sexually transmitted infection sexually transmitted infection sexually transmitted infections (stis), also referred to as sexually transmitted diseases (stds) and the older term venereal diseases, are infections that are spread by sexual activity, especially vaginal intercourse, anal sex, and oral sex. stis often do not initially cause symptoms, which results in a risk of passing the infection on to others. symptoms and signs of stis may include vaginal discharge, penile discharge, ulcers on or around the genitals, and pelvic pain. some stis can cause infertility. "sexual disease" redirects here. not to be confused with sexual dysfunction. sexually transmitted infectionother namessexually transmitted disease (std);venereal disease (vd)herpes genitalisspecialtyinfectious diseasesymptomsnone, vaginal discharge, penile discharge, ulcers on or around the genitals, pelvic paincomplicationsinfertilitycausesinfections commonly spread by sexpreventionnot having sex, vaccinations, condomsfrequency1.1 billion (stis other than hiv/aids, 2015)deaths108,000 (stis other than hiv/aids, 2015) bacterial stis include chlamydia, gonorrhea, and syphilis. viral stis include genital herpes, hiv/aids, and genital warts. parasitic stis include trichomoniasis. sti diagnostic tests are usually easily available in the developed world, but they are often unavailable in the developing world. some vaccinations may also decrease the risk of certain infections including hepatitis b and some types of hpv. safe sex practices, such as use of condoms, having a smaller number of sexual partners, and being in a relationship in which each person only has sex with the other also decreases the risk of stis. comprehensive sex education may also be useful. most stis are treatable and curable; of the most common infections, syphilis, gonorrhea, chlamydia, and trichomoniasis are curable, while hiv/aids and genital herpes are not curable. in 2015, about 1.1 billion people had stis other than hiv/aids. about 500 million were infected with either syphilis, gonorrhea, chlamydia or trichomoniasis. at least an additional 530 million people have genital herpes, and 290 million women have human papillomavirus. stis other than hiv resulted in 108,000 deaths in 2015. in the united states, there were 19 million new cases of stis in 2010. historical documentation of stis in antiquity dates back to at least the ebers papyrus (c. 1550 bce) and the hebrew bible/old testament (8th/7th centuries bce). there is often shame and stigma associated with stis. the term sexually transmitted infection is generally preferred over sexually transmitted disease or venereal disease, as it includes those who do not have symptomatic disease. signs and symptoms not all stis are symptomatic, and symptoms may not appear immediately after infection. in some instances a disease can be carried with no symptoms, which leaves a greater risk of passing the disease on to others. depending on the disease, some untreated stis can lead to infertility, chronic pain or death. the presence of an sti in prepubescent children may indicate sexual abuse. cause transmission a sexually transmitted infection present in a pregnant woman may be passed on to the infant before or after birth. risk of transmission per unprotected sexual act with an infected person known risks possible performing oral sex on a man throat chlamydia throat gonorrhea (25–30%) herpes (rare) hpv syphilis (1%) hepatitis b (low risk) hiv (0.01%) hepatitis c (unknown) performing oral sex on a woman herpes hpv throat gonorrhea throat chlamydia receiving oral sex—man chlamydia gonorrhea herpes syphilis (1%) hpv receiving oral sex—woman herpes hpv bacterial vaginosis gonorrhea vaginal sex—man chlamydia (30–50%) crabs scabies gonorrhea (22%) hepatitis b herpes (0.07% for hsv-2) hiv (0.05%) hpv (high: around 40–50%) mycoplasma hominis infection mycoplasma genitalium syphilis trichomoniasis ureaplasma infection hepatitis c vaginal sex—woman chlamydia (30–50%) crabs scabies gonorrhea (47%) hepatitis b (50–70%) herpes hiv (0.1%) hpv (high; around 40–50%) mycoplasma hominis infection syphilis trichomoniasis ureaplasma infection hepatitis c anal sex—insertive chlamydia crabs scabies (40%) gonorrhea hepatitis b herpes hiv (0.62%) hpv syphilis (14%) hepatitis c anal sex—receptive chlamydia crabs scabies gonorrhea hepatitis b herpes hiv (1.7%) hpv syphilis (1.4%) hepatitis c anilingus amoebiasis cryptosporidiosis (1%) giardiasis hepatitis a(1%) shigellosis (1%) hpv (1%) bacterial chancroid (haemophilus ducreyi) chlamydia (chlamydia trachomatis) gonorrhea (neisseria gonorrhoeae) granuloma inguinale or (klebsiella granulomatis) mycoplasma genitalium mycoplasma hominis syphilis (treponema pallidum) ureaplasma infection viral micrograph showing the viral cytopathic effect of herpes (ground glass nuclear inclusions, multi-nucleation). pap test. pap stain. viral hepatitis (hepatitis b virus)—saliva, venereal fluids.