Spring brings warmer weather, longer evenings, and more time outside with your pets. It also brings mosquitoes, and in Alabama, mosquito season is basically every season.
Alabama consistently ranks among the top five states in the country for heartworm incidence, according to the American Heartworm Society. Central Alabama clinics regularly see over 90 heartworm cases per year. That’s not a scare tactic. It’s the reality of living in a warm, humid climate where mosquitoes don’t fully go away, even in winter.
How Heartworm Disease Actually Works
Heartworm disease is caused by a parasitic worm called Dirofilaria immitis. It spreads through the bite of a mosquito carrying heartworm larvae. Once those larvae enter your pet’s bloodstream, they migrate to the heart and pulmonary arteries and mature into adult worms over the next several months.
Adult heartworms grow up to 12 inches long and can survive in a dog’s body for five to seven years. A single infected dog can carry hundreds of worms. The damage they cause, including lung disease, heart failure, and blocked blood flow, is serious and often irreversible.
Cats respond differently. Heartworms don’t reach full maturity as often in cats, but even immature worms cause a dangerous inflammatory response in the lungs called heartworm-associated respiratory disease (HARD). There is no approved treatment for feline heartworm, which makes prevention the only option.
Why Year-Round Prevention Matters in Alabama
Some pet owners assume they can skip prevention during the cooler months. In most of the country, that logic at least has some seasonal basis. In Alabama, it doesn’t.
In Alabama, we really don’t have a time of year where there are absolutely no mosquitoes. It only takes one mosquito.
The American Heartworm Society recommends year-round prevention nationwide, and both the AVMA and AHS emphasize that even pets kept primarily indoors are at risk. Indoor cats account for roughly 30 percent of feline heartworm cases. A single mosquito that gets inside is all it takes.
What Happens If You Miss a Dose
Monthly heartworm preventives work by eliminating larvae that have accumulated over the past 30 days. If a dose is missed, any larvae picked up during that window are no longer covered. Even one missed month requires retesting before restarting prevention, because giving prevention to a heartworm-positive dog can cause a dangerous reaction.
The Companion Animal Parasite Council (CAPC) 2025 forecast confirmed that heartworm risk continues to expand across the country, with the Southeast remaining the highest-risk region. Consistent prevention is the simplest, most cost-effective way to protect your pet.
What Prevention Looks Like
Monthly oral or topical preventives are the most common option. Injectable preventives that last six to 12 months are available and ideal for pets with owners who find monthly scheduling difficult. All prescription preventives require an annual heartworm test before dispensing, which is also the standard of care recommended by the AHS even for pets on continuous prevention.
At Trace Crossings Veterinary + Pet Wellness, heartworm testing and prevention are part of every annual wellness exam. We tailor prevention protocols to your pet’s lifestyle, size, and risk factors, and we send reminders when products are due for refill through our online pharmacy.
Prevention starts with a simple test and one easy conversation.
Book your pet’s annual wellness exam and heartworm screening today at tracecrossingspets.com or call (205) 509-1499.