Seasonality and changing prevalence of common canine gastrointestinal nematodes in the USA

BACKGROUND: The three most commonly diagnosed gastrointestinal parasites of pet dogs within the USA are the whipworm, the hookworm, and the roundworm. The collection of large data sets from various sources throughout the industry have produced a number of publications on parasite prevalence in recent years. In this study, we look at data captured by the Companion Animal Parasite Council from 2012–2018, which includes 4.3–7.2 million annual fecal exams, to evaluate not only changes in prevalence, but also possible seasonal fluctuations of the three most common canine gastrointestinal parasites. METHODS: Annual and monthly data were collected from the CAPC parasite prevalence maps for canine roundworms, hookworms and whipworm. The map data were provided to CAPC by two large national reference laboratories. The data were evaluated for changes in prevalence on a monthly basis throughout each year as well as changes in prevalence from year to year from 2012–2018. Additionally, positive test results and total tests performed for each of the three parasites from 2012–2018 during individual months were totaled without using the year as a variable in order to evaluate the results for seasonality (i.e. all tests and positive results occurring in January, regardless of year, were totaled and analyzed). RESULTS: Evaluation of gastrointestinal nematode prevalence data from over 39 million fecal samples examined over a 7-year period revealed a subtle, yet significant, increasing prevalence for roundworms, an increasing prevalence for hookworms, and a slightly decreasing prevalence for whipworms. Seasonality was demonstrated for roundworms, hookworms, and to our knowledge, for the first time canine whipworms. Highest seasonal prevalence for roundworms, hookworms, and whipworms occurred during December–January, July–August, and January–February, respectively. CONCLUSIONS: Evaluation of monthly gastrointestinal parasite prevalence data from over 39 million fecal samples collected over a 7-year period revealed a slightly increasing prevalence for roundworms, an increasing prevalence for hookworms, and a slightly decreasing prevalence for whipworms. In addition to the annual changes in prevalence, seasonal prevalence was shown for the first time for whipworms. Prevalence of both whipworm and roundworm peaked in the winter, while prevalence of hookworm peaked in the late summer and early autumn.