FREQUENT DETECTION OF REVIRAEMIA IN DUCKS PERSISTENTLY INFECTED WITH AVIAN-LEUKOSIS RETROVIRUSES

Ducks intraembryonally infected with avian leukosis viruses of subgrou p C (ALV-C) were followed for a long period (up to 6.8 years), and the viraemia and production of virus-neutralizing antibodies were measure d, In three independent experiments comprising ducks inoculated with u ncloned and/or molecularly cloned ALV-C, we found that after the elimi nation of primary post-hatching viraemia, reviraemia could be detected in 60-70% of infected animals, Based on the course of viraemia, the i ndividual ducks were assigned to four different groups: Group I (no re viraemia), Group II (one transient reviraemic period), Group III (one persistent reviraemic period), Group IV (fluctuating reviraemia),In co mparison to sera from ducks included in Group I and/or II, a significa nt decrease in neutralizing acitivity of sera from animals comprised i n Group III and/or IV was observed, Two out of four reviraemic viruses were not neutralized by antiserum against ALV-C, instead their infect ivity was enhanced, Long-term follow-up of the cell-associated virus r evealed that its rescuability by cocultivation with chicken embryo fib roblasts fluctuated in about 50% of animals, In the reviraemic phase o f infection, integrated proviruses could be detected by Southern blott ing in a majority of tissues examined, Our data document that many fea tures recognized in lentiviruses are valid also for oncoviruses transm itted to heterologous hosts and substantiate further the suitability o f ALV-C-infected ducks as a model for studying persistent retroviral i nfection.