When Tropical Storm Chantal lingered over central North Carolina this summer, rushing water swallowed streets and left parking lots shimmering like ponds. Homes were damaged, cars were stranded, and in the days that followed, the floodwater became a perfect breeding ground for mosquitoes.

Veterinarians warn that the surge in mosquitoes following heavy storms can fuel another crisis: heartworm, a parasite spread by mosquito bites that can quietly kill dogs and cats.

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“After storms, we see higher incidence of heartworm infection,” said Dr. Jessica Nolan, area chief of staff with Banfield Pet Hospital in Raleigh. “Warm air, high humidity, and standing water where there didn’t used to be all increase mosquito populations and therefore the risk of heartworm.”

More mosquito days, more risk

Heartworm has long been a serious problem in the Southeast, where North Carolina ranks among the top 10 states with the highest incidence of infection. Veterinarians caution there is no such thing as a “heartworm season” here.

“It really is all year long,” Dr. Nolan said. She recently treated a puppy just seven months old that had likely been exposed during the winter, an example of how climate change is altering the calendar for mosquito-borne disease.

Climate Central data shows mosquito-friendly weather is lasting longer. The Raleigh area now experiences 27 more mosquito days per year than it did in 1979, with humidity and temperatures in the sweet spot for mosquito activity.

“The planet is warmer, and that’s changing the mosquito landscape,” said Michael Reiskind, an entomology professor at North Carolina State University. “What we’re seeing today is very different than it was 40 or 50 years ago.”

Pets overlooked in disaster plans

Pet advocates say animals are often an afterthought in emergency planning. Darci VanderSlik, director of communications for the SPCA of Wake County, said shelters that are already full struggle when storms displace pets.

“Our pets don’t always pop into mind when we’re talking about victims of major disasters,” VanderSlik said. “Having a kit prepared for them with prevention, food, water, medications and photos can be a life-or-death resource.”

Mosquitoes need very little water to reproduce. “They can lay eggs in something the size of a thimble,” VanderSlik said. “So when you have flooding after hurricanes, that is a breeding ground.”

A changing climate, a growing threat

Scientists say storms like Chantal are becoming more damaging as the atmosphere warms. Data from the National Oceanic and Atmospheric Administration shows rainfall intensity in the Triangle area has increased 21% since 1970.

“As greenhouse gases trap more heat, the atmosphere can absorb more moisture,” said Shel Winkley, a meteorologist with Climate Central. “That’s fuel for heavier rainfall, which leads to more flooding. When you add that to a warming climate that’s friendlier to mosquitoes, it creates a real risk for disease.”

How pet owners can prepare

Veterinarians and shelters stress that prevention is the best defense. Monthly or injectable medications protect against heartworm, and low-cost clinics can help families struggling with the cost.

Pet owners are encouraged to keep a go-bag with food, medications and a copy of veterinary records. Updated ID tags and microchips help reunite lost animals more quickly and prevent shelter overcrowding.

“The cost of treating heartworm is about the same as 12 years of prevention,” Dr. Nolan said. “For most pets, that is their entire lifespan. Prevention is far less painful and far less deadly.”