For the first time in the agency’s 70-year history, the Centers for Disease Control (CDC) in early August issued a travel advisory for part of the continental United States, warning pregnant women to stay away from a neighborhood in Miami. The culprit: the Zika virus.

Zika is a mosquito-borne illness associated with a rise in cases of microcephaly, which can cause children to be born with abnormally small heads. While the United States has recorded nearly 2,000 cases of Zika, until now all of these were associated with people who had traveled to Brazil and other parts of Latin America — or who had come in contact with people who had traveled to those regions.

But cases spread by mosquitoes in the United States are now appearing, a worrisome development. Puerto Rico already has reported more than 10,500 Zika cases, and the hot and humid conditions throughout the southern United States may make a good habitat for Zika-bearing mosquitoes.

Congress did not fund Zika control and research

While the CDC and Miami quickly moved to conduct aerial spraying of mosquitoes and launch community-based efforts to identify all Zika cases in the Miami area, Congress has failed to pass appropriations to fund Zika control and ongoing efforts to develop a vaccine.

A February proposal from President Obama for $1.9 billion in emergency Zika funding failed to reach a compromise in Congress. Instead, lawmakers authorized peeling money away from funds previously appropriated for fighting Ebola — and attached controversial language that would have allowed flying the Confederate flag at veterans’ cemeteries. With the Obama administration declaring a state of emergency on Aug. 12 for Zika in Puerto Rico, there have been calls for Congress to return from its August recess to fund the Zika response.

What sort of message would convince Americans to care about Zika?

The politics of the Ebola crisis can help explain the challenges of mobilizing money for Zika. In 2014, the United States faced a similar situation when Obama requested $6.2 billion to fight the Ebola virus in West Africa. While Congress didn’t appropriate the full amount, it did include more than $5.4 billion for Ebola as part of an omnibus budget.

In late 2014, I designed a survey experiment to test what persuasive messages would convince the U.S. public to support appropriations to fight Ebola. The findings of that survey may have relevance for the current experience with Zika.

In my previous work on AIDS, I found that Americans were convinced to care about that problem when activists made it a moral issue, pointing out the global injustice that millions lacked access to lifesaving drugs. In a forthcoming article with Ethan Kapstein in the journal Global Health Governance, we found that framing access to medicines as a human right was no more persuasive than saying we have a moral obligation to help provide people with access to lifesaving medicines.

But Ebola and Zika might have a different claim on the imagination of Americans because the newness and potential transmissibility of both diseases could cause fear and panic among Americans worried about infections. AIDS certainly had this effect when it first emerged in the early 1980s. Such fears have largely subsided with the emergence of life-extending antiretroviral drugs.

In 2014, the potential salience of fear led me to bring in Bethany Albertson and Shana Gadarian, whose book “Anxious Politics” shows how certain problems can trigger anxiety among the public. This anxiety, in turn, motivates citizens to support policies to protect them from harm. This type of support could include appropriations but also more restrictive policies on freedom of movement such as quarantines.

So, in consultation with Albertson and Gadarian, I designed an experiment about Ebola that would randomize whether people received one of four conditions or scenarios about Ebola. The first was a control condition where respondents got no message about Ebola. The second was a “fear” condition where respondents read a mock news story that emphasized the threat to America along with a photo of a health worker hosing down a corpse with bleach. The third “moral” condition showed a picture of an Ebola survivor, and the story emphasized the moral obligation to help people suffering from Ebola. Finally, the last “human rights” scenario showed the same photo but the story emphasized that access to health is a human right.

We carried out a nationally representative online survey of 1,425 Americans using the research firm YouGov in January 2015, just after Congress approved the Ebola funding without much fanfare.

After people received one of the four Ebola messages, we then asked whether they would support a hypothetical appropriation for Ebola. We also asked their support for a quarantine and other restrictive policies on immigration, as well as their willingness to engage in political behavior such as signing a petition or joining a group.

Interestingly, in the full sample, we did not find a statistically significant difference in support for Ebola funding between the control and the experimental conditions. However, we did find statistically significant increases in support for appropriations among women and among people who knew a lot about Ebola. Women’s support for funding increased in all three conditions, with the largest increases in the moral condition (see Figure 1).

The finding on women’s attitudes is particularly important when we think about the populations most affected by Zika — pregnant mothers and their infants. The finding regarding respondents who had a high degree of knowledge on Ebola was consistent with previous work Albertson and I carried out on climate change, suggesting that the challenge is persuading Americans who are not very engaged or informed.

These findings have some significance for how to communicate effectively on the danger of the Zika virus. One observation is that it’s challenging in a single, one-off experiment to generate anxiety or fear about a particular disease to trigger increased support for particular policies.

A second observation is that public concern about diseases may not spike until there are widely publicized threats to the American homeland. This might come too late to facilitate timely pressure on Congress to spend money, because by the time the public is concerned, the diseases are already here and spreading.

In the case of Ebola, concern about the virus among the U.S. mass public had come and gone by the time Congress authorized the funding. Public concern appeared to peak in October 2014 after nurses in Dallas were infected with the virus after coming into contact with a patient (see Figure 2).

Congressional appropriations lagged far behind actual events. While emergency appropriations sailed through the Congress in January 2015 for Ebola, funding arguably could have been more effective if deployed earlier. The spike of concern about Zika right now still pales in comparison to the Ebola virus. So waiting for public concern about Zika means we already have waited too long to set aside resources. While the Department of Health and Human Services has moved money around to support development of a Zika vaccine, those funds are set to run out at the end of August.

Public framing is no substitute for contingency funding

Amy Patterson has argued here in the Monkey Cage that the World Health Organization labeled Zika a global health emergency faster than Ebola because Zika was framed as a threat to rich countries. However, as the delay in Zika funding in the United States demonstrates, efforts by Laurie Garrett and others to alert the American public have yet to break through.

Perhaps one of the frames we deployed in our experiment will be useful to generate pressure on Congress so that the country is prepared for the Zika crisis. Or it may take a variety of frames to convince Americans to care about Zika and other diseases.

Ultimately, it may be harder to generate timely concern so long as the perceived threats remain largely overseas. For these reasons, the Obama administration’s former Ebola czar Ron Klain has endorsed an emergency contingency fund that the Centers for Disease Control could tap when needed to combat global health concerns like Zika. A contingency fund was the main piece of the Obama administration’s Ebola proposal that Congress did not fund. Whether the Zika virus will spur Congress to invest more in disease preparedness remains to be seen. As it stands, we’ve not dealt with this one yet.

Joshua Busby is an associate professor at the LBJ School of Public Affairs at the University of Texas at Austin. His last book, “AIDS Drugs for All,” with Ethan Kapstein, was published by Cambridge University Press in 2013.