DISEASE E&E (Transmission 1) Flashcards
Taxonomic overview of pathogens and parasites
-viruses
-bacteria
Eukaryotes:
-protozoan
-fungi
-nematoda (roundworms)
-platyhelminthes (flatworms)
-arthropods
Helminths:
-nematoda
-platyhelminthes
Platyhelminthes:
-cestoda (tapeworms)
-trematoda (flukes)
Arthropods:
-mites
-ticks
-lice
-mosquitoes
-flies
Epidemiological models:
-distinguished between microparasites vs. microparasites
Microparasites:
-viruses, bacteria, protozoans
-acellular and unicellular
-small and replicate inside the host (numerous)
>don’t grow and develop
Macroparasites:
-multi-cellular
-helminths, arthropods
-grow and develop inside the host (don’t multiply)
*large and few
Microparasite models:
-modelled with SIR models
-model the dynamics by tracking NUMBER of susceptible, infected, and recovered HOSTS
-all infected individuals are the same (*percent of infected individuals is informative)
Probability of transmission (or recovery): microparasites
-does NOT depend on NUMBER of microparasites in host
Helminth worms: microparasitic models
-have different lifecycle stages: eggs, larvae, adults
-often aggregated in their hosts
Macroparasite models:
-must tack the developmental stages
*measure PARASITIC BURDEN
-percent of infected individuals is of limited value
Parasitic burden:
-the number of parasites per host
-influences transmission
Ex. host with 10 adult worms sheds more eggs than a host with 1 worm
Transmission: microparasite vs. macroparasite
-microparasite: direct, vector-borne
-macroparasite: direct, complex life cycles
Effect on host fitness: microparasite vs. macroparasite
-microparasite: mortality (IMMUNE system gets OVERWHELMED)
-macroparasite: morbidity
Steps in the parasite life-cycle:
- Finding a host
- Infection through the outer barrier and establishment in the host (Ex. skin)
- Growth or multiplication of the parasite inside the host
- Reproduction
- Development of transmission stages and transmission to the next host
Reproduction example:
-by exchange of genetic material between co-infecting strains
Lifecycle of rabies:
- Dog bit breaks the skin and dog saliva with virus contaminates the tissue
- Virus uses PNS as transport system to enter the CNS including the brain=preferred tissues
- Infection of CNS causes changes in behaviour that enhance virus transmission
- Rabies virus contaminates salivary glands
Rabies infection of CNS behaviour change:
-increased aggression and biting
Rabies contaminates salivary glands:
-so that the infected host will transmit the virus to a naïve host following a bite
Pathogen lifecycle determines:
-mode of transmission
-tissue tropism
-pathology
-disease symptoms
Respiratory pathogens:
-colonize the mucous membranes of the respiratory system
-cause symptoms like mucous production and coughing that facilitate pathogen transmission
GI pathogens:
-colonize the mucous membranes of the GI tract
-cause symptoms like diarrhea that facilitate pathogen transmission
Vector borne pathogens (VBPs):
-colonize the circulatory system to facilitate acquisition by blood-feeding arthropod vectors