Pathogens And Immunity Flashcards
What are the major routes of infection?
- airborne transmission
- food or waterborne transmission
- Vertical transmission
- Contact transmission
- Vector transmission
What body system is the main entrance point for pathogens being transmitted through the air?
Respiratory system
What is vertical transmission?
Where and when does it occur?
What is the name for a disease transmitted in this way?
Vertical transmission is when a pathogen is passed from the mother to the baby through the placenta in utero.
The disease is congenital.
What are two route that an infection can be transfered from the mom to the baby?
- vertical transmission through the placenta in utero
2. contact transmission from the vagina or urethra during birth
Where are three places where contact transmission of pathogens take place?
- urethra
- vagina
- skin
What is vector transmission?
What is the major pathogen spread via vectors?
It is when the pathogen is passed through another organism (ex. a mosquito)
Malaria is transmitted by vector and Lyme Disease is spread by ticks
What are the four classes of microbes that the immune system must protect against?
What is an example of each?
- Bacteria- salmonella and mycobacterium tuberculosis
- Virus- influenza
- Fungi- candida albicans (pneumonia)
- a. Parasitic protozoa - plasmodium
flaciparum (malaria)
b. Parasitic worms- schistosoma
What class of microbe is responsible for the cause of malaria?
Parasitic protozoa - plasmodium flaciparum
How does a prokaryotic cell differ from a eukaryotic cell in terms of size and content? (5 ways)
Prokaryotic cells:
- are 10x smaller
- lack a nucleus
- have a single chromosome
- have 70s ribosomes
- Have a cell wall made of peptidoglycan
What color do gram positive bacteria stain and why?
Gram positive cells have a thicker peptidoglycan cell wall so they maintain the original violet stain. When the cell is rinsed with alcohol, the stain does not get removed. When the counter stain is added, it looks dark purple.
What color do gram negative bacteria stain and why?
Gram negative bacteria stain pink because after the original staining, when the cell is washed with alcohol, the stain washes away. The counter stain makes it look pink.
The original stain washes away because it has a thinner peptidoglycan cell wall that does not hold the stain.
Do gram negative or gram positive bacteria have a thicker peptidoglycan cell wall?
Gram positive
What bacteria are not stained by the gram stain? (2 examples)
- Spirochetes- like treponema pallidum (syphilis)
2. mycobacterium tuberculosis
What are the three major virulence factors?
- endotoxins
- exotoxins
- bacterial capsules
Which type of bacteria have endotoxins?
What does an endotoxin do?
gram negative bacteria because their cell walls have lipopolysaccharides (LPS).
This is a major inflammatory stimulus
What is an example of a bacteria with endotoxins?
Neissenia Meningitis
How does an endotoxin spread the pathogen?
- When a gram (-) bacteria dies, it releases LPS endotoxin.
- Endotoxin binds to a receptor on macrophage and sends a signal to the DNA
- Macrophage secretes inflammatory cytokines lke IL1a and TNF
- Vasodilation occurs allowing more gram (-) bacteria to enter the blood stream and lead to sepsis, temperature rises, BP falls
What cytokines are released by macrophages when an endotoxin binds to it?
IL1a and TNF
What does the release of cytokine from the macrophage after the binding of an endotoxin do?
- Vasodilation to let bacteria enter bloodstream
- decrease BP
- raise temp
Which type of bacteria have capsules and what are they made of?
gram positive- polysaccharide polymers
What do capsules allow the bacteria to do?
- become resistant to complement lysis in the blood
- anti-phagocytic so make them resistant to being killed by neutrophils and monocytes (if they are phagocytized, they are more resistant to killing by lysosomes)
How are encapsulated bacteria able to be eliminated?
the adaptive immune system will make antibodies to the polysaccharides on the capsule facilitating phagocytosis.
What is an example of a bacteria that uses encapsulation as a virulence factor?
Streptococcus pneumoniae (pneumococcus)
How does an exotoxin work?
A bacteria releases a toxin that allows it to invade and colonize host tissue easier by killing host cells at the barrier to infection
Why is passive immunization so important for tetanus?
The amount of tetanus toxin necessary to kill someone is very small. It is crucial that the adaptive immune system has developed antibodies against the toxin because if you wait for primary immune response, it would be too late.
What are three examples of pathogens who cause disease predominantly or exclusively by the release of their toxins?
- Tetanus
- Diptheria
- Cholera
What type of toxin does clostridium tentani produce?
neurotoxin that does not stimulate an immune response because it is in such low quantity
How does diptheria get transmitted?
How does it cause its pathogenesis?
It is transmitted via respiratory secretions and colonizes the pharynx. When it secretes its toxin, it kills epithelial cells in the throat.
A pseudomembrane of dead epithelial cells form and the airway swells
What body system does cholera affect?
GI tract. It causes up to 20L/day of diarrhea
What are the three ways antibodies can control bacterial pathogens?
- directly kill them via complement lytic components
- neutralize exotoxins
- enhance phagocytosis of encapsulated bacteria (opsonization)
In general, what are the steps of the viral life cycle?
- attachment to cell membrane
- penetration
- replication
- transcription
- translation
- assembly
- release
How do viruses attach to cells?
via a highly specific, high affinity receptor
What are the two ways a virus can penetrate a host cell?
- endocytosis
2. move directly through plasma membrane
After a virus is assembled and released from a host cell, what can it do?
Infect other cells in the same host or get transmitted to another host
What is cellular tropism?
