An Electron Microscopic Study of the Epidermal Lesion of Molluscum Contagiosum

Abstract

The lesion of molluscum contagiosum is a small nodule occurring only in the epidermis of man. The elementary bodies of the virus causing the lesion are relatively large and occur within the molluscum bodies, which begin to form in the lower layers of the skin and mature toward the upper layers. Theoretically, one would assume that all phases of the life cycle of the virus could be represented in a single section. For these reasons, emphasizing the fact that molluscum contagiosum is a readily accessible human viral lesion, we chose it as a promising subject for study.The first observations on the lesions of molluscum contagiosum, using thin sections in the electron microscope, were made with the embedding matrix removed," e , which destroyed fine detail and much of the cellular and cytoplasmic structure. Gaylord and Melnick4 published several electronmicrographs of molluscum contagiosum without the embedding material removed and pointed out that the developmental bodies were similar to those of vaccinia and ectromelia. No further work using thin sections was published until Wadas observed that the inclusions eventually replaced the cytoplasm, except for a thin layer around the periphery of the cell, and that old inclusions were made up exclusively of elementary bodies, which replaced even the septa within the inclusions.Most recently Dourmashkin el aL6! for the first time were able to grow the virus outside the human host in cultures of HeLa cells. They reported preliminary observations on the culture material and on human epithelial lesions. In the skin lesions they observed very osmiophilic condensations within the nucleus of infected cells, very osmiophilic granules in the matrix of the inclusion that morphologically resemble the nucleoid of the virus, structures containing a nucleoid, and lobulated masses of viroplasm. Their observations on the infected HeLa cells will be referred to later. Material and MethodsMolluscum lesions together with a small piece of surrounding skin were obtained from the back of a young boy. They were fixed for 3 hours in Palade's buffered osmium: washed for 236 hours in the Veronal-acetate buffer, dehydrated in a graded seriesof ethyl alcohol, infiltratedwith 1 part methyl: 7 parts butyl methacrylate containing a 1 per cent concentration of benzoyl peroxide as a catalyst, and polymerized in a 60" C. oven. Sectioning was performed on a Porter-Blum microtome with motor drive. ResultsFIGURE 1 is a photomicrograph of a section through a molluscum contagi-The first changes take place in the cytoplasm just above the osum lesion. 145