Heartworm seropositivity in cats
There is one finding in the recent study “Seroprevalence of heartworm infection, risk factors for seropositivity, and frequency of prescribing heartworm preventives for cats in the United States and Canada”1 that caught my interest. Table 1, which reports results of bivariate analyses of putative risk factors for heartworm seropositivity in cats, indicates that seroprevalence was 0.5% among cats for which heartworm preventive had been prescribed and 0.4% among cats for which it had not been. There was no significant difference between these values.
I did not see any mention or analysis of the possible importance of these results in the text. I know that the goal of the study was not to evaluate the effectiveness of heartworm prevention in cats, but I found this result to be disturbing. I would have expected there to be a lower prevalence in cats receiving preventive medication.
Kenneth M. Kornheiser, dvm
Plainwell, Mich
1. Levy JK, Burling AN, Crandall MM, et al. Seroprevalence of heartworm infection, risk factors for seropositivity, and frequency of prescribing heartworm preventives for cats in the United States and Canada. J Am Vet Med Assoc 2017; 250: 873–880.
The authors respond:
In our study, respondents were asked whether heartworm preventive medication was dispensed at the time of testing for heartworm antigen, but it was unknown whether cats had already been receiving preventives or whether clients had been compliant with continuous treatment. The published results indicate that compliance with guidelines to provide all cats with heartworm preventive is low, even in regions where infection in dogs is high.
Julie Levy, dvm, phd
Maddie's Shelter Medicine Program College of Veterinary Medicine University of Florida Gainesville, Fla
Systemically versus cutaneously distributed ectoparasiticides
In a recent letter, Dr. Ernest Rogers1 questioned whether there is reliable information on the efficacy of topically applied tick repellents versus orally administered tick preventatives. This is an important issue, because protecting dogs and cats against ticks and tick-borne diseases is becoming increasingly important. I recently reviewed available literature on the efficacy of systemically and cutaneously distributed ectoparasiticides.2
An important issue in this regard is that cutaneously distributed ectoparasiticides, such as permethrin and permethrin-containing spot-on products, are not necessarily equally distributed over the entire body surface, and that some areas, mainly distal, will not have the same ectoparasiticide concentration as areas close to the application site.3 Efficacy studies2 of topical 65% permethrin found mean efficacies against Dermacentor variabilis and Ixodes scapularis 24 hours after treatment that ranged from 75% to 100%. The same product had 49% to 70% efficacy against Rhipicephalus sanguineus three days after application, whereas efficacy two days after application was 96.3% against Ixodes ricinus and 100% against Dermacentor reticulatus. Combinations of permethrin with other active ingredients had efficacies against R sanguineus two days after application of 54.3% to 100% and efficacy against Amblyomma americanum of 93.5%. Long-term studies found that 28 to 30 days after treatment, efficacy (measured 24 to 48 hours after infestation) was 81.4% to 97.6% against R sanguineus, > 92% against D variabilis, and > 95% against A americanum.
In general, studies with permethrin have found that maximum anti-tick efficacy is detected about seven days after application, with maximum efficacy of approximately 98% lasting seven to ten days.2 Dryden at al4 showed that repelled ticks can survive after imidacloprid-permethrin treatment. Specifically, they found that only 8.3% of A americanum ticks that appeared moribund or dead three hours after a 10-minute exposure to dogs that had been treated 21 days earlier were still considered dead or moribund 24 hours later.
Overall, cutaneously distributed tick repellents have been found to have varying acaricidal efficacy that is not dose dependent. Permethrin products are effective against ticks; however, most efficacies are < 100%, and repellent acaricides do not completely eliminate the risk of tick infestation or transmission of tick-borne infections.
Owing to their rapid absorption following oral or transdermal administration, maximum plasma concentrations of the isoxazoline ectoparasiticides (ie, fluralaner, afoxolaner, and sarolaner) are reached within 24 hours after administration. Tick-killing activity of fluralaner was 89.6% four hours after oral administration, 97.9% eight hours after oral administration, and 100% 12 and 24 hours after oral administration.5 The rapid tick-killing activity of the isoxazolines means that any attaching I ricinus ticks are quickly killed,2 and the rapid systemic distribution of the isoxazolines means that ticks attached on any body location are targeted. A single oral dose of fluralaner resulted in > 98% efficacy against I ricinus for 12 weeks after administration5 and protected dogs against challenge with Babesia canis–infected D reticulatus ticks up to 84 days after treatment.2
The speed of kill of isoxazolines coincides with the transmission time for most tick-borne diseases, suggesting that these drugs can interrupt transmission. Thus, systemically distributed ectoparasiticides would seem to provide an excellent alternative to cutaneously distributed treatments. Of course, no treatment—whether systemically or cutaneously distributed—can completely prevent tick-borne pathogen transmission.
Kurt Pfister, prof dr med vet em
Department of Veterinary Sciences Faculty of Veterinary Medicine Ludwig-Maximilians-University Munich Munich, Germany
1. Rogers E. Call for research on tick-prevention products (lett). J Am Vet Med Assoc 2017; 250: 1224.
2. Pfister K, Armstrong R. Systemically and cutaneously distributed ectoparasiticides: a review of the efficacy against ticks and fleas on dogs. Parasit Vectors 2016; 9: 436.
