final study Flashcards
causal agent
microorganisms that use a host’s resources to reproduce, resulting in an immune response or physiological disruption
host
organism that is the target of an infecting action of a specific infectious agent
pathogen
microorganisms that cause disease
what are the major groups of pathogens that infect humans
viruses, bacteria, protozoa, fungi, helminths, prions (6 total)
what age group is most affected by infectious diseases?
neonatal (0-27 days) & postnatal (1-59 months)
zoonotic diseases (zoonosis/zoonoses)
infectious diseases caused by pathogens that spread between animals (usually vertebrates) and humans
virulence
the severity of a disease brought on by a pathogen
Koch’s postulates
a set of criteria that establish whether a particular organism is the cause of a particular disease
- Pathogen must always be found in persons with the disease
- Pathogen must be isolated and grown in pure culture
- The culture should cause the disease when introduced into a healthy individual
- Pathogen can be isolated from second individual and grown in culture
viruses
DNA or RNA surrounded by protein
obligate parasites
a parasitic organism that cannot complete its life-cycle without exploiting a suitable host
bacteria
single-celled prokaryotic organism (no nucleus)
how do bacteria reproduce
duplicating DNA and dividing
how many genera of bacteria and how many are known to cause disease in humans
400, 40
protozoa
- Single-celled eukaryotic organisms (has a cell nucleus) - Able to evade host’s immune defenses
- Infections are difficult to treat and symptoms may be chronic because their cellular structures are similar to host mammal
vectors
any agent which carries and transmits an infectious pathogen into another living organism
fungi
- Eukaryotic organisms (have a cell nucleus)
- 70,000 species, though only a few are harmful to humans
- Low virulence, unless host is immunocompromised
variability in fungi
yeasts, spores
Helminths (worms)
Multicellular organisms, difficult to treat, tough outer coatings
which helminths cause disease in humans
Roundworms, tapeworms, flukes
transmission of helminths through…
Intermediate hosts and water, soil, food
Prions
Infectious proteins
- Unclear how they replicate: no RNA or DNA
Transmissible spongiform encephalopathies
- Humans:
– Creutzfeld-Jakob disease
– Kuru
- Non-human:
–Bovine spongiform encephalopathy
– Scrapie
Transmission
- Exposure to brain tissue and spinal cord fluid from infected individuals
- Untreatable and fatal
Direct transmission
Epithelial cells– exploitation of most permeable part of host’s body
- Skin, reproductive tract, respiratory and digestive systems
Droplet transmission
Microbes are spread in mucus droplets that travel short distance (less than 1 meter)
- Coughing, sneezing
Vector-borne
Intermediate species or material that can take a pathogen from one host to another
- Insects, animals (zoonosis), food, water, fecal-oral, utensils, needles
Factors favoring selection for higher virulence – evolution of virulence (paul ewald)
- Intermediary disease vectors
- Transmission does not require host to be mobile
Factors favoring selection for lower virulence – evolution of virulence (paul ewald)
- Causal human-to-human transmission
- Transmission requires host to be mobile
- Domesticating diseases requires disrupting modes of transmission, which will create conditions for the pathogen to evolve to mildness
First line defenses against pathogens
- Skin
- Mucous membranes
– Cilia
– Coughing and sneezing
– Secretions of the skin and mucous membranes
– Low pH of stomach acid
symptoms of pathogens
- Vomiting and diarrhea; coughing and sneezing
- Fever
- Iron sequestering
To treat or not to treat? - Individual comfort vs. evolutionary adaptation vs. public health
immune system functions
- recognize pathogen
- destroy pathogen
- communication between cells of the immune system to coordinate 1 and 2
how to identify “self” versus “non-self”
which cells require an immunological response and which do not
problems with “self/non-self dichotomy”
- Many cells in the body are non-self and are not pathogenic
- Many cells in the body are self and are pathogenic
criterion of continuity
Immune system recognizes strong discontinuities in molecular patterns, whether endogenous or exogenous origin
two interactive systems in human immunity
innate and adaptive
features of the innate system
- quick response (minutes to hours)
- broad recognition of pathogens
