ABSTRACT
This chapter provides a brief account of the development of studies on structure, composition, properties, cytopathology, and taxonomy of Carlaviruses. The Carlaviruses form a rather homogeneous group. Some of them cause serious disease but a number are symptomless at least in certain hosts; this is true for carnation latent virus, which gives its name to the group. Carlavirus particles are fairly stiff but flexible rods 12 to 13 nm in diameter and between 610 and 700 nm in length. Many viruses have been isolated with some characteristics of Carlaviruses: however, decisions as to what constitute separate viruses are difficult because many members are distinguished according to their host ranges while being related serologically. The particles of Carlaviruses are slightly flexuous rods often appearing curved to one side, both in negatively stained and shadowed preparations. There may be some differences in the modal lengths of certain Carlaviruses, and this is a character that might be useful taxonomically.
