Potentially precancerous cervical cell changes and some types of warts are not visible to the naked eye. Infected people without symptoms may still be able to transmit the virus. Women must have regular follow-up Pap smears. Some cell changes, especially on the cervix, can be precancerous. Recurrences are possible.
Barrier methods are only partially protective.
With condoms, for example, lesions may be present in areas not covered. Only total absence of any touching of infected tissue will avoid transmission. Transmission most common with exposure through vaginal or anal sex. Casual contact considered to be safe. Many people with trich experience no symptoms.