(note: hepatitis a and hepatitis e are transmitted via the fecal-oral route; hepatitis c is rarely sexually transmittable, and the route of transmission of hepatitis d (only if infected with b) is uncertain, but may include sexual transmission.) herpes simplex (herpes simplex virus 1, 2) skin and mucosal, transmissible with or without visible blisters hiv (human immunodeficiency virus)—venereal fluids, semen, breast milk, blood hpv (human papillomavirus)—skin and mucosal contact. 'high risk' types of hpv cause almost all cervical cancers, as well as some anal, penile, and vulvar cancer. some other types of hpv cause genital warts. molluscum contagiosum (molluscum contagiosum virus mcv)—close contact zika virus parasites crab louse, colloquially known as "crabs" or "pubic lice" (pthirus pubis). the infestation and accompanying inflammation is pediculosis pubis scabies (sarcoptes scabiei) trichomoniasis (trichomonas vaginalis), colloquially known as "trich" main types sexually transmitted infections include: chlamydia is a sexually transmitted infection caused by the bacterium chlamydia trachomatis. in women, symptoms may include abnormal vaginal discharge, burning during urination, and bleeding in between periods, although most women do not experience any symptoms. symptoms in men include pain when urinating, and abnormal discharge from their penis. if left untreated in both men and women, chlamydia can infect the urinary tract and potentially lead to pelvic inflammatory disease (pid). pid can cause serious problems during pregnancy and even has the potential to cause infertility. it can cause a woman to have a potentially deadly ectopic pregnancy, in which the egg implants outside of the uterus. however, chlamydia can be cured with antibiotics. the two most common forms of herpes are caused by infection with herpes simplex virus (hsv). hsv-1 is typically acquired orally and causes cold sores, hsv-2 is usually acquired during sexual contact and affects the genitals, however, either strain may affect either site. some people are asymptomatic or have very mild symptoms. those that do experience symptoms usually notice them 2 to 20 days after exposure which lasts 2 to 4 weeks. symptoms can include small fluid-filled blisters, headaches, backaches, itching or tingling sensations in the genital or anal area, pain during urination, flu like symptoms, swollen glands, or fever. herpes is spread through skin contact with a person infected with the virus. the virus affects the areas where it entered the body. this can occur through kissing, vaginal intercourse, oral sex or anal sex. the virus is most infectious during times when there are visible symptoms, however, those who are asymptomatic can still spread the virus through skin contact. the initial infection and symptoms are usually the most severe because the body does not have any antibodies built up. after the primary attack, one might have recurring attacks that are milder or might not even have future attacks. there is no cure for the disease but there are antiviral medications that treat its symptoms and lower the risk of transmission (valtrex). although hsv-1 is typically the "oral" version of the virus, and hsv-2 is typically the "genital" version of the virus, a person with hsv-1 orally can transmit that virus to their partner genitally. the virus, either type, will settle into a nerve bundle either at the top of the spine, producing the "oral" outbreak, or a second nerve bundle at the base of the spine, producing the genital outbreak. the human papillomavirus (hpv) is the most common sti in the united states. there are more than 40 different strands of hpv and many do not cause any health problems. in 90% of cases, the body's immune system clears the infection naturally within two years. some cases may not be cleared and can lead to genital warts (bumps around the genitals that can be small or large, raised or flat, or shaped like cauliflower) or cervical cancer and other hpv related cancers. symptoms might not show up until advanced stages. it is important