Serological diagnosis of goose circovirus infections

Infections with goose circovirus (GoCV) are associated with growth retardation and developmental problems in farmed geese. An indirect immunofluorescence assay for detecting virus-specific serum antibody was developed for diagnostic and epidemiological purposes. In the absence of a method for growing GoCV in cell culture, the assay was based on the reaction of antibodies with the GoCV capsid protein produced within baby hamster kidney cells using the eukaryotic Semliki forest virus expression vector. Using an optimized test that involved screening sera at 1:50 dilution and the use of a fluorescein isothiocyanate anti-duck immunoglobulin conjugate, GoCV-specific antibody was detected in 141 (88.6%) of 159 samples obtained from 27 of 28 breeder flocks aged from 1 to 6 years. Testing also showed the presence of GoCV-specific antibody in 85 (40.9%) of 208 serum samples from birds aged 30 weeks or less. Although maternally derived antibody was detected in birds when 1 and 4 days old, actively acquired antibody was first detected in birds aged 53 days. Following experimental inoculation of 21-day-old geese with tissue homogenate containing GoCV, virus-specific antibody was detected in serum samples collected at 27 and 34 days post inoculation. It is concluded that the SFV expression vector approach may prove useful for developing serological tests for other viruses, including other avian circoviruses, that do not grow in cell culture.