viruses, with an average genome size of 5000 nucleotides. They are classified as group II viruses in Baltimore classification of viruses. Parvoviruses are among the smallest viruses (hence the name, from Latin parvus meaning small) and are 18–28 nm in diameter. Parvoviruses can cause disease in some animals, including starfish and humans. Because the viruses require actively dividing cells to replicate, the type of tissue infected varies with the age of the animal. The gastrointestinal tract and lymphatic system can be affected at any age, leading to vomiting, diarrhea and immunosuppression but cerebellar hypoplasia is only seen in cats that were infected in the womb or at less than two weeks of age, and disease of the myocardium is seen in puppies infected between the ages of three and eight weeks. See also Bat virome History of virology Social history of viruses Virus evolution References Molecular biology Animal viral diseases