Health, disease and the development of medicines Study Guide

Pathogens, including bacteria, fungi, and protists, cause infectious diseases and spread through various routes. Cholera, caused by bacteria, is typically waterborne, transmitted when contaminated water or food is consumed. This spread can be reduced by ensuring access to clean drinking water and proper sanitation. Tuberculosis (TB), a bacterial infection, is primarily airborne. It spreads when an infected person coughs or sneezes, releasing tiny droplets containing the bacteria into the air, which can then be inhaled by others. Reducing this spread involves good ventilation, isolating infected individuals, and maintaining personal hygiene such as covering coughs. Chalara ash dieback, a fungal disease, affects ash trees and is also airborne; its spores are carried by wind. Preventing its spread involves restricting the movement of infected plant material and planting resistant varieties. Malaria, caused by protists, uses animal vectors, specifically mosquitoes, to transmit the pathogen between human hosts. Control measures focus on managing the mosquito population through insecticides, removing stagnant water breeding sites, and using mosquito nets, as well as drug treatments to prevent infection in humans.

The human body's specific immune system provides a targeted defence against disease. When a pathogen, such as a bacterium or virus, enters the body, it has specific molecules on its surface called antigens. These antigens are unique to that particular pathogen. The presence of these antigens triggers an immune response. This response involves specialised white blood cells called lymphocytes.

Upon initial exposure, specific B-lymphocytes recognise and bind to the antigens. This binding, often with the help of T-lymphocytes, activates the B-lymphocytes, causing them to multiply and differentiate into plasma cells. These plasma cells then produce and release large quantities of specific antibodies into the bloodstream. Antibodies are proteins that are specially shaped to bind to the antigens on the pathogen. This binding can neutralise the pathogen, clump pathogens together for easier phagocytosis, or mark them for destruction by other immune cells.

Crucially, this initial exposure also leads to the production of memory lymphocytes (both B and T memory cells). These memory cells persist in the body for a long time, sometimes even for decades. They are sensitised to the specific antigen encountered. If the same pathogen re-enters the body at a later date, these memory lymphocytes rapidly recognise it. This triggers a much faster and stronger secondary immune response. This rapid and potent response, characterised by quick and extensive antibody production, often eliminates the pathogen before symptoms of the disease can develop, providing immunity.