False-colour transmission electron micrograph of the orf virus, a brick-shaped poxvirus. Notice the characteristic 'ball of wool' appearance under the electron microscope. The virus is responsible for contagious pustular dermatitis, a disease which mainly effects sheep, cattle and goats but is also transmissible to humans. Orf in humans is commonest amongst people in close contact with lambs. The lesions produced are usually painless and disappear after about five weeks. Magnification: x85,000 at 6x4.5cm size.