Mosquitoes are an essential part of the heartworm disease cycle. Irrigation, commercial and residential expansion has expanded the habitat for mosquitoes. These environmental changes and the movement of animals (wildlife and pets) support the potential for mosquito transmission of heartworm disease.
What causes Heartworm Disease?
Heartworm is a parasitic worm (Dirofilaria immitis) that can grow quite large, 14 inches. The adult worm resides in the heart, lungs and associated blood vessels. The parasitic worms lead to severe lung disease, heart failure and damage to other organs in the body. Adult female heartworms produce microscopic baby worms called microfilaria that circulate in the bloodstream. Mosquitoes ingest the microfilaria circulating in an infected dog. Once ingested the small parasite continues to develop. The mosquito bites another dog and inoculates the animal with the small larval heartworm. The larval heartworm then migrates to the heart and matures into an adult worm.
What are the signs of Heartworm Disease?
Heartworm disease is a serious, progressive disease. In an early infection, your dog may present healthy with no apparent signs that infection is developing. As the infection persists the following clinical signs may present:
- Mild persistent cough,
- Reluctance to exercise,
- Fatigue after moderate activity,
- Decreased appetite, and weight loss.
As heartworm disease progresses to advanced stages, your dog may develop heart failure.
Prevention and Testing
Heartworm disease can be prevented with the regular and appropriate use of preventive medications. These medications are prescribed by your veterinarian and are available as a once-a-month chewable or a once-a-month topical.
It takes at least 6 months for a dog to test positive after it has been infected with heartworms. Puppies under 7 months of age can be started on heartworm prevention without a heartworm test. Adult dogs over 7 months of age and previously not on a preventive need to be tested prior to starting heartworm prevention. Testing requires a small collection of blood. This is evaluated for the adult female heartworm antigen.
Should I Continue Heartworm Prevention During Winter?
Yes, year-round prevention is recommended.
Urban sprawl has created “heat islands,” or areas that retain a warmer climate in our communities. These areas then support mosquito vectors during colder months. Your neighborhood may have a greater prevalence of heartworm disease than you realize. Stray and neglected dogs and wildlife such as coyotes, wolves, and foxes can be carriers of heartworms.
I Missed My Dog’s Heartworm Prevention for 2 Months, What Should I Do?
Contact your veterinarian, and re-start your dog on monthly preventive. It is then recommended to retest your dog 6 months later. Remember, the reason for re-testing is that heartworms must be approximately 7 months old before the infection can be diagnosed.