Infectious diseases may be older than previously thought
Field evidence collected by Pardis Sabeti and his research team suggests that some people who live in areas where Ebola and Lassa are common may have developed an immunity to the diseases. In 2011, blood tests showed that as much as 55 percent of the population in a Guinea community had been exposed to Lassa with 22 percent exposed to Ebola, Medical Xpress reports.
Even though Ebola and Lass only reportedly started infecting people in the past half century, building up immunity to a disease typically takes many generations.
Researchers found that Lassa seems to have diverged from a family of hemorrhagic diseases approximately 500 years ago. Ebola apparently diverged from the Marburg virus approximately 10,000 years ago.
The team also found that Ebola and Lassa may cause differing symptoms in populations where immunity may be present. Instead of mucosal and internal bleeding, the victims might experience cough, sore throat or fever.
The researchers suggest that if Ebola and Lassa are diseases that are newly diagnosed, rather than emerging, the phenomenon may be the case with other diseases as well.
"Recent epidemiologic and genetic studies of Lassa and Ebola fevers suggest that these diseases may have widespread prevalence and ancient origins," the team said, according to Medical Xpress. "They raise the possibility that some viral infections may reflect 'emerging diagnoses' of diseases that are circulating more widely than thought, with an emerging character primarily a matter of improved detection of the culprit pathogens."
Future research to determine which populations might harbor the diseases could better predict when outbreaks might occur, Medical Xpress reports.