More than 30 different bacteria, viruses and parasites are known to be transmitted through sexual contact, including vaginal, anal and oral sex. Some STIs can also be transmitted from mother-to-child during pregnancy, childbirth and breastfeeding. Eight pathogens are linked to the greatest incidence of STIs. Of these, 4 are currently curable: syphilis, gonorrhoea, chlamydia and trichomoniasis. The other 4 are incurable viral infections: hepatitis B, herpes simplex virus (HSV), HIV and human papillomavirus (HPV).

More than 1 million sexually transmitted infections (STIs) are acquired every day worldwide, the majority of which are asymptomatic. STIs have a direct impact on sexual and reproductive health through stigmatization, infertility, cancers and pregnancy complications and can increase the risk of HIV.


Sexually transmitted infections (STIs), also known as sexually transmitted diseases (STDs), are a group of infectious diseases that are primarily transmitted through sexual contact. They can be caused by bacteria, viruses, parasites, or fungi and can affect both men and women. STIs can be passed from one person to another during vaginal, anal, or oral sex, as well as through other forms of intimate contact.


The pathophysiology of sexually transmitted infections (STIs) varies depending on the specific infectious agent involved. However, there are some common underlying mechanisms and processes that contribute to the development and spread of STIs. Mechanisms of the general pathophysiology of STIs include:

  1. Transmission: STIs are primarily transmitted through sexual contact, including vaginal, anal, and oral sex. The infectious agents responsible for STIs can be present in genital secretions, blood, or other bodily fluids. Transmission can occur when these fluids come into contact with mucous membranes or breaks in the skin.
  2. Invasion and Colonization: After transmission, the infectious agent gains entry into the body. It may invade and colonize the mucous membranes of the genital tract, urethra, rectum, or oral cavity. The specific site of infection depends on the nature of the STI and the type of sexual activity involved.
  3. Adherence and Multiplication: The infectious agent attaches itself to the cells of the mucous membranes and begins to multiply. This process often involves the production of adhesins or other surface proteins that facilitate attachment to host cells. The agent then replicates and spreads, causing localized tissue damage and inflammation.
  4. Inflammation and Immune Response: The presence of the infectious agent triggers an inflammatory response by the immune system. Inflammatory cells, such as neutrophils and macrophages, migrate to the infected site to combat the invading pathogens. The release of pro-inflammatory substances and the recruitment of immune cells can lead to symptoms such as redness, swelling, pain, and discharge.
  5. Tissue Damage and Complications: Persistent infection or untreated STIs can lead to progressive tissue damage and various complications. Inflammatory responses, combined with the virulence factors produced by the pathogens, can cause cellular injury and destruction. This damage can extend to surrounding tissues, leading to the formation of ulcers, sores, or lesions. In some cases, the infectious agent may disseminate throughout the body, affecting multiple organ systems.
  6. Transmission and Spread: STIs can be transmitted from an infected individual to a susceptible partner through sexual contact, perpetuating the cycle of infection. Additionally, certain STIs can also be transmitted vertically from an infected mother to her child during pregnancy, childbirth, or breastfeeding.


Sexually transmitted infections (STIs) are caused by various infectious agents that can be transmitted through sexual contact. The primary causes of STIs include:

  1. Bacteria
    • Chlamydia: Caused by the bacterium Chlamydia trachomatis, it is one of the most common STIs worldwide.
    • Gonorrhea: Caused by the bacterium Neisseria gonorrhoeae, it can cause infections in the genitals, rectum, and throat.
    • Syphilis: Caused by the bacterium Treponema pallidum, it progresses through stages and can affect various organs if left untreated.
  2. Viruses
    • Human Papillomavirus (HPV): A viral infection that can cause genital warts and various types of cancer, including cervical, anal, and throat cancer. There are numerous strains of HPV, some of which are considered high-risk for cancer.
    • Herpes Simplex Virus (HSV): There are two types of HSV: HSV-1, which is commonly associated with oral herpes, and HSV-2, which is typically linked to genital herpes. These viruses can cause painful sores or blisters in the genital area or mouth.
    • Human Immunodeficiency Virus (HIV): HIV is a retrovirus that attacks the immune system, leading to acquired immunodeficiency syndrome (AIDS). It is primarily transmitted through unprotected sexual intercourse, sharing contaminated needles, or from an infected mother to her child during childbirth or breastfeeding.
  3. Parasites: Certain STIs are caused by parasitic infections. One example is trichomoniasis which caused by the parasite Trichomonas vaginalis, it can cause infection in the genitals of both men and women. It is more common in women and often asymptomatic in men.
  4. Fungi: While less common, some STIs are caused by fungal infections. One example is candidiasis which caused by the yeast Candida, it can lead to vaginal or penile infections characterized by itching, burning, and discharge.

