Researchers have found that protein found in human semen significantly increases Ebola virus infection, explaining how sexual transmission has led to the virus' resurgence.

Although Ebola is transmitted primarily through direct contact with blood and other body fluids from infected people, follow-up studies from the 2014 epidemic found that men can harbour the virus in their semen for at least 2.5 years, with the potential to transmit the virus sexually during that time.

The findings showed that the protein fragments -- called amyloid fibrils -- also protect the virus against harsh environmental conditions such as heat and dehydration. Thus, targetting amyloids in the semen could prevent a sexually transmitted spread of the Ebola virus, suggested the study, published in the journal Proceedings of the National Academy of Sciences.

"Given the potential for sexual transmission to spark new Ebola infection chains, we feel we have found relevant factors that may be important targets for inhibiting the spread of Ebola," said Stephen Bart, a postdoctoral student at the University of Pennsylvania in the US. To test the ability of amyloids to enhance infection, benign viruses with the distinctive Ebola glycoprotein -- a marker on the outside of the virus particle -- were incubated with physiological concentrations of semen amyloids before infecting a variety of human cell types including macrophages, a primary target of Ebola virus in humans.

It was found that infection levels of cells with this benign Ebola virus and amyloids were about 20 times higher compared to cells with the virus alone. The team also found that amyloids enhanced the binding of the virus to cells and increased its ability to be internalised by host cells.

The team's next steps are to determine if the amyloids have an effect on Ebola in models of vaginal infection and if compounds that disrupt the amyloids are protective. Additionally they plan to analyse amyloids found in other sites, such as the human gut, to see if they play a role in other types of viral infections.