ABSTRACT
Morphology. The unique ovoid morphology of parapoxvirus virions forms the basis for their inclusion as a separate group in the poxvirus family [1]. Electron microscopy reveals a virion with a long axis of approximately 260 nm and a short axis of 160 nm [2,3]. Negatively stained preparations appear in two forms. In the capsular form where the stain has penetrated the virion, a nely crenulate membrane appears to surround an inner amorphous core. Whereas virions that are impervious to the stain reveal a regular array of tubule-like structures arranged in a criss-cross manner along the length of the particle [3,4]. The criss-cross pattern seen by electron microscopy is apparently due to superimposed images of the tubule-like structure as it winds its way in a spiral around the viral particle. More recently the surface ultra structure of ORFV has been described using ultra high resolution scanning electron microscopy [5] and electron tomography [6] where spirally running protrusions are visible on the surface of the virion.
