Regional and seasonal variability in canine parasitism across the United States

Seasonality has been shown to influence the prevalence of parasitic infections in dogs. Given that seasonal and climatic patterns vary across different geographic regions of the United States (US), our hypothesis was that seasonal effects on the prevalence of canine parasitism would differ significantly by region. Three main study objectives were to: (1) determine the overall prevalence of canine parasitism and identify the most commonly detected parasites for further analysis; (2) compare the prevalence of parasitism by region and by month; and (3) analyze the effect of regional and seasonal interactions on the prevalence of parasitism. A total of 48,510 cases from January 1 to December 31, 2023, were analyzed. At least one parasite was identified in 5954 cases (12.27 %). The five most common parasites were Giardia intestinalis (5.27 %), Ancylostoma spp. (3.14 %), Toxocara canis (2.07 %), Cystoisospora spp. (1.95 %), and Trichuris vulpis (0.88 %). Regional differences significantly influenced the prevalence of overall parasitism (P < 0.0001), as well as that of G. intestinalis (P < 0.0001), Ancylostoma spp. (P < 0.0001), T. canis (P < 0.0001), and T. vulpis (P = 0.0035). Monthly differences were also significant for the prevalence of total and individual parasites. A significant effect of the interactions between region and season was observed for the prevalence of overall parasites (P = 0.0397), Ancylostoma spp. (P = 0.0303), and T. canis (P = 0.0046), but not for G. intestinalis (P = 0.1591), Cystoisospora spp. (P = 0.7195), or T. vulpis (P = 0.2644). These findings highlight the complexity of host-parasite-environment interactions and suggest that risk factors affecting the prevalence of canine parasitism vary by different parasite species.