Rodents comprise a major component of cat (Felis catus) diets in many ecosystems, and life cycle diagrams of Toxoplasma gondii typically depict small rodents as quintessential intermediate hosts. Counter-intuitively, small rodents often experience a lower T. gondii seroprevalence than do larger sympatric mammals. This observation has repeatedly caused confusion about the relative importance of small rodents to the ecology of T. gondii. To address this confusion, we modified the Reed-Frost epidemic model to develop a simple binomial equation to model T. gondii transmission from prey to feline predators. This equation takes into account variations in prey seroprevalence and the frequency with which they are consumed by felids. Even when T. gondii seroprevalence in prey is < 1%, computation reveals that the risk of feline exposure to T. gondii can easily exceed 50 % annually. For example, if cats eat an average of 1 mouse per day, a seroprevalence of 0.2 % (1/500) in mice will cause 51.9 % of cats to be exposed to T. gondii annually. Our simple equation demonstrates that both prey seroprevalence and the rate at which prey are consumed are of approximately equal importance to the ecology of T. gondii. When inferring the importance of various prey species to the ecology of T. gondii, researchers must consider the predation and dietary habits of felids from within their study system. Our simple binomial equation could also be used to predict T. gondii exposure rates of humans or other carnivorous animals from various dietary sources or be applied to other predator-prey parasite life cycles.

啮齿动物是许多生态系统中猫（猫属）饮食的主要成分，弓形虫的生命周期图通常将小型啮齿动物描绘为典型的中间宿主。与直觉相反，小型啮齿类动物的弓形虫血清感染率通常低于大型同伴哺乳动物。这一观察结果一再引起人们对小型啮齿动物对弓形虫生态学的相对重要性的困惑。为了解决这种困惑，我们修改了Reed-Frost流行病模型，以开发一个简单的二项式方程式来建模T. gondii从猎物传播到猫食肉动物。该方程式考虑了猎物血清阳性率的变化以及猫科动物食用它们的频率。即使当刚地弓形虫的血清阳性率＜1％时，计算仍表明猫每年接触刚地弓形虫的风险很容易超过50％。例如，如果猫每天平均吃掉一只老鼠，则小鼠的血清阳性率0.2％（1/500）将导致每年有51.9％的猫被弓形虫暴露。我们的简单方程式表明，猎物的血清阳性率和猎物的消耗速度对弓形虫的生态学具有同等重要的意义。当推断出各种猎物对生态系统的重要性时刚地弓形虫，研究人员必须在其研究系统内考虑猫科动物的捕食和饮食习惯。我们的简单二项式方程式还可用于预测来自各种饮食来源的人类或其他食肉动物的弓形虫暴露率，或将其应用于其他捕食者-猎物寄生生物的生命周期。