This week in Zika: Revised risk, new mosquito threat, U.S. on the brink

The whipsaw of recent Zika news — good, then grim, then good again — paints a dizzying picture of the epidemic’s reach, risks and how to fight it.

On July 25, Colombia announced that the Zika epidemic there was over — good news for a country with nearly 100,000 cases of infection reported so far. But days later, the news was back to being bad: Honduras reported nine new babies born with birth defects linked to Zika.

The take-home: The worst may have passed in some countries, but others could still be facing a fight.

And the United States might be next. So far, except for in the territories, U.S. cases of Zika have been traced to international travel or sex with an infected person. But a smattering of new cases hints that Zika virus may now be spreading locally, from Zika-carrying mosquitoes living (and biting) in some states. Health officials in Florida are keeping an eye on four cases of Zika infection – two just reported July 27 – that may have come from bites of mosquitoes buzzing in that state. Travel has already been ruled out as a cause for the two earlier suspicious cases. And last week, another mysterious case was reported in Utah. Together, these new infections could signal the start of an outbreak in the continental United States.

In other news:

• Throughout Latin America and the Caribbean, 1.65 million women of childbearing age could be infected with Zika virus before the end of the current epidemic, Alex Perkins and colleagues report July 25 in Nature Microbiology.

  A previous estimate had suggested that millions more women might be at risk — 5.42 million, to be exact — but didn’t take into account herd immunity, writes Perkins, an epidemiologist at the University of Notre Dame in Indiana. People who’ve caught the virus once are immune to subsequent infections, and act as a sort of firewall blocking Zika’s spread. So, even in Zika-afflicted regions, large groups of uninfected people may be protected .

  In total, 93.4 million people in the region risk infection by Zika, the researchers predict.

• Of the potential 500,000 visitors traveling to Brazil for the 2016 Olympics, just three to 37 infected people will bring Zika home, Yale University epidemiologist Albert Ko and colleagues estimate July 25 in the Annals of Internal Medicine.

  And that’s the worst-case scenario, the study’s authors write. It’s a remarkably small number of infected travelers, considering recent hubbub over holding the Olympics in Rio de Janeiro. But given the rate of Zika infection, the transmission intensity in August in Brazil (typically low for mosquito-borne diseases), and the average length of time Zika stays in an infected person’s blood (9.9 days), the risk to Olympic attendees is low, Ko’s team argues.

  (In fact, the researchers point out, Zika probably poses less of a risk to Olympic attendees than to the Brazilian population itself — visitors may be more likely to spend time in mosquito-free, screened-in, air-conditioned dwellings.)

  The new work supports what the World Health Organization and the U.S. Centers for Disease Control and Prevention have asserted for months: unless you’re a pregnant women, attending the Olympics just isn’t that risky.

• Samples of a common mosquito species, Culex quinquefasciatus, have tested positive for the presence of Zika virus, the Oswaldo Cruz Foundation in Brazil announced last week. Collected in the city of Recife, samples contained the virus, although that is just one piece of information necessary to determine whether this species will join two Aedes species as recognized possible spreaders of the disease. C. quinquefasciatus’ range reaches up into the southern United States.

  

• Antibodies against Zika could potentially offer scientists a way to fight the infection. Two new studies have reported that Zika antibodies (from both mice and humans) protect mice injected with what would otherwise be lethal doses of Zika virus. Without the antibodies, mice infected with the virus lost weight and died, researchers report July 14 in Science. A different team reports similar results July 27 in Cell.

  The work begins to carve out a path for the development of Zika-preventative drugs, both teams suggest. One day, women could potentially take the antibodies during pregnancy to ward off infection.

Susan Milius contributed to this story.