Sexually Transmitted Infections (Cambridge (CIE) IGCSE Biology): Revision Note

Unprotected sexual intercourse can lead to the transfer of pathogens via exchange of body fluids

Infections passed on in this way are known as sexually transmitted infections (STIs)

An example of an STI is HIV (Human Immunodeficiency Virus), the virus that usually leads to the development of acquired immunodeficiency disease (AIDS)

HIV can also be spread via sharing needles with an infected person, blood transfusions with infected blood and from mother to foetus through the placenta and mother to baby via breastfeeding

Immediately after infection, people often suffer mild flu-like symptoms

These symptoms pass and for a period of time infected people might not know they are infected

The virus infects a certain type of lymphocyte of the body's immune system

Normally lymphocytes seek out and destroy pathogens that enter the body, producing antibodies that attach to pathogens, enhancing phagocytic activity

However HIV avoids being recognised and destroyed by lymphocytes by repeatedly changing its protein coat

It then infects a certain type of lymphocyte and uses the cells’ machinery to multiply

This reduces the number of lymphocytes of the immune system, and also the number of antibodies that can be made

This decreases the body’s ability to fight off infections, eventually leading to AIDS (Acquired immunodeficiency)

The spread of STIs such as HIV are best controlled by:

• limiting the number of sexual partners an individual has

• not having unprotected sex, but making sure to always use a condom

• getting tested if unprotected sex or sex with multiple partners has occurred

• raising awareness by education programmes