Understanding how diseases interact explains why having one illness can make you much more likely to develop another. According to the OCR specification, health is defined as a state of complete physical and mental well-being, not just the absence of disease.
Health can be compromised by several factors, including genetics, environment, lifestyle, trauma, or infection by a pathogen. A communicable disease is an illness caused by a pathogen (such as a bacteria or virus) that can be passed between organisms. In contrast, a non-communicable disease is not caused by a pathogen and cannot be spread between individuals.
Diseases rarely act in isolation. Having one disease can increase a person's susceptibility to another, meaning they are more predisposed to developing it. Alternatively, one disease can act as a direct trigger, initiating a biological process that leads to a secondary condition.
Imagine catching a mild infection and your body being completely unable to fight it off. This happens when an individual is immunocompromised, meaning a defect in their immune system prevents them from destroying pathogens effectively.
The most common example is the Human Immunodeficiency Virus (HIV). HIV specifically targets and destroys lymphocytes, which are a vital type of white blood cell. As lymphocyte numbers drop, the immune system fails to respond to new infections, leading to Acquired Immunodeficiency Syndrome (AIDS).
Once a person has AIDS, they become highly vulnerable to opportunistic infections. For example, their compromised immune system cannot fight off the bacteria that cause Tuberculosis (TB).
Step 1: HIV enters the body and infects lymphocytes.
Step 2: The virus replicates inside the lymphocytes and destroys them.
Step 3: The immune system is severely weakened (AIDS onset).
Step 4: The individual contracts a communicable disease like TB, which becomes life-threatening.
Viral infections are estimated to be responsible for approximately 15% of all human cancers worldwide. Viruses living inside host cells can act as triggers for non-communicable diseases by altering the host cell's genetic material.
When a virus inserts its genetic material into a host cell, it can cause a mutation, which is a change in the DNA sequence. This disrupts the normal cell cycle and leads to rapid, uncontrolled cell division, forming a tumour known as cancer.
A key example is the Human Papilloma Virus (HPV), which is a major trigger for cervical cancer.
Step 1: HPV infects the cervical cells.
Step 2: Viral DNA causes mutations that disrupt cell cycle regulation.
Step 3: Uncontrolled cell division (mitosis) forms a malignant tumour.
Every time someone develops a sudden skin rash after an illness, their immune system may have made a mistake. An immune response initially triggered by a pathogen can sometimes cause the immune system to become overactive or hypersensitive.
Following the initial infection, the immune system begins to misidentify harmless foreign substances as dangerous antigens. This triggers an allergy, which is an inflammatory immune overreaction. Common examples of this interaction include the sudden onset of skin rashes or the triggering of asthma symptoms after a respiratory infection.
Why does being diagnosed with a long-term physical illness often affect a person's mood? Physical health and mental health share a bidirectional relationship, meaning each can significantly impact the other.
Severe physical ill health can lead to mental health issues such as depression or anxiety. For instance, a patient with a non-communicable disease like diabetes or heart disease may experience chronic pain, social isolation, and anxiety about their future.
Conversely, poor mental health can negatively impact physical health. Chronic stress causes the body to release cortisol, which weakens the immune system and increases susceptibility to communicable diseases. It also raises the risk of non-communicable conditions like cardiovascular disease.
Students often state that the HPV vaccine 'cures' cervical cancer. It does not; it prevents the initial viral infection that acts as the trigger for the cancer.
When asked to define 'health' in an exam, you must explicitly mention both physical AND mental well-being to secure the marks.
In 'Describe' questions about HIV, examiners award marks for a step-by-step account: always state that HIV specifically targets and destroys 'lymphocytes' rather than just saying 'white blood cells'.
Use the phrase 'increases the risk of' rather than 'causes' when discussing how one condition influences another (e.g., 'HPV increases the risk of cervical cancer').
If asked to suggest why a physical disease might lead to depression, always mention factors like loss of independence, social isolation, or anxiety about the future.
Health
A state of complete physical and mental well-being, not just the absence of disease.
Pathogen
A harmful microorganism (such as a bacteria, virus, fungi, or protist) that causes disease.
Communicable disease
A disease caused by a pathogen that can be passed from one organism to another.
Non-communicable disease
A disease that is not caused by a pathogen and cannot be spread between individuals.
Susceptibility
The state of being predisposed or more likely to develop a disease due to existing health conditions or immune defects.
Trigger
An agent or factor (like a virus) that initiates a biological process leading to a secondary disease.
Lymphocytes
A specific type of white blood cell that is targeted and destroyed by HIV.
Mutation
A change in the DNA sequence of a cell.
Cancer
A non-communicable disease characterised by uncontrolled cell growth and division, forming a tumour.
Allergy
An overreaction of the immune system to a harmless foreign substance.
Put your knowledge into practice — try past paper questions for Biology B
Health
A state of complete physical and mental well-being, not just the absence of disease.
Pathogen
A harmful microorganism (such as a bacteria, virus, fungi, or protist) that causes disease.
Communicable disease
A disease caused by a pathogen that can be passed from one organism to another.
Non-communicable disease
A disease that is not caused by a pathogen and cannot be spread between individuals.
Susceptibility
The state of being predisposed or more likely to develop a disease due to existing health conditions or immune defects.
Trigger
An agent or factor (like a virus) that initiates a biological process leading to a secondary disease.
Lymphocytes
A specific type of white blood cell that is targeted and destroyed by HIV.
Mutation
A change in the DNA sequence of a cell.
Cancer
A non-communicable disease characterised by uncontrolled cell growth and division, forming a tumour.
Allergy
An overreaction of the immune system to a harmless foreign substance.