Week 1: Infection as a Mechanism of Disease Flashcards
Why are infections still a major global concern despite advances in medicine?
Vaccine hesitancy
AMR (antimicrobial resistance)
Poor Healthcare
High threat pathogens (MDR-TB)
What are the key features of the bubonic plague?
Spread by bite from infected flea off rodent (vector borne)
Can be fatal within 24 hours
Causes painful swollen lymph nodes in groin and armpit
Can cause gangrene (lack of blood flow from narrowed/blocked/hardened arteries blackens tissue)
Highest rates in DRC, Madagascar and Peru
What pathogen causes bubonic plague?
Yersinia Pestis - zoonotic microbe with fleas as a vector
What are the key features of cholera?
Acute diarrhoeal disease
Fatal within hours
Endemic in many countries
Spread by contaminated food/water
What pathogen causes cholera?
Vibrio cholerae - bacteria
What is the pathogen responsible for the Spanish flu?
Influenza A virus
Common fever, sore throat and headache
Often developed pneumonia and died
What are the different types of microbes that can cause infection?
Bacteria
Viruses
Prions
Viroids
Fungi
Parasites
Helmiths
What are prions?
Give examples of diseases they cause
normal prion proteins to become abnormal and clump together causing brain damage
E.g CJD (mad cow disease), Kuru and FFI
What are viroids?
Examples?
Free RNA molecules (no viral coat)
Hepatitis D - which requires hepatitis B virus in order to replicate
What type of infection does Staphylococcus aureus cause?
Skin infections
What type of infection does E.Coli cause?
UTIs
Diahorreal
Neonatal meningitis
Pneumonia
What bacteria typically causes tonsilitis?
Streptococcus pyrogenes
What pathogen is normally responsible for a yeast infection?
Candida albicans - a fungi
Often caused by overuse of penicillin
What is a common parasite?
Malaria
What is a parasite?
Lives on or in a host, gets food at the expense of the host
What is a helminth?
What is a common example?
Cysticercosis - tape warm
Are a subset of intestinal macroparasites, typically cause abdominal pain, bloating and bloody stool
Define disease from a microbiology perspective
Suboptimal functioning of an organism due to infection or other causes
Define infection
When a foreign microbe invades and replicates in a host
What is an endogenously acquired infection?
Caused by microbes on or in us.
- alteration of microbiome by antibiotics
- commensal on skin enters by wound
What is an exogenously acquired infection?
Caused by pathogens in the external environment
- Food, air, water, objects, animal or insect bites
What are commensals?
A microorganisms that lives on/in a host, replicates. but does not interact with the host so rarely causes disease
What are some common examples of commensals?
Staphylococcus epidermis on the skin
Lactobacillus in the gut
Streptococcus salvarius - oral microbiome
What are opportunistic pathogens?
When microorganisms commonly found in the microbiome with causing disease, exploit compromised immunity to cause disease
What are some common opportunistic pathogens?
S, aureus if enters blood stream
Candida albicans - thrush in penicillin use
P.aeruginosa - serious infection in immunocompromised such as CF patients
Define apparent infection
An infection that causes symptoms
What is an acute infection?
Symptoms within 4 weeks (rapid) e.g Influenza
What is a subacute infection?
Slower onset of symptoms within4-12 weeks e.g endocarditis
What is a chronic infection?
Long duration before symptoms >12 weeks e.g TB
What is a recurrent infection?
Repeated episodes of infection e.g UTI, thursh
What is a local infection?
Affects only one body part/ara (tonsilitis)
What is a systemic infection?
Affects entire body system (sepsis)
What is an active infection?
When pathogen is replicating so able to spread to new hosts
What is a subclinical infection?
Active infection with no symptoms (asymptomatic or inapparent)
What is a latent infection?
Inactive or dormat - pathogen not replicating so unable to spread.
With reference to the host pathogen interaction explain how a pathogen can spread between individuals?
Microbe infects one host
Leaves host and enters another susceptible host
What are the three stages of the host-pathogen interaction?
Transmission
Spread
Infection
What are the different ways an infection can be transmitted?
Direct or indirect contact
respiratory
Contaminated food/water
Faecal oral route
Sexual transmission
Vertical transmission
Vectors
In the host pathogen interaction what is meant by the spread of the pathogen?
