Treatment of heartworm (Dirofilaria immitis) disease in dogs in the USA: general findings and cost of disease

BACKGROUND: Heartworm (HW) disease is caused by the adult worms of Dirofilaria immitis. Treatment of HW disease is costly and often challenging. Therefore, the mainstay of HW disease management is to prevent the development of adult worms. The objective of this retrospective study was to use a transaction database to collect information and cost estimates on the prevention and treatment of canine HW disease in the USA. METHODS: Anonymized transaction data from clinics throughout the USA were used. For the HW disease treatment group (TG) dogs were identified that had a transaction record for adulticidal therapy using melarsomine between August 2022 and July 2023. These dogs were tracked up to 95 days before the first melarsomine treatment for transactions given current American Heartworm Society (AHS) guidelines for the treatment of HW disease. Clinics with records of at least one dog with HW treatment were included. End of the tracking period was 5 days after the last melarsomine injection for the cost evaluation and 12-months for the evaluation of mortality. Included clinics were searched for dogs in the preventive group (PG), i.e., dogs that had a HW test between August 2022 and July 2023, followed by transaction of at least 8.9 HW preventive medication doses over the total observation period of 12 months, starting with the first transaction of HW preventive medication. RESULTS: A total of 2425 dogs were included in the TG and 235,188 dogs qualified for the PG. The adherence to AHS guidelines was low in our study, with stipulated medications and treatments missing in many dogs. Total costs for an average dog with HW disease were calculated at $1457, not considering indirect or intangible costs. Costs of HW preventive medication in year-round purchase compliant dogs were estimated at $182.90. Dogs up to 9 years of age that were treated for HW disease had a significantly higher risk of mortality than dogs in the PG (p < 0.05). CONCLUSIONS: Costs of HW disease treatment are substantial, not considering the intangible effects on the animal and dog owner. The high costs and potential burden of disease underscore the benefit of year-round heartworm disease prevention.