16.7) Sexually transmitted infections (STIs)

16.7) Sexually transmitted infections (STIs)


Sexually transmitted infection is an infection that is transmitted via body fluids through sexual contact.



  • Acquired immune deficiency syndrome. ( A ‘syndrome’ is a pattern of symptoms associated with a particular disease.)
  • The virus that causes AIDS is the human immunodeficiency virus.
  • HIV is transmitted by direct infection of the blood.
  • Drug users who share needles contaminated with infected blood run a high risk of the disease.
  • It can also be transmitted sexually.
  • Babies born to HIV carriers may become infected with HIV.
  • If HIV antibodies are present in the blood, the person is said the be HIV positive.


Control of the spread of STIs:

  • The best way to avoid STI is to avoid having sexual intercourse with an infected person.
  • The risk of catching a STD can be reduced by using condoms or femidoms.
  • STIs that are caused by a bacterium, such as syphilis and gonorrhoea, can be treated with antibiotics if the symptoms are recognised early enough. However, HIV is viral so antibiotics are not effective.


The effects of HIV on the immune system:

  • HIV attacks certain kinds of lymphocyte, so the number of these cells in the body decreases.
  • Lymphocytes produce antibodies against infections. If the body cannot respond to infections through the immune system, it becomes vulnerable to pathogens that might not otherwise by life-threatening.
  • As a result, the patient has little or no resistance to a wide range of diseases such a influenza, pneumonia, blood disorders, skin cancer or damage to the nervous system, which the body cannot resist.