Pathogen infected host
Pathogen proliferates locally at site of infection
Invades other sites directly
Spreads indirectly by lymphatics, blood or nerves
How can a pathogen establish infection? (reference to the host pathogen interaction)
Pathogen expresses virulence factors to overcome host defences
Host defences are compromised
What is the circular link between evolution of hosts and pathogens?
Pathogen evolves to better invade host and escape immune defences
Host evolves more methods to detect the pathogen and defend against it
What are the different mechanisms a pathogen may evolve to exploit host resources and cause damage?
- Adhesion molecules
- Invasion methods
- Colonisation methods
- Immune evasion
How can pathogens exploit host resources to adhere to host?
Example
Express cell membrane Adhesion molecules allow initial contact to host cell receptors
Example: Shigella spp produces molecules to attract dendritic cells and spread within them
How can pathogens exploit host resources to better invade the host tissue?
Example
Evolved methods to cross host barriers such as mucus membranes and skin
N.meningitidis down regulates capsule to adhere to host and invade, then upregulates capsule to avoid phagocytosis once in the blood stream
How can pathogens exploit host resources to better colonise the host?
Example
Pathogens can multiply and form colonies within the host.
Staphylococcus Aureus, produces Staphyloccus protein A which binds to the constant regions of antibodies, prevents recognition of antibodies, so antibodies struggle to mediate the killing of S.aureus
How can pathogens exploit host resources to avoid immune detection?
Example
Pathogens may deploy stratergies to evade the host immune system or damage components of the system
M.Tuberculosis, hides in alveolar macrophages and secretes tyrosin phosphatase to prevent phagolyosomal fusion.
What are the host defence mechanisms against infection?
Barrier defenses
Innate Immunity
Adaptive Immunity
What pathogens are typically spread by needlesticks?
HIV and Hepatitis
What pathogens are typically spread by bites?
Lyme disease
Malaria
Rabies
What pathogens typically cause ciliary paralysis?
H.Influenza
What pathogens typically have acid resistant eggs?
Parasites
What pathogens are typically spread by local trauma?
STIs
HPV
What does the chain of infection show?
What are the different stages in the chain?
Chain of infection shows six points to how a pathogen spreads from person to person, hence six point where spread can be stopped.
Infectious microbe
Reservoir of infection
Portal of exit
Mechanism of transmission
portal of entry
Susceptible host
What is the most effective way to break to chain of infection?
Wash hands - stops mode of transmission
Define latency period
Time from initial contact of a pathogen and a host till pathogen starts replicating, hence becomes infectious.
What is the incubation period?
The time from initial contact of pathogen with a host to when symptoms start
What is the infectious period?
The time in which a pathogen can replicate within host hence can spread to a new host.
Specific incubation period of diseases
Table from pp.
Where is the human microbiota typicallt found?
Skin
Upper respiratory tract
Oral cavity
Intestine
Vaginal tract
Where is the human microbiota noticably reduced/absent?
Lower respiratory tract
Muscle tissue
Blood and tissue fluid
CSF
Meninges
Peritoneum
Pericardium
What problems can the human mictobiota cause if invade wrong location or become unbalanced?
Disease (opportunistic pathogens)
Allergies
inflammation
What are the benefits of the human microbiota?
Nutrient producing (E.coli and Vit K)
Competition for pathogens
Digestion of soluble fibre complex carbohydrates
Produce short chain fatty acids for energy
Educate immune system to detect harmless and pathogenic microbes
Produces enzymes humans do not make
How can E.coli found normally in the gut become pathogenic?
Exchange genes with other strains or E.coli to other types of bacteria
Gains virulence genes
What is symbiosis?
The interaction between two different species in close proximity to each other over a long period of time
What are the three types of symbiosis?
How are they different
Mutalism - both species benefit - E.coli
Commensalism - one benefits, other neutral - S epidermis
Parasitism - one benefits, other harmed - N meningitidis
What does -emia mean
Prescense of something
Bacteremia
Septecemia
What is the difference between a communicable and contagious disease?
Communicable disease spreads between individuals
Contagious disease - spreads easily between two individuals
What are fomites?
Inanimate objects capable of being intermediate in the indirect transition of an infectious disease
What is the difference between a biological animal vector and a mechanical animal vector?
Both cases the pathogen lives on the animal, and uses it to transfer to a susceptible host
Biological - infectious agent incubates in animal (replicates) as part of life cycle
Mechanical - does not incubate or grow on the vector only travels by it
