Clinical Challenge: Canine Heartworm Disease
Sponsored by Elanco
Heartworm disease was once confined largely to the southeastern United States; however, the range of this canine parasite has now expanded to all 50 states.1,2 Although transmission rates decrease in colder months, mosquitoes can persist in warm microenvironments, making them a year-round threat.2
Considering the increased potential for heartworm infection, all veterinarians must be prepared to recommend effective, consistent prevention. In addition, all veterinarians should be able to recognize and confidently manage heartworm disease when infections occur.
Meet Lola: A New Addition to the Family
Lola, a 2-year-old female, spayed Labrador retriever crossbreed, was presented for a new patient examination. Four days earlier, Lola was adopted from a local animal shelter. She was initially picked up by the shelter staff as a stray, and her medical history was unknown.
Lola spent ≈1 month at the shelter prior to adoption, during which time she received veterinary care. Upon shelter intake, she received a physical examination, heartworm test, fecal parasite examination, rabies vaccine, and distemper, adenovirus, parainfluenza, and parvovirus (DAPP) vaccine. Lola’s physical examination was within normal limits, except for the presence of fleas. The shelter administered a flea treatment, although the records did not indicate what treatment was administered. Lola’s in-house heartworm antigen ELISA test upon admission to the shelter was negative, and fecal parasite examination revealed hookworms. Lola was given 1 dose of heartworm preventive (ivermectin/pyrantel) to prevent heartworm infection and treat her hookworm infection. Prior to adoption, Lola received a DAPP booster and a second dose of heartworm preventive.
At Lola’s new patient examination, her owners reported that she was doing well at home, and they had no concerns. A physical examination was performed and was unremarkable, except for the presence of mild dental calculus at the gumline. Lola’s BCS was 5/9. Given Lola’s history of hookworm infection, the veterinarian recommended another fecal parasite examination, which was negative. The veterinarian also discussed other preventive care recommendations with Lola’s owners. Based on a lifestyle assessment, Lola received a leptospirosis vaccine, a Lyme vaccine, and an injectable Bordetella bronchiseptica vaccine.
The veterinarian recommended Credelio Quattro™/Credelio Quattro-CA1 (lotilaner, moxidectin, praziquantel, and pyrantel chewable tablets) for parasite coverage due to its coverage against fleas, ticks, heartworm disease, roundworms, hookworms, and 3 species of tapeworms.a Credelio Quattro-CA1 is also conditionally approved for the treatment of New World screwworm larvae infestations in dogs pending a full demonstration of effectiveness.
However, Lola’s owners declined Credelio Quattro/Credelio Quattro-CA1 at this visit and instead purchased an ivermectin-based heartworm preventive and said they would use an over-the-counter flea/tick preventive.
Given that there was likely a lapse in heartworm prevention before Lola entered the shelter, Lola should receive a heartworm test 6 months after her initial negative test.2 This follow-up test accounts for the possibility that Lola was harboring a prepatent heartworm infection when she was initially tested. An in-house heartworm test looks for antigens released by adult, female heartworms; early infections may lack sufficient numbers of adult females to lead to a positive test result.
Lola’s owners scheduled an appointment for booster vaccines in 3 weeks and scheduled an appointment for a follow-up heartworm test in 5 months.
Lola Returns for Vaccine Boosters
Three weeks later, Lola returned for her leptospirosis, Lyme, and Bordetella bronchiseptica vaccine boosters. Her owners reported that she was doing well at home, and a brief technician examination was within normal limits. Lola’s owners were reminded of their scheduled appointment for a repeat heartworm test to confirm that she was negative for heartworm disease.
Lola Returns for a Repeat Heartworm Test
Five months after her initial visit, Lola returned for a repeat heartworm test. Lola’s owners reported that she was doing well at home, both medically and behaviorally. On physical examination, Lola appeared healthy, except for mild dental calculus. Unfortunately, however, Lola’s in-house heartworm antigen ELISA test was positive.
