The infection is caused by the protozoan Trichomonas vaginalis. Half of infections progress without any signs or symptoms; although women woman may experience a yellowish-greenish discharge of unpleasant smell, itching, burning sensations or pain in the genital area, 4 to 28 days after infection. In men, the symptoms are less marked; they may include foamy or purulent discharge from the urethra and a burning sensation on urination. In most men the infection passes without treatment, which does not apply to women. The infection is transmitted especially among heterosexual couples; it may also be transmitted by women having sexual intercourses with other women, especially through shared sex accessories. The infection is treated by an appropriate antibiotic.