A stochastic model for disease transmission in a managed herd, motivated by Neospora caninum amongst dairy cattle

A stochastic model for the spread of Neospora caninum infection within a he rd of dairy cattle is studied, in particular the long-term (equilibrium) be haviour of the model. The model incorporates the interesting feature that t otal herd size is constrained to lie within a fairly small interval, but no t held exactly constant. Approximations for the joint distribution of numbe rs of susceptible and infected individuals present in equilibrium are deriv ed based upon a diffusion approximation to the infection process. The effec t of both 'typical herd size' and 'the amount of permitted variation in her d size' upon disease prevalence in equilibrium are considered using both th e exact equilibrium distribution of the process and our approximations. (C) 2001 Elsevier Science Inc. All rights reserved.