A small number of strains of HPV are implicated in cervical cancer. Oddly, the dangerous strains in one place may differ completely from the important cancer-causing strains in another. For instance, in North America and England two HPV strains—types 16 and 18—are responsible for about 70 percent of cases of cervical cancer. But in West Africa, the predominant strain is type 45, and in Latin America it is types 39 and 59.