Polymerase chain reaction for detection of avian leukosis virus subgroup J in feather pulp

Feather pulp from experimentally infected chickens was used as a source of DNA for polymerase chain reaction (PCR) amplification of avian leukosis virus subgroup J (ALV-J) proviral DNA. A primer set that produces a large amplicon (approximately 2,125) was used to detect ALV-J proviral DNA. This primer set was used in lieu of previously published primers because it allows for sequencing of the entire envelope gene and because it was able to detect diagnostically a number of North American ALV-J isolates that could not be detected with previously published primers and PCR conditions. ALV-J proviral DNA was detected in feather pulp at 7 days of age in more than 90% of birds infected as embryos and 7 days postinoculation in over 50% of chickens infected at 3 days of age. The results obtained with PCR on feather pulp were compared with those of virus isolation. In the embryo-inoculated birds, the percentages of agreement between PCR and virus isolation were 92.5% at 7 days of age and 100% at 28, 42, 49, and 56 days of age. However, the overall sensitivity of virus isolation in embryo-infected birds was higher, particularly at 7 and 56 days of age. In chickens inoculated at 3 days of age, the percentages of agreement of detection between PCR and virus isolation ranged from 75% at 10 days of age to 100% at 42 days of age. Agreement of negative results of ALV-J detection by PCR and virus isolation in chickens infected posthatch ranged between 66.6% and 100% between the ages of 10 and 42 days. Virus isolation requires chicken embryo fibroblasts of specific genetic lines, and the process takes onaverage 7-9 days. Aseptic collection of blood and tissues for virus isolation and molecular detection of ALV-J requires sterile necropsy instruments as well as syringes and needles for each individual chicken, whereas sterile microcentrifuge tubes and gloves are the only equipment necessary for aseptic feather pulp collection for ALV-J detection by PCR. PCR-based detection of ALV-J in feather pulp is especially suitable when ALV-J infection must be diagnosed rapidly and unequivocally without killing the chicken(s) and in situations where crucial reagents or suitable virus propagation substrates are not readily available for isolation and propagation of ALV-J in cell culture.