A public-health nightmare is unfolding in Brazil, where the mosquito-borne virus Zika has been linked to nearly 4,000 cases of microcephaly – infants born with abnormally small brains and heads. Around 20% of adults with Zika don’t develop symptoms, which include fever, rash, and joint pain, so pregnant women may not even know they were infected. The list of places with active Zika transmisison currently includes 19 countries plus Puerto Rico in the Americas, as well as Samoa and Cape Verde.

While the link between Zika and microcephaly “hasn’t been proved definitely,” NPR’s Jason Beaubien explains, “health officials are operating under the assumption that there is one.” It’s also not clear why the virus, which has turned up sporadically in Africa and Southeast Asia after being identified in Uganda in 1947, is now spreading so rapidly.

Researchers are also investigating the possibility that some cases of Zika virus may lead to Guillain-Barré syndrome, in which the immune system attacks the nervous system, causing paralysis and sometimes death. “Almost every country has some cases of Guillain-Barré every year; it strikes about 1 person out of 100,000,” write Simon Romero and Donald J. McNeil Jr. in the New York Times. “Although its cause is unknown, it sometimes follows bouts of flu, bacterial infections, surgery or even vaccination.”

There is no vaccine for Zika, and the only treatment is supportive care for symptoms, so prevention is key. Reducing transmission requires preventing bites from the Aedes aegypti mosquito, the same species that transmits dengue and chikungunya. “Cities across Brazil are working to educate residents about the dangers of pooled and stagnant water, where mosquitoes reproduce, and in some cases have targeted breeding areas with insecticides,” reports Paulo Prada of Reuters. Forbes contributor Judy Stone reports that Oxitec is expanding its use of genetically modified mosquitos in Brazil; the modified male mosquitos have a gene that causes their offspring to die at the larval stage, and trials have found them to be 90% effective in reducing Aedes aegypti mosquitos.

Several affected countries are urging women to delay pregnancy – but, advocates warn, such advice is “incredibly naïve” in places where access to contraception is difficult, sex education is limited, and sexual violence is prevalent.

Zika in the US

CDC has issued a Level 2 travel alert for visiting countries with ongoing transmission of Zika. The agency advises travelers to prevent mosquito bites covering exposed skin, using EPA-registered insect repellents and permethrin-treated clothing, and staying in screened-in or air-conditioned rooms. As interim guidance until more is known about Zika virus and microcephaly, CDC recommends special precautions for two groups:

• Women who are pregnant (in any trimester):
  • Consider postponing travel to any area where Zika virus transmission is ongoing.
  • If you must travel to one of these areas, talk to your doctor first and strictly follow steps to prevent mosquito bites during your trip.
• Women who are trying to become pregnant:
  • Before you travel, talk to your doctor about your plans to become pregnant and the risk of Zika virus infection.
  • Strictly follow steps to prevent mosquito bites during your trip.

A dozen Zika virus cases have been confirmed in the US. “Florida, Illinois, New Jersey, Texas and Hawaii have confirmed that residents who recently traveled to countries where Zika virus has been found in mosquitoes have tested positive for the virus,” reports the Washington Post’s Ariana Eunjung Cha. A baby with microcephaly has been born in Hawaii to a mother who lived in Brazil while pregnant.

With Brazil scheduled to host the Olympic games in August, travelers who’d planned to attend Olympic events may be rethinking their visits. Brazil has announced it will start Olympic facility inspections four months before the Games to eradicate mosquito breeding grounds. During the games, they will conduct daily sweeps and consider fumigation on a case-by-case basis. There tend to be fewer cases of mosquito-borne viruses in Brazil during August, when the southern hemisphere experiences winter weather.

As travelers from Zika-endemic areas continue to land in the US, it becomes increasingly likely that mosquitos will start spreading the virus here — something that has already happened with dengue in Florida. Forbes contributor Tara Haelle got the perspective on this prospect from Peter Hotez, director of Texas Children’s Hospital Center for Vaccine Development in Houston:

“The concern is what if we start having transmission of the disease in Texas or the Gulf Coast by the spring when things start to heating up in the spring,” said Hotez, also the founding dean of the National School of Tropical Medicine at Baylor College of Medicine in Houston, Texas. “Texas and the Gulf Coast have the perfect storm that makes us vulnerable to arboviruses, diseases spread by insect vectors. Houston is kind of a ground zero for this.”

That perfect storm includes the presence of the two main mosquito vectors that carry Zika and other tropical diseases, Aedes Aegypti (the primary vector for Zika) and Aedes Albopictus (at least one case of Zika carriage in Africa), and the warm subtropical climate whose temperature, water and rainfall patterns allows them to thrive. Other parts of the U.S. with similar climates include Tucson, New Orleans and much of Florida. The third less appreciated but very important factor in Zika’s spread is extreme poverty.

“The Fifth Ward of Houston, for example, is a financially poor area where you see an absence of window screens and dilapidated housing, which means people have more exposure,” Hotez said. “There’s a lot of environmental degradation, with garbage piled up and tires discarded along the side of the road filling with water, that creates an environment that is quite suitable for the mosquitos.”

Hotez emphasizes the importance of clarifying guidelines on insect repellent use during pregnancy and developing a Zika vaccine. Judy Stone has some related thoughts in an addendum to her useful piece on slowing the Zika epidemic:

After this posted, the CDC issued new recommendations for pregnant women, including considering an amniocentesis to test for Zika virus, and serial ultrasounds. This would collect useful information for learning about pregnancy outcomes but likely do little for the affected women, as abortions are illegal in much of Latin America. This, too, disproportionately affects poor women, as heartbreakingly recounted in “Pregnant and Desperate in Evangelical Brazil.” When Zika is established in the U.S., it will likely hit cities like Houston and New Orleans especially hard. Texas already has very restricted access to abortion, even for serious health problems, resulting in more women trying to terminate pregnancies themselves in unsafe ways. The Gulf states are also ones that most stridently opposed Medicaid expansion. Poor women who have a baby born with severe microcephaly will also carry a disproportionate burden for the infant’s future care.

Access to healthy housing and all forms of reproductive healthcare are good for public health. It’s not surprising they’re also important for reducing the toll of Zika virus.