Some types of HPV are sexually transmitted, other types can be transmitted through casual contact. The types (genotypes) of HPV that effect the genitals (genital warts, dysplasia) are usually only transmitted through genital/genital contact, however it can be transmitted from mother to child during birth if mother had an active infection at the time. Because this is a virus, it does not always follow all the rules...i.e., there are a small percentage of cases (like the nuns, etc) that indicate other modes of transmission may exist. That research is currently inconclusive. A similar example of a virus transmission can be seen with herpes. There are multiple genotypes of herpes. Herpes simplex I causes cold sores--most people have been exposed to this and have antibodies to keep it in check. But this same virus can be transmitted to genitals and actually transform itself into herpes simplex II. The same virus but different genotype causes Shingles. Virus' are radical and unpredictable. The best defense is keeping your immune system in check.

BTW, I recently I asked 3 different Drs if HPV was transmittable through semen. I got three different answers: "Yes", "No", and "it can be detected in semen but it's not likely transmittable through bodily fluids. The point is, you cannot take what any one clinical practioner says as the gospel truth rearding HPV (or much of anything else viral). On another note--perfectly healthy skin (genital skin) of an HPV infected male or female may harbor and transmit this virus. In case where men have been found to have sub-clinical lesions, those lesions may be removed and biopsied but show no viral cells. Yet healthy skin removed from the same penis biopsied found HPV viral particles.