Heartworm ‘lack of effectiveness’ claims in the Mississippi delta: Computerized analysis of owner compliance – 2004–2011

Abstract

A retrospective medical record review was conducted to identify factors from veterinary clinic medical records that may have contributed to suspected ineffectiveness of a heartworm preventive product. Patient records of 271 dogs, comprising 301 instances of positive heartworm antigen test results while the dogs were receiving heartworm preventive were evaluated. Nineteen veterinary practices in 17 counties and parishes in Arkansas, Louisiana, Mississippi, and Tennessee participated in the study. Records were selected by the veterinary clinics as representative of cases of suspected lack of effectiveness for a heartworm preventive, and for which an owner satisfaction claim had been filed with the manufacturer. Medical record data were entered into a software program, and a graphic representation was created to facilitate analysis of whether pet owners had purchased sufficient heartworm preventive for the dog to be compliant during the period when infection with Dirofilaria immitis could have led to the positive heartworm antigen test result for that patient ("window of infection"). In 243 (80.7%) cases, there was insufficient heartworm preventive purchased, leading to a gap in protection during the "window of infection". In only five cases (1.7%) there were no purchase lapses or extenuating circumstances (underdosing of medication, multiple purchase gaps outside the established window of infection, or dogs have been diagnosed with heartworm infection more than once during the period studied). Half the cases were from multiple-dog households, and in many of these households, sharing of product between pets was acknowledged. In another 28% of the cases from multiple-dog households, more product was purchased than was needed for one dog, suggesting that the product was being shared between more than one pet. In most cases, there was at least one reason that a dog did not receive sufficient heartworm preventive product, placing the dog at risk of developing an infection with mature heartworms. Several actions were identified that veterinary clinics can take to improve heartworm disease prevention in their patients.

Mosquito-borne heartworm Dirofilaria immitis in dogs from Australia

“…Alternatively, it can be a reflection of larger market share of products with milbemycin oxime for heartworm prevention over other MLs in the locality. To document any loss of efficacy to MLs, a full history of prevention and annual antigen test would be required [ 35 ]. Therefore, a reduced efficacy of MLs in these Australian cases must be treated as ‘remotely possible’ due to incomplete information [ 21 ].…”

Efficacy of four commercially available heartworm preventive products against the JYD-34 laboratory strain of Dirofilaria immitis

“…Resistance to available heartworm preventives was previously considered among potential causes of increased reports of failed heartworm prevention in dogs [ 3 ]. Prevention failures have also been attributed to the interplay of factors in the heartworm life-cycle, erratic treatment compliance, as well as diagnostic, prevention and therapeutic variables [ 4 – 7 ]. However, recent research has confirmed that certain heartworm isolates possess reduced susceptibility to macrocyclic lactone preventives [ 5 , 8 – 10 ].…”

Efficacy of a novel orally administered combination product containing sarolaner, moxidectin and pyrantel (Simparica Trio™) against induced infestations of five common tick species infesting dogs in the USA

“…While numerous parasite preventives are currently available for use in dogs, extensive protection against both ecto-and endoparasites usually requires multiple medications often with varying administration routes and directions [29]. Recent research in both the USA and Europe shows owner compliance in the prevention and treatment of internal and external parasites frequently falls short of expert recommendations [30][31][32][33][34]. Within the USA, 73% of dog owners in one survey believed their dog should receive year-round flea and tick preventives but only 13% actually purchased sufficient medication to achieve year-round protection [32], and owner compliance in the correct administration of canine heartworm preventive is documented as well below 100% [30,35].…”

“…Recent research in both the USA and Europe shows owner compliance in the prevention and treatment of internal and external parasites frequently falls short of expert recommendations [30][31][32][33][34]. Within the USA, 73% of dog owners in one survey believed their dog should receive year-round flea and tick preventives but only 13% actually purchased sufficient medication to achieve year-round protection [32], and owner compliance in the correct administration of canine heartworm preventive is documented as well below 100% [30,35]. The use of multiple medications may add further hurdles for owners; an analysis of clinic transaction records for 231,565 dogs receiving flea and tick medication showed approximately 66% of owners purchased insufficient protection to provide the veterinarian's recommended yearround protection [31].…”