Zika virus can enter and infect the body through the mouth, shows a non-human primate study published in Nature Communications this week, which indicates that contact transmission of Zika virus can occur via the oral route. However, the study also shows that saliva of infected animals is not sufficient to transmit the virus to naive animals, suggesting that contact transmission occurs through other body fluids.

Although Zika virus is mainly transmitted through mosquitoes or sexual contact, there has been at least one case of human-to-human nonsexual transmission in a hospital. Zika virus can be detected in many body fluids, including saliva, tears, sweat and breast milk. The source of infectious Zika virus that resulted in transmission to a naive person and the route of infection are unknown.

Thomas Friedrich and colleagues estimate the risk of Zika virus transmission by saliva in non-human primates. They show that a high dose of virus administered to the tonsils spreads in the animals. The viral levels in blood and urine are similar to those observed after subcutaneous injection, suggesting that Zika virus transmission through the oral route is possible. However, the study also shows that saliva from infected animals is not sufficient to infect naive animals when administered to the eyes, nose, or tonsils. This suggests that the risk of Zika virus transmission with saliva is low.

Although further studies are necessary to evaluate contact transmission of Zika in more detail, the current study suggests that Zika virus can be transmitted through the oral route if the ingested dose is high enough. This has implications for understanding how Zika virus can spread through populations.