Timely surveillance warranted to help prevent "the Next Epidemic"
A family of viruses that can be deadly may have taken the leap in Africa from fruit bats into humans, a new study finds. The researchers have laid out the first initial scientific evidence that this transition is under way.
Strains of the henipaviruses vary in severity-some are not dangerous, while others have mortality rates akin to Ebola (up to 90 percent).
"Our study found the first evidence - written in the immune cells of people living in our African study area - that humans have been exposed to henipaviruses, and also that the risk of infection goes up with exposure to a bat's bodily fluids," says virologist Benhur Lee, MD, the Ward-Coleman Chair in Microbiology at the Icahn School of Medicine at Mount Sinai, New York, and lead author of the study.
Previously, Lee spent 12 years as a member of the Department of Microbiology, Immunology & Molecular Genetics and the Department of Pathology and Laboratory Medicine at the David Geffen School of Medicine at the University of California, Los Angeles.
"The tragedy of Ebola, which also jumped into humans from bats in Africa, argues that we must heighten our surveillance of viruses on the verge of spillover from animals into humans. HIV, SARS, and West Nile virus were also unknown until they emerged," he says.
Henipavirus has been on scientists' radar since emerging in Australia and Southeast Asia less than two decades ago. It was believed that infections were limited to undeveloped places near bat habitats in these places-that is, until a startling new study found that the common fruit bat species across Africa were host to several related viruses.
Researchers sought to find out if the African viruses were arising in people as they encroach further into established bat habitats. They believe that henipavirus infections are more common than once thought, and may be disguised as undiagnosed brain infections (encephalitis) in remote villages, or erroneously blamed on malaria, yellow fever, or typhoid. Or, it could be that the strains encountered in Africa do not cause serious symptoms-further research should yield those answers.
While animals serve as long-term hosts for a virus, they may not become ill from it-the virus may become lethal when it infects people, whose immune systems cannot handle it. HIV, SARS, influenza, and Ebola are among the diseases that infected animals first. We learn much about a virus's survival strategy from studying its animal hosts.
The researchers designed a highly sensitive and specific test that indicates whether or not humans may have been exposed to henipaviruses in a region with infected bats. The test involves a shrewd use of antibodies. The researchers ask, if henipaviruses are so deadly, then why are there living survivors in which to find antibodies? It could be that the henipaviruses infecting the current study participants were not deadly like those seen in some past Asian outbreaks. "It's also possible that what we are seeing is the tip of the iceberg in Africa, and that we are finding the survivors out of those that have lost their lives to such viruses without being diagnosed," Lee says.
"It's important to note that much broader surveillance efforts will be required before we can make generalizations about the risks of henipavirus spillover across Africa," Lee says. "On the other hand, for a disease that is not supposed to exist, a 3 to 4 percent henipavirus infection rate in a village would be highly significant if seen in other villages. The prevalence of HIV in Cameroon is 5 percent, and it's perceived as an African epidemic."
The study was recently published in the journal Nature Communications.