Parvoviruses. Coloured transmission electron micrograph (TEM) of parvovirus B19 particles. Parvoviruses are small and consist of a single- stranded DNA genome surrounded by an icosahedral protein capsid (coat, yellow). Parvovirus B19 is the cause of erythema infectiosum, or Fifth disease. This childhood disease causes a red rash on the face, similar to a slap mark, which earns it the common name of slapped cheek disease. It usually causes a slight fever, but bed rest is the only treatment needed. It is more serious in adults, causing swelling and joint pain. In immun- osuppressed people, it can cause anaemia and death. Magnification: x63,000 at 6x7cm size.