Ancylostoma caninum, a roundworm, is the most common “hookworm” in domestic dogs in North America. As other intestinal parasites, hookworms can be potentially transmitted to people under unsanitary conditions. Dewormers (anthelmintics) commonly used for treatment of roundworms include the following classes: benzimidazoles (eg, fenbendazole, febantel), tetrahydropyrimidines (eg, pyrantel pamoate), and macrocyclic lactones (eg, milbemycin oxime, moxidectin).
Greyhounds were originally reported to have hookworms resistant to common dewormers in 1987. During the past few years, I received numerous consults regarding what appeared to be hookworms infestations resistant to multiple dewormers. A recent article described a deworming protocol that appears to minimize or eliminate resistance in greyhounds with hookworms (Hess, L. B., Millward, L. M., Rudinsky, A., Vincent, E., & Marsh, A. (2019). Combination Anthelmintic Treatment for Persistent Ancylostoma caninumOva Shedding in Greyhounds. Journal of the American Animal Hospital Association, JAAHA–MS–6904–7. http://doi.org/10.5326/JAAHA-MS-6904). Administration of monthly doses of a combination pyrantel, febantel, and moxidectin appeared to be an effective treatment for nonresponsive or persistent A. caninum ova shedding. Another study documented multidrug resistance (MDR) in hookworms from greyhounds (Castro, P., Howell, S. B., Schaefer, J. J., Parasites, R. A., 2019. Multiple drug resistance in the canine hookworm Ancylostoma caninum: an emerging threat? Springer. http://doi.org/10.1101/676007).
A brand new publication by Drs. Jimenez Castro and Kaplan further expands on the mechanism of resistance. They propose that the development of MDR in A. caninum is most likely the result of a combination of long-term intensive use of anthelmintics and the epidemiologic dynamics that exist on greyhound breeding farms. A. caninum is extremely common on greyhound breeding farms, likely due to an ideal environment for larval development and transmission conferred by sand and dirt exercise runs. The adoption of thousands of retired racing greyhounds each year has likely led to the spread of these MDR parasites to the general pet population. The only existing practical method to diagnose anthelmintic resistance in A. caninum is the fecal egg count reduction test, in which the number of worm eggs per gram of feces is measured both prior to and two weeks after treatment. Potential new anthelmintics are currently being investigated. Please discuss this issue with your veterinarian if you have concerns about hookworms in your hound.