Human herpes virus 6 (HHV6) and human herpes virus 7 (HHV7): Roseola is usually caused by HHV6, but it can also be caused by HHV7. These two forms do not cause cold sores and genital herpes infections; they cause several days of fever followed by a rash. Roseola is contagious and can be spread by contact with an infected person's respiratory secretions or saliva. Activities such as laughing, sneezing, talking, or coughing may spread roseola. Also, individuals can spread roseola when they have a fever, even before showing signs of a rash.