Amyloid fibrils in semen enhance the infection potential of Ebola virus

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Primarily transferred via direct contact with the blood or bodily fluids of infected people, the Ebola virus receives a significant boost to its infective properties from amyloid fibrils in human semen, according to a study published in the Proceedings of the National Academy of Sciences.

Follow-up studies from the 2014 epidemic demonstrated that men can harbor the virus for at least 2.5 years in their semen, which helps to protect it from harsh environmental conditions such as heat and dehydration. Infected men have the potential to sexually transmit the virus during that period.

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The study comes amidst a resurgence of Ebola in Guinea, previously declared Ebola-free during the West Africa outbreak, which has been linked to sexual transmission. The team, from the University of Pennsylvania (PA, USA), surmised that targeting amyloids in semen could prevent a sexually transmitted spread of the Ebola virus.

To test the ability of amyloids to enhance infection, benign viruses with the distinctive Ebola glycoprotein were incubated with physiological concentrations of semen amyloids. They were then used to infect a variety of human cell types including macrophages, a primary target of Ebola virus in humans. The team discovered that the infection levels of cells with the benign Ebola virus and amyloids were approximately 20-times higher in comparison with cells containing the virus alone.

Researchers also found that amyloids enhanced the binding of the virus to cells, increasing its ability to be internalized by host cells. The fibrils working within semen significantly altered the physical properties of the virus, making it better able to survive in drier high-temperature internal body environments.

Several types of amyloids found in semen enhance the transmission and infection of other viruses, such as HIV, by helping the virus attach to the membrane surrounding host cells. Strategies for countering amyloids have been developed to slow or halt HIV transmission, and researchers suggest that the same approach could be tested for its ability to reduce infection in models of sexually transmitted Ebola.

“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,” commented Stephen Barts (University of Pennsylvania School of Medicine).

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 analyze amyloids found in other sites, such as the human gut, to see if they play a role in other types of viral infections.

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Source: Bart SM, Cohen C, Dye JM, Shorter J, Bates P. Enhancement of Ebola virus infection by seminal amyloid fibrils. Proc. Natl Acad. Sci. USA. doi: 10.1073/pnas.1721646115 (2018) (Epub ahead of print); www.pennmedicine.org/news/news-releases/2018/june/proteins-found-in-semen-increase-the-spread-of-ebola-virus-infection

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