Communicable diseases, disease prevention...

• Tuberculosis (TB)


  Caused by the bacterium Mycobacterium tuberculosis, primarily affects the lungs but can also affect other parts of the body, spreads through the air when an infected person coughs or sneezes, highly contagious
• Bacterial meningitis


  Inflammation of the protective membranes covering the brain and spinal cord, caused by various bacteria including Neisseria meningitidis, Streptococcus pneumoniae, and Haemophilus influenzae, symptoms include fever, headache, stiff neck, and sensitivity to light
• Ring rot (affecting potatoes and tomatoes)

  Bacterial disease affecting potatoes and tomatoes, caused by the bacterium Clavibacter michiganensis, symptoms include wilting, yellowing, and necrosis of leaves, as well as circular, brown lesions on tubers and fruits
• HIV/AIDS (human)


  Human Immunodeficiency Virus (HIV) leads to Acquired Immunodeficiency Syndrome (AIDS), attacks the body's immune system, specifically CD4 cells, weakening the immune system and making it vulnerable to various infections and diseases, primarily transmitted through sexual contact, sharing needles, or from mother to child during childbirth or breastfeeding
• Influenza (animals)


  Highly contagious viral respiratory infection affecting animals and humans, caused by influenza viruses, primarily types A, B, and C, symptoms include fever, cough, sore throat, muscle aches, and fatigue
• Tobacco Mosaic Virus (plants)


  Plant pathogen that infects a wide range of plants, including tobacco, tomatoes, peppers, and cucumbers, causes characteristic mosaic patterns on leaves, stunting of growth, and reduced yield
• Malaria


  Caused by the protozoan parasite Plasmodium, transmitted to humans through the bite of infected female Anopheles mosquitoes, the parasites multiply in the liver and then infect red blood cells, causing symptoms such as fever, chills, and anaemia
• Potato/tomato late blight


  Fungal disease affecting potatoes and tomatoes, caused by the oomycete pathogen Phytophthora infestans, leads to dark, water-soaked lesions on leaves, stems, and fruits, ultimately resulting in plant death
• Black sigatoka (bananas)


  Fungal disease affecting banana plants, caused by the fungus Mycosphaerella fijiensis, leads to the development of dark spots on the leaves, affecting photosynthesis and eventually causing the plant to die
• Ringworm (cattle)


  Fungal skin infection affecting cattle and other animals, as well as humans, caused by dermatophyte fungi, such as Trichophyton verrucosum, symptoms include circular, raised lesions with a red ring-like appearance on the skin
• Athlete's foot (humans)


  Fungal infection of the skin that primarily affects the feet, caused by dermatophyte fungi, such as Trichophyton rubrum, symptoms include itching, burning, and cracked, peeling skin between the toes
• Direct transmission


  Occurs through physical contact between an infected individual and a susceptible host, e.g., a person with the flu can spread the virus to others through coughing or sneezing
• Indirect transmission


  Involves the transfer of pathogens through intermediary objects or substances, e.g., contaminated surfaces or objects can harbour pathogens and transmit them to individuals who touch or ingest them
• Vectors


  Organisms that transmit pathogens from one host to another, e.g., mosquitoes act as vectors for diseases such as malaria and dengue fever, while aphids can transmit viruses to plants
• Spores


  Reproductive structures produced by fungi and some bacteria, can survive harsh environmental conditions and spread pathogens to new hosts, e.g., fungal spores can be dispersed by wind or water, infecting plants over long distances
• Plants produce various chemicals to defend against pathogens, such as phytoalexins, terpenoids, and phenolics
• Callose deposition


  Involves the deposition of a polysaccharide called callose at the site of infection, forming a barrier to prevent pathogen movement
• Skin as a primary defence mechanism

  Serves as a physical barrier, preventing pathogens from entering the body, also has acidic pH and antimicrobial peptides to provide further protection against microbial colonisation
• Blood clotting


  When blood vessels are damaged, platelets adhere to the site and release clotting factors, leading to the formation of a blood clot, preventing the entry of pathogens and reducing blood loss
• Inflammation


  Localised response to infection or tissue injury, involves the release of inflammatory mediators, such as histamine and cytokines, which increase blood flow to the affected area and recruit immune cells to eliminate pathogens
• Mucous membranes and expulsive reflexes

  Mucous membranes line the respiratory, gastrointestinal, and urogenital tracts, providing a physical barrier against pathogens, they also produce mucus containing antimicrobial substances, trapping and neutralising microbes before they can invade tissues
• Phagocytes


  Specialised immune cells, including neutrophils and macrophages, that engulf and digest pathogens through a process called phagocytosis
• Phagocytosis


  Phagocytes recognize pathogens through pattern recognition receptors (PRRs) on their surface, which bind to pathogen-associated molecular patterns (PAMPs), triggering signalling pathways that lead to cytoskeletal rearrangements and engulfment of the pathogen, the phagosome then fuses with lysosomes, exposing the pathogen to antimicrobial substances that degrade it
• Cytokines, opsonins, phagosomes, and lysosomes


  Cytokines regulate immune responses and recruit phagocytes, opsonins enhance phagocytosis by coating pathogens, phagosomes are vesicles formed by the engulfment of pathogens, which fuse with lysosomes containing digestive enzymes to form phagolysosomes where pathogens are degraded
• B Lymphocytes


  Produce antibodies and are involved in humoral immunity, when activated by antigens, they undergo clonal selection and differentiation into plasma cells, which secrete antibodies specific to the antigen
• T Lymphocytes


  Mediate cell-mediated immunity and include helper T cells, cytotoxic T cells, and regulatory T cells, helper T cells release cytokines that activate B cells and other immune cells, cytotoxic T cells recognize and destroy infected cells, while regulatory T cells suppress excessive immune responses to prevent autoimmune reactions
• Cell signalling, interleukins, clonal selection, and clonal expansion

  Cell signalling and interleukins coordinate immune responses, interleukins are signalling proteins that regulate the growth, differentiation, and activation of immune cells, clonal selection and expansion involve the proliferation of antigen-specific B and T cells in response to encountering their cognate antigen, leading to the generation of effector cells and memory cells
• Plasma cells, T helper cells, T killer cells, and T regulatory cells


  Plasma cells produce antibodies specific to the antigen encountered, T helper cells assist in the activation of other immune cells, T killer cells recognize and eliminate infected or abnormal cells, T regulatory cells modulate immune responses and maintain tolerance to self-antigens, preventing autoimmunity
• Primary immune response


  Occurs upon initial exposure to an antigen, during which B and T cells undergo clonal selection and proliferation. Memory B and T cells are generated, providing long-term immunity and allowing for a faster and more robust secondary immune response upon re-exposure to the same antigen.
• Secondary immune response


  Memory cells rapidly differentiate into effector cells, producing antibodies and cytokines to eliminate the pathogen more efficiently.
• T memory cells and B memory cells

  • They are long-lived immune cells that persist after the resolution of an infection or vaccination
  • They provide immunological memory, enabling a more rapid and robust secondary immune response upon re-exposure to the same antigen
  • They can quickly differentiate into effector cells, enhancing the clearance of pathogens and providing long-term protection against reinfection
• Functions of antibodies


  • Neutralising pathogens
  • Promoting phagocytosis
  • Activating complement proteins
  • Facilitating the clearance of immune complexes
• Opsonisation

  Opsonins, such as antibodies and complement proteins, coat pathogens and promote their recognition by phagocytes
• Agglutination


  Antibodies cause pathogens to clump together, facilitating their clearance by immune cells
• Antitoxin action


  Antibodies neutralise toxins produced by pathogens, preventing them from damaging host cells
• Active immunity


  • Immune system generates a response to an antigen, resulting in the production of memory cells and long-lasting protection
  • Can be acquired naturally through infection or artificially through vaccination
• Passive immunity


  • Transfer of preformed antibodies or immune cells from one individual to another, providing immediate but temporary protection
  • Can be natural, such as maternal antibodies transferred to the foetus, or artificial, such as administration of antibodies as a treatment
• Natural immunity


  Immunity acquired through natural exposure to pathogens, such as infection
• Artificial immunity


  Immunity acquired through deliberate interventions, such as vaccination
• Autoimmune disease


  Immune system mistakenly attacks the body's own tissues, leading to inflammation and tissue damage