Health, disease and the development of medicines Revision Notes

Modes of Pathogen Transmission

Pathogens spread through different mechanisms. Cholera bacteria are transmitted via contaminated water or food (waterborne). Tuberculosis bacteria are spread through respiratory droplets in the air (airborne). Chalara ash dieback fungi disperse spores via wind (airborne). Malaria protists are transmitted through the bites of infected mosquitoes (animal vectors).

Preventing Pathogen Spread

Various strategies can reduce or prevent pathogen transmission. For waterborne diseases like cholera, ensuring clean water and effective sewage treatment is crucial. For airborne diseases such as tuberculosis and Chalara ash dieback, good ventilation, isolation of infected individuals, and controlling movement of infected material are key. For vector-borne diseases like malaria, controlling the vector population (e.g., mosquitoes) is essential, alongside using protective measures and anti-malarial drugs.

Specific Pathogen Examples

Cholera (bacteria): Waterborne, spreads via contaminated water/food. Prevention includes clean water, sanitation. Tuberculosis (bacteria): Airborne, spreads via respiratory droplets. Prevention involves ventilation, isolation, hygiene. Chalara ash dieback (fungi): Airborne, spreads via wind-borne spores. Prevention includes managing infected plants. Malaria (protists): Vector-borne (mosquitoes). Prevention involves mosquito control, nets, antimalarial drugs.

Initial Exposure to a Pathogen

When the body is first exposed to a pathogen, its unique surface antigens are recognised by the immune system. This initial contact activates specific lymphocytes, leading to a primary immune response which involves the production of antibodies and memory cells.

Antigen-Triggered Immune Response

Antigens on pathogens stimulate B-lymphocytes to differentiate into plasma cells, which then produce specific antibodies. These antibodies bind to the antigens, helping to neutralise the pathogen or mark it for destruction by other immune cells.

Formation of Memory Lymphocytes

Alongside antibody production, the initial immune response generates memory B and T lymphocytes. These memory cells remain in the body, 'remembering' the specific pathogen and its antigens, providing long-term immunity.

Secondary Immune Response

Upon subsequent exposure to the same pathogen, memory lymphocytes enable a rapid and robust secondary immune response. This response is much faster and produces a higher concentration of antibodies, often preventing the onset of disease symptoms.

Discovery Phase

The initial stage focuses on identifying potential new drugs. This can involve understanding disease mechanisms, screening large libraries of compounds (synthetic or natural), and using computational modelling to predict active molecules. The goal is to find a 'lead compound' that shows promise against a specific target.

Preclinical Testing

Once a lead compound is found, it undergoes extensive testing in laboratories. This involves: 1. In vitro (test tube) studies using isolated cells and tissues to assess initial effectiveness and toxicity. 2. In vivo (live organism) studies, typically using animals, to evaluate efficacy, suitable dosage, and potential side effects in a whole system. These studies are crucial for gathering safety data before human trials.

Clinical Testing (Human Trials)

If preclinical tests show acceptable safety and efficacy, the drug proceeds to human trials, divided into phases:

• Phase 1: Small group of healthy volunteers (20-100) to assess safety, dosage range, and pharmacokinetics. Low doses are used initially.
• Phase 2: Larger group of patients (100-300) with the target condition to evaluate effectiveness and further assess safety and side effects.
• Phase 3: Large group of patients (several hundreds to thousands) in multiple locations to confirm effectiveness, monitor side effects, compare to existing treatments, and collect data for regulatory approval. This phase is double-blind, where neither patients nor researchers know who gets the drug or placebo.
• Phase 4: Post-marketing surveillance; ongoing monitoring after approval to detect rare side effects and gather long-term data.

Regulatory Approval and Monitoring

After successful clinical trials, an application is submitted to regulatory bodies (e.g., FDA in the US, MHRA in the UK) for approval. They review all submitted data on safety, efficacy, and quality. If approved, the drug can be marketed, but ongoing monitoring (Phase 4 trials) continues to track long-term effects and potential rare side effects not seen in earlier, smaller trials.

Medication for CVD

Medications are often prescribed long-term to manage cardiovascular disease. Statins are used to lower blood cholesterol levels, reducing the risk of plaque formation. Anticoagulants or antiplatelets (e.g., aspirin) help prevent blood clots. Beta-blockers can slow the heart rate and reduce blood pressure. ACE inhibitors relax blood vessels, lowering blood pressure. Loop diuretics reduce fluid retention. These drugs often require lifelong adherence and can have side effects. Benefits include managing symptoms and reducing risk of severe events like heart attacks or strokes.

Surgical Procedures for CVD

Surgical interventions are used when medication and lifestyle changes are insufficient. Stents are small mesh tubes inserted into arteries to keep them open after balloon angioplasty. This procedure improves blood flow to the heart. Coronary artery bypass grafting (CABG) involves taking a healthy blood vessel from another part of the body and using it to bypass a blocked coronary artery, restoring blood supply to the heart muscle. Pacemakers can regulate erratic heart rhythms. These procedures carry risks like infection, bleeding, and adverse reactions to anaesthesia, but can significantly improve quality of life and life expectancy.

Lifestyle Changes for CVD

Lifestyle modifications are fundamental for both preventing and managing cardiovascular disease. These include adopting a balanced diet low in saturated fats, salt, and sugar, and rich in fruits, vegetables, and whole grains. Regular physical activity strengthens the heart and improves circulation. Quitting smoking is paramount, as smoking severely damages blood vessels. Maintaining a healthy weight reduces strain on the heart. Limiting alcohol intake and managing stress also contribute positively. Lifestyle changes have minimal side effects and offer holistic health benefits, potentially reducing the need for medication or surgery, though they require significant personal commitment.