In Brownsville, Texas, an intensive mosquito surveillance program warns of a broader U.S. threat

Brownsville, Texas, has become an early warning post in a widening U.S. threat from mosquito-borne disease, city health officials say, as travel, urban growth and a warming climate create conditions that allow viruses such as Zika and dengue to take root. The city’s modest but intensive surveillance program — a handful of technicians, networks of traps and an on-site PCR lab inside a repurposed shipping container — is designed to find dangerous pathogens in mosquitoes and people before outbreaks expand.

On a humid summer day in Brownsville, entomologist Yaziri Gonzalez checks a gravid trap: a black plastic basin full of smelly water under a bush, capped by a small fan that pulls mosquitoes into a mesh net. The adults are examined to determine what they’ve been biting and to test for pathogens. The traps are joined by baited cylindrical devices that emulate human breath and sweat, emitting carbon dioxide and lactic-acid scents to attract host-seeking mosquitoes.

The Brownsville program grew in response to local transmission of Zika in 2016. Cameron County reported 26 locally acquired Zika cases that year, and Texas reported 315 cases statewide, prompting the city to build a sustained mosquito-control operation. Gonzalez joined the team in October 2020 and now helps deploy and monitor traps across neighborhoods, industrial sites and roadsides. When a mosquito or a human case tests positive, the city traces the likely geographic epicenter, conducts targeted spraying, eliminates breeding sites and informs residents.

The city does much of the testing itself in a modular laboratory equipped with a PCR machine, microscope and ultra-cold storage. That capability, Gonzalez and public health officials say, has sped up response times compared with the previous system of sending specimens to state labs in Austin. Brownsville’s vector control staff numbers three full-time technicians and operates on an annual budget of roughly $400,000; about three-quarters of the budget goes to chemicals and equipment. Individual traps can cost up to $300 and a PCR machine about $15,000.

Officials in Brownsville say the city’s location on the U.S.-Mexico border and its mix of cross-border travel, migrant transit and rapid suburban development make it a sentinel for emerging vector threats. "We usually get the first of everything and anything," said Gonzalez. Arturo Rodriguez, Brownsville’s director of health, wellness and animal services, said human movement brings pathogens from other countries, while warmer temperatures and altered rainfall patterns increase mosquito populations and change where outbreaks can occur.

Nationwide, vector-borne reported disease cases have doubled over the past 20 years, according to the Centers for Disease Control and Prevention. Many of the mosquito species that spread disease thrive in small amounts of standing water and near homes. Aedes mosquitoes, responsible for spreading Zika, dengue and chikungunya, can breed in a bottle cap’s worth of water, making urban and suburban landscaping, storm drains and retention ponds potential breeding grounds.

Brownsville uses mapping software to integrate trap data, resident reports, GPS-tracked spraying routes and larvicide deployments. Public health analyst Alexis de la Cruz said the data has challenged assumptions about risk: higher-income neighborhoods that water lawns heavily can have as severe mosquito problems as lower-income areas because irrigation sends water into storm drains and stagnant pools.

Applying controls presents further complications. Of more than 200 mosquito species in the United States, only about a dozen are known to transmit disease. Spraying can harm non-target insects such as bees and butterflies, and mosquitoes can develop resistance to pesticides, requiring careful targeting and rotating treatments. The most dangerous species are often crepuscular or nocturnal, hiding by day and biting at dusk, complicating suppression efforts.

Public health physicians and researchers in the Rio Grande Valley say surveillance must be paired with clinician awareness and community support. Jose Campo Maldonado, an infectious disease physician at the University of Texas Health Rio Grande Valley, said clinicians are improving at recognizing vector-borne illnesses but gaps remain because these infections can occur with other chronic diseases and in patients with unstable housing or limited access to care. Outreach to encourage protective measures and to improve housing and health access is part of a comprehensive response, he said.

Brownsville leaders say their effort, while robust for a city of 190,000, cannot substitute for a broader national response. "We have a limited view," Gonzalez said, noting that surveillance gaps across neighboring regions and Mexico make it difficult to know when new threats will arrive. "We have one state entomologist and everyone thinks because she’s available that she’s going to be able to respond to an outbreak, and it’s not the case," Gonzalez added.

Researchers warn that past U.S. successes in pushing mosquito-borne disease to the margins relied on disruptive and environmentally harmful tactics such as draining wetlands and widespread DDT spraying that are no longer acceptable. Christopher Romero, a health researcher in Brownsville, said emerging strategies include more targeted insecticides, improved surveillance, disease-risk forecasting and local laboratory capacity. He called the issue a national security concern, arguing the country cannot take historical gains for granted against pathogens that evolve quickly.

Brownsville’s leaders underscore the costs of sustained preparedness. The city’s vector control program requires trained staff, equipment, chemicals and ongoing community engagement. "Zika, for us, was the big moment," Rodriguez said. Officials hope their model — combining traps, laboratory testing, GPS-based mapping and public outreach — can serve as a template for other municipalities as warming temperatures, travel and land-use change raise the odds that mosquito-borne infections will expand in the United States.

Even with local successes, public health experts say containment demands coordinated federal, state and local investment in surveillance, laboratory capacity, clinician training and community-level prevention to prevent small outbreaks from becoming larger public health crises. Brownsville’s experience illustrates how a modest, persistent surveillance effort can detect and respond to threats early, but it also highlights how tenuous those defenses are when resources are limited and the environment shifts in ways that favor mosquitoes.