Saron Wyatt pointed to the secluded end of her small street in Houston's impoverished Fifth Ward, where a mound of old tires keeps popping up.

Always a trashy nuisance, it's now a growing danger. Tires collect water and become prime breeding grounds for mosquitoes — especially the ones that spread Zika virus disease and other tropical mosquito-borne illnesses.

Wyatt, a mother of five, doesn't know where the tires are coming from. But she's worried about it, and so are health officials.

Spraying for the type of mosquito that carries Zika is not always effective, and they can breed in pools of standing water as small as a Styrofoam cup. That means vacant lots or messy yards may need to be cleaned up, whether the owner of the mess wants it cleaned or not.

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Dr. Umair Shah, the head of Houston's county health department, called getting the cooperation of local residents his department's biggest issue. "It's really about a neighbor who might have sources of breeding on their property that can impact a neighbor two or three houses down," he said.

Experts believe the vast majority of neighbors will comply. But not all. For months now, the federal government has been urging local health officials to review local nuisance ordinances and plot how to handle property owners who are combative or can't be found.

During a recent outbreak of dengue fever in Hawaii that involved the same mosquito that can spread Zika, health officials went to more than 500 properties to survey or spray. In 23 cases, residents refused requests to enter.

It happened again in March, when health officials went to see a Kauai resident who was infected with Zika after traveling to an outbreak area in Latin America. Initially, the person would not allow health officials onto the rental property. But when a team returned for a follow-up visit, a family member let them in to look for mosquito breeding areas.

"For the most part, we do get good cooperation," said Keith Kawaoka, deputy director for environmental health at Hawaii's state health department. But sometimes cooperation only comes only after a couple of conversations.

Zika has been sweeping through Latin America and the Caribbean in recent months, and the fear is that it will get worse there and arrive in the U.S. with the onset of mosquito season this summer. Zika causes only a mild and brief illness, at worst, in most people. But it can cause fetal deaths and severe birth defects in the children of women infected during pregnancy.

After West Nile Virus, another mosquito-borne disease, hit the United States in 1999, the response was often to spray wide areas using trucks and aircraft.

But the kinds of mosquitoes that primarily spread West Nile are different from the Aedes aegypti mosquito that spreads Zika and dengue. That tropical pest likes to live very close to people, and immediately around their homes.

If someone is diagnosed with Zika and health officials determine that they were infected by a local mosquito, officials will draw a circle around their house with a radius of about 150 yards. That's roughly half a block in many cities. An Aedes aegypti mosquito doesn't travel farther than that during its typical three-week lifespan.

Next, health officials or mosquito control workers will visit the properties within that circle and look for standing water where mosquitoes may be breeding, including Styrofoam cups, flower pots, and old tires. They will work with the property owner to remove them, or treat them with chemicals that kill mosquito larvae.

Some people may not want such an intrusion.

In Hawaii during its dengue outbreak, much of the resistance came from organic farmers and beekeepers wary of chemical sprays, Kawaoka said.

But there may be other cases in which a property occupant is hiding an illegal activity and doesn't want health officials snooping around. Or, there may be people who simply don't want anyone from the government on their land, some experts said.

"In modern America, there's been a lot of focus on individual autonomy," said Lawrence Gostin, a public health law expert at Georgetown University.

Health officials think health they would be able to beat back a legal challenge to government intervention because courts have long allowed the government to intrude onto private property to deal with situations that may be harmful to the public, Gostin said.

Wyatt doesn't know where the tires on her street in Houston come from, but she doesn't think it's her neighbors. She considers the people on her block to be quiet people who don't come out of their houses much but don't appear to cause any trouble.

"They all look out for one another," she said.

But health officials in Harris County have had mixed results trying to clear up dumping grounds and standing water.

And mosquito control staff are fielding complaints from people tired of seeing staffers walk on their property to monitor mosquito traps that officials have set up to try to detect Zika before human infection, said Martin Reyna Nava, technical operations manager for the county's mosquito control division.

He stressed that the vast majority of people cooperate. But Shah and others are concerned that some trouble spots will keep popping up, at least until a local Zika case occurs in the community and makes people realize that the danger is real.

"There may be folks who say, 'Nah, I'm not really interested in helping,'" Shah said. "That's where the challenge comes in."