Trich . Trich is a slang name for trichomoniasis. Trichomoniasis is a sexually transmitted disease (std) caused by infection with a parasite called trichomonas vaginalis. One of the problems regarding spreading this disease is that a person might not know that he or she is infected. Usually it is spread by contact of a vagina and a penis or possibly a vagina and a vagina. As a result, some people mistakenly feel safe having other types of sex such as oral sex or anal sex. Although it is rarer; it is still possible to spread this infection through oral or anal sex. The parasite can also survive for brief periods outside the body, so that is another venue for infection.