Prospects of toxoplasmosis control by cat vaccination.

• We model how a the implementation of a hypothetical cat vaccine against T. gondii infection could reduce the incidence of oocyst-originated human toxoplasmosis. • A oocyst ingestion dose–response relation for T. gondii infection is calculated, with uncertainty included. Oocysts are extremely infectious to intermediate hosts, one oocyst infects with probability 0.46 (0.31–0.57, 95% confidence level. • Two model approaches for oocyst distribution in the environment are compared, one where oocysts are homogeneously distributed and one where they are clustered. • Vaccination coverage needed for reduction of toxoplasmosis incidence is not feasible for large populations of cats. • Small populations of cats can benefit of vaccination, e.g., meat production farms, as only a few cats may be left unvaccinated for the pathogen not to proliferate. Toxoplasmosis has high disease burden in the Netherlands and in the rest of Europe. It can be acquired directly by ingestion of Toxoplasma gondii (T. gondii) oocysts shed by infected cats, or indirectly via consumption of undercooked meat from infected livestock. Cat vaccination has been proposed for reducing oocyst-acquired human infections but it remains unclear whether such an intervention can be effective. In this study we quantified the effects of using cat vaccination on reducing oocyst-originated T. gondii human infections. By using a disease dynamics compartmental model for T. gondii infections in cats and mice we studied the effects of a hypothetical cat vaccine on the presence of T. gondii oocysts in the environment. A fitted dose response model was used to assess the effect of oocyst reduction on the expected human infections. For rats, mice and pigs, and possibly intermediate hosts in general, ingestion of one oocyst provides 30%–60% probability of T. gondii infection. Assuming a favourable ideal scenario where vaccination completely prevents oocyst shedding and predation rate is of one mouse per week per cat, eight cats can be left susceptible in order to achieve elimination and stop oocyst-originated transmission, independent of the total cat population. Considering populations of 1000, 100, 50 and 20 cats, cat vaccination coverage of 94%, 68%, 54% and 35%, respectively, would reduce expected oocyst-originated human cases by 50%. For attaining elimination of oocyst-originated human infections, only few cats may remain unvaccinated, regardless of the cat-population size, and only a few more cats may remain unvaccinated for reducing infections substantially. Such vaccination coverages can in practice be achieved only when small cat-populations are considered, but in larger cat-populations the large efficacy and vaccination coverage needed are unfeasible. [ABSTRACT FROM AUTHOR]