- principle cells/recognition: phagocytes
- secreted molecules: cytokines, histamine
- disposal: phagocytosis
- no memory
- inborn
features of the adaptive system
- responds slowly (days)
- high specificity of recognition of pathogens
- principle cells: lymphocytes, white blood cells, T cells, B cells
- recognition: b-cell for extracellular, t-cell for intracellular
- secreted molecules: antibodies (produced by b-cells), cytokines (produced by T-cells)
- disposal: b-cells (antibody initiated or phagocytosis), t-cells (cytotoxic t-cells, helper t-cells via B-cell or macrophage activation
- has a memory
- acquired with exposures (vertebrates only)
recognition systems of the innate system
Macrophages (phagocytes) have cell surface receptors (epitopes) that have broad recognition for molecular patterns of pathogens
Macrophages engulf pathogens and destroy them through the process of phagocytosis
recognition system of the adaptive system
lymphocytes recognize specific epitopes in pathogens
epitope
sections of pathogen proteins that are identifiable as non-self
- system can remember 100 million epitopes
antigen
large molecule or cell with epitopes on its surface
adaptive immune system: mechanism of action
lymphocytes (type of white blood cell) recognizes a single epitope (part of antigen), proliferation occurs and lymphocytes also replicate in response to pathogen
- b-cells, t-cells, and memory cells play a role
b-cells
found in bone marrow, monitors extracellular spaces — (e.g. blood and other fluids)
- antibodies: immunoglobulins
b-cell recognizes antigen –> proliferation of antibody (Y-shape) –> antibody binds to antigen –> “labels” pathogen for destruction by other cells of the innate system
immunoglobulins
IgA, IgD, IgE, IgG, IgM
t-cells
recognizes intracellular pathogens through the major histocompatibility complex (MHC)
Major Histocompatibility Complex (MHC)
Molecules that move pieces of pathogenic proteins out to the surface of the cell where T-cells can recognize them
- T-cell with matching receptor binds to MHC + protein and marks for destruction
- Genes that code for MHC are most variable in human genome
destruction of pathogenic cells
Inflammation
- Mast cells release histamine, which increases permeability of blood vessels allowing greater access of immune cells to infected sites
Innate system
- Phagocytes (e.g. macrophages)
Adaptive system
- Cytotoxic-T-cells (viruses) and helper T-cells (stimulate macrophages and B-cells)
what happens when the immune system responds to non-threatening antigens
allergic immune response
- non-threatening antigens: allergens
hypotheses to explain atopic disease rates increasing over time and higher among industrialized populations
Hygiene and helminth/ “Old Friends” hypotheses
pathogen recognition and destruction: innate immune system
- First immune response after pathogen has penetrated the body’s barrier defenses
- Macrophages have surface cell receptors that have broad recognition for molecular patterns of pathogens
- Macrophages engulf pathogens and destroy them through the process of phagocytosis
Pathogen recognition and destruction: Adaptive immune system; antibody-mediated immunity
- B-cells floating in blood or other fluids directly recognize extracellular pathogens via antibodies on the B-cell surface
- Each B-cell makes one kind of antibody that matches only one antigen
- Binding of antigen to antibody results in B-cell activation
Proliferation of antibodies
- Antibodies can disable pathogen; or
- “Labeling” of pathogen for destruction of phagocytes (innate system)
- Production of memory B-cells to respond quickly with antibody if same pathogen encountered again
Pathogen recognition: adaptive immune system; cell-mediated immunity
T-cells recognize intracellular pathogens via antigen-presenting cells that contain Major Histocompatibility Complex (MHC) molecules
- MHC molecules move pieces of pathogenic proteins out to the surface of the cell where T-cells can recognize them
- T-cell with matching receptor binds to MHC + a pathogenic protein and depending on the pathogen:
- Cytotoxic T-cells destroy the pathogen containing cell; or
- Helper T-cells (TH1 or TH2) are produced which secrete cytokines to activate: Macrophages (TH1) and B-cells (TH2)
allergies + reaction
Immune system reaction to foreign substance in the environment that are harmless to most people (allergens)
Reaction:
- Mild: (coughing, sneezing, congestion, wheezing, vomiting, or diarrhea)
- Severe: (anaphylaxis)