CDC: Sexual Transmission of Zika Possible Without Symptoms

August 26, 2016

The Centers for Disease Control and Prevention (CDC) today released the first solid evidence that a man infected with Zika, but who never develops symptoms, can sexually transmit the virus to a female partner.

An article published online in the agency's Morbidity and Mortality Weekly Report (MMWR) described the case of a woman who contracted Zika after having condomless vaginal intercourse and fellatio with a male partner after he came back from the Dominican Republic, where mosquitos are spreading the virus. The man said he had been exposed to mosquitos during his travels, but had not experienced fever, rash, conjunctivitis, or other hallmarks of Zika before or after returning to the United States. He said he had felt fatigued, but chalked that up to travel.

The man 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 authors of the MMWR article, except for one CDC investigator, were public health officials in Maryland, where the case came to light.

It is already known that the Zika virus can be sexually transmitted by infected men who are symptomatic. However, most people who are infected with Zika do not experience symptoms.

The CDC has cautioned for some time that it might be possible for an infected asymptomatic man to transmit the virus to his female partner, based on a single published report of suspected sexual transmission. However, in that instance, both the man and woman had traveled to a country with a mosquito-borne Zika outbreak, and both had been exposed to mosquitos, the authors of today's MMWR article explain. Thus it was not possible to rule out that the woman became infected through a mosquito bite and not through sexual intercourse with her infected partner.

Such was not the situation with the newly described case of the woman who contracted the virus from her asymptomatic male partner.

"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 traveller reports symptoms of Zika virus infection," the authors write.

Clinicians Treating Zika Should Think About Guillain-Barré Syndrome

In another article also published online today in MMWR, the CDC said that the US territory of Puerto Rico is running true to form for regions experiencing widespread transmission of the Zika virus — the paralyzing autoimmune disorder called Guillain-Barré syndrome (GBS) is following in its wake.

CDC investigators, Puerto Rican public health officials, and other researchers reported that among 56 patients with confirmed or suspected GBS in Puerto Rico with onset of neurologic symptoms between January 1 and July 31, 34 tested positive for Zika — which is a flavivirus — or other flaviviruses, which include dengue, West Nile, and yellow fever.

Of these 34 patients, Zika was confirmed in 10 by the presence of Zika virus nucleic acid in patient specimens. Another 24 were said to have a presumptive Zika infection because they tested positive for Zika antibodies.

The median age of the 34 patients with both a flavivirus infection and GBS was 55 years. Fifty-nine percent were female. All 34 were hospitalized, and one died.

"The potential severity and burden of GBS on the healthcare system are highlighted by the death described here and by the large proportion of patients that required intensive care services, including mechanical ventilation," the authors wrote.

The number of confirmed and suspected GBS cases linked to Zika rose steadily from April through July, matching an upward trend in confirmed and presumptive Zika infections in Puerto Rico in the spring and summer. As of August 24, the CDC counted almost 8800 laboratory-confirmed cases of Zika infection in Puerto Rico.

In addition, the greatest concentration of patients with GBS and some sort of flavivirus infection was in a public health district on the island that includes the nation's capital, San Juan. This district is one of the hardest hit by the Zika virus.

"Given the potential increase in GBS incidence during ongoing Zika virus transmission," write the authors of the MMWR article, "healthcare providers in areas with ongoing local transmission should be familiar with the clinical features of GBS to ensure timely patient diagnosis and treatment."

In another alarming finding, the authors reported that another seven patients with confirmed or presumptive Zika infections developed neurologic disorders other than GBS — namely, encephalitis, myelitis, acute neurologic deficit, and postinfectious papilledema.

Follow Robert Lowes on Twitter @LowesRobert


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