Pattern of latrine use by domestic cats on dairy farms and the implications for Toxoplasma gondii transmission

Toxoplasma gondii is the parasite responsible for toxoplasmosis, a highly prevalent zoonosis that affects humans and warm-blooded animals. Faeces of infected cats can contain millions of T. gondii oocysts, which remain infectious in the environment for months. Sites repeatedly used by cats for defecation ('latrines') are recognised as hotspots of T. gondii soil contamination, but this contamination varies from one latrine to another. To understand this spatial heterogeneity, camera traps were deployed in 39 cat latrines on three dairy farms with high-density cat populations and programmed to record visits during sixteen 10-day sessions, rotating between three farms over a period of a year. Generalized Linear Mixed Models were used to test the effects of cat sexual maturity, latrine location and season on the number of cat faeces deposited and on the number of cats defecating per latrine, as determined from the analysis of 41,282 video recordings. Sexually immature cats defecated 6.60-fold (95% CI = [2.87-15.25]) more often in latrines located close to a feeding site than in other latrines. This pattern was also observed for mature males (odds ratio [OR] = 9.42, 95% CI = [3.29-26.91]), especially during winter, but not for mature females (OR = 1.77, 95% CI = [0.80-3.94]). The number of defecating cats was also 2.67-fold (95% CI = [1.66-4.30], P 0.001) higher in latrines located close to a feeding point than in those located far from it, regardless of cat category and season. Visits by intermediate T. gondii hosts (micromammals, birds and others) were also recorded. Out of the 39 latrines, 30 (76.92%) were visited by at least one intermediate host during the study period, and some latrines were highly frequented (up to 8.74 visits/day on average). These results provide evidence that the location of food resources in dairy farms influences the latrine use pattern by cats. Highly frequented latrines can be of high risk of T. gondii infection for definitive and intermediate hosts.