Examples of STIs/STDs Trichomonas: Trichomoniasis is a common sexually transmitted infection (STI) caused by the protozoan Trichomonas vaginalis. It causes itching and painful urination. It is treatable and curable. Chlamydia: Chlamydia is a common sexually transmitted disease (STD) caused by bacteria called Chlamydia trachomatis. Chlamydia can be easily contracted and it often doesn’t cause symptoms,…