The Preventable Battle with Heartworms

By: Dr. Sarah Beechler at CARE Animal Emergency Services

Doc is a 1 year old, male neutered, Beagle Mix that presented to CARE Animal ER for lethargy, decreased appetite, vomiting and difficulty breathing. Doc was presented by his foster mom (he was a rescue dog), but he was at someone else's house over the weekend and had gotten into the garbage. Doc is also heartworm positive and had been treated for heartworm over the past week. On physical examination, Doc was depressed, dehydrated, painful on mid-abdominal palpation and he was tachypneic (breathing rapidly). Radiographs performed revealed enlargement of his heart, specifically his right ventricle, dilation of the main pulmonary artery, and tortuous pulmonary vessels. These signs are all consistent with heartworm disease. There was also mild pleural effusion, or fluid around the lungs, and a mixed lung pattern with increased opacity over his caudodorsal lung fields. Bloodwork showed an elevated white cell count as well as mild elevation of a liver enzyme. Doc was hospitalized and started on IV fluids, broad spectrum antibiotics (in case of pneumonia), as well as nebulization treatments. Doc remained hospitalized for the next 7 days. Initially there was little improvement with respect to his breathing. An ultrasound was performed of Doc's heart and revealed a large worm burden within the right side. When there was no response to antibiotics, he was started on prednisone (a steroid) to help with inflammation secondary to his heartworm disease, which was likely causing his issues breathing. Within the next few days, he started to respond and was discharged from the hospital on prednisone and doxycycline.

Heartworm disease is caused by a parasite that lives in the arteries of lungs and right side of the heart in dogs, cat, and other mammals. It eventually can lead to heart failure if left untreated. This parasite is transmitted via mosquitoes. A mosquito first takes a blood meal from an infected animal (already carrying heartworm) and then bites another uninfected animal, let's say a dog. The larvae enter through the bite wound and then mature into an adult worm, traveling to the lungs and heart causing infection in the dog. The worms can live up to 7 years, all the while doing damage to those arteries.

In dogs, signs of heartworm disease can be nonexistent to a mild cough, lethargy, decreased appetite, weight loss or fatigue after exercise. In cats, signs can vary from vomiting, gagging, lethargy, weight loss, difficulty breathing or a rapid respiratory rate. Unlike dogs, cats usually have a smaller worm burden but the presence of just 1 or 2 worms can lead to these signs as well as death.

Diagnosis of heartworm disease is done through a blood test. This test is recommended yearly and is done through your veterinarian. It takes approximately 7 months after infection to have a positive test result because that is how long it takes for the larvae to turn into mature adults. This is why we do not test young puppies or kittens, at least not until they are 6-7 months old.

The best treatment for heartworm disease is prevention. Heartworm disease is preventable! There are numerous products on the market from monthly tablets or topical medications to a six month injection available to dogs. The preventative medication interrupts the development of the heartworm before the adult worms reach the lungs and cause disease. We recommend dogs and cats be on heartworm prevention year round.

If your dog does become infected with heartworm disease, there is a treatment. It consists of a series of injections that kill the adult worms. It does not come without risks or potential complications and it can be costly. Treatment can cost more than 15x that of a year's worth of heartworm prevention.* Unfortunately for cats, there is no treatment for heartworm once infected.

Doc did have heartworm disease and did go through a series of injections for his disease. He also had complications following his injections. As stated earlier, the worms cause damage to the lungs and heart as they continue to grow longer and longer. It is not uncommon for a dog to have more than 30 worms present and they can grow to be 12 inches or longer.* The treatment that is given to dogs causes these worms to die. As the worms die, they decompose and fragments can lodge in the vessels blocking blood flow and causing a clot or a thromboembolism to form. Steroids can sometimes help with the signs of thromboembolism or with inflammation, as in the case of Doc.

Since discharge, Doc is doing great. He has been adopted out to a wonderful family and we will plan to recheck his heartworm status six months post treatment.

Heartworm disease affects dogs and cats of any age, size or breed. It is prevalent in all 50 states. And it has been estimated that a million dogs in the U.S. have heartworm disease today. This number seems to be increasing. It may be weather related as mosquitoes are blown further distances or as infected animals are relocated to previously uninfected areas. Whatever the reason, this disease is preventable so please inquire with your veterinarian and get your pets protected.

*www.heartwormsociety.org