3. Lüssenhop J, Stahl J, Wolken S, et al. Distribution of permethirin in hair and stratum corneum after topical administration of four different formulations in dogs. J Vet Pharmacol Ther 2012; 35: 206–208.
4. Dryden MW, Payne PA, Smith V, et al. Evaluation of an imidacloprid (8.8% w/w)–permethrin (44.0% w/w) topical spot-on and a fipronil (9.8% w/w)–(S)-methoprene (8.8% w/w) topical spot-on to repel, prevent attachment, and kill adult Ixodes scapularis and Amblyomma americanum ticks on dogs. Vet Ther 2006; 7: 173–186.
5. Wengenmayer C, Williams H, Zschiesche E, et al. The speed of kill of fluralaner (Bravecto) against Ixodes ricinus ticks on dogs. Parasit Vectors 2014; 7: 525.
On establishing a specialty of veterinary botanical medicine
In his recent letter, Dr. Peter Eyre1 reminded us of the long history of plant use in veterinary medicine. Information on plants appeared in veterinary texts as late as the 1960s, but then disappeared. Now, plant extracts have made their way back into veterinary use, and as Dr. Eyre stated, plant extracts appear in a plethora of human and animal products available online.
Consider the following clinical scenarios.
You receive an emergency call regarding a cat that has swallowed a 500-mg Salix alba tablet. What do you do?
A client's dog that is receiving chemotherapy is not coping well with the adverse effects despite conventional treatment. The owner wants to use liu jun zi tang. What is this product? Is there evidence it is effective? What is the dose? Do you need to be concerned about herb-drug interactions?
A client purchased a herbal “heart pack” from an online herbalist, and the dog has developed gastric ulcers since then. Could it be the product?
Another dog has vacuolar hepatopathy. Could the herbal product the owner purchased online have been involved?
A clinical pharmacologist might be able to give advice, but these real cases were presented by specialists and colleagues for my advice just recently.
What about the owner who has a dog that is resistant to chemotherapy and wants to try herbs? Where will that owner go? Right now, the owner could google “herb and pet” and receive not just 37 million hits but also contact information for many lay individuals only too happy to take on the case. That is the reality today.
The veterinary profession has a simple choice. It can continue to drive animal owners to the internet and lay people willing to offer animal health advice, or it can recognize that herbs form an important economic and consumer-driven part of the animal health industry. The profession can choose to support and respect qualified veterinary herbalists trained not only in pharmacognosy, but also in the materia medica of plant-based medicines; the manufacture, quality control, safety, and dosing of herbs; herb-drug interactions and the effects of combining herbs or of combining herbs and drugs; and the research underpinning herbal medicine.
A veterinary botanical medicine speciality will ensure that diplomates are trained to the highest level in a scientific context, providing support to the profession and a service to animal owners. Veterinary herbalists want science to underpin the speciality: the kind of science represented by the > 3,000 botanical studies published in mainstream veterinary journals in the past 10 years, not counting the > 30,000 publications involving rats, mice, and rabbits.
Barbara Fougere, bsc, bvms
President-Elect, American College of Veterinary Botanical Medicine Russell Lea, NSW, Australia
1. Eyre P. Botanical medicine, homeopathy, and the placebo effect (lett). J Am Vet Med Assoc 2017; 251: 29.
I applaud Dr. Eyre on his concise rebuttal to the proposed specialty of veterinary botanical medicine and his additional comments regarding homeopathy.1 I have written separately to the AVMA's American Board of Veterinary Specialties in response to its request for input as the board considers the application by the American College of Veterinary Botanical Medicine,2 and heartily agree that botanical medicine is well within the purview of the already recognized specialty of clinical pharmacology.
In particular, I worry that establishment of a separate college devoted to botanical medicine could lead to a blurring of the line between treatments based on vigorous scientific testing—including the potential for refutation—and those based on faith, anecdote, or plausibility. I believe that the American Board of Veterinary Specialties should deny this application and that, as a profession, we should continue to educate the public to resist the lure of unfounded claims and channel ideas for clinical treatment of patients into recognized and scientifically established methods. It doesn't matter how much interest there is in a particular treatment, how long into history there have been claims of the efficacy of that treatment, or whether you or someone you know seems to have benefitted from the treatment. What matters is whether the treatment in question can stand up to rigorous testing through valid scientific methods. If it does, it is not “alternative,” “complementary,” “holistic,” or “integrative,” it's just medicine. And if it cannot be proven to provide a benefit beyond placebo, then it has no place in what we should recognize as the practice of medicine.
James M. Fingeroth, dvm
Orchard Park Veterinary Medical Center Orchard Park, NY
1. Eyre P. Botanical medicine, homeopathy, and the placebo effect (lett). J Am Vet Med Assoc 2017; 251: 29.
2. Comments invited on proposed veterinary botanical medicine specialty. J Am Vet Med Assoc 2017; 250: 827.
