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examBoard: Pearson Edexcel
examType: IGCSE
lessonTitle: Pathogens and Disease
Every day, your body battles millions of tiny invaders that could make you ill. These microscopic organisms are called pathogens and they're responsible for causing diseases ranging from the common cold to more serious conditions like malaria or tuberculosis.
Key Definitions:
There are four main types of pathogens you need to know about:
Pathogens cause disease in different ways:
Bacteria are single-celled organisms that lack a nucleus. While many bacteria are harmless or even beneficial, some can cause serious diseases.
Bacteria typically cause disease by:
Pathogen: Mycobacterium tuberculosis
Symptoms: Persistent cough, weight loss, night sweats, fatigue
Transmission: Airborne droplets from coughs and sneezes
Pathogen: Vibrio cholerae
Symptoms: Severe watery diarrhoea, vomiting, dehydration
Transmission: Contaminated water and food
Pathogen: Salmonella bacteria
Symptoms: Diarrhoea, fever, abdominal cramps
Transmission: Contaminated food, especially eggs, meat and poultry
Viruses are not cells but particles containing genetic material (DNA or RNA) surrounded by a protein coat. They can only reproduce inside host cells.
Viruses invade cells and use the cell's machinery to make copies of themselves. This often kills the host cell, causing tissue damage and disease symptoms.
Pathogen: Influenza virus
Symptoms: Fever, cough, sore throat, body aches, fatigue
Transmission: Airborne droplets, direct contact
Pathogen: Human Immunodeficiency Virus
Effect: Attacks immune system cells, leading to Acquired Immune Deficiency Syndrome (AIDS)
Transmission: Body fluids including blood, semen, vaginal fluids, breast milk
Pathogen: Measles virus
Symptoms: Rash, high fever, cough, runny nose, red eyes
Transmission: Highly contagious through airborne droplets
The COVID-19 pandemic, caused by the SARS-CoV-2 virus, demonstrated how quickly a new viral disease can spread globally. The virus primarily affects the respiratory system and can cause a range of symptoms from mild to severe. It spreads mainly through respiratory droplets when an infected person coughs, sneezes, or talks. The pandemic highlighted the importance of public health measures like hand washing, mask-wearing and vaccination in controlling infectious diseases.
Fungi are eukaryotic organisms with cell walls made of chitin. They can cause diseases in humans, animals and plants.
Examples:
Protists are single-celled eukaryotic organisms. Some can cause serious diseases, particularly in tropical regions.
Example: Malaria
Understanding how diseases spread is crucial for preventing infections. Pathogens can be transmitted in several ways:
Person-to-person through:
Examples: Common cold, HIV, athlete's foot
Through contaminated:
Examples: Cholera, influenza, COVID-19
Via living organisms that carry pathogens:
Examples: Malaria, Lyme disease, plague
Your body has multiple layers of defence against pathogens:
The first line of defence includes:
If pathogens breach physical barriers, the immune system responds:
We can prevent the spread of infectious diseases through:
Different types of pathogens require different treatments:
Bacteria can evolve to become resistant to antibiotics, making infections harder to treat. This happens when antibiotics are overused or used incorrectly. To prevent antibiotic resistance:
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