Strains 16, 18. As HPV is the precursor to cervical cancer, it is especially important to know its symptoms. Because HPV is a virus, it can be transmitted to another person even if the host shows no physical symptoms. And not all strains of the virus produce visible symptoms. Certain strains—6 and 11 produce visible genital warts. Strains 16 and 18 are responsible for most cases of cervical cancer.