Publication date: 
July 8, 2016

In the midst of a contentious Congressional battle over funding for Zika prevention and research, IHME is providing Congressional staff with objective information to guide decision-making.

With Congress returning from its Fourth of July recess, the Washington Global Health Alliance, in collaboration with Representatives Adam Smith, Sheila Jackson-Lee, and Raul Ruiz, MD, recently invited a panel of experts to participate in a briefing on the Zika virus for Congressional staff. The panel discussion (video available here), which included Dr. David Pigott, Assistant Professor at IHME, focused on Zika transmission and prevention in the US.

Zika can be transmitted in several ways, among them mosquito bites, sexual contact, and blood transfusions. So far, the Centers for Disease Control has counted 2,961 cases of Zika in the United States and its territories, but looking separately at cases in states and territories is revealing: almost all of the Zika cases in US territories (Puerto Rico, American Samoa, and the US Virgin Islands) arose locally through mosquito-to-human or human-to-human transmission, while cases in the continental US came from travelers who entered the US with an existing Zika infection. It does not appear that Zika has gained a local foothold in the continental US.

But according to Dr. Pigott, that may be about to change. He pointed to two overlapping conditions that may result in outbreaks of locally acquired Zika virus in the US: summer weather and the oncoming mosquito season. In previous work, IHME researchers, including Dr. Pigott, demonstrated that Zika transmission is exacerbated by higher temperatures, humidity, and precipitation. In addition, noted Dr. Pigott, “We’re coming to the critical period in terms of mosquito abundance across the country. In the next couple of months, we’re going to see an uptick in the population numbers” of both Aedes aegypti, a known Zika carrier, and Aedes albopictus, a suspected carrier. Both species live in the United States.

Experts like Dr. Pigott worry that this summer’s mosquitos will bite infected travelers returning to the US and then infect others, causing local outbreaks. Since areas of the US (as discussed in a previous post, Getting ahead of Zika’s spread) are suitable for local Zika transmission, said Dr. Pigott, “The chance that a local transmission could occur through mosquitos is going to be increasing as the summer goes by.”

Prevention efforts will be key in limiting the spread of the disease. Baylor College’s Dr. Joseph Gathe, Jr., noted that his hometown of Houston, Texas – which matches the hot, humid, and rainy profile identified by IHME researchers as particularly conducive to Zika’s spread – will need to work at prevention if it wants to limit Zika. It will be vital to remove standing water (including that left from this spring’s floods), adhere to a robust insecticide spraying schedule, and to teach people to prevent mosquito bites. Dr. Gathe worried particularly about Zika risk among poor people in the US South whose homes may not be mosquito-proofed and who may lack access to up-to-date information about Zika prevention.

The panel also discussed diagnostic and medical responses to Zika. “We have to be able to screen the blood supply for potential Zika virus infection and we also have to invest in technologies that can inactivate the Zika virus if it is in donated blood,” said Dr. Rick Bright of the Biomedical Advanced Research and Development Authority, adding, “and then most important, I think, is the need for vaccines.” While Dr. Bright thinks the chances of developing an effective vaccine are favorable, the earliest date that one could possibly be available is 2018.

Since a Zika vaccine may be years away, public health experts will be watching the next few mosquito seasons closely for signs of local Zika transmissions in the US. It may be ­– even with increased funding for diagnostic testing and vaccine development – that surveillance and prevention will be necessary to contain Zika in the US.