Risk Factors

  1. Unprotected Sexual Activity: Engaging in sexual activities without using barrier methods, such as condoms or dental dams, significantly increases the risk of contracting STIs. Unprotected vaginal, anal, or oral sex can allow the exchange of infectious agents between partners.
  2. Multiple Sexual Partners: Having multiple sexual partners, or engaging in sexual relationships with individuals who have multiple partners, increases the risk of exposure to STIs. The more sexual partners an individual has, the higher the likelihood of encountering someone with an STI.
  3. Lack of Regular STI Screenings: Failing to undergo regular screenings for STIs can increase the risk of undetected infections. Regular screenings allow for early detection and timely treatment, reducing the risk of transmitting infections to sexual partners.
  4. History of STIs: A previous history of STIs, particularly viral infections like herpes or HPV, increases the susceptibility to acquiring or transmitting other STIs, including HIV. Certain STIs can also lead to chronic infections, making individuals more prone to recurrent infections or complications.
  5. Substance Abuse: The use of drugs or alcohol can impair judgment and lead to risky sexual behaviors, such as unprotected sex or engaging in sexual activities with multiple partners. Substance abuse can also increase the likelihood of sharing needles, which can transmit blood-borne infections like HIV or hepatitis.
  6. Age: Certain age groups may be more susceptible to STIs. Adolescents and young adults, in particular, often engage in high-risk sexual behaviors, have multiple partners, and may be less likely to use protection consistently. Older adults may also be at risk if they are sexually active and engage in unprotected sex.
  7. Lack of Comprehensive Sexual Education: Insufficient knowledge about sexual health, including safe sex practices, STIs, and their consequences, can contribute to higher STI rates. Comprehensive sexual education programs that promote accurate information and teach prevention strategies are crucial in reducing the risk of STIs.
  8. Socioeconomic Factors: Socioeconomic factors, such as limited access to healthcare, poverty, or lack of education, can influence the risk of STIs. Limited access to healthcare services may hinder regular screenings, timely diagnosis, and treatment of STIs. Socioeconomic disparities can also impact the availability of preventive measures, such as vaccines and condoms.
  9. Gender Disparities: In some cases, gender disparities can contribute to differential risks of STIs. For example, women may be at a higher risk of acquiring STIs due to the anatomy of the female genital tract, which can facilitate the entry of infectious agents. Additionally, societal factors like power dynamics, gender-based violence, and limited control over sexual decision-making can contribute to increased vulnerability to STIs among certain populations.

Signs & Symptoms

  1. Genital Sores or Ulcers: Some STIs, such as herpes and syphilis, can cause the development of painful sores, ulcers, or lesions in the genital area, including the penis, vulva, vagina, anus, or mouth. These sores may be accompanied by pain, itching, or a burning sensation.
  2. Abnormal Discharge: Certain STIs, including chlamydia and gonorrhea, can cause unusual discharge from the penis, vagina, or rectum. The discharge may have an unusual color (yellowish, greenish) or consistency (thick, frothy).
  3. Pain or Burning Sensation: STIs can lead to pain or a burning sensation during urination or sexual intercourse. This symptom is commonly associated with infections such as chlamydia, gonorrhea, or urinary tract infections (UTIs) caused by STIs.
  4. Genital Itching or Irritation: Itching or irritation in the genital area can be a symptom of various STIs, including pubic lice (crabs), trichomoniasis, or certain fungal infections like yeast infections.
  5. Swollen Lymph Nodes: In response to an STI, the body’s immune system may activate and cause the enlargement of nearby lymph nodes, such as those in the groin or armpits. Swollen lymph nodes can occur with STIs such as syphilis or genital herpes.
  6. Rash or Skin Lesions: Some STIs can cause skin changes or rashes on the genital area, buttocks, thighs, or other parts of the body. Examples include syphilis, genital herpes, or certain types of human papillomavirus (HPV) infections.
  7. Flu-like Symptoms: In some cases, certain STIs, such as early-stage HIV infection, can produce flu-like symptoms like fever, fatigue, headache, muscle aches, or swollen glands. These symptoms may appear within a few weeks of exposure.