Although in-house heartworm antigen ELISA tests have a high specificity, positive results should always be confirmed with additional testing.2 Recommended confirmatory tests include microfilaria testing, retesting with a different manufacturer’s test, or cardiac ultrasonography.2
Lola’s blood sample was sent to a reference laboratory, where a different antigen test was performed. This test was also positive, confirming a diagnosis of heartworm disease.
Lola’s owners were frustrated by these results, assuming the shelter lied about Lola’s results or that Lola’s current heartworm preventive was ineffective. The veterinarian responded by educating Lola’s owners about the heartworm life cycle, explaining that it typically takes ≈6 months after infection for a dog to test positive on an antigen test. Lola was likely infected while running loose as a stray before she entered the shelter. Although the shelter was correct to test her, the test likely occurred during the disease’s prepatent period. Lola was infected at the time of her test, but there were not enough adult female heartworms present to be detected on a heartworm antigen test.
After receiving thorough client education, Lola’s owners elected to decline additional diagnostics (eg, radiography, echocardiography) for disease staging and opted to initiate treatment.
Doxycycline (10 mg/kg PO every 12 hours for 28 days) should be administered prior to melarsomine treatment in all dogs with heartworm disease, regardless of whether they have clinical signs.2 Doxycycline is used to treat Wolbachia spp, intracellular bacteria commonly found in heartworm microfilariae. The results of a retrospective study suggest that including doxycycline in treatment protocols for heartworm disease can lead to a decrease in respiratory complications and mortality rates during heartworm treatment.3
Lola’s veterinarian prescribed doxycycline (10 mg/kg PO every 12 hours for 28 days) at the time of diagnosis. She also educated Lola’s owners about proper home care. Lola’s owners were instructed to begin strict activity restriction and monthly ectoparasite protection with demonstrated mosquito-killing activity and to continue Lola’s monthly heartworm preventive.
The veterinarian prepared a treatment plan for the remainder of Lola’s heartworm treatment using the American Heartworm Society’s Heartworm Toolkit to calculate treatment dates and doses.4 Lola’s owners reviewed this plan and agreed to the proposed treatment.
Lola’s Heartworm Treatment
Two months after receiving her initial diagnosis, Lola returned to the veterinary clinic. The veterinarian confirmed that Lola had completed her entire course of doxycycline and that Lola had been receiving her heartworm preventive. The veterinarian administered Lola’s first melarsomine injection at a dose of 2.5 mg/kg IM in Lola’s left epaxial muscle. Lola was hospitalized for the day and monitored for pain and anaphylaxis.
Lola was discharged with a tapering dose of prednisone (0.5 mg/kg PO every 12 hours for 1 week, then 0.5 mg/kg PO every 24 hours for 1 week, then 0.5 mg/kg PO every 48 hours for 2 weeks). Lola’s owners were also instructed to continue her heartworm preventive as well as strict activity restriction.
Three months after Lola’s initial diagnosis, she returned for 2 days of hospitalization. She received her second and third melarsomine injections (2.5 mg/kg IM) 24 hours apart in opposite epaxial muscles. Again, she was monitored closely for pain and anaphylaxis after each injection and was discharged with another tapering course of prednisone as previously administered. In addition, her owners were instructed to continue strict activity restrictions for 1 to 2 months and to continue giving monthly heartworm preventive.
Confirming the Resolution of Lola’s Heartworm Disease
One month after Lola’s final melarsomine injection, she returned for a modified Knott’s test to look for microfilariae, according to the American Heartworm Society treatment protocol.4 Lola’s test was negative.
Eight months later (1 year after her initial heartworm diagnosis), Lola returned for an in-house heartworm antigen ELISA test. This test was negative, confirming that Lola’s heartworm infection was successfully eliminated. At this visit, however, the veterinarian noted the presence of live fleas and flea dirt on Lola’s coat. Lola’s owners acknowledged that they had been using an over-the-counter flea preventive and that it did not seem to be working very well for Lola. Lola’s veterinarian recommended an all-in-1 product that would protect against heartworm disease, fleas, and other parasites of concern.
