In the sweltering Rio Grande Valley, just north of the Texas-Mexico border, concerns about Zika virus travel through the streets.
Rafael Prado is a volunteer who goes door-to-door passing out health department warnings in neighborhoods in Hidalgo and Starr counties.
At one home he finds Irma Castillo, pregnant and due in November, worried about Zika infection.
"Well, it scares you. I mean, it being my first child, it's something that really concerns me," expressed Castillo.
Mosquito transmission of Zika could happen almost anywhere in Texas, but some experts fear counties along the Mexican border and the Gulf Coast are among the areas most at risk.
Neighborhoods near the border, known as the Colonias, present some of the biggest concerns for health officials. There are many vacant lots and places for mosquitoes to breed, and many families who live there travel back and forth to Mexico all the time where Zika has already taken hold.
But despite the risks, an NBC 5 investigation found few people have been tested for Zika in some border and Gulf Coast counties in Texas.
More than 800,000 live in Hidalgo County, but the local health department said it has submitted Zika tests for just 25 people to the state health department.
The local health department said only nine people have been tested in Brazoria County, 12 in El Paso County, four in Webb County and just six in Nueces County.
In several other nearby counties, Zapata, Duval and Jim Hogg, a health official tells NBC 5 Investigates not one Zika test has been submitted to the state.
Dr. Peter Hotez is the dean of the National School of Tropical Medicine in Houston. NBC 5 Investigates shared those numbers and his reaction is that of concern.
"It means there's no active surveillance. We are not doing any active detection of Zika transmission," said Hotez.
He fears a lack of testing in some south Texas counties could cause dangerous delays in detecting the first cases of local transmission of Zika.
"A key point here is that we may already have transmission underway in Texas, Louisiana and the Gulf Coast," said Hotez.
Hotez thinks transmission could be happening without anyone knowing, because no one is looking hard enough.
Hotez believes health officials need to implement "active surveillance" teams in hospitals or clinics in some counties to aggressively test more people with fevers and rashes, seeking out possible Zika cases.
Eddie Olivarez, the Hidalgo County health director, said his county does not have funding to conduct active surveillance like Hotez suggests.
In his county health lab, they have a tiny room where they can analyze mosquitoes but there's no equipment for human Zika testing. They depend on the state for that.
And there's no staff here to run a more aggressive active surveillance program even if it might help.
"Definitely would be very helpful -- it would be very supportive of the community if that capacity was made available to us to expand the number of people being tested, of course, within the guidance and criteria to provide testing for," said Olivarez.
NBC 5 Investigates went to the Centers for Disease Control and Prevention in Atlanta to see if they can do more to help Texas.
At the CDC's operations center, NBC 5 Investigates interviewed Dr. Lyle Peterson, who's in charge of the federal government's Zika response.
Petersen said he's concerned not enough testing is being done but that the CDC can't afford to put active surveillance teams in Texas.
Less than two weeks ago, the CDC announced it's nearly out of Zika funding. Plus, Peterson said frontline testing is really the state's job.
"Public health in the United States is really the domain of the states. We assist health departments, but it's really up to the health departments to mobilize the troops out there," said Peterson.
But at the state health department in Austin, officials told NBC 5 Investigates they can't afford an active surveillance program either.
"If we were given money to do that kind of sentinel surveillance that Dr. Hotez is very interested in, we would do it. We don't have the funds and we don't have the system in place to get that done," said Dr. John Hellerstedt, commissioner of the Texas Department of State Health Services.
Hellerstedt said it would also be hard to choose where to send active surveillance teams because the possibility of local transmission is widespread across the state. But even without those surveillance teams, he's confident Texas doctors will spot any possible Zika cases and get patients tested.
"I have every reason to believe the physicians are doing a good job of referring these people for testing," said Hellerstedt.
Hellerstedt said the state is doing a lot of outreach to doctors to encourage them to test more patients with symptoms.
But some experts fear the process of sending tests to the state lab is time consuming and many doctors won't do it if the patient only has mild symptoms or is not pregnant. That could miss opportunities to spot locally transmission as early as possible.
Hotez argues the low number of tests sent from some counties proves that.
"It's expecting too much, because they're not doing it," said Hotez.
NBC 5 Investigates spoke to doctors who said the paperwork involved with submitting Zika tests to the state can take 30 minutes to complete and that discourages some doctors from doing it.
The state said it recognizes the time it takes to fill out the paperwork, but argues the information needed on the forms is important so they won't change the process.
Some doctors are now sending tests to private labs to avoid the state process, and that has likely increased the amount of testing occurring in some places.
Hotez said the state and feds need to find the funding to do what's best to protect people.
"Month after month after month passed and really, right now, no program is in place in terms of active surveillance," said Hotez.
As more weeks go by he worries about pregnant women, like Irma Castillo.
"You know, just to be inside a certain amount of time, it's not a good thing," said Castillo, who is staying indoors to avoid mosquito bites.
She lives in a place where the risk is high and the warnings are out. But it's a place where some still wonder if health officials are missing chances to protect people.
"We have had so much lead time and that is what's so astonishing," said Hotez.
NBC 5 Investigates found much more testing is occurring in Dallas and Tarrant counties because local health department labs can now conduct Zika tests on their own, and they've partnered with local hospitals to make the process easier for doctors. But that is not happened in many smaller counties with fewer resources.