Modelling the effect of surveillance programmes on spread of bovine herpesvirus 1 between certified cattle herds

For the eradication of an infectious agent, like bovine herpesvirus 1 (BHV- 1), surveillance and certification can be used to reduce the transmission b etween herds. The goal of surveillance is that a certified herd that become s infected is detected timely so that infection of several other certified herds is prevented. What counts is whether the reproduction ratio R, i.e. t he average number of certified herds infected by one infected certified her d can be kept below 1. To support policy makers in making decisions about t he minimal demands for a surveillance programme in an eradication campaign of BHV-1 in cattle, two mathematical models were investigated. With these m odels, the basic reproduction ratio between herds was calculated. The surve illance programmes were characterised with sample size, sampling frequency, test sensitivity, herd size, vaccination status, and contacts between herd s. When R between herds is below 1, then the surveillance programme is suff iciently good to prevent spread of infection, provided that R is estimated well. In the model based on bulk milk testing sample size was replaced by a threshold at which bulk milk can be found positive. The R between herds wa s mainly influenced by the vaccination status, sampling frequency, and cont acts between herds. Herd size moderately affected the outcome. Test sensiti vity and sample size, however, were of minor importance. If herds of 50 cow s became free of BHV-1 without vaccination, then spread of infection betwee n herds might be prevented when animals within herds are sampled once a yea r (milk or blood samples). This frequency needs to be intensified, being tw ice a year, for larger herds and/or herds with extensive contacts with othe r herds. When bulk milk is sampled instead, sampling should be done at leas t every 5 months and more intensively, beingeach month, with larger herd si zes and more contacts between herds. (C) 2001 Elsevier Science B.V. All rig hts reserved.