This negative-stained transmission electron micrograph (TEM) image depicted the ultrastructural details of an Orf virus, a member of the genus Parapoxvirus. Note the spiral arrangement of the external tubular ridges on the ovoid-shaped virus particle, or virion. The criss-cross pattern is an artefact caused by superimposition of images of top and bottom surfaces of the virion.

The orf virus is a pathogen common to sheep and goats, but can at times be transmitted to humans, in which case the virus is known as being “zoonotic”. When a human being becomes infected, the symptoms are mainly confined to the skin, and consist of “weeping” nodules manifesting upon the dorsum, or back of the hands, and which heal in approximately thirty-five days in a spontaneous fashion.

Photo credit: Cynthia Goldsmith

Source:CDC's Public Health Image Library Image #8434

This image is a work of the Centers for Disease Control and Prevention, part of the United States Department of Health and Human Services, taken or made as part of an employee's official duties. As a work of the U.S. federal government, the image is in the public domain.