Health and Disease
Different types of diseases
communicable, which can be transferred from one person to another, or from one organism to another, eg in humans, these include measles, food poisoning and malaria
non-communicable, which are not transferred between people or other organisms
Interactions between different types of diseases
Different types of disease may interact. This can mean that the presence of one disease can lead to a higher chance of developing another disease.
Defects in the immune system mean that an individual is more likely to suffer from infectious diseases. For instance, human immunodeficiency virus infections, known as HIV, which leads to AIDS, affect the immune system and lead to an increase in susceptibility to infectious diseases.
Viruses living in cells can be the trigger for cancers. For instance, the majority of cases of cancer of the cervix are linked with a virus present in the female reproductive system.
The reaction of the immune system to pathogens and other foreign bodies can trigger allergic reactions that lead to skin rashes and asthma. For instance, severe respiratory infections in babies can lead to asthma in later childhood.
Severe physical ill health can lead to depression and other types of mental illness.
Pathogens
A pathogen is an organism that causes a disease. There are four main types of pathogen:
Bacteria
Fungi
Viruses
Protists
All types of pathogen have a simple life cycle. They infect a host, reproduce themselves or replicate if it is a virus, spread from their host and infect other organisms. They also all have structural adaptations that make them successful at completing their life cycles, which enable them to cause more disease.
Diseases caused by pathogens are called communicable diseases. This means the disease can be transferred from an infected organism to another organism.
There are other types of disease which cannot be passed from organism to organism. These are called non-communicable diseases:
Inherited genetic disorders like cystic fibrosis can be passed to offspring but not to anyone else.
Deficiency diseases which are caused by a lack of essential vitamins or minerals, such as scurvy which occurs when an individual has insufficient vitamin C.
Diseases like cancer that develop as a result of exposure to carcinogens or develop naturally as cell division occurs incorrectly.
Transmission
Transmission can occur in a number of important ways, as shown in the table below
How to prevent diseases
Method - Sterilising water Example - Cholera How it works - Chemicals or UV light kill pathogens in unclean water.
Method - Suitable hygiene: food Example - Salmonella How it works - Cooking foods thoroughly and preparing them in hygienic conditions kills pathogens.
Method - Suitable hygiene: personal Example - Athlete's foot How it works - Washing surfaces with disinfectants kills pathogens. Treating existing cases of infection kills pathogens.
Method - Vaccination Example - Tuberculosis How it works - Immunisations introduce a small or weakened version of a pathogen into your body, and the immune system learns how to defend itself.
Method - Contraception Example - HIV/AIDS How it works - By using barrier contraception like condoms, it stops the transfer of bodily fluids and sexually transmitted diseases.