Health, disease and the development of medicines Revision Notes

Weakened Immune System

An existing disease often diminishes the immune system's effectiveness. This makes the body less capable of recognising and fighting off new pathogens, increasing the risk of subsequent infections. Conditions like HIV/AIDS directly target immune cells, leaving the body defenceless against common illnesses.

Physical Damage and Entry Points

Some diseases cause physical damage to tissues and organs. This damage can create openings or weakened areas that pathogens can exploit to enter the body or establish new infections. For example, a severe flu infection can damage the respiratory lining, making an individual more prone to bacterial pneumonia.

Chronic Stress and Nutritional Deficiencies

Long-term illnesses can lead to chronic stress on the body and may result in nutritional deficiencies due to altered metabolism or reduced appetite. These factors further compromise the immune system and overall health, reducing resistance to new diseases. Chronic inflammation associated with some diseases can also suppress immune responses.

Overwhelmed Body Systems

When the body is already battling one disease, its resources and energy are diverted to fight that existing threat. This leaves fewer resources available to mount an effective response against a new pathogen, making it easier for a secondary infection to take hold and cause illness.

Understanding Pathogens

Pathogens are harmful microorganisms that cause infectious disease in their hosts. They may infect animals, including humans, or plants by damaging cells or interfering with normal functions.

Four Main Groups of Pathogens

1. Viruses: Non-cellular; reproduce by entering and hijacking host cells.
2. Bacteria: Single-celled prokaryotes; can release toxins or invade tissues.
3. Fungi: May be single-celled or multicellular; invade tissues or secrete enzymes.
4. Protists: Single-celled eukaryotes; some are parasites damaging their host from the inside.

Bacterial and Fungal Infections

Some common infections are caused by bacteria or fungi. Cholera is a bacterial infection that primarily affects the small intestine, leading to severe diarrhoea and dehydration. Tuberculosis (TB), another bacterial disease, mainly impacts the lungs, causing persistent coughs and damage. Helicobacter pylori is a bacterium known to cause stomach ulcers by eroding the stomach lining. Chalara ash dieback is a fungal disease affecting ash trees, causing lesions on the bark and leaves, ultimately leading to leaf loss and potentially tree death.

Viral and Protist Infections

Viruses and protists also cause significant diseases. HIV is a virus that targets and destroys white blood cells, which are crucial for the immune system. This destruction severely compromises the body's ability to fight off other infections, leading to AIDS over time. Ebola, another viral infection, causes haemorrhagic fever, characterised by internal and external bleeding, and is often fatal. Malaria is caused by a protist (Plasmodium) transmitted through mosquito bites. This protist multiplies in the liver and then infects red blood cells, causing symptoms like fever, chills, and anaemia.

Modes of Pathogen Transmission

Pathogens spread through various routes. Cholera bacteria are waterborne, meaning they spread through contaminated water. Tuberculosis and Chalara ash dieback are airborne, transmitting via microscopic particles or spores in the air. Malaria protists use animal vectors, like mosquitoes, to transfer from one host to another. Helicobacter pylori causes stomach ulcers and often spreads through oral transmission. Ebola virus transmission occurs through direct contact with infected body fluids.

Strategies for Prevention and Control

Preventing pathogen spread requires specific measures tailored to the transmission method. Clean water and sanitation prevent waterborne diseases like cholera. Isolating infected individuals and vaccination help control airborne diseases like tuberculosis. Restricting movement of infected material and removing diseased plants reduce the spread of Chalara ash dieback. Mosquito control and antimalarial drugs are effective against vector-borne diseases like malaria. Good hygiene and sanitation are crucial for preventing orally transmitted illnesses like those caused by Helicobacter. Strict infection control and safe handling of body fluids are vital for containing diseases like Ebola.

Specific Pathogen Examples

Cholera (bacteria) spreads via contaminated water, prevented by clean water access. Tuberculosis (bacteria) is airborne, prevented by isolation and vaccination. Chalara ash dieback (fungi) is airborne, controlled by managing diseased trees. Malaria (protists) is spread by mosquito vectors, prevented by mosquito control. Helicobacter pylori (bacteria) transmission is oral, reduced by good hygiene. Ebola (virus) spreads via body fluids, contained by strict infection control.