What are two examples?
A specific virus infects a narrow range of eukaryotic hosts
ex. HIV infects T cells and macrophages
Herpes simplex infects neurons
What are the four consequences of viral infection in human disease?
- Lysis
- Chronic/persistant infection
- Reactivation
- Transformation
What is the lytic pathway of viruses?
What is an example of a virus that follows this path?
When the first cell that is infected lysis and many virus are released at once to infect other cells or get transmitted to a new host.
Rhinovirus is an example (common cold)
What is the transforming pathway of a virus and what is an example of a virus that uses this pathway?
When the cell that was infected is dysregulated and the infection persists in the host.
An example is HPV and it causes warts from the dysregulated cells.
What is the chronic/persistent pathway of viral infection and what is an example of a virus that does this?
The virus infects and proliferates at a low level only occassionaly releasing the virus to infect more areas.
Ex. are HepC (hepatocytes), HIV (macrophages or Tcells) Epstein Barr (B lymphocytes), Human cytomegalovirus (salivary glands)
What does Epstein Barr Virus infect? What kind of viral pathway does it take?
It infects B lymphocytes and is chronic/persistant
What does HIV infect? What kind of viral pathway does it take?
macrophages and lymphocytes and it is chronic persistant
What does the Human Cytomegalovirus infect?
It is chronic/persistent infection of salivary glands
What is the latent/proviral pathway of viruses? What is an example of a virus that takes this path?
It is when the virus lays dormant in a host cell without replicating.
Periodically the virus is released and can cause recurrent outbreak.
Ex. Herpes Zoster (chicken pox/shingles) and Herpes Simplex (neuronal cells)
What cell population aids in killing viruses that have already infected cells?
CD8 T cells
What are the two major differences between fungal cells and human cells?
- Fungi have a carbohydrate polymer cell wall
2. Fungi have a surrounding matrix of mannoproteins or mannans
What are mannoproteins?
Where are they found?
What do they do?
They are polymer chains consisting mainly of mannose that form a matrix around fungal cells.
They stimulate innate immunity via Toll-like Receptors (TLR) and are targets for phagocytosis by mannose binding lectin
What is mannose binding lectin?
a scavenger receptor that binds to mannoproteins on fungal cells to target them for phagocytosis.
What are the two major types of fungi and how do they differ in morphology?
- Yeast- single celled organisms that asexually bud
2. Mould - grows as filamentous complexes
What is it called when a fungi can transition between yeast and mould?
What set of diseases does this type of fungi cause?
dimorphic fungi cause endemic mycoses because of their limited geographical distribution
What is the major factor that determines whether a dimorphic fungi will be a yeast or a mould?
Temperature.
Soil- mould
Body temp- yeast
What is an example of a dimorphic fungi?
histoplasma capsulatum
Where do most fungi live inside a host?
extracellularly although the notable exception is the histoplasma capsulatum which grows inside macrophages
What type of fungi is Candida?
Where are they found?
Yeast that colonize skin and mucousal surfaces of the body. They are opportunistic pathogens
Under what four situations can candida cause infection?
- when antibiotic treatment reduces normal bacteria and the yeast overgrows its normal area (yeast infection after UTI)
- after chemo when neutrophils are extremely low, candida can be a blood infection
- In advanced AIDS there is Candida overgrowth in the esophagus
- Other immunodeficiency disorders
Is Cryptococcus neoformans yeast, mould or dimorphic?
Yeast
How does cryptococcus neoformans spread?
What does it cause?
What are the two major forms of cryptococcus neoformans?
It is an air pathogen that can be inhaled and cause pneumonia.
There is a polysaccharide encapsulated form and an unencapsulated avirulent form.
Where is cryptococcus neoformans usually found? What happens if it diseminates?
It usually will form small lesions in the lungs. If it disseminates it will cause meningitis.
Is histoplasma capsulatum yeast, mould, or dimorphic?
Dimorphic (mould in soil and yeast after inhalation)
Where does histoplasma capsulatum proliferate?
It gets phagocytosed by alveolar macrophages and gets transported to lymph nodes. It is encapsulated though and resists killing in the macrophage.
What eventually controls histoplasma capsulatum?
Cell-mediated immunity
Is aspergillus mould, yeast or dimorphic?
Where is it located?
Who does it affect?
Mould that is opportunistic and normally contained in alveolar macrophages in the lungs.
It does not affect immunocompetent patients but will cause pneumonia in cancer patients with low neutrophil, count
What are the two types of parasites?
- protozoa- single-celled
2. worms- multi-celled
What are the four types of parasitic protozoa?
- ameba
- ciliates
- flagellates
- sporozoa
What is an example of an ameba protozoa and what does it causE?
Entamoeba histolytica lives in the intestines and causes ulcers
What are two examples of flagellate protozoa?
What do they cause?
- Plasmodium- malaria
2. Trypanosoma- African Sleeping Sickness
What does plasmodium cause?
Where does the parasite mature?
Malaria.
The parasite matures in RBC or liver cells. (although there are 5 known extracellular strains)
What is the other name for parasitic worms?
helminths
During a parasitic worms invasive phase, what does it do?
Eggs, larva or adult worms migrate through the vertebrae host
How are parasitic worms able to resist phagocytosis?
They are too large to be engulfed
What cell typically “attacks” parasitic worms?
eosinophils (although plasma cells and mast cells are present as well)
What is a major problem associated with parastic worms?
They cause chronic inflammation resulting in fibrosis