Lotilaner is an effective flea and tick preventive when given monthly.
Lola’s veterinarian prescribed Credelio Quattro/Credelio Quattro-CA1 for convenient coverage against fleas, ticks, heartworm disease, roundworms, hookworms, 3 species of tapeworms, and New World screwworm larvae in a convenient, chewable, monthly tablet. Moxidectin-containing heartworm disease preventives have been shown to provide the highest levels of efficacy against resistant isolates of heartworms in studies evaluating commercially available options.2,5
Conclusion
Lola’s owners were relieved that Lola’s heartworm infection was treated safely and effectively. After treatment, however, they admitted that they had been somewhat lax in administering heartworm preventives to previous dogs they had owned. The clients now understood the importance of monthly heartworm prevention and set reminders in their phone to ensure that Lola always received her parasite protection, including heartworm disease preventives, on schedule moving forward
Although heartworm disease poses a serious threat to dogs, it can be prevented through the use of safe and effective heartworm preventives. All members of the veterinary team should be comfortable discussing the benefits associated with parasite protection. In addition, all veterinarians should be familiar with the diagnosis and treatment of canine heartworm disease.
a Credelio Quattro protects dogs against ticks, fleas, heartworm disease, roundworms, hookworms, and tapeworms. Credelio Quattro-CA1 is conditionally approved for the treatment of New World screwworm larvae infestations in dogs pending a full demonstration of effectiveness.
INDICATIONS
Credelio Quattro is indicated for the prevention of heartworm disease caused by Dirofilaria immitis and for the treatment and control of roundworm (immature adult and adult Toxocara canis and adult Toxascaris leonina), hookworm (fourth stage larvae, immature adult, and adult Ancylostoma caninum and adult Uncinaria stenocephala), and tapeworm (Dipylidium caninum, Taenia pisiformis, and Echinococcus granulosus) infections. Credelio Quattro kills adult fleas and is indicated for the treatment and prevention of flea infestations (Ctenocephalides felis) and the treatment and control of tick infestations [Amblyomma americanum (lone star tick), Dermacentor variabilis (American dog tick), Ixodes scapularis (black-legged tick), Rhipicephalus sanguineus (brown dog tick), and Haemaphysalis longicornis (longhorned tick)] for one month in dogs and puppies 8 weeks of age and older, and weighing 3.3 pounds or greater. Credelio Quattro is indicated for the prevention of Borrelia burgdorferi infections (also known as Lyme disease) as a direct result of killing Ixodes scapularis vector ticks.
Credelio Quattro-CA1 is conditionally approved for the treatment of infestations caused by New World screwworm (NWS; Cochliomyia hominivorax) larvae (myiasis) in dogs and puppies 8 weeks of age and older and weighing 3.3 pounds or greater.
IMPORTANT SAFETY INFORMATION
Lotilaner, an ingredient in Credelio Quattro/Credelio Quattro-CA1, belongs to the isoxazoline class and has been associated with neurologic adverse reactions like tremors, ataxia, and seizures even in dogs without a history of seizures. Use with caution in dogs with a history of seizures or neurologic disorders. Dogs should be tested for existing heartworm infections before Credelio Quattro/Credelio Quattro-CA1 administration as it is not effective against adult D. immitis. The safe use in breeding, pregnant, or lactating dogs has not been evaluated. The most frequently reported adverse reactions in clinical trials were vomiting and diarrhea.
Credelio Quattro-CA1 is conditionally approved by the FDA pending a full demonstration of effectiveness under application number 141-619. Treatment of NWS myiasis includes removal of the larvae, lesion cleaning and surgical debridement. Implement appropriate wound care and pain management.
For full prescribing information, see the Credelio Quattro/Credelio Quattro-CA1 package insert.
Credelio Quattro, Elanco, and the diagonal bar logo are trademarks of Elanco or its affiliates. PM-US-26-1403
