There is a great deal we still don't know about the Zika virus, but given its suspected link to profound birth defects, public health agencies around the globe are faced with a difficult decision:
Do you wait for irrefutable proof of harm, or do you warn people based on the available (and often anecdotal) evidence, in hopes of preventing needless tragedies?
Given the devastating effects that microcephalic birth defects have on families and society, most health agencies would prefer to be proactive, even if it risks raising some degree of alarm.
In this regard, this week the UK's PHE (Public Health England) has issued some specific advice to sexually active men who have recently returned from regions where Zika has been reported, based on limited reports that the virus may be sexually transmitted.
The notion that Zika might be transmitted direct contact first came to light in 2011 when the EID Journal carried a dispatch on the first Probable Non–Vector-borne Transmission of Zika Virus, Colorado, USA, involving two researchers infected in Africa, one of whom returned to the Untied States and passed the virus (presumably via sexual contact) on to his wife.
This was the first instance where sexual transmission of an Arbovirus was suspected, the author’s writing:
Results also support ZIKV transmission from patient 1 to patient 3. Patient 3 had never traveled to Africa or Asia and had not left the United States since 2007. ZIKV has never been reported in the Western Hemisphere. Circumstantial evidence suggests direct person-to-person, possibly sexual, transmission of the virus.
A second clue came a year ago, when the CDC's EID journal carried a dispatch called:
In December 2013, during a Zika virus (ZIKV) outbreak in French Polynesia, a patient in Tahiti sought treatment for hematospermia, and ZIKV was isolated from his semen. ZIKV transmission by sexual intercourse has been previously suspected. This observation supports the possibility that ZIKV could be transmitted sexually.
Even if sexual transmission is possible, this would be a minor route of infection compared to the mosquito-vectored virus. But as we've seen with Ebola in West Africa, some viruses can persist in the host long after they have physically recovered, and so this potential route of infection must be considered.
In addition to providing Zika virus: travel advice for pregnant women, this week the UK government updated their detailed guidance - The characteristics, symptoms, diagnosis and epidemiology of Zika - with the following advice on sexual transmission of the virus.
Sexual transmissionSexual transmission of Zika virus has been recorded in a limited number of cases, and the risk of sexual transmission of Zika virus is thought to be very low. However, if a female partner is at risk of getting pregnant, or is already pregnant, condom use is advised for a male traveller :
This is a precaution and may be revised as more information becomes available. Individuals with further concerns regarding potential sexual transmission of Zika virus should contact their GP for advice.
- for 28 days after his return from a Zika transmission area if he had no symptoms of unexplained fever and rash
- for 6 months following recovery if a clinical illness compatible with Zika virus infection or laboratory confirmed Zika virus infection was reported
The data is very limited, and the risks of sexual transmission are likely very low. But there is still much we still don't know about how the Zika virus affects the human body, how it is shed, and the potential for non–vector-borne transmission of the virus.
For another look on how the Zika virus is shed from the human body, earlier today Dr. Ian Mackay looked at the detection of Zika virus in urine, in his VDU blog: