Health, disease and the development of medicines Revision Notes

What are Pathogens?

Pathogens are microorganisms or other agents that cause infectious diseases. They can infect humans, animals, and plants. The main types of pathogens include viruses, bacteria, fungi, and protists. Diseases caused by pathogens are infectious and can spread from one host to another.

Types of Pathogens and their Characteristics

Viruses are very small, non-living particles that must infect a living host cell to reproduce. They take over the host cell's machinery to make more viruses, often destroying the cell in the process. Bacteria are single-celled prokaryotic organisms. They cause disease by rapidly multiplying in the body, producing toxins, or directly damaging cells. Fungi can be single-celled or multicellular. They cause disease by invading tissues or releasing spores, often leading to conditions like athlete's foot or thrush. Protists are a diverse group, mostly single-celled eukaryotes. Many are parasitic and live on or in a host, causing diseases such as malaria.

How Pathogens Cause Disease

Each type of pathogen has unique ways of causing disease. Viruses replicate within host cells, using the cell's resources and often leading to cell damage or death. Bacteria can grow rapidly and produce harmful toxins that disrupt normal body functions, or they can directly invade tissues. Fungi release enzymes that break down host tissues for nutrients, leading to tissue damage. Protists often have complex life cycles involving different hosts and can damage host cells or tissues as they multiply and spread throughout the body.

Modes of STI Transmission

STIs, such as Chlamydia (bacterial) and HIV (viral), are primarily transmitted through sexual contact. This means engaging in unprotected vaginal, anal, or oral sex facilitates the exchange of bodily fluids containing the infectious agents. For HIV, additional transmission routes include sharing contaminated needles or syringes, and mother-to-child transmission during gestation, birth, or lactation. Chlamydia mainly spreads through sexual contact only.

Preventing and Controlling STI Spread

To reduce the incidence of STIs, several preventative measures are crucial. Consistent and correct use of condoms during sexual activity provides an effective barrier. Regular screening and testing for STIs, especially after unprotected sex or with new partners, helps in early detection and treatment. Limiting the number of sexual partners can also reduce exposure risk. Education about safe sex practices, access to STI testing centres, and prompt treatment for infected individuals are vital for reducing community transmission.

Chlamydia (Bacteria)

Chlamydia is a common bacterial STI. Many people infected with Chlamydia do not experience symptoms, which allows the infection to spread unknowingly. If left untreated, it can lead to serious reproductive health complications, including pelvic inflammatory disease in women, which can cause chronic pain and infertility. It is treatable with antibiotics.

HIV (Virus)

HIV is a viral STI that targets the immune system, specifically white blood cells called T-helper cells. Over time, it weakens the body's ability to fight off infections and diseases, leading to Acquired Immunodeficiency Syndrome (AIDS). There is no cure for HIV, but antiretroviral therapy (ART) can manage the virus, allowing individuals to live long, healthy lives and significantly reducing the risk of transmission. HIV is not transmitted through casual contact.