Infectious agents around the world Flashcards
What is an infectious agent?
Agent that can replicate within or on another organism whose progeny can spread onward to new hosts
What causes the manifestation of disease pathology?
Invader fights host
What are 8 types of infectious agents?
Bacteria
Viruses
Fungi
Flatworms
Roundworms
Arthropods
Proctists
Prions
Characteristics of bacteria
Prokaryotic
Not all species are harmful - can reside as helpful commensals on body
Whether helpful/beneficial depends on time and place
Only agent susceptible to antibiotics
Characteristics of fungi
Significant infectious agents in immunocompromised patients
Characteristics of protozoa
Single-celled eukaryotes
All body compartments - spectrum of disease
Infect people intracellularly and extracellularly
Characteristics of roundworms
Nematodes
Broad class - thousands of species
50% of species = parasitic
Characteristics of flatworms
Large, segmented, highly organised invertebrates
Some reside parasitically within human host - host needed for transmission
Characteristics of prions
Infectious protein
Not alive
Replicates to cause pathology
How do prions cause pathology?
Converts normal proteins into prions
Causes protein misfoding of normal cellular proteins
Example of bacteria
E. Coli
Example of fungus
Candida
Example of virus
Herpes
Example of roundworm
C. Elegans
Example of flatworm
Tapeworm
Fluke
Example of prion
Mad cow disease
Example of proctist
Malaria
Leishmania
Trichomonas
Toxoplasma
Example of arthropods
Head louse
Mite
What three terms refer to frequency of infectious agents in humans?
Endemic
Epidemic
Pandemic
What is an endemic?
Persistently present in population
What is an epidemic?
Increase in frequency of disease in population
What is a pandemic?
Global epidemic
What are animal reservoirs?
In animal reservoirs, pathogens can be maintained permanently
Infection can be trasmitted to humans
Pathogen does not normallyb cause disease in animal host
What is an example of an infectious agent arising from animal reservoir?
Influenza
What does the term epizootic mean?
Animal epidemic
What does the term enzootic mean?
Animal endemic
What does the term zoonotic mean?
Interspecies transmission of infectious agents
From animal to human
60% of human pathogens are zoonoses
Animal transmitting the disease = vector
What is the name given to the process by which an infectious agent from humans infects animals?
Antroponosis
What percentage of human pathogens are zoonoses?
60%
Why do zoonotic infections happen?
Infection may come from:
- natural reservoir
- one-off accidental inter-species jump
What is commensalism?
Two organisms live together and confer benefits to host/ bacteria
What is the dictionary definition of commensalism?
The two organisms don’t benefit nor lose
What is colonization?
Invasion and multiplication of organisms that are not commensal
What does the term persistence/latency refer to?
State of infection where host cannot get rid of the pathogen
What is the difference between latency and persistance?
Latency = no symptoms
Persistance = symptoms
What does the term virulence/pathogenicity mean?
Ability to harm host
Determined by genetic factors of pathogen
Proteins encoded by genes = virulence factors
What are examples of virulence factors?
How well pathogen spreads
How well pathogen attaches to host cells
How well pathogen replicates
How well pathogen invades
What does the term infectivity mean?
Ability to spread to new host and establish infection
What determines the infectivity of a pathogen?
Ability to survive outside host
Receptors pathogen bears to gain foothold into new host
What is the incubation period of an infectious agent?
Time between establishment of infection and physical manifestation of the disease
Describe the concept of cat and mouse evolution of pathogens
Pathogen and host constantly evolve in response to another
Exert selecton pressure
- Pathogen becomes virulent
- Host responds by mutating defences
- Pathogen counter-responds by overcoming defences
The higher the population density, the easier the spread of infection
TRUE or FALSE
TRUE
Does host resistance and immunity vary between individuals?
Yes
Hosts have varying susceptibility to pathogens depending on
Genes and relative immnunity
Example of a host having increased immunity to a pathogen
Sickle cell anaemia sufferers
Resistant to malaria
Can commensal microbes cause disease?
Yes
Immune impairment or alterations in host microbial flora can cause disease by commensal microbes
What damage can arise when trying to eradicate pathogenic infection?
Damage may be caused by host-mediated or pathogen-mediated mechanisms
Can trigger autoimmunity
May lead to irreversible damage
What happens if host is unable to eradicate infection?
Acquisition of microbe can be followed by colonozation
Colonization leads to disease
State of colonization leads to persistance
Persistent infections may reactivate and cause disease
If sufficient damage is incurred due to host-microbe interaction, death ensues
What are the two ways by which the host can eliminate pathogen?
Physical defenses
Immune mechanisms
