Infection Processes & Inflamation
What is a pathogen?
An agent that will cause a disease.
Name 5 infectious agents.
What are prions?
Protein particles that lack a genome (RNA or DNA).
Symptoms: transmissible neurodegenerative diseases.
e.g. mad cow disease
What is a virus?
A virus is not considered alive because it's not cellular and cannot reproduce on its own.
A virus consists of a bit of nucleic acid, wrapped in a protein coat called a capsid and in some cases, a membrane envelope.
What is a latent virus?
A virus that waits for the right opportunity to flourish once it's in your body, usually when your immune system is compromised.
What is an HIV virus?
HIV virus is a retrovirus that has a viral enzyme, reverse transcriptase, to translate viral RNA into host's DNA.
What is bacteria?
Bacteria are prokaryotes that have all the cellular mechanisms to self replicate without a host.
What are the 3 different types of shapes of bacteria?
- Cocci - spherical prokaryotic cells. Sometimes occur in chains called streptococci.
- Bacilli - rod-shaped prokaryotes. May also be threadlike, or filamentous.
- Spiral - prokaryotes are like corkscrew. Short and rigid prokaryotes are called spirilla. Longer, more flexible cells are called spirochetes.
What do prokaryotic cells have that humans don't? What does this do? What is this made of?
A cell wall.
Provides physical protection and prevents the cell wall from bursting in a hypotonic environment.
The cell wall is made of a polymer called peptidoglycan.
Other than the different shapes of bacteria, how else can you differentiate between the different types of bacteria in a lab?
By staining the cell walls of the bacteria with gram stain.
Gram-positive - simpler cell walls containing peptidoglycan, stains purple
Gram-negative - more complex with less peptigoglycan and more likely to cause disease, stains red
What are the growth parameters of bacteria?
What are fungi and what do they do?
Fungi are eukaryotes that secrete powerful enzymes to digest food externally, and acquire their nutrients by absorption.
What are two groups of fungi?
- Molds - any rapidly growing fungus that reproduces asexually by producing spores
- Yeasts - single-celled fungi that reproduce asexually by cell division or budding
What do these two fungi look like?
- Molds - cottony or powdery colonies
- Yeast - smooth, with a waxy or creamy texture colonies
How many different species are parasitic on animals?
What is the general term for a fungal infection?
What are some skin mycosis?
- Ringworm - circular red areas on the skin
- Athlete's foot - also caused by the ringworm fungus
- Vaginal yeast infections
- Deadly lung diseases
Why is fungi not susceptible to effects of penicillin-like antibiotics?
Unique rigid cell wall.
What are parasites? What do they do?
They are part of the animal kingdom.
Parasites derive their nutrition from a living host.
Name the different parasites.
- Protozoa - unicellular eukaryotes (e.g. can cause malaria, dysentery)
- Helminths - wormlike parasites (e.g. can cause tapeworm, trichinosis)
- Arthropods - vectors of infection (e.g. ticks and mosquitoes)
- Ectoparasites - infect external body surfaces causing local tissue damage and inflammation (e.g. mites, lice, fleas)
What is the chain of infection?
- Infectious agent
- Portal of exit
- Mode of transmission
- Portal of entry
- Susceptible host
What is a reservoir in the chain of infection?
A place where the pathogen can live, grow and reproduce. (e.g. water, food, soil, contaminated medical equipment)
What is a portal of exit in the chain of infection? Name some.
Path by which pathogen leaves the host.
- Skin, mucous membranes
- Reproductive tract
What are the modes of transmission in the chain of infection?
- Contact transmission - direct, indirect
- Vehicle transmission
- Airborne transmission
- Vector borne
What is the portal of entry in the chain of infection? Name some.
Path by which pathogen enters the host.
Same route as portal of exit.
- Penetration (e.g. indwelling devices such as catheters, IVs)
- Direct contact (e.g. sexually transmitted diseases, congenital infections, MRSA, VRE)
What does susceptibility depend on in a host in the chain of infection?
A person's level of resistance.
What are eukaryotes and prokaryotes? Differentiate between the two.
- Eukaryotes - fungi and parasites, have a membrane bound nucleus
- Prokaryotes - bacteria
Both are organisms capable of metabolism and replication.
What is epidemiology?
How it all started.
According to what are infectious diseases classified as?
- Portal of entry
- Disease course
- Site of infection
What are the different types of portal of entries of an infection?
- Ingestion - through oral cavity or GI tract
- Inhalation - respiratory tract
- Direct contact
What are the sources of an infection?
- Nosocomial - hospital acquired
- Community acquired - outside of the hospital
What are the different types of symptoms of an infection?
- Specific (e.g. respiratory distress in children)
- Nonspecific (e.g. fever)
What are the different stages of disease course of an infection? Describe them.
- Incubation period - pathogen begins active replication without producing symptoms in host
- Prodromal stage - initial appearance of symptoms
- Acute stage - maximum impact of infection due to rapid proliferation and spread of pathogen, symptoms are more specific
- Resolution stage - total elimination of pathogen without residual signs or symptoms
What is a differential diagnosis?
The determination of which two or more diseases with similar symptoms is the patient suffering from based on analysis and lab tests.
Why is a patient told to come back to see the doctor if the symptoms persist more than 7 days?
