A glut of Zika cases in Puerto Rico suggests that the virus has a preferred victim: women.
It’s an idea that has come up before, in previous reports from Brazil and El Salvador. But a new analysis from the U.S. Centers for Disease Control and Prevention adds some heft to the story. Of nearly 30,000 Zika cases in Puerto Rico from November 2015 to October 2016, 63 percent were female, the CDC reported online November 11.
This preference is yet another one of Zika’s peculiarities. Two other mosquito-borne diseases, dengue and chikungunya, don’t seem to discriminate between men and women. In previous years in Puerto Rico, cases of these diseases were split evenly.
Researchers are still grappling with how to explain the disparity. Zika and all of its mysteries could be on scientists’ radar for the long term. Though infections may soon wind down within the continental United States, case counts are still ticking upwards in some places. Puerto Rico has reported more than 33,000 confirmed cases and Florida is up to 1,169 cases as of November 16.
This week, scientists picked up a clue to the gender bias mystery, and learned more about how Zika may be transmitted — and how to clean it up.
Zika thwarts vaginal tissue’s defenses
The vaginal immune systems of mice don’t get riled up for Zika virus, Shazada Khan and colleagues report November 16 in the Journal of Experimental Medicine.
Mice infected with Zika in the vagina had a sluggish immune response and didn’t immediately release the virus-fighting molecules that would usually combat Zika. The same was true of another RNA-based virus called LCMV, the researchers found.
For these viruses, “vaginal tissue is exceptionally vulnerable to infection,” writes Khan, of the Gladstone Institutes in San Francisco. It’s a possible molecular answer for why women may be at a greater risk for Zika than men.
Mosquito bites could deliver double dose of disease
A single mosquito bite may be able to transmit both Zika and chikungunya at the same time, Claudia Rückert, Greg Ebel and colleagues reported November 14 at the annual meeting of the American Society of Tropical Medicine and Hygiene in Atlanta.
Researchers let mosquitoes feed on blood spiked with chikungunya, Zika or both. The team then measured the amount of each virus in the mosquitoes’ saliva.
Mosquitoes infected with only Zika virus had about the same number of Zika genome copies in their saliva as those infected with both viruses. The same was true for chikungunya. Basically, the doubly infected mosquitoes were carrying a double load of virus, says Rückert, of Colorado State University in Fort Collins.
That could mean that mosquitoes are spreading two diseases from person to person, she says.
Zika can survive for hours outside the body
Zika can survive for at least eight hours in dried blood on a glass surface, researchers reported November 15 at the annual meeting of the American Association of Pharmaceutical Scientists in Denver.
When the team scraped the glass clean and added the virus and blood mixture to monkey kidney cells, it was still infectious. But the virus isn’t invincible. Washing the blood-stained glass with 70 percent isopropyl alcohol for 15 seconds was enough to inactivate 99.999 percent of the virus, says virologist Steve Zhou of a division of Microbac Laboratories Inc. in Sterling, Va.
Concentrated bleach worked too, he adds.