A Plaque Assay for Duck Plague Virus.pdfVIP

A Plaque Assay for Duck Plague Virus A. H. Dardiri and W. R. Hesst ABSTRACT A plaque assay for duck plague virus was developed for a chicken embryo-adapted virus and a duck lethal virus and used to determine the identity of these viruses. Using the plaque inhibition neutralization test, duck plague virus was differentiated from Newcastle disease, fowl plague, and duck hepatitis viruses. The plaque morphology is described. INTRODUCTION If a virus initially, or after passage, will produce plaques in cell cultures, it is often possible to devise an accurate and versatile assay method which may serve to enumer- ate infectious virus particles in suspen- sions, detect and measure neutralizing antibodies in serums and to select pure lines from a mixed virus population. It is the purpose of this paper to describe a plaque method for the assay of duck plague virus and report on its use in confirming the serologic relationship between an at- tenuated strain of duck plague virus from Holland and a virulent American isolate, and to differentiate these viruses from the agents of Newcastle disease, fowl plague and duck virus hepatitis. tPlum Island Animal Disease Laboratory, Animal Dis- ease and Parasite Research Division, Agricultural Re- search Service, U.S.D.A., Greenport, Long Island, New York 11944. MATERIALS AND METHODS VIRUSES 1. Holland duck plague attenuated virus (HDPAV)* which had undergone ap- proximately 12 serial passages in duck em- bryo (DE) and 20 or more passages in chicken embryo (CE) (3) was received in the form of infected chorio-allantoic mem- branes of CE. It was serially passed twice in CE and 4 times in DE cell cultures in this laboratory before use. 2. A virus, designated duck plague Long Island virulent virus (DPLIVV),** was isolated from ducks that died during a dis- ease outbreak occurring on commercial duck farms on Long Island, New York, U.S.A., in January, 1967 (1). The 2 viruses used were serologically identical to a virulent duck plague virus als