurked as enzootic viruses in the environment and that their 'discovery' was related to the scientific capacity to make the diagnosis rather than their 'emergence,''' McCormick said. "However, it also means that we also now know more about the risks of encountering them and therefore, how to identify those who may be at risk for infection."

He said the designation would aid in the diagnosis. "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. All of this information will lead to a more proactive approach for detection and prevention," McCormick said. "Antibody tests now allow public health officials to gauge the exposure of the public to these viruses."

With this information, McCormick, the James H. Steele Professor of Epidemiology at the UT School of Public Health, said public health officials could develop strategies for prevention and mitigation of epidemics that have characterized these viruses in the past.

McCormick said that with the ease and rapidity of global transportation, it is also important for caregivers in other parts of the world to familiarize themselves with the signs and symptoms. "The symptoms in the early stages are fever, headache and nausea and can easily be misdiagnosed as the flu," said McCormick, adding that physicians need to ask about the travel history of feverish patients.

McCormick is one of the world's foremost authorities on the Ebola and Lassa viruses. He also led the first HIV investigation in Africa and is the investigator who isolated the oldest HIV strain, which is recounted in the book, "Level 4: Virus Hunters of the CDC," which he co-authored with Susan Fisher-Hoch, M.D. She is a professor of epidemiology at the UT School of Public Health Brownsville Regional Campus. McCormick and Fisher-Hoch are also on the faculty of The University of Texas Graduate School of Biomedical Sciences at Houston.

Contributors to the article include Stephen Gire, Matthew Stremlau, Ph.D., Kristian G. Andersen, Ph.D., Stephen Schaffner, Ph.D., Zach Bjørnson , Kathleen Rubins, Ph.D., Lisa Hensley, Ph.D., Eric S. Lander, Ph.D., Robert Garry Jr., Ph.D., Christian Happi, Ph.D., and Pardis C. Sabeti, M.D., Ph.D.