Health and Disease

Definition and Types of Diseases

A disease is a disorder of structure or function in a human, especially one that produces specific signs or symptoms.
Diseases may be caused by external factors such as pathogens, or by internal dysfunctions, such as autoimmune diseases.
They are broadly split into two categories: infectious diseases, caused by organisms like bacteria, viruses and fungi; and non-infectious diseases, which can not be transmitted between individuals.

Bacteria, viruses, parasites and fungi are all able to cause disease in humans.
They can spread through a number of routes, including direct contact with an infected individual, through the air, via food and water, and by vectors such as mosquitoes or ticks.
The severity and type of disease they cause can vary widely, from mild illnesses to severe, life-threatening conditions.

When the body is invaded by a pathogen, the immune system responds to eliminate the threat.
This process involves recognition of the pathogen, triggering of an immune response, and the destruction or neutralisation of the pathogen.
The immune response can be split into the innate immune response, which is non-specific and occurs immediately; and the adaptive immune response, which is specific to the pathogen and develops over time.

Vaccines can provide immunity to certain diseases by stimulating the immune system to recognise and fight off specific pathogens.
Antibiotics and antiviral drugs can be used to treat bacterial and viral infections respectively.
Good hygiene practices and sanitation are key to preventing the spread of many diseases.

Diseases have a significant impact on societies around the world, particularly in countries with poor healthcare infrastructure.
They can lead to loss of life, decreased productivity, and large-scale social disruption.
Epidemics and pandemics, where a disease spreads across a large area affecting a substantial number of people, can have significant global impacts.

Some common infectious diseases include influenza, HIV/AIDS, malaria, and tuberculosis.
Influenza and HIV/AIDS are caused by viruses, malaria is caused by a parasite, and tuberculosis is caused by a bacterium.
Vaccination, early detection, and effective treatment can control the spread of these diseases.