Communicable Diseases, Disease Prevention And The Immune System Flashcards
Name 4 groups of pathogen that can cause communicable diseases
Bacteria
Fungi
Protocista
Viruses
How does Mycobacterium tuberculosis cause disease
- Triggers inflammatory response by infecting phagocytes in lungs
- Infected phagocytes are sealed in waxy-coated tubercles so bacteria remain dormant. First infection has no symptoms
- If another factor weakens immune system, bacteria become active and destroy lung tissue
How does HIV result in the symptoms of AIDS
- Attachment proteins bind to complementary CD4 receptor on TH cells
- HIV particles replicate inside TH cells, killing or damaging them.
- AIDS develops when there are too few TH cells for the immune system to function
- Individuals cannot destroy other pathogens and suffer from secondary diseases / infections
May cause death
How does the tabacco mosaic virus cause disease?
Affects plants. Mainly transmitted via infected sap
Contains ssRNA, which is directly transcribed by host cell to assemble new virions
Virions enter other cells via plasmodesmata then enter xylem and phloem
Causes stunted growth and mottled leaves
How does the influenza virus cause disease
Transmitted via: droplet infection, contact with mucus containing virus, zoonotic infection, contact with formites
Injects viral RNA into ciliated epithelial cells of throat and lungs. Viral RNA hijacks cell biochemistry to produce new virions. Cell lysis releases virions
5-7 days of headache, coughing, sneezing, sore throat, vomiting, fever, muscular / joint pain
What causes malaria?
Female Anopheles mosquito acts as vector for Plasmodium spp. protocista when it transfers saliva to another organism during feeding
Parasite reproduces asexually in red blood cell in liver, causing lysis
What causes potato / tomato late blight?
What causes ring rot of potatoes?
Blight: The protocista Phytophthora infestans behaves similarly to a fungus. Mainly transmitted via spores
Ring Rot: Sepedonicus subspecies of the Clavibacter michiganensis. Mainly transmitted by planting infected seeds / contact with fomites. Plant-to-plant transmission in rare
What causes bacterial meningitis?
Often meningococcal bacteria A, B, C, W, X, Y, Z. Also caused by pneumococcal bacteria and Haemophilus influenzae type b (Hib) bacteria. Affects meninges (protective membranes around the brain)
Transmitted by droplet infection & direct contact with saliva e.g. kissing. Usually spread by carriers of the bacteria who are not ill and occasionally by individuals with meningitis
Describe three fungal infections
The sac fungus Mycosphaerella fijiensislack causes the leaf-spot disease Black Sigatoka in banana plants
About 40 types of fungus cause ringworm. Transmitted by contact with formites, zoonotic infection, direct contact with infected individuals. Particularly affects cattle
Athletes foot in humans (tinea pedis) is caused by a range of fungi which can also affect hands or nails
How are communicable pathogens transmitted directly
Inhalation - droplet infection
Skin-to-skin contacts or exchange of fluids
Penetrate skin actively using enzymes or passively through wounds, hair follicles or sweat glands
How are communicable pathogens transmitted indirectly
Consumption of contaminated food
Via a vector e.g. mosquitoes transmit Plasmodium parasite
Spores
How do living conditions affect disease transmission
Overcrowding increases direct transmission
Climate determines which organisms can survive e.g. malaria is more prevalent in tropical countries, where the vector (mosquito) can breed
Social factors can influence how quickly people are treated, which can increase / decrease direct transmission
Name 4 physical barriers to pathogen entry in plants
Cellulose cell walls
Lignified layer
Waxy upper cuticle
Old vascular tissue is blocked to prevent pathogens from spreading inside the plant
Describe two mechanical responses to infection in plants
Guard cells close stomata
The thick polysaccharide callose is produced and deposited between the cell wall and plasma membrane to increase entry distance and limit spread
What is necrosis
Injury activates intracellular enzymes in plants that kill cells near the site of infection to prevent pathogen from spreading
Necrosis of woody tissue is known as canker
Describe the chemical defences plants use against pathogens
- Terpenoids (essential oils) e.g. menthols act as antibacterials
- Phenols e.g. tannin inhibits insects from attacking by interfering with digestion
- Alkaloids e.g. caffeine and morphins deter herbivores from feeding because they taste bitter
- Defensins (cysteine-rich proteins) inhibit transport channels
- Hydrolytic enzymes e.g. chitinases break down cell wall of invading organisms
Name 5 barriers to infection in animals
- Skin is tough keratin layer
- Blood clotting prevents pathogens from entering skin lesions
- Hydrochloric acid in stomach kills bacteria
- Harmless bacteria in gut and on skin surface increase interspecific competition with pathogens
- Mucous membranes trap pathogens and may secrete antimicrobial enzymes
What are explusive reflexes
Body attempts to force foreign substances out:
- Irritation of mucous membranes in nostrils causes sneezing
- Irritation of ciliated epithelium in respiratory tract causes coughing
Name 4 ways the non-specific immune system responds to infection
- Inflammation
- Phagocytosis
- Digestive action of lysozymes
- Production of interferon (antiviral agent)
Outline the process of inflammation
- Damaged blood vessels release histamines, causing vasodilation
- Blood flow and permeability of blood vessels increase
- White blood cells and plasma move into the infection
How does blood clotting occur
- Blood platelets form plug and release chemicals that enhance clotting e.g. thromboplastin
- Prothrombin changes into thrombin, its active form
- Fibrinogen changes into insoluble fibrin which covers wound
Name the 2 types of white blood cell involved in phagocytosis
Neutrophils
Macrophages (can become antigen presenting cells)
How does phagocytosis destroy pathogens
- Phagocyte moves towards pathogen which may have been marked by opsonins via chemotaxis
- Phagocyte engulfs pathogen via endocytosis to form a phagosome
- Phagosomes fuses with lysosome (phagolysosome)
- Lysozymes digest pathogen
- Phagocyte absorbs the products from pathogen hydrolysis
Explain the role of Antigen presenting cells (APCs)
Macrophage displays antigen from pathogen on its surface (after hydrolysis in phagocytosis)
Enhances recognition by T helper cells which cannot directly interface with pathogens or antigens in body fluid
Secrete cytokines that are involved in stimulating specific immune response
What are lysozymes
Digestive enzymes. Found in lysosomes as well as many secretions e.g. tears and mucus. Damage bacterial cell walls causing osomotic lysis
Outline how to prepare blood to be observed under a microscope
- Smear a drop of blood onto a slide using a spreader held at 45 degrees
- Add leishman stain then a buffer. Rinse.
