Estimates of the annual incidence density and financial losses of equine monocytic ehrlichiosis in New York state

Abstract

Very little is known about the incidence density of equine monocytic ehrlichiosis (EME) in New York state. Obtaining a valid estimate of the state-wide incidence density would provide a measure for how common EME is in the New York state equine population, provide a historical benchmark of the incidence density for future comparisons, and aid in the estimation of the financial losses associated with EME. In this study we used four sets of state-wide data to obtain four estimates of the annual incidence density of EME in New York state. Two methods were used to calculate the incidence density: the average incidence rate of EME over a period of time, and transforming the point prevalence of exposure to Ehrlichia risticii into an incidence density. Given the incidence density, an estimate of the annual state-wide financial losses associated with this disease was calculated. Three of the four estimated ranges of the incidence density fell within the range of 0.44–1.73 per 1000 horse-years at risk. Therefore, given that there were approximately 182 000 horses in New York state in 1988, among which 92.7% (168 714) were susceptible at one time, we would expect 74–292 cases of EME per year under steady-state conditions. Since the mean cost (direct and indirect) associated with a case of EME in New York state was estimated at $1030.00, the annual state-wide financial losses associated with clinical EME for equine owners was $76 220–300 760.