  1. Medical History and Physical Examination: Healthcare providers will typically begin by taking a detailed medical history, including sexual history, symptoms, and potential exposure to STIs. They will perform a physical examination to check for visible signs of infection, such as sores, ulcers, discharge, or skin lesions. This information helps guide further diagnostic steps.
  2. Laboratory Testing
    • Blood Tests: Blood tests can detect the presence of certain STIs, such as HIV, syphilis, or hepatitis. These tests often look for specific antibodies or antigens associated with the infections.
    • Urine Tests: Urine samples can be collected to test for STIs like chlamydia and gonorrhea. Polymerase chain reaction (PCR) tests are commonly used to identify the genetic material (DNA or RNA) of the infecting organisms.
    • Swab Tests: Swabs are used to collect samples from the affected area, such as the cervix, urethra, vagina, anus, throat, or mouth. These samples can be tested for various STIs, including chlamydia, gonorrhea, herpes, and trichomoniasis. PCR, culture, or antigen tests may be performed on the swab samples.
    • Fluid Analysis: In cases of suspected genital herpes, a sample of fluid from a blister or sore can be analyzed for the presence of the herpes simplex virus (HSV) using PCR or viral culture.
    • Pap Smear: A Pap smear, also known as a cervical cytology test, is used to screen for cervical cancer or detect abnormal cervical cells associated with HPV infection.
    • Imaging and Biopsy: In some cases, imaging tests such as ultrasound or X-rays may be used to assess the extent of infection or associated complications. Biopsy, which involves the removal of a small tissue sample for examination under a microscope, may be necessary to diagnose certain STIs like genital warts or syphilis.


  1. Antibiotics: Bacterial STIs like chlamydia, gonorrhea, and syphilis are typically treated with antibiotics. The specific antibiotic and treatment duration may vary depending on the type of infection, drug resistance patterns, and individual factors. It is important to complete the full course of antibiotics as prescribed, even if symptoms improve before completing the treatment.
  2. Antiviral Medications: Viral STIs such as herpes and HIV are managed with antiviral medications. While these medications cannot cure the infections, they can help reduce symptoms, prevent outbreaks, and control viral replication. In the case of HIV, antiretroviral therapy (ART) is the standard treatment to suppress the virus and maintain immune function.
  3. Antifungal Medications: Fungal STIs like yeast infections or certain types of jock itch can be treated with antifungal medications. These medications may be available in various forms such as creams, ointments, suppositories, or oral tablets.
  4. Vaccination: Some STIs, such as human papillomavirus (HPV) and hepatitis B, can be prevented through vaccination. Vaccines are typically recommended before potential exposure to the virus, such as during childhood or adolescence. HPV vaccination is also available for older individuals who have not been previously vaccinated.
  5. Partner Treatment: Treating sexual partners of individuals diagnosed with an STI is crucial to prevent reinfection and transmission. Sexual partners should be notified and encouraged to seek medical evaluation and treatment. This is especially important for bacterial STIs like chlamydia and gonorrhea, where partners are often treated simultaneously to prevent re-infection.
  6. Counseling and Support: The psychological and emotional impact of an STI diagnosis can be significant. Counseling and support services are essential in helping individuals cope with the diagnosis, understand preventive measures, and navigate discussions with sexual partners.


