When Zika is expected to hit the U.S.

Many public health officials had predicted that by now, a third of the way through summer, mosquitoes would be transmitting the virus. Anthony Fauci, director of the U.S. National Institute of Allergy and Infectious Diseases, predicted in late May that Zika would start spreading “in the next month or so.”

That hasn’t happened, or at least local transmission hasn’t been detected yet. The more than 1,000 U.S. cases of Zika, which causes severe birth defects and a rare nervous system disorder, have occurred only among people who traveled or had contact with a traveler.

Public health experts say they’re not terribly surprised it’s not spreading around the U.S., but they predict local transmission will start by September, especially in areas of the country such as Florida and Texas where the weather is warm and many travelers already have picked up the virus.

“I would be shocked if we did not see pockets of local transmission by the end of the summer,” said Julie Fischer, a health policy professor at Georgetown University Medical Center.

Members of Congress have echoed the dire warnings. “There’s no documented case of … anyone contracting the virus in the United States, but that’s going to change very soon because the mosquito and the threat has been inching its way, and now is on our nation’s doorstep,” Sen. John Cornyn, R-Texas, said late last month.

It’s not clear exactly why Zika-laden mosquitoes haven’t started carrying the virus from one person to another, other than the right combination of factors haven’t come together. Those factors include: enough Zika-infected people, enough mosquitoes to bite them and a warm climate so they spread the virus to uninfected people.

“It’s trying to look at the math of that triad and interrupt the critical variables,” Fischer said.

The ranks of Zika patients in the U.S. are multiplying weekly. The Centers for Disease Control and Prevention says 1,133 cases have been reported, 14 of them sexually transmitted and the rest travel-related. One-quarter of the patients are in New York and 18 percent are in Florida, with the rest scattered among 43 other states.

That’s not a huge figure, public health experts say. And given factors in the U.S. such as widespread mosquito control and air conditioning, they don’t expect that hundreds of thousands, much less millions, of Americans will be infected with Zika. But they do expect some local transmission.

It may have already started and officials just don’t know it yet, as there’s a lag time in some of the tests to detect it, said Scott Weaver, a microbiology professor at the University of Texas Medical Branch.

It takes only a few days to get results for an initial polymerase chain reaction, or PCR, test. But as a negative on a PCR test is inconclusive, a second antibody test is often performed. Currently, it takes several weeks for results on those tests, as the CDC is performing most of them, Weaver said.

If and when Zika starts spreading, it could put mounting pressure on President Obama and Congress to fund prevention and research efforts aimed at stemming the population of mosquitoes that can spread the virus and developing a vaccine for it.

House Republicans have passed a $1.1 billion funding measure, but Senate Democrats have blocked it, complaining that it falls short of the $1.9 billion Obama requested. Lawmakers have just one week left to forge an agreement, with Congress poised to leave for an extended summer recess until September.

“We have not seen the House and Senate come together in a sensible way to put forward the dollars that we have requested to get the job done,” Obama said recently. “I expect Congress to get this funding done before they adjourn, as part of their basic responsibility.”

But for now, public sentiment on Zika doesn’t seem to be providing enough motivation for lawmakers to compromise. Polls show that Americans are less scared of Zika spreading than they were of the last major public health crisis, the 2014 Ebola outbreak.

“I think during the peak of the Ebola epidemic in West Africa, the level of concern seemed quite a bit higher to me,” Weaver said. “People in this part of Texas thought they were at high risk of getting Ebola even though that was never the case.”

Twenty-two percent of Americans feared a widespread outbreak in the U.S. during the height of the Ebola crisis, while 16 percent currently fear a widespread outbreak of Zika, according to polls by the Kaiser Family Foundation. And while just two-thirds of Americans know there are Zika cases in the U.S., nearly nine in 10 said Ebola was here, even though just a handful of cases were ever confirmed on U.S. soil.

“Ebola was very frightening,” Fischer said. “We were responding to the fear as well as to the public health threat, so convincing decision-makers to mobilize resources to deal with this very frightening outbreak wasn’t such a hard sell.”