Do Dogs Need Heartworm Medicine All Year?by Amanda Williams
Heartworm disease is caused by the parasite known as Dirofilaria immitis, which is carried by infected mosquitoes. After being bit by an infected mosquito, the worms develop near the heart and lungs of their canine hosts, growing up to a foot in length. To avoid a heartworm infection, your veterinarian will provide your dog with a preventative medication that should be taken year-round.
Initially, a dog bitten by a mosquito carrying Dirofilaria immitis will show no symptoms. After five to seven months, heartworms are in their adult stage. At this time, infected dogs will show common symptoms such as coughing, fatigue after exercise, weight loss and a decreased appetite. Eventually, if left untreated, the worms will cause their host's belly to swell with fluid and the dog may experience heart failure. The severity of symptoms depends on several factors, including the dog's health history, how active the dog is and how many worms there are. Your vet will perform tests such as an X-ray, blood test or ultrasound to screen for heartworms. If your dog is severely infected, surgical removal of the worms may be necessary.
To prevent a heartworm infection, it is essential for your dog to be on a strict preventative medication schedule. Heartworm screenings are routine blood tests performed by veterinarians before mosquito season or before your dog starts a new preventative medicine. These screens also ensure that the preventative medication your pooch is currently on is effective. Preventative heartworm medications do not deter mosquitoes from biting your dog. Instead, different types of heartworm preventative medications kill the different stages of larvae already infecting your dog so that they don't develop into adult heartworms.
Although different heartworm preventative medications have different schedules, veterinarians and the American Heartworm Society recommend that dogs receive year-round treatment. Whether your dog receives heartworm medications once every six months or once every month, you should not stop giving your pooch his medications just because there aren't anymore mosquitoes. Warm weather can show up unannounced at any time, even during winter and attract mosquitoes to your pooch. If he isn't currently on preventive medications, he can become infected with heartworms. Remember: Prevention is cheaper than treatment.
Your veterinarian tests the effectiveness of your dog's preventative medications for several reasons. One of these reasons is product effectiveness. If the product fails, despite your dog being on a strict medication schedule, your veterinarian will need to start treatment immediately. Additionally, veterinarians check the effectiveness of preventative heartworm medications because sometimes your dog is sneaky about taking his medicine. He may spit out chewable medicine when you're not looking or vomit them if he is sick. This means that your dog is susceptible to infected mosquitoes and must begin a new medication cycle if he is parasite-free.
- Purdue University College of Veterinary Medicine: Frequently Asked Questions About Heartworm Preventative
- American Heartworm Society: Frequently Asked Questions (FAQs)
- Claws and Paws Veterinary Hospital: Heartworm Prevention, Why Your Dog Needs It
- ASPCA: Heartworm
- VCA Animal Hospitals: Heartworm Disease in Dogs
- LWA/Larry Williams/Blend Images/Getty Images