  1. Infertility: Infections such as chlamydia and gonorrhea can cause inflammation and scarring in the reproductive organs, including the fallopian tubes in women and the epididymis in men. These complications can lead to blocked tubes or damage to the sperm ducts, increasing the risk of infertility.
  2. Pelvic Inflammatory Disease (PID): Untreated bacterial infections like chlamydia or gonorrhea can spread to the reproductive organs, leading to PID. PID is a serious condition characterized by inflammation of the uterus, fallopian tubes, or ovaries. It can cause chronic pelvic pain, ectopic pregnancy, and increase the risk of infertility.
  3. Increased Risk of HIV Transmission: STIs can facilitate the transmission of human immunodeficiency virus (HIV) by causing inflammation and breaks in the skin or mucous membranes, which provide entry points for the virus. Having an STI can increase the risk of acquiring or transmitting HIV.
  4. Pregnancy Complications: Certain STIs can pose risks to pregnant individuals and their unborn babies. For example, untreated syphilis can lead to miscarriage, stillbirth, or severe congenital abnormalities. HIV can be transmitted from mother to child during pregnancy, childbirth, or breastfeeding. Other STIs like chlamydia or gonorrhea can cause complications during pregnancy, such as preterm labor or neonatal infections.
  5. Chronic Pain and Discomfort: Some STIs, such as herpes or genital warts, can cause recurring outbreaks and chronic discomfort in the affected areas. These conditions may require ongoing management and can have a significant impact on an individual’s quality of life.
  6. Increased Risk of Certain Cancers: Infection with certain types of human papillomavirus (HPV) can increase the risk of developing various types of cancer, including cervical, anal, penile, vaginal, and throat cancers. Regular screenings, HPV vaccination, and appropriate follow-up care are important in reducing the risk and detecting these cancers at early stages.
  7. Joint and Organ Damage: In rare cases, certain STIs, such as untreated syphilis, can progress to affect multiple organ systems, including the heart, brain, and nervous system. These complications can lead to cardiovascular disease, neurologic disorders, or even death if left untreated.
  8. Psychological and Emotional Impact: STIs can have a significant psychological and emotional impact on individuals. The stigma associated with STIs, concerns about transmitting the infection to partners, and the potential for long-term consequences can cause distress, anxiety, and depression.


  1. Safe Sexual Practices
    • Using Condoms: Consistently and correctly using latex or polyurethane condoms can greatly reduce the risk of STI transmission. Condoms should be used during vaginal, anal, and oral sex.
    • Dental Dams and Gloves: Dental dams and gloves can provide a barrier for oral-vaginal, oral-anal, or manual-genital contact, reducing the risk of STI transmission.
    • Limit Sexual Partners: Reducing the number of sexual partners and engaging in monogamous relationships with individuals who have been tested for STIs can lower the risk of exposure.
    • Regular STI Screenings: Regular screenings for STIs are crucial, especially if you are sexually active or have engaged in high-risk behaviors. Testing can detect infections early, allowing for timely treatment and prevention of complications. Speak with a healthcare professional to determine the appropriate testing frequency and methods based on your individual circumstances.
  2. Vaccination
    • Human Papillomavirus (HPV) Vaccine: HPV vaccination is recommended for both males and females before sexual activity begins, typically in the early teens. It protects against certain high-risk strains of HPV that can cause genital warts and various types of cancers, including cervical, anal, and throat cancers.
    • Hepatitis B Vaccine: The hepatitis B vaccine is recommended for individuals at risk of hepatitis B infection, including sexually active individuals and those who engage in high-risk behaviors.
  3. Open Communication
    • Discussing STI History: Honest and open communication about sexual health, including previous STI diagnoses, with sexual partners is important for making informed decisions and reducing the risk of transmission.
    • Communication with Healthcare Providers: Discuss any concerns or questions about sexual health with healthcare providers. They can provide information, guidance, and appropriate screenings or vaccinations.
    • Substance Abuse Prevention
    • Avoiding Sharing Needles: Sharing needles for drug use or other activities increases the risk of blood-borne infections like HIV and hepatitis.
    • Alcohol and Drug Use: Substance abuse can impair judgment and lead to risky sexual behaviors. Reducing or avoiding excessive alcohol or drug use can help make safer decisions about sexual activity.
  4. Education and Awareness
    • Sexual Health Education: Access accurate and comprehensive sexual health education that covers topics such as STI prevention, safe sex practices, and the importance of regular screenings.
    • Awareness of STI Risks: Understanding the risks associated with different sexual activities and being aware of the signs and symptoms of STIs can empower individuals to take preventive measures and seek timely medical care.

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