Possible sexual transmission of Zika virus – Expert reaction

The Ministry of Health has reported a case of possible sexual transmission of the Zika virus in New Zealand.

zikaA full release from the Ministry is available here.

The SMC gathered the following expert commentary on the announcement.

Prof Michael Baker, Department of Public Health, University of Otago, Wellington, comments:

“If confirmed, this possible case of sexual transmission of Zika virus in New Zealand would be quite significant.  According to recent reports from the US Centres for Disease Control and Prevention and World Health Organisation there have been only two previously documented cases of probable sexual transmission of this infection, plus one case where Zika virus was detected in human semen.

“There is therefore likely to be a small but measurable risk of sexual transmission of Zika virus. As a result, the CDC guidelines released last month recommend that “Men who reside in or have travelled to an area of active Zika virus transmission who have a pregnant partner should abstain from sexual activity or consistently and correctly use condoms during sex … for the duration of the pregnancy.” 

“There are many unanswered questions about sexual transmission of Zika, including the level of risk, whether asymptomatic cases can transmit the virus, and the period during which transmission can occur.  Consequently, it is important that New Zealand investigates this possible case of sexually transmission of Zika in a thorough manner.

“At the same time, we should remember that the predominant mode of transmission of Zika is through being bitten by a mosquito while in an area where Zika virus is established.  Consequently, the most important precautions are still for travellers to take precautions against such bites or avoid travel to such areas if pregnant.”

Dr Siouxsie Wiles, Senior Lecturer, Faculty of Medical and Health Sciences, University of Auckland, comments:

“The Ministry has reported a case of Zika infection in a person who hasn’t travelled to a Zika infected country. There are two possible explanations. One is that the virus was passed via sexual transmission. The other is that the person was bitten by an infected mosquito that entered the country in her partner’s luggage.

“The infected mosquito coming in the luggage is improbable; I think it is less likely than the possibility of sexual transmission.

“There are now a handful of cases documenting possible sexual transmission of the virus. They have all been cases of transmission from men to women; so far there have been no cases of transmission from women to men.

“There has also been a case of a man who didn’t transmit the Zika virus to his partner but the virus was detected in his semen.

“Sexual transmission of the virus is not the main route of infection. It is still quite rare.

“It is important to note that in New Zealand we don’t see the kind of sustained spread or transmission is happening in countries like Brazil. We don’t have the mosquitoes that carry the virus here in New Zealand.

“The advice from authorities has been clear from the beginning. The Centers for Disease Control in the US, the World Health Organisation and UK’s National Health Service all say: if you are a man who has travelled to an infected country and you have a fever or likely have Zika, you should either abstain from having sex or use a condom.

“The advice on how long you should wear a condom or abstain from sex for varies. The WHO says four weeks, but the UK is saying up to six months. The reason for this is because at this stage they have no idea of exactly how long a man with Zika infection is likely to have the virus in his semen.”