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The spreading, or transmission, of disease from one individual to another can occur in a number of ways, as shown in the table below.

Examples of communicable diseases

HIV/AIDS

HIV stands for Human Immunodeficiency Virus. This infection is transmitted by body fluids, often during unprotected sex, but also through cuts and injecting drugs using shared needles. Immediately after infection, people often suffer mild flu-like symptoms. These pass, and for a period of time infected people might not know they are infected.

AIDS stands for Acquired Immune Deficiency Syndrome. Months or years after infection by the HIV virus, it becomes active and starts to attack the patient’s immune system. At this point HIV has become AIDS.

There is no cure for HIV/AIDS, although many scientists are trying to find one. Currently, infected people are given antiviral drugs which can slow the development of AIDS.

Chlamydia

Chlamydia is the most common sexually transmitted disease in Britain. It is caused by a bacterium called Chlamydia trachomatis, and is transmitted by direct contact during sexual intercourse via the vagina and urethra. Its spread can be prevented by the use of condoms, and it can be treated with antibiotics such as tetracycline or erythromycin.

If left untreated it can cause infertility in adults, and can also cause conjunctivitis in babies soon after birth if the mother is infected.

It can also spread to the lungs of babies as they pass through the birth canal, causing pneumonia.

Malaria

Malaria is a disease spread by mosquitoes which carry the Plasmodium protist. Mosquitoes are mainly found in regions of the world with high temperatures, such as Africa, Asia, and South and Central America, but not the UK. Mosquitoes suck blood containing the protist from an infected person. They then pass the protist to other people when they suck blood from them. Because mosquitoes transmit the disease and do not become ill themselves, they are called vectors.

The symptoms of malaria include fever, sweats and chills, headache, vomiting and diarrhoea. Of the 200 million people infected each year, up to half die from the disease. After decades of research scientists developed the first malaria vaccine in 2021. Infection continues to be reduced by stopping individuals from being bitten. People sleep under mosquito nets and wear insect repellent to avoid bites. Anti-malarial drugs are also taken, which treat the symptoms and can prevent infection.