communicable diseases

• Bacteria and viruses are the main disease causing pathogens in humans
• Bacteria are prokaryotic cells with no membrane-bound organelles and their genetic information is stored in a circular strand of DNA
• Viruses consist of nucleic acid enclosed in a protein coat and their genetic material can be DNA or RNA
• Bacteria do not require a host to survive, while viruses are entirely dependent on their hosts and cannot survive without them
• Viruses are significantly smaller than bacteria
• Bacteria have a cell membrane, cell wall, cytoplasm, ribosomes, plasmids, flagellum, and pili, while viruses do not possess such structures
• An example of a bacterial disease is tuberculosis (TB) caused by Mycobacterium tuberculosis
• TB infects phagocytes in the lungs and can lead to breathing problems, coughing, weight loss, and fever
• Meningitis can be caused by bacterial infection of the meninges
• An example of a viral infection is HIV (Human Immunodeficiency Virus) which causes AIDS
• HIV symptoms include fevers, tiredness, and headaches
• Influenza infects the ciliated epithelial cells of the gas exchange system
• Athlete’s foot in humans is caused by a fungus and spread by direct contact with spores
• Malaria is transmitted indirectly via a vector, a female Anopheles mosquito
• Plants have physical and chemical defences against pathogens
• Physical barriers include cellulose cell walls, lignin layer, waxy cuticles, and blocking of old vascular tissue
• Chemical defences include menthols, phenols, alkaloids, defensins, and hydrolytic enzymes
• Primary non-specific defences in animals
• Physical barriers include skin with keratin, stomach acid, and natural bacterial flora competing with pathogens
• Non-specific responses include inflammation, lysozyme action, interferon, phagocytosis, and blood clotting
• After engulfing and destroying a pathogen, antigens are presented on the surface of the phagocyte to activate other immune cells
• The specific immune response is antigen-specific and involves B cells and T cells
• Memory cells replicate themselves for a faster immune response
• B effector/plasma cells produce antibodies
• T helper cells stimulate B cells and T killer cells
• T killer cells destroy pathogen-infected cells
• Antibodies are globular protein molecules produced by lymphocytes
• Antibodies are complementary in shape to specific antigens and can neutralize pathogens in various ways
• Antibodies have constant and variable regions, as well as hinge regions for flexibility
• Immunity can be active or passive, natural or artificial
• Active immunity results from the immune system producing antibodies in response to an antigen
• Passive immunity results from the introduction of antibodies from another source
• Antibiotics can be bactericidal (kill bacteria) or bacteriostatic (inhibit bacterial growth)
• Some bacteria become resistant to antibiotics through natural selection, leading to antibiotic-resistant bacterial infections like MRSA
• Hospitals control the spread of antibiotic-resistant infections through screening, isolation, completing antibiotic courses, and strict hygiene regimes