Time series analysis of the prevalence of endoparasitic infections in cats and dogs presented to a veterinary teaching hospital.

The apparent prevalence of endoparasitic infections of cats and dogs presented to the small animal Veterinary Hospital of the University of Pennsylvania was measured between 1984 and 1991. Two thousand feline and 8077 canine fecal samples were examined along with 6830 canine blood samples. The overall mean monthly prevalence of feline infections was 16% for ascarids, 0.9% for hookworms, 4.0% for tapeworms, 2.4% for Giardia spp. and 4.2% for coccidia. The overall mean monthly prevalence of canine infections was 5.7% for ascarids, 9.7% for hookworms, 9.7% for whipworms. 1.8% for tapeworms, 4.7% for Giardia spp. and 3.1% for coccidia. There was a significant downward trend in the prevalence of hookworms and heartworms in dogs (P < 0.001 in both cases). There was a significant upward trend in the prevalence of tapeworms in cats (P < 0.05). There were no significant long-term trends in any of the other time series. The smoothed data were analyzed for seasonal trends. None of the autocorrelation analyses gave incontrovertible evidence of seasonality. The repeated peaks at the 6, 12 and 24 month lags in the case of ascarid infections were suggestive of a 12 month seasonality with a peak prevalence in December, but the results were not statistically significant at the 5% level. Hookworms and whipworms in dogs occurred together more than would be expected by chance in 4 out of the 6 years for which data were available.