Abstract
In 1992 an annual Simian herpes B virus (BV) screening programme for an experimental group of macaque monkeys (Macaca mulatta and Macaca fascicularis) was initiated with the aim of establishing a specific pathogen free (SPF) colony. In June 1999 one animal was found to be unexpectedly BV positive (non-negative). The investigation of this result highlights some of the issues and difficulties that may be encountered in such a programme.