Just weeks after taking similar actions in Escondido, crews began spraying insecticide in Vista on Friday, working to kill any mosquitoes carrying dengue virus after detecting the second locally acquired case in San Diego County. But while workers wielding hand-held sprayers were the most visible part of the ongoing dengue fight, they were far from the only ones with this particular pathogen in their crosshairs. Twenty miles south and west, a different crew has been laboring on the Torrey Pines mesa for years to find just the right stuff to block dengue after it enters the body. At the Calibr-Skaggs Institute, the drug discovery and development arm of Scripps Research, researchers partially funded by the Bill and Melinda Gates Foundation have zeroed in on a molecule that blocks the virus’ ability to make new copies of itself after invading host cells. This compound is a product of Calibr’s ReFRAME library, the world’s largest open-source collection of approved and safety-tested drugs that can be screened against all sorts of threats, including viruses such as dengue. One of the more than 12,000 drugs in the collection is tubercidin, a cancer drug that showed surprising activity against dengue. Chemists were then able to use this drug as a starting point for further refinement, customizing its molecular structure to be more effective against dengue. The nice thing, explains medicinal chemist Arnab Chatterjee, a Calibr vice president and leader of the organization’s dengue fever programs, is that ReFRAME drugs have already been tested in humans, making it more likely that a modified version will be successful in clinical trials. Arnab Chatterjee is the vice president of medicinal chemistry at Calibr-Skaggs. (Scripps Research) This new compound, he said, will take 12 to 18 more months in preclinical safety trials before it is ready for human investigation. The most exciting aspect, he added, is that it would be a third anti-viral drug heading toward approval. Massive drug companies Johnson & Johnson and Novartis also have dengue anti-viral drugs in clinical trials, but they follow a different path of action. As has proven to be the case with antibiotics, relying on only one vector of attack can quickly kill off all viruses that are susceptible, leaving those that are resistant behind to flourish. “Using single drugs against a virus is dangerous,” Chatterjee said. “It’s expected that these molecules will work well together based on the fact that they hit different targets that are essential for the virus to replicate.” The World Health Organization has reported a global increase in dengue infections over the last five years, with the most significant caseloads detected in South America. While the disease is common closer to the equator, it has only become locally transmittable in North America with the arrival of Aedes aegypti mosquitoes, tiny insects that have come north with warmer weather patterns often attributed to climate change. Drugs that can block dengue virus replication in the body, then, would be a big help in preventing severe illness among the estimated 7.6 million cases reported to the WHO worldwide, a total that included more than 3,000 deaths in 2024. And the potential of this reframe is actually much bigger. Chatterjee explained that tweaked versions of about 10 pre-existing compounds also show similar replication-blocking capabilities in other flaviviruses, such as West Nile. “Interestingly enough, this series of compounds we found not only have activity against flaviviruses, they also have some activity against influenza virus and coronaviruses,” Chatterjee said. Homer Miranda, senior vector control technician, dons protective gear in advance of spraying insecticide at a home in Vista on Friday afternoon. San Diego County is spraying for mosquitoes connected to a local dengue transmission case. (John Gastaldo / For The San Diego Union-Tribune) For now, though, fighting dengue is down to mosquito control. Aedes mosquitoes generally do not fly far — only about 150 feet — so vector control programs simply seek to eliminate as many bugs as they can, preventing any that might be infected after feasting on the blood of an infected person from passing the virus on to the next person they bite. County crews started Friday with backpack sprayers covering areas around a neighborhood of about 60 homes in central Vista just east of South Santa Fe Avenue and west of Civic Center Drive. Truck-mounted spraying is to continue on Saturday, Sunday and Monday. Allison Bray, supervisor of the county’s Environmental Health and Quality Vector Control Program, said hand treatment is performed closer to the location where a case occurred while truck spraying, which does not penetrate quite so deeply, is used farther out. “The backpacks are much more effective at getting into all the little nooks and crannies where mosquitoes can hide,” Bray said. “In the key area where we’re seeing a lot of mosquitoes, and we think there might be an elevated risk, we’re going in with the backpacks to try to get into as many little crevices as we can. “The truck treatments, then, are follow-up. We want to really make sure that we’re lowering the overall mosquito populations in the neighborhood.” Vista, CA_10_25_24_San Diego County is spraying for mosquitoes connected to a local dengue local transmission case. John Gastaldo for the Union-Tribune Vista, CA_10_25_24_San Diego County vector control technicians get ready to spray for mosquitoes connected to a local dengue local transmission case at a home in Vista Friday afternoon. John Gastaldo for the Union-Tribune Vista, CA_10_25_24_San Diego County vector control technicians sprayed for mosquitoes connected to a local dengue local transmission case at a home in Vista Friday afternoon. John Gastaldo for the Union-Tribune Vista, CA_10_25_24_San Diego County vector control technicians sprayed for mosquitoes connected to a local dengue local transmission case at a home in Vista Friday afternoon. John Gastaldo for the Union-Tribune Show Caption1 of 4Vista, CA_10_25_24_San Diego County is spraying for mosquitoes connected to a local dengue local transmission case. John Gastaldo for the Union-Tribune Expand Symptoms of dengue infection generally appear four to seven days after a mosquito bite and include fever, chills, aches and pains, nausea, vomiting and rash. Most people recover without significant medical consequences; however, some who suffer severe cases can experience deadly symptoms such as shock and respiratory distress. Officials said that the individual who tested positive for dengue infection in Vista was hospitalized after he or she experienced symptoms of possible sepsis, but they have since been discharged home.