Endemic stability - a veterinary idea applied to human public health

Endemic stability is an epidemiological state of a population, in which cli nical disease is scarce despite high level of infection. The notion was dev eloped to describe patterns of tick-borne disease in cattle. However, we pr opose a general model of endemic stability that is applicable to a broader range of diseases that are important in public health, including malaria, r ubella, and mumps. We postulate that endemic stability requires only that ( 1) the probability, or severity, of clinical disease after infection increa ses with age, and (2) after one infection, the probability that subsequent infections result in disease is reduced. We present these criteria in simpl e mathematical terms. Our hypothesis predicts that partial disease control activities might, under certain mathematical circumstances, interventions.