Sexually Transmitted Diseases: MDCAT Biology notes
Sexually transmitted diseases MDCAT notes: syphilis, gonorrhoea, genital herpes and AIDS, their causative agents, transmission, symptoms and prevention.
What STDs are
Sexually transmitted diseases (STDs) are infections spread mainly through sexual contact with an infected person. Some, such as syphilis and AIDS, can also pass from mother to baby, and AIDS also spreads through infected blood. They are caused by bacteria, viruses and other microbes. They are not spread by insects, contaminated water, or respiratory droplets. Tuberculosis, influenza, typhoid, cholera and dengue are not STDs.
The major STDs
| Disease | Causative agent | Type |
|---|---|---|
| Syphilis | Treponema pallidum | Bacterium, a spirochaete (spiral-shaped) |
| Gonorrhoea | Neisseria gonorrhoeae | Bacterium, a diplococcus |
| Genital herpes | Herpes simplex virus type 2 | DNA virus |
| AIDS | HIV | RNA retrovirus |
Syphilis
- It is caused by the spirochaete Treponema pallidum, and its major source of transmission is sexual contact. An infected mother can also pass it to her unborn child across the placenta.
- Primary stage: a painless sore (chancre) appears at the site of infection.
- Secondary stage: skin rash, fever and swollen lymph nodes.
- Tertiary stage: if untreated, after years it can damage the heart, blood vessels and nervous system.
- Being bacterial, it is treated with antibiotics, especially penicillin.
Gonorrhoea
- It is caused by Neisseria gonorrhoeae and transmitted by unsafe sex.
- It infects the lining of the urinogenital tract. Symptoms include painful urination and discharge.
- Untreated, it can spread to the reproductive organs and cause sterility. A baby born to an infected mother can get an eye infection.
- It is treated with antibiotics.
Genital herpes
Genital herpes is caused by herpes simplex virus type 2. It produces painful blisters in the genital area, which can come back. Because it is viral, antibiotics do not cure it.
AIDS
AIDS is caused by HIV and spreads through sexual contact, infected blood, shared needles, and from mother to child. HIV destroys helper T cells, so the patient suffers opportunistic infections. Typical signs include sudden weight loss, fever, night sweats, swollen lymph glands and diarrhoea. In advanced disease, rare cancers such as Kaposi's sarcoma can occur. There is no vaccine or cure, so prevention is essential.
Prevention
- Avoid unsafe sexual contact, and keep a faithful relationship with one partner.
- Screen blood before transfusion, and use sterile, disposable syringes.
- Diagnose and treat bacterial STDs early with antibiotics, and treat partners as well.
- Educate the public about how these diseases spread.
Common MDCAT traps
- Syphilis is caused by a spirochaete (Treponema), not a coccus. Gonorrhoea is caused by a coccus (Neisseria).
- HIV causes AIDS, not syphilis.
- The main route of syphilis is sexual contact, not blood transfusion or insect bites.
- Tuberculosis, influenza and typhoid are distractors, not STDs.
- Antibiotics work on syphilis and gonorrhoea but not on viral STDs.
Quick revision
- Syphilis is caused by Treponema pallidum.
- Gonorrhoea is caused by Neisseria gonorrhoeae.
- Genital herpes is caused by HSV type 2.
- AIDS is a viral STD caused by HIV.
- Untreated gonorrhoea can cause sterility.