How to Contain Zika in the US.

The Centers for Disease Control and Prevention recently established a causal link between Zika virus infection during pregnancy and a devastating array of congenital malformations, including microcephaly. We will likely see similar causal links established with Guillian-Barre syndrome and other serious complications in adults and children. There is, at least for now, doubt about how frequently these complications occur. Ongoing studies in Brazil and Colombia should provide solid estimates in the months to come.

The blooms of competent mosquito vectors arriving this spring may pose a real risk to limited populations of the US, particularly in the humid Southern states. While the specific Zika vector, Aedes aegypti, is well adapted to areas of high-population density, we are not likely to see the same explosive outbreak of disease here. Sporadic cases of local transmission may well occur, but a better built living environment in the US (air conditioning, intact window screens) will greatly diminish human exposure to infected mosquitoes and thus the likelihood that Zika will establish the human reservoir necessary for large-scale outbreaks. This has thus far been true with dengue, also transmitted by Aedes aegypti, which has spread extensively through Latin America and the Caribbean but has produced only one limited outbreak in Key West, Florida, in 2010.

At present, without a vaccine, medical prophylaxis, or treatment, the only way to avoid Zika is to avoid being bitten by an infected mosquito. This is not an easy task. Mosquitoes become more efficient transmitters of all their human pathogens in conditions of high heat and humidity, and there is little reason to believe that we will not experience a 12th consecutive year of record-breaking heat in 2016. The current powerful El Niño produced the highest temperatures on record last year in the Southern Hemisphere. During the 1997–1998 El Niño, outbreaks of malaria increased by 440 percent. Emerging scientific consensus deems this year’s El Niño a strong contributor to the massive dengue outbreak last year in Latin America and this year’s explosive spread of Zika through Brazil and beyond.

At the end of the day, mosquitoes are here to stay, at least for the foreseeable future. And it seems likely that newer emerging diseases will continue to appear and challenge us. What, then, can we do to limit the spread of Zika—and other mosquito-borne diseases—in the US? I suggest four approaches.

First, the rates of mosquito-borne disease transmission are dramatically different between cities with well-developed systems of control for stagnant water and those that do not. The increase in mosquito-borne diseases in many cities in middle-income countries is directly linked to the challenges posed by informal settlements to the control of potential mosquito-breeding grounds. It is ironic, and deeply unfortunate, that governments of some of the countries that have thus far been affected by Zika have only now started paying attention to these challenges, after years of systematic disinvestment in the infrastructure that could have limited mosquito spread to begin with. In the US, we will need to mount aggressive community-based campaigns to rid our yards of standing water, identify and repair broken screens, and conduct targeted spraying of undrainable breeding sites.

Second, methods have now been developed to collapse whole populations of Aedes mosquitoes. One approach involves genetically modifying mosquitoes by inserting second-generation suicide genes into male mosquitoes. This has led to an 80 percent decrease in Aedes mosquito populations in experimental trials. While promising, it remains to be proven if this is effective in the real world beyond small areas and temporary periods. Impractical numbers of genetically altered male mosquitoes would be needed to have a large or sustained effect.

Third, replication of viral pathogens within the Aedes mosquito may be blocked by the experimental introduction of a symbiotic bacterial species, Wolbachia, which is known to infect large portions of the insect kingdom, but not Aedes. By also being passed to all of the mosquitoes’ progeny, this forms a transgenerational “insect vaccine” that may be able to self-propagate through large insect populations and substantially diminish or eliminate transmission of dengue and, hopefully, other human arboviral pathogens. Wolbachia is harmless to humans and is too big to travel down the mosquito’s salivary duct and into the human blood stream.

Fourth, we need to provide women access to easy and full access to reproductive health services. While solely advising women not to get pregnant is a dubious public health approach, ensuring reproductive health care access is both an urgent need and good public health policy. However, among the six Southern states at most risk of local Zika spread, only Louisiana has adopted the Medicaid expansion. Medicaid is the single largest source of public funding for family planning services and plays a primary role financing sexual and reproductive health care services for millions of low-income women of childbearing age. Along with proposed funding cuts to Planned Parenthood, poor women in these Southern states with the highest exposure risk to Zika will have little help against the now established risk of these devastating birth outcomes.

Zika is not the last new or re-emerging mosquito borne infectious disease we will see, although it poses unique public health challenges. The Paris Agreement on climate change is a good start at a long-term strategy to combat the increasing reach and efficiency of mosquito vectors. In addition to developing more promising near-term innovations that affect vector biology, for now we need to dry out and clean up potential breeding sites and insure that vulnerable populations have full access to all the information, tools, and most importantly, reproductive health services necessary to protect themselves from this potentially calamitous infection.

Donald Thea is a professor of global health and director of the Center for Global Health & Development.