Although the word “virus” has become a part of the everyday vernacular, what exactly are retroviruses? Marc Johnson explains that they can be grouped into RNA viruses and DNA viruses. RNA viruses cause short-term diseases such as the flu and the common cold, whereas DNA viruses cause more long-term illnesses like herpes or cancer. “Retroviruses are a unique blend,” he explains. “They are like a DNA virus that can replicate with RNA strategies.” HIV is a retrovirus.