Heartworm disease is a serious, potentially life-threatening disease caused by a blood parasite called Dirofilaria immitis. The adult worms reside in the dog’s heart and in the blood vessels that lead from the heart to the lungs. This article discusses the transmission, treatment, and prevention of heartworm disease.
Where do Heartworms Come From?
Heartworms are transmitted to the dog from a mosquito bite! All it takes is one bite from an infected mosquito to transmit heartworm larva into the dog’s blood stream.
When a mosquito bites a dog that is infected with heartworms, it ingests the larvae, and these larvae grow into microfilariae (baby heartworms) over the span of 10 days. Once this mosquito bites another dog, these microfilariae are transferred into the dog’s blood stream.
The microfilariae mature into adult heartworms over the span of 6 months inside of the dog. These mature adult worms continue to produce offspring (microfilariae) inside of the animal.
How do Heartworms Affect My Dog?
Heartworms can cause inflammation in the heart and arteries leading to the lungs, which can cause scarring and narrowing of these tissues. Over time, these changes can decrease how well the heart works and can eventually cause heart failure.
Signs of heartworm disease may not show until several years after initial infection. Signs can include coughing, decreased ability to exercise (exercise intolerance), shortness of breath, and fatigue.
How is Heartworm Disease Diagnosed?
A simple blood test is performed to diagnose the dog with heartworm disease. Your dog should be screened yearly for heartworm disease, even if they are currently on heartworm prevention.
Chest x-rays can be performed if the dog is diagnosed with heartworm disease to assess any damage to the heart or lungs themselves.
How do you Treat Heartworm Disease?
Treatment typically occurs in two steps; the first step targets the baby worms, and the second step targets the adult worms.
The first step, often called “slow kill treatment” is meant to get rid of the baby heartworms. The dog will be put on an antibiotic (Doxycycline), a steroid (Prednisone/Prednisolone), and a monthly heartworm preventative. The antibiotic is used to kill a bacteria called Wolbachia that is secreted from the baby worms. The steroid is to help decrease inflammation. This first treatment lasts for 4 weeks (1 month). A month-long resting period occurs after the first step of treatment, and then we begin the second step.
The second step includes a series of 3 injections with an adulticide that targets and kills adult heartworms. During this series, the dog will remain on the monthly heartworm preventative to ensure that it remains free of the baby heartworms. The dog will receive the initial injection which is followed by a month of rest. Then, the 2nd and 3rd injections are given 24 hours apart.
During the treatment period, especially with injections, exercise restriction is VERY IMPORTANT. When the adult worms begin to die, they can break into pieces and can act like clots in the blood vessels. This can be dangerous for the dog.
How do you Prevent Heartworm Disease?
You can prevent heartworm disease in your pet by giving them a heartworm preventative. Some preventatives are chewable tablets that are given monthly (every 30 days), and some clinics offer injectable heartworm preventatives that can last 6-12 months.
