Health, disease and the development of medicines Revision Notes

Chlamydia: A Bacterial STI

Chlamydia is a bacterial infection spread through unprotected sexual contact (vaginal, anal, oral). Many infected individuals show no symptoms, especially in the early stages, making it easy to unwittingly transmit the infection. Symptoms, if present, can include unusual discharge, pain during urination, or abdominal pain. Left untreated, Chlamydia can lead to serious health issues such as pelvic inflammatory disease (PID) in women, which can cause infertility, or epididymitis in men. It is treatable with antibiotics.

HIV: A Viral STI

HIV (Human Immunodeficiency Virus) is a viral infection that primarily spreads through specific bodily fluids during sexual activity, sharing needles, or from mother to child. HIV attacks CD4+ T cells, which are crucial components of the immune system. This weakens the body's ability to fight off other infections and diseases. While there is no cure for HIV, antiretroviral therapy (ART) can effectively manage the viral load, allowing individuals with HIV to live long, healthy lives and significantly reducing the risk of transmission. Without treatment, HIV can progress to AIDS (Acquired Immunodeficiency Syndrome).

Preventing STI Spread

Prevention of STIs like Chlamydia and HIV largely relies on stopping the transmission routes. Key strategies include: consistent and correct use of barrier methods such as condoms during all types of sexual activity; regular STI testing, especially between partners or after unprotected encounters; reducing the number of sexual partners; and avoiding the sharing of needles or injection equipment. Education on sexual health and access to testing and treatment services are vital in controlling the spread of these infections in wider populations.

Sterilisation of Equipment and Media

To prevent contamination, all equipment and growth media must be sterile before use. An autoclave uses high-pressure steam at temperatures around 121°C for about 15-20 minutes, effectively killing bacteria, spores, and viruses. This method is crucial for sterilising things like nutrient agar, broth, and empty Petri dishes. Without proper sterilisation, unwanted microorganisms would grow alongside the desired culture, rendering experimental results unreliable and potentially creating biohazards. Other methods include dry heat for glassware or filtration for heat-sensitive liquids.

Transferring Microorganisms Aseptically

When transferring microorganisms, sterile inoculating loops are essential. These loops, made of wire, are typically sterilised by passing them through a Bunsen flame until red hot, immediately before and after each transfer. This process incinerates any microbes present on the loop. The cooled, sterile loop is then used to pick up and transfer microorganisms to new growth media. It's crucial to cool the loop to avoid killing the culture or melting the agar. Minimising exposure of cultures and media to the air is also vital; this often means working quickly and close to a flame to utilise the sterile updraft it creates.

Maintaining Culture Purity

Keeping Petri dishes and culture vials covered at all times, except for the brief moment of inoculation or sampling, is a fundamental aseptic practice. The lids act as physical barriers against airborne contaminants like dust and spores. When opening a culture vessel or dish, it should be done quickly and close to a sterile zone, such as near a Bunsen flame, to minimise the time the sterile contents are exposed to non-sterile air. The base should be lifted off the lid, rather than the lid off the base, to reduce the chance of airborne particles falling in.

Introduction to Non-Communicable Diseases (NCDs)

Non-communicable diseases (NCDs) are medical conditions or diseases that are not caused by infectious agents. They are chronic diseases that progress slowly and are of long duration. Examples include heart disease, cancer, diabetes, and chronic respiratory diseases. A key characteristic of many NCDs is that they often result from a complex interplay of various factors rather than a single cause.

Categories of Interacting Factors

The development of NCDs is typically influenced by four main categories of interacting factors: inherited factors (genetics), lifestyle choices (diet, exercise, smoking, alcohol), environmental factors (pollution, carcinogens), and social conditions (access to healthcare, education). These factors can combine in numerous ways, increasing or decreasing an individual's risk. For instance, an individual might have a genetic predisposition to a condition, but lifestyle choices could either trigger or mitigate its onset.

Cardiovascular Diseases (CVDs)

CVDs, including heart attacks and strokes, are primarily influenced by diet high in saturated fats, trans fats, and sodium; lack of physical activity; smoking; excessive alcohol consumption; and genetic factors. High blood pressure and high cholesterol are often a result of these interactions and contribute to CVD risk.

Cancers

Many cancers result from a combination of genetic mutations (inherited or acquired) and environmental triggers. Lifestyle factors such as smoking, alcohol, poor diet, obesity, and exposure to UV radiation or certain chemicals (environmental factors) significantly increase cancer risk.

Lung and Liver Diseases

Chronic lung diseases, like emphysema and chronic bronchitis, are strongly linked to smoking (lifestyle) and air pollution (environmental). Liver diseases, such as cirrhosis, can be caused by excessive alcohol consumption (lifestyle), viral infections (though this is less common for non-communicable context), or inherited conditions (genetics).

Diseases Influenced by Nutrition

Nutritional factors play a critical role in many NCDs. Obesity, a major risk factor for type 2 diabetes, CVDs, and some cancers, is largely driven by dietary choices and lack of physical activity. Type 2 diabetes itself arises from a combination of genetic predisposition, obesity, and sedentary lifestyle.

Benefits of Immunisation

Immunisation offers significant advantages for both individuals and communities. For individuals, it provides protection against specific diseases, preventing severe illness, complications, hospitalisation, and death. It trains the immune system to recognise and fight off pathogens quickly. From a public health perspective, widespread immunisation contributes to herd immunity, reducing disease transmission and protecting vulnerable groups who cannot be vaccinated.

Limitations of Immunisation

While highly effective, immunisation also has limitations. Some individuals may experience mild side effects like soreness at the injection site, fever, or fatigue. More severe reactions are rare but possible. Vaccines are not 100% effective for everyone, meaning a small percentage of vaccinated individuals can still contract the disease. Pathogens can mutate, requiring new vaccine development (e.g., influenza), and logistical challenges exist in vaccine distribution and administration in some areas. Public misinformation can also impact uptake.

Herd Immunity Explained

Herd immunity, or community immunity, describes a form of indirect protection from infectious disease that occurs when a large percentage of a population has become immune to an infection, thereby providing a measure of protection for individuals who are not immune. For example, if 95% of a population is vaccinated against measles, the remaining 5% (including infants and medically vulnerable individuals) are less likely to be exposed to the virus because its spread is significantly curtailed within the community.