Electron microscopic identification of papova virus in laryngeal papilloma
Authors: Boyle William F. , Riggs John L. , Oshiro Lyndon S. , Lennette Edwin H. 
Published: September 2006

Attempts to propagate a laryngeal papilloma virus in cell culture by the establishment of tissue culture lines from 27 papilloma specimens which were removed endoscopically from the larynx of 19 patients of all age groups were unsuccessful. By light microscopy, all the lesions, with one exception, exhibited the usual features of a typical squamous papilloma. Laryngeal papillomas were removed endoscopically from an adult male Caucasian on three separate occasions with intervening intervals of 13 and seven months. Tissue removed at each procedure was submitted for study. Tumor obtained from the first two operative procedures exhibited the features of a benign squamous papilloma. Histologic diagnosis of the most recent excised laryngeal neoplasm was consistent with carcinoma.

Two papillomas which contained papova‐like virus when examined by electron microscopy were among the excised specimens cultured. Laryngeal papillomas were removed endoscopically on two occasions at an interval of five months from a 22‐year‐old Caucasian male who had a one‐month history of hoarseness. Electron microscopic examination of the most recently excised tissue revealed intranuclear viral particles which were in the shape of an icosahedron and measured approximately 45 mμ in diameter. The particles contained a densely staining core and were generally scattered throughout the nucleus. Occasionally, they were seen in crystalline arrays. The nuclear site of replication, their size and shape fit the description of the agents belonging to the papova virus group. Papova‐like viruses were also seen in laryngeal papillomas from an 18‐month‐old Negro child born of a mother with venereal warts.

Although many attempts at propagating the human papilloma virus have been reported,1 the virus known to cause common warts has to date never been successfully grown for continuous passage in tissue culture. The difficulty in isolating the laryngeal papilloma virus in tissue culture is also apparent.2

Serial studies done on an adult laryngeal papilloma showed transition of the tumor from a benign to a malignant lesion. It is interesting to speculate on this possibly viral‐induced laryngeal malignancy. That viruses can cause malignancy in non‐human species is well known, and there is no reason to presume that man is different from such species in this respect. Clinical evidence of the transmissability of this disease from infected genital warts to the newborn was suggested by the development of laryngeal warts in the young child. The electron microscopic identification of virus in the laryngeal papilloma that is morphologically similar to the genital wart virus, supports this theory of transmissability. The ultrastructure of human laryngeal papilloma has been described previously3 and the presence of virus4 and virus‐like particles suggested;5 however, the crystalline lattice assemblies, characteristic of the papova group, have never been described heretofore. The results of these studies add strong morphologic and clinical evidence of the viral etiology of laryngeal papilloma; however, the evidence is not conclusive. The ultimate aim of this project is to propagate the papilloma virus in tissue culture.