Name the 2 types of specific immune response
- Cell-mediated
- Humoral
Outline the process of the cell-mediated response
- Complementary T helper lymphocytes bind to foreign antigen on APC
- Cell signalling via secretion of interleukins stimulates:
a) clonal expansion of complementary T helper cells (rapid mitosis): become memory cells or trigger humoral response
b) clonal expansion of cytotoxic T cells: Secrete enzyme perforin to destroy infected cells
Outline the process of the humoral response
- Complementary T helper lymphocytes bind to foreign antigen on antigen-presenting cells
- Release cytokines that stimulate clonal expansion (rapid mitosis) of complementary B lymphocytes
- B cells differentiate into plasma cells
- Plasma cells secrete antibodies with complementary variable region to antibody
Describe the structure and function of B and T lymphocytes
Many specific receptors and immunoglobulins on surface
B cells differentiate into plasma cells to secrete antibodies
3 types of T cells:
T helper - secrete cytokines
T killer - secrete perforin
T regulator - suppress other immune cells to prevent autoimmune disease
What is an antibody, Describe its structure
Proteins secreted by plasma cells
Quarternary structure: 2 ‘light chains’ held by disulphide bridgesm 2 longer ‘heavy chains’
Binding sites on variavle region of light chains have specific tertiary structure complementary to antigen
The rest of the molecule is known as the constant region
How do antibodies lead to the destruction of a pathogen
Agglutinins form antigen-antibody complexes to enhance phagocytosis
Activation of complement
Opsonins mark microbes for phagocytes
Antitoxins make toxins insoluble via precipitation or neutralisation
What are memory cells
Specialised T helper / B cells produced from primary immune response
Remain in low levels in the blood
Can divide very rapidly by mitosis if organism encounters the same pathogen again
Contrast the primary and secondary immune response
Secondary response:
Faster rate of antigen response
Shorter time lag between exposure and antibody production
Higher concentration of antibodies
Antibody level remains higher after the secondary response
Pathogen usually destroyed before any symptoms
Compare and contrast passive and active immunity
Both can be artificial or natural and both involve antibodies
Passive:
No memory cells and antibodies not replaced when broken down
Immediate
Antibodies from external source
No direct contact with antigen necessary
Active:
Memory cells produced - long term
Time lag
Lymphocytes produce antibodies
Needs direct contact with antigen
Give examples of passive and active immunity
Passive natural: Antibodies in breast milk or across placenta
Passive artificial: Anti-venom, needle stick injections
Active natural: Humoral response to infection
Active artificial: Vaccination
Define autoimmune disease and give examples
Immune system produces antibodies against its own tissues
Rheumatoid arthritis: immune system targets synovium lined joints causing inflammation
Lupus: Results in inflammation throughout body
Explain the principles of vaccination
- Vaccine contains dead or innoculated version of a pathogen
- Triggers primary immune response
- Memory cells are produced and remain in the bloodstream so secondary response is rapid and produces higher concentration of antibodies
- Pathogen is destroyed before it causes symptoms
Define endemic and epidemic
Endemic: Disease occurs routinely in a geographical area
Epidemic: Temporary rapid increase in incidence of disease in a geographical area
What role do vaccines play in preventing epidemics
Routine vaccination of 80-90% if population reduces available carriers of pathogen, resulting in herd immunity
Limited by countries resources
Vaccinating close contacts of infected individuals limits spread of pathogen, but raises issue of distributive justice
Programs have changed to account for informed consent and maximum beneficence even during epidemics
List possible natural sources of medicines
Microorganisms e.g. streptomycin, neomycin. Chloraphenicol = various species of Streptomyces genus
Fungi e.g. Penicillin
Plants e.g. Taxol for chemotherapy - yew, quinine for malaria - cinchona
Maintaining biodiversity means new natural treatments can be discovered in the future
What is personalised medicine and synthetic biology
Personalised medicine: Genome sequencing has enabled scientists to predict an individuals response to diseases or certain medicines so prescriptions can be targeted
Synthetic biology: engineering that targets biochemical processes
What are the benefits of using antibiotics to treat bacterial infection
Effectively reduce population of bacterial colony. Used widely since discovery of penicillin in mid 20th century
Bacteriostatic antibiotic prevent protein synthesis / inhibit formation of nucleic acids and therefore growth
Bactericidal antibiotics prevent formation of peptoglycan cross links in cells walls leading to osmotic lysis
What are the risks of using antibiotics to treat bacterial infection
Overuse of antibiotics increases selection pressure for resistant strains of bacteria. Antibiotic-resistant infections e.g. caused by MRSA and Clostridium difficile are difficult to treat
