Heartworm Disease 
in Dogs and Cats
                      ~by Miranda Blaauboer

What is Heartworm Disease?

Heartworm disease is a dangerous disease in pets that is caused by long worms (Dirofilaria immitis) that live in the heart and lungs causing lung disease, heart failure and internal organ damage. Heartworm can be found in dogs, cats, ferrets, and wild species, such as foxes and coyotes. Dogs are natural hosts for the disease and are often found with hundreds of worms within their bodies. Cats are often found with only a few adult worms, but these worms can cause just as much damage to the heart, lungs and other internal organs.

How is Heartworm Transmitted?

Heartworm is spread by mosquitoes. Adult female heartworms living in an animal produce baby worms (microfilaria) that are microscopic and circulate through the bloodstream. When a mosquito bites and takes blood from the infected animal, it takes with them the baby worms that grow into larvae. Once the mosquito bites another animal, the larvae are deposited onto the surface of the skin and enter the body through the bite. Over six to seven months, the larvae will grow into adult heartworms.

What Symptoms Occur?

Mature heartworms can live five to seven years in an infected dog and may not cause symptoms right away. The longer the infection goes untreated, the more likely dogs are to exhibit symptoms such as coughing, hesitancy to exercise, fatigue after activity, weight loss and decreased appetite. Cats may exhibit severe signs or very subtle signs, depending on the individual case. Some symptoms in cats are coughing, vomiting, loss of appetite, weight loss, and asthma-like attacks, but most often sudden collapse occurs.

How Can We Prevent Heartworm Disease in Our Pets?

To help prevent your dog from becoming infected with heartworm, heartworm prevention should be given all twelve months of the year, and screening should be done annually to test for heartworm. Earlier disease detection increases the chances of successful treatment and recovery. The annual test is a small blood sample testing to see if there are heartworm proteins present. Even if your dog is on heartworm prevention year round, it is still necessary to test to ensure prevention is working effectively. Heartworm disease is found in all 50 states, so it is important to stay up to date no matter where you live. For cats, an annual test is not required and year-round preventive is recommended. 

What Happens When a Dog or Cat Tests Positive For Heartworm?

Heartworm infection in dogs is determined by a blood test that looks for the presence of microfilaria in the bloodstream. Once a dog is confirmed heartworm positive, further tests are performed to evaluate the dog's condition. These tests may include comprehensive blood work to evaluate internal organs as well as radiographs. Treatment for heartworm is only started once the dog's condition is stable. Treatment may include antibiotics and anti-inflammatory medication and a series of injections that are administered during scheduled hospital stays. Throughout the weeks or months of treatment, the dog must stay extremely calm and rested. Some dogs are placed on crate rest. Unfortunately, there is no approved treatment of heartworm for cats. The infection may be managed with anti-inflammatory, bronchodilators, or steroid medications and other supportive treatments.

How Can We Help?

For dogs, we can prescribe a monthly oral tablet for you to give at home. We carry Interceptor Plus and Simparica Trio, and either medication can be purchased by the dose or by the box (six doses). For dogs who don't take medication easily, we offer an injection called Proheart that protects against heartworm for twelve months. For cats, we recommend a topical product called Revolution Plus, which not only protects against heartworm transmission but also fleas, ear mites, roundworm and hookworm. 

In addition, we are here to help your dog feel comfortable during his or her annual blood draw! As a Fear Free Practice, we work with your pets to make sure they are as calm and comfortable as possible during their appointments. Please don't hesitate to reach out to us with questions about heartworm and preventive medications for your pets or to schedule their next appointment!