Zika Virus Sexually Transmitted by Asymptomatic Men

The Zika virus (Flaviviridae flavivirus) is a mosquito-borne virus first isolated in the Zika Forest of Uganda in 1947.  Zika is related to the dengue, yellow fever, Japanese encephalitis, and West Nile viruses.  It was previously confined to a narrow equatorial belt in Africa and Asia, but in 2007 began to spread eastward across the Pacific to the Americas.  There is currently a Zika virus epidemic, and the virus is now being found in mosquitoes in south Florida.

Microcephalic child

Microcephalic child

The virus produces a fever comparable to a mild form of Dengue Fever, and there is currently no vaccine or cure for the illness.  The worst threats from Zika are not from the initial illness, however, but from, (1) the risk of severe birth defects—microcephaly and brain malformation—in the children of pregnant women who contract the virus, and (2) a paralyzing autoimmune disorder called Guillain-Barré syndrome (GBS) that sometimes follows in the wake of a Zika infection.  

Sexual transmission of Zika has been documented in six countries – Argentina, Chile, France, Italy, New Zealand and the United States.  What was not known with certainty until a few days ago is that Zika virus can be spread by sexual contact with men who are not yet showing symptoms.

An article published in the CDC’s Morbidity and Mortality Weekly Report (MMWR) described the case of a woman who contracted Zika after having unprotected vaginal intercourse and female-on-male oral sex with a male partner. The man had been exposed to mosquitoes while traveling in the Dominican Republic, but had not experienced fever, rash, conjunctivitis, or other symptoms of Zika before or after returning to the United States. He felt fatigued, but had chalked that up to the travel.  He subsequently tested positive for antibodies against both Zika virus and dengue virus. The woman, who developed fever, rash, and other Zika symptoms, tested positive for Zika virus RNA in her urine.

The CDC had cautioned that it might be possible for an infected asymptomatic man to transmit the virus to his female partner, based on a single published report. In that instance, however, both the man and the woman had traveled to a country with a mosquito-borne Zika outbreak, and both had been exposed, so it was not possible to rule out that the woman became infected through a mosquito bite rather than through sex with her infected partner.

Aedes  mosquito-- the genus that spreads Zika

Aedes mosquito-- the genus that spreads Zika

"The findings in this report indicate that it might be appropriate to consider persons who have condomless sex with partners returning from areas with ongoing Zika virus transmission as exposed to Zika virus, regardless of whether the returning traveler reports symptoms of Zika virus infection," the authors write.

It is also known, based upon a published CDC report, that the virus can be tranmitted by unprotected anal intercourse between two men.  In that case, one of the men had traveled to Venezuela and come into contact with the virus, then returned to Dallas, where he had unprotected anal sex with a partner with whom he reportedly had been exclusive for 10 years.  In fact, it is likely that the Zika virus can be spread much more easily by anal sex than by vaginal sex.  According to a literature review published in 2010 in the International Journal of Epidemiology, the risk of HIV transmission during anal intercourse may be around 18 times greater than during vaginal intercourse.  

I’m wondering if it was just a coincidence that the first domestic outbreak of Zika in the United States was in Wynwood, a one square-mile area of Miami that is famous for its many art galleries and gay bars.  There have been 37 cases of Zika reported in Wynwood so far, and the Wynwood outbreak started before any Zika-bearing mosquitoes had actually been found in Florida.  Strange.  I suspect that Zika is being passed from gays to mosquitoes as often as vice versa

That this dangerous virus can be transmitted sexually as well as by mosquitoes magnifies the threat of a pandemic.   According to CDC statistics as of August 24, the overwhelming majority of cases in the United States are from travel outside of the U.S., but 29 people have contracted it from mosquitoes inside the U.S. and 22 people have contract the disease from sexual transmission.  In other words, even according to CDC statistics, which may be biased against sexual transmission, a non-traveling American is almost as likely to contract Zika through sexual contact as from an insect. 

This is a public health crisis.  For purposes of public health, when a sexually transmitted epidemic is on the march, public health authorities need people to be able to name all of their recent sexual partners.  Anonymous sex is a threat to public health.  In light of the fact that Zika can be sexually transmitted, and can be transmitted by carriers before they present symptoms the disease, steps need to be taken immediately to close down places where anonymous sex takes place.  These include gay bath houses and any place that has “glory holes” to facilitate anonymous sexual encounters.