B-VIRUS SPECIFIC-PATHOGEN-FREE BREEDING COLONIES OF MACAQUES (MACACA MULATTA) : RETROSPECTIVE STUDY OF SEVEN YEARS OF TESTING

144 There has been interest in establishing B virus-free breeding colonies of macaques for at least 25 years. In 1972, DiGiacomo and Shah (1) concluded that laboratory rearing of rhesus monkeys can exclude infection with B virus and that there is virtually no spread of B-virus infection to individually caged monkeys in a well-established colony. This was based on the retrospective observation that prevalence was age dependent in natural populations and that laboratory populations that were raised in a nursery and caged individually were virtually free of infection. In a prospective effort from 1986 to 1989, Olson et al. (2) brought a colony of 102 rhesus monkeys to a seronegative status by housing individually, monitoring periodically, acquiring them only if they were seronegative, and culling them if they converted to positive status. They found that the seroreactivity of 92 monkeys did not change after acute immunosupression, but six juveniles lost detectable antibody, and four juveniles converted to positive status. By the end of 3 years, the number of seropositive macaques in the colony was reduced to three through attrition and culling. In 1987, a less rigorous attempt to establish a seronegative colony failed when seropositive macaques were isolated but kept in the breeding program (3). After 3 years in that program, latent infections led to an increase in seroconversion and presence of indeter-