Because the patient is still in the beginning of the disease course. Sometimes the progression of illness is required before the correct diagnosis is made.
What are some diagnostic techniques of an infection?
- Culture (e.g. blood, skin)
- Serology - looks for changes in blood
- DNA or RNA sequencing
What are some diagnostic tests of an infection?
- C&S specimens - need to be collected before giving antibiotics
- CBC - monitor WBC
How does culture work? Which virus cannot be cultured?
Blood, skin is taken and placed in a controlled environment until growth of microorganism becomes detectable, then is identified by microscope or biochemical reactions.
Hepatitis B virus cannot be cultured.
How does serology work?
By measuring serum antibodies in host.
Direct antigen detection uses purified antibodies to detect antigens on pathogens which can be identified by different means such as fluorescent dyes.
How does DNA or RNA sequencing work?
Polymerase chain reaction (PCR).
- Two unique reagents - primers, heat-stable DNA
- Extremely sensitive, difficult or impossible to culture
- Rapid identification of pathogen to facilitate treatment
What are the treatments for an infection?
- Antimicrobial agents - antibacterial agents, antiviral agents
- Surgical interventions
What is the mechanism of antibiotic action?
- Interference with cell wall synthesis
- Inhibition of protein synthesis
- Interruption of nucleic acid synthesis
- Interference with normal metabolism
What are some resistance to antibiotics?
- Bacteria produce enzymes that inactivate antibiotics
- Genetic mutations alter antibiotic binding sites
- Alternative metabolic pathways bypass antibiotic activity
- Changes in filtration of cell wall that prevent access of antibiotic
What do antivirals do?
Not many because of damage to host cell reproduction. (e.g. H1N1 vaccine)
Antivirals target viral RNA or DNA synthesis.
What do antifungals do?
- Target cytoplasm of yeasts or molds and forms holes in them
What is the white blood cell response in an infection?
- Leukocytosis or increase in WBCs especially in bacterial infections (normal value 4000-10000 cells/microlitre)
- Neutrophils have a lifespan of 10 hours
- Immature neutrophils are produced with more severe infections
Describe what happens to white blood cells in different types of infections.
- Bacterial infections cause increase in neutrophils
- Parasitic or allergic reactions cause increase in eosinophils
- Viral infections decrease neutrophils and increase in lymphocytes
- Leukopenia (decrease in WBCs) may occur with overwhelming infection or impairment of WBC production
What are the different types of infection? Explain them.
- Local - limited to one area of the body (e.g. warmth, edema, pain)
- Systemic - affecting the entire body (e.g. fever, anorexia)
- Acute - clinical signs appear suddenly with sever manifestations and have a limited duration
- Chronic - infections are not totally destroyed and persist, with mild symptoms and possible acute episodes
What occurs in a severe bacterial infection such as sepsis? What does it cause?
Systemic inflammatory response - uncontrolled response with production and release of enormous quantities of cytokines.
Causes generalized vasodilation, increased vascular permeability, intravascular fluid loss, myocardial depression and circulatory shock.
What is affected in the body by temperature and how? How is the body temperature regulated? What is the core temperature? What is the thermostatic set point?
All biochemical processes are affected. Metabolic processes speed up or slow down depending whether the temperature is rising or falling.
Regulated by the thermoregulatory center in the hypothalamus.
Core temperature is 36.0 to 37.5 degrees Celcius.
Thermostatic set point is the level at which body temperature is regulated.
Describe the mechanisms of heat production.
- Metabolism is responsible for heat production in the body
- Sympathetic neurotransmitters (epinephrine and norepinephrine) are released to shift the body metabolism to heat production rather than energy generation
- Shivering initiated by hypothalamus and oscillating rhythmic tremor occurs through spinal reflex that controls muscle tone
- Shivering can produce a 3 to 5 time increase in body temperature
Describe the mechanism of heat loss.
- Most of body's heat is produced in the deep tissues and transferred to the body's surface to be released into the environment
- Pilomotor muscles of the skin contract to decrease surface area for heat loss
- Arteriovenous shunts under the skin's surface are opened to dissipate heat
- Blood flow in the arteriovenous shunts controlled by sympathetic nervous system
- Flow of blood volume influences transfer of heat to the body's surface
What is the cause of fever? How does it act?
What type of fever is it if it can't be treated with antipyretics and there's no sweating?
Fever is caused by pyrogens.
- Exogenous pyrogens can act indirectly and take several hours to produce fever
- Act on host cells, leukocytes and macrophages to produce endogenous pyrogens which act as fever producing mediators
- Endogenous pyrogens increase set point of hypothalamus through prostaglandin E2
Neurogenic fever. It originates from the central nervous system due to neuro trauma.
What is the purpose of fever?
- Signals presence of infection
- Small elevations enhance immune function
- Growth of many microorganisms inhibited by febrile temperatures
What are the four stages of febrile response? Describe them.
- Prodromal period - temperature begins to rise, non-specific symptoms, slight chill, fatigue, mild headache, slight aches and pains
- Chill stage - uncomfortable feeling of chill, shaking, vasoconstriction and piloerection. When thermostatic point of fever is reached, shivering ceases and feeling of warmth develops.
- Flush stage - cutaneous vasodilation occurs, where skin become warm and reddened
- Defervescence stage - marked by sweating
What are some manifestations of fever?