for women to get pap smears in order to check for and treat cancers. there are also two vaccines available for women (cervarix and gardasil) that protect against the types of hpv that cause cervical cancer. hpv can be passed through genital-to-genital contact as well as during oral sex. the infected partner might not have any symptoms. gonorrhea is caused by bacterium that lives on moist mucous membranes in the urethra, vagina, rectum, mouth, throat, and eyes. the infection can spread through contact with the penis, vagina, mouth, or anus. symptoms of gonorrhea usually appear two to five days after contact with an infected partner however, some men might not notice symptoms for up to a month. symptoms in men include burning and pain while urinating, increased urinary frequency, discharge from the penis (white, green, or yellow in color), red or swollen urethra, swollen or tender testicles, or sore throat. symptoms in women may include vaginal discharge, burning or itching while urinating, painful sexual intercourse, severe pain in lower abdomen (if infection spreads to fallopian tubes), or fever (if infection spreads to fallopian tubes); however, many women do not show any symptoms. antibiotic resistant strains of gonorrhea are a significant concern, but most cases can be cured with existing antibiotics. secondary syphilis syphilis is an sti caused by a bacterium. untreated, it can lead to complications and death. clinical manifestations of syphilis include the ulceration of the uro-genital tract, mouth or rectum; if left untreated the symptoms worsen. in recent years, the prevalence of syphilis has declined in western europe, but it has increased in eastern europe (former soviet states). a high incidence of syphilis can be found in places such as cameroon, cambodia, papua new guinea. syphilis infections are increasing in the united states. trichomoniasis is a common sti that is caused by infection with a protozoan parasite called trichomonas vaginalis. trichomoniasis affects both women and men, but symptoms are more common in women. most patients are treated with an antibiotic called metronidazole, which is very effective. hiv (human immunodeficiency virus) damages the body's immune system, which interferes with its ability to fight off disease-causing agents. the virus kills cd4 cells, which are white blood cells that help fight off various infections. hiv is carried in body fluids and is spread by sexual activity. it can also be spread by contact with infected blood, breastfeeding, childbirth, and from mother to child during pregnancy. when hiv is at its most advanced stage, an individual is said to have aids (acquired immunodeficiency syndrome). there are different stages of the progression of and hiv infection. the stages include primary infection, asymptomatic infection, symptomatic infection, and aids. in the primary infection stage, an individual will have flu-like symptoms (headache, fatigue, fever, muscle aches) for about two weeks. in the asymptomatic stage, symptoms usually disappear, and the patient can remain asymptomatic for years. when hiv progresses to the symptomatic stage, the immune system is weakened and has a low cell count of cd4+ t cells. when the hiv infection becomes life-threatening, it is called aids. people with aids fall prey to opportunistic infections and die as a result. when the disease was first discovered in the 1980s, those who had aids were not likely to live longer than a few years. there are now antiretroviral drugs (arvs) available to treat hiv infections. there is no known cure for hiv or aids but the drugs help suppress the virus. by suppressing the amount of virus in the body, people can lead longer and healthier lives. even though their virus levels may be low they can still spread the virus to others. viruses in semen twenty-seven different viruses have been identified in semen. information on whether or not transmission occurs or whether the viruses cause disease is uncertain. some of these microbes are known to be sexually transmitted. pathophysiology many stis are (more easily) transmitted through the mucous membranes of the penis, vulva, rectum, urinary tract and (less often—depending on type of infection) the mouth, throat, respiratory tract and eyes. the visible membrane covering the head of the penis is a mucous membrane, though it produces no mucus (similar to the lips of the mouth). mucous membranes differ from skin in that they allow certain pathogens into the body. the amount of