Author: Karen L. McGlothlin, DVM, PhD
Veterinarian: Dr. McGlothlin
Patient: Lily Stahl
Age: 6 years old
Background: April was National Heartworm Awareness Month – it’s designated as the official month to spread the word about a disease that affects more than one million pets annually and can cause lasting damage to the hearts and lungs of those afflicted. While we stress the importance of life-long use of heartworm preventatives, this is a disease that is still on the rise, as illustrated in incidence maps that are renewed every 3 years and posted on the American Heartworm Society’s website at https://www.heartwormsociety.org/pet-owner-resources/incidence-maps.
One of our patients, Lily Stahl, was lucky enough to be adopted from a breeding facility by the family that had previously acquired one of her puppies and wanted a second dog. Lily had not had any previous visits to a veterinarian prior to her adoption by the Stahls. On her initial visit, Lily looked reasonably healthy overall, she was well-fleshed and had some prominent mammary glands because she had recently weaned her last litter of puppies. Lily had some moderate tartar, but other than that she was healthy in appearance and there were no abnormalities in her heart or lung sounds.
As part of Lily’s first visit, a heartworm test and a fecal evaluation were performed. The heartworm test that we use at Lawndale Veterinary Hospital is the Idexx SNAP 4DX test. With this in-house test, a quick blood draw can detect heartworm antigen as well as antibodies to Borrelia burgdorferi, Anaplasma phagocytophilum, Anaplasma platys, Ehrlichis canis, and Ehrlichia ewingii, which are species of bacteria that can spread Lyme disease, anaplasmosis, and ehrlichiosis.
The SNAP 4DX test runs in 8 minutes and when Lily’s test had concluded, the results showed that she was positive for heartworm. The next step was to look at a drop of Lily’s blood under the microscope to check for the presence of microfilaria, which are larval heartworms, and to send some of Lily’s blood out for a second (different) test to confirm the diagnosis. While Lily did not have any larval heartworms in her blood, her confirmatory test was also positive.
Heartworm Treatment: Ms. Stahl decided to have Lily go through adulticide therapy to kill the adult worms, so Lily was started on three oral medications to stabilize her heartworm disease: Heartguard Plus (an ivermectin-based heartworm preventative that kills larval heartworms), doxycycline (an antibiotic), and prednisone (a steroid). The treatment guidelines published by the American Heartworm Society recommend this treatment protocol for the first 30 days, before a schedule of three injections of adulticide medication is started.
Prior to receiving adulticide treatment, Lily was brought in for thoracic (chest) radiographs and a comprehensive blood panel to make sure that she was healthy enough to tolerate adulticide therapy. While Lily’s chest radiographs looked good, her liver values were initially elevated, so
we added in some liver support supplements and medication and delayed her adulticide therapy for one month. At the time of Lily’s next visit, her bloodwork was rechecked and the liver values had normalized, so we felt confident that she could tolerate the first injection of melarsomine dihydrochloride, the only FDA-approved drug used to kill adult heartworms. Melarsomine dihydrochloride (which is known by the trade names Immiticide and Diroban) is an arsenical compound and, while there are some risks involved in receiving this drug, the risks of not treating heartworm infection are far more substantial. The lifespan of an adult heartworm has been determined to be 5-7 years and an adult female heartworm can reach 10-12 inches in length, while adult males may reach 4-6 inches in length. Even a small number of worms occupying space in the heart and lungs for that length of time can cause considerable permanent damage.
Update: Lily went through the three-injection protocol, which is the protocol recommended by the American Heartworm Society. In late December, 2022, Lily was given an injection of melarsomine hydrochloride deep in the epaxial muscles on the left side of her lower back. The injection itself is uncomfortable and can result in soreness for the dog for the next few days after injection. Lily tolerated her injection well and did not experience any adverse effects or injection site reactions.
Lily returned in late January, 2023, for her second adulticide treatment. This time, melarsomine was injected first into the deep epaxial muscles on the right side of her lower back. Twenty-four hours later, a second melarsomine injection was administered into the deep epaxial muscles on the left side. The administration of two injections, 24 hours apart, has been shown to have a synergistic effect in the killing of the remaining adult worms. Once she had gone through her heartworm adulticide treatment, Lily was brought in for a dental cleaning and she was spayed at that time, as well. Lily is currently enjoying retirement, living her best life, and getting her heartworm preventative every month!
As previously mentioned, April was National Heartworm Awareness Month and we are so happy to have helped Lily become healthier and go through the process of adulticide treatment for her heartworms. Please do your pets a favor and keep them on heartworm preventatives all year long. Please take a minute to read our previous blog post on why it is important to do this – heartworms are spread through mosquito bites and our climate is so mild that they are active all year. Heartworm adulticide treatment is risky and it is expensive – it has been estimated that the cost of adulticide therapy is equivalent to the cost of 7 YEARS worth of heartworm preventative products!
American Heartworm Society Website – Pet Owner Resources. https://www.heartwormsociety.org/pet-owner-resources
American Veterinary Medical Association Website. https://www.heartwormsociety.org/pet-owner-resources