B virus-specific pathogen-free (SPF) breeding colonies of macaques: issues, surveillance, and results in 1992

The NIH's National Center for Research Resources, Comparative Medicine Program has sponsored a multi-institutional program for the establishment of specific pathogen-free (SPF) macaque colonies. Herpes B virus (Cercopithecine herpesvirus I) has been targeted as part of this surveillance. Participating institutions have established individual timetables for frequency of testing, types of monitoring, and husbandry techniques, all with the common goal of producing pathogen-free monkeys for research. From January 1990 through December 1992, we screened animals for evidence of B virus infection, using ELISA and immunoblot to detect humoral antibodies. A total of 984 animals were tested during the first year of the program. At the start of the third year, 631 animals remained in our testing program. Of the 36.9% eliminated for all causes over a 3-year period, B virus screening accounted for 12.1, 1.2, and 0.5% during years 1, 2, and 3, respectively. The greatest threat to the success of the program comes from failure to detect seronegative animals with latent infections, if they do indeed exist, either in first-year animals or animals introduced in subsequent years. The best assurance that a colony is SPF comes from negative results of repeated testing. Introducing new animals into an established SPF colony should be done only after careful screening. Simulations using mathematical models suggest that the best way to detect seronegative animals with latent infections is monthly or bimonthly testing separated by a waiting period. Duration of the waiting period cannot be defined precisely until more is known about the reactivation potential of putative seronegative animals with latent infections.