Is there any general rule to say this must be RNA virus infection and the other one DNA virus infection?
Example of a case: 5 children develop a bright red rash on the face and turns violet after a few days and then disappears. Then maculopapular rash appears on the trunk, buttocks and extremities. It soon fades from the trunk but persists on the thights and forearms. Two children have also had a slight fever and a sore throat, but all were not terribly sick. What is the genetic material of the most likely causative agent?
Right answer is: Single-stranded DNA, since most probably causative agent is erythema infectiosum caused by parvovirus B19.
I do not want to remember all microbes by heart. How can you deduce that this must be a DNA infection and probably single-stranded?