Person to person Zika virus transmission

The title of a Eurosurveillance article, “An autochthonous case of Zika due to possible sexual transmission, Florence, Italy, 2014” was written to make the headlines. The title should be “An autochthonous case of Zika due to person to person contact, Florence, Italy, 2014.”

An Italian man returns from a 10 day holiday in Thailand and a day later develops a rash with fever and headache. Within 6 days the rash has subsided. About two weeks later his girlfriend develops a similar disease. As this was 2014 no one looked for Zika virus and both were presumed to have dengue virus infection.

The serum samples taken from the patients were pulled from the freezer after Zika virus becomes a household word in 2015. Both patients’ sera are shown to contain neutralizing antibodies against Zika virus, with a clear rise between samples taken early in illness and after recovery.

Apparently the couple had sex between the time the man’s rash subsided, and the onset of the girlfriend’s symptoms. The authors of the paper conclude that transmission by semen is suggested.

Inexplicably, the authors write:

Other transmission modalities (i.e. direct contact with other bodily fluids) are unlikely to play a role but may not be completely ruled out.

Why is it unlikely that the man had a residual rash, possibly leaking virus, which he then transferred to the woman, perhaps on one or more mucus membranes? This mode of transmission is also known as ‘close contact’ between individuals. I am waiting for a similar case report in which the couple used condoms, yet Zika virus infection was still transmitted.

Like everyone else, the authors are seduced by the possibility of sexual transmission of Zika virus. I have yet to see any clear, convincing evidence of sexual transmission of Zika virus. At worst, the risk is extremely low, although probably not zero, given that Zika virus RNA (not virus) has been found in semen of one individual. Consider these facts and act accordingly.