Identification of a Cell-Associated Morbillivirus from Cattle Affected with Malignant Catarrhal Fever: Antigenic Differentiation and Cytologic Characterization

Abstract

SUMMARY Cell-associated syncytiogenic viruses were isolated from a calf (No. 72-P-535) with experimentally induced malignant catarrhal fever. The isolate from leukocytes was further characterized by studying its interactions with low-passage fetal bovine cells and mammalian erythrocytes. Conditions required for storage and in vitro propagation were also investigated. All isolates were identified antigenically, using direct and indirect fluorescent antibody techniques. The representative 72-P-535 leukocyte isolate multiplied and induced polykaryons in fetal bovine spleen, adrenal, kidney and thyroid monolayers. Cytoplasmic or nuclear inclusions were not observed in Giemsa-stained, infected monolayers. Infected cells continued to fuse with adjacent cells until monolayers contained polykaryons with numerous randomly arranged nuclei and until large polykaryons became detached and the monolayer degenerated. Infectivity remained associated with the cells. Sonication and freeze-thawing eliminated infectivity and cell-free fluids were noninfective. Guinea pig, human O, and bovine erythrocytes were not agglutinated by cell-free culture fluids or cell lysates, nor did they adsorb to infected cells. Using the indirect fluorescent antibody test, identical fluorescence patterns were observed when cells infected with any of the 72-P-535 isolates were reacted with the same reference antiserum. Cells infected with the 72-P-535 leukocyte isolate gave cytoplasmic and nuclear fluoresence when reacted with measles or rinderpest virus antisera. Cytoplasmic, but not nuclear, fluorescence was observed when canine distemper virus antiserum was used in a direct test. Fluorescence was not observed in infected cells when antisera to parainfluenza type 3, bovine respiratory syncytial virus, or bovine syncytial virus were used. Immunofluorescence results were supported by tests in which only the antisera to morbilliviruses suppressed polykaryocytosis in infected monolayers. These characteristics indicate that the 72-P-535 isolates are the same virus, and that they represent the first morbillivirus isolates reported from North American cattle.