Sexual transmission could reignite contained Ebola outbreaks

Sexual transmission of the deadly 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, a study says.

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 realised that this could be a hidden source of the virus," said senior author Andrew Park, an associate professor University of Georgia Odum School of Ecology and College of Veterinary Medicine in the US. 

"We wanted to find out what role sexual transmission might play in the dynamics of an outbreak," Park noted.

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

The model showed 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," lead author John Vinson, doctoral student in the Odum School.

"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," Vinson noted.

The study was published in the journal Biology letters.

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