Nav: Home

Sexual transmission of Ebola likely to impact course of outbreaks

June 07, 2016

Athens, Ga. - Sexual transmission of the Ebola virus could have a major impact on the dynamics of the disease, potentially reigniting an outbreak that has been contained by public health interventions, according to research by University of Georgia ecologists just published in the Royal Society journal Biology Letters.

The potential for sexual transmission is high for three to four months after the virus has been cleared from the bloodstream, and possible for an average of seven months.

The research was prompted by the publication of data showing that viable Ebola virus remained in the semen of disease survivors for months after it was no longer detectable in their blood -- and by a study reporting at least one instance of sexual transmission of Ebola.

"We realized that this could be a hidden source of the virus," said senior author Andrew Park, an associate professor in the UGA Odum School of Ecology and College of Veterinary Medicine's department of infectious diseases. "We wanted to find out what role sexual transmission might play in the dynamics of an outbreak."

The researchers developed a mathematical model to test various outbreak scenarios.

First, they created a model population of 1,000 individuals and introduced Ebola virus to track its spread via regular transmission. Based on the experience of the 2014 outbreak, they assumed that many actions would be taken, from individual behavior changes to public health interventions, to control the outbreak. In the parameterized model, this resulted in one in four individuals infected throughout the population.

"An important point to make is that without the behavior changes and interventions, it would have been more like 80 percent of individuals infected," said Park. "The actions taken in West Africa were very effective."

Next, they set out to determine the impact that sexual transmission could have.

"We wanted to know what it would mean in terms of the size of an outbreak, how long an outbreak lasts, how likely an outbreak is to occur and the reproductive ratio of the parasite, a measure of how effectively the parasite transmits in populations," said the study's lead author John Vinson, a doctoral student in the Odum School.

There were, however, two components of sexual transmission about which very little is known. The first is what proportion of people who survive Ebola are actually able to transmit the virus through sexual contact; the second is how the rate of sexual transmission compares to that of regular transmission.

To overcome this lack of data, they ran the model using values that varied widely for both questions but within plausible limits.

Their results showed a clear impact from sexual transmission. When the values of both parameters--the number of sexually infectious individuals and the rate of transmission--were low, outbreaks were smaller and ended more quickly, but as the values increased, so did the size and duration of outbreaks.

The model shows that even the smallest and shortest outbreaks in the presence of sexual transmission were larger and longer-lasting than outbreaks where no sexual transmission occurred.

"Whenever we had die-outs of the directly transmitted infectious individuals, which would otherwise have spelled the end of the outbreak, we had reignition from the sexually infectious individuals transmitting the virus to the susceptible people left in the population, who then served as a source of direct transmission," Vinson said. "Thinking about it from the parasite's point of view, the parasite is able to persist in that population even without the direct contact transmission by symptomatic individuals."

Park said the findings point to the importance of considering alternative pathways of disease transmission.

"There's an increasing awareness that sexual transmission can happen in addition to a more clearly evidenced transmission route and not just with Ebola," he said. "But there's been very little written about how it works or what it means for the metrics that the public health community uses. Our model is ultimately translatable to other disease systems and shows how it can be done even under uncertainty of key parameters."
-end-
The study, "The potential for sexual transmission to compromise control of Ebola virus outbreaks," is available online at http://dx.doi.org/10.1098/rsbl.2015.1079.

Co-authors are John Drake, an associate professor in the Odum School, and Pejman Rohani, a professor in the Odum School and College of Veterinary Medicine. Support for the research was provided by the National Institute of General Medical Sciences of the National Institutes of Health under award number U01GM110744 and by the National Science Foundation.

University of Georgia

Related Ebola Articles:

Ebola survivors have a 'unique' retinal scar
Researchers from the University of Liverpool have conducted a study of Ebola survivors to determine if the virus has any specific effects on the back on the eye using an ultra widefield retinal camera.
Ebola: Lives to be saved with new management approach
Ebola outbreaks are set to be managed quickly and efficiently -- saving lives -- with a new approach developed by an international team of researchers, including the University of Warwick, which helps to streamline outbreak decision-making.
Ebola vaccines provide immune responses after 1 year
Immune responses to Ebola vaccines at one year after vaccination are examined in a new study appearing in the March 14 issue of JAMA.
New scoring system predicts Ebola severity
While Ebola virus disease (EVD) is notorious for being one of the world's most deadly infections, it actually has a wide range of outcomes, where asymptomatic presentation may be as common as fatality.
Could co-infection with other viruses affect the survival of those with Ebola virus?
Could co-infection with other viruses have a detrimental affect on Ebola survival, and why did some show Ebola symptoms without having the virus?
Antimalarial being tested as possible Ebola virus drug
The National Center for Advancing Translational Sciences (NCATS) recently awarded $596,533.00 to Collaborations Pharmaceuticals, Inc.
Ebola map may help prepare for future outbreaks
To be prepared for new Ebola virus disease cases, it is fundamental to start by identifying the range of the virus and the regions that are more favorable for its propagation.
Sexual transmission of Ebola likely to impact course of outbreaks
Sexual transmission of the Ebola virus could have a major impact on the dynamics of the disease, potentially reigniting an outbreak that has been contained by public health interventions, according to research by University of Georgia ecologists just published in the Royal Society journal Biology Letters.
Ebola vaccine: Promising phase I trials
The clinical phase I trial of a potential vaccine against the dreaded Ebola virus has been successfully completed at four partner sites in Africa and Europe.
Improving treatments for post-Ebola syndrome sufferers
Researchers from the University of Liverpool and the King's Sierra Leone Partnership are to present new findings into post-Ebola syndrome at a major European conference this week.

Related Ebola Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Digital Manipulation
Technology has reshaped our lives in amazing ways. But at what cost? This hour, TED speakers reveal how what we see, read, believe — even how we vote — can be manipulated by the technology we use. Guests include journalist Carole Cadwalladr, consumer advocate Finn Myrstad, writer and marketing professor Scott Galloway, behavioral designer Nir Eyal, and computer graphics researcher Doug Roble.
Now Playing: Science for the People

#530 Why Aren't We Dead Yet?
We only notice our immune systems when they aren't working properly, or when they're under attack. How does our immune system understand what bits of us are us, and what bits are invading germs and viruses? How different are human immune systems from the immune systems of other creatures? And is the immune system so often the target of sketchy medical advice? Those questions and more, this week in our conversation with author Idan Ben-Barak about his book "Why Aren't We Dead Yet?: The Survivor’s Guide to the Immune System".