Parasitology Flashcards
What is the definition of parasitism?
Organisms that use another organism, with deleterious but not lethal effects on the host
What is the difference between symbiosis and commensalism?
Symbiosis - positive for both
Commensalism - no negatives for the host
Describe convergent evolution in parasites
Parasites with different origins facing same selection pressures and challenges evolve to be similar
What 3 things does the host provide?
- Energy and nutrients
- Shelter
- Mobility and dissemination
What is immunomodulation?
Calibrating immune respones to make host more efficient
Hookworm -> reduces likelihood of autoimmune disease
How do parasites cause direct behaviour modification of hosts?
Switching genes on and off to favour their transmission
Eg Toxiplasma living in brain of rats to get inside cats
What does landscape of disgust cause?
Aniamls to move on from an infected area even if there is food there
What does coevolution cause?
Results in balance between host and parasite causing lower-cost immune response and decreased pathogenicity
“learn to live with each other”
What are 2 key attributes that decrease during coevolution?
Host immune response
Parasite virulence
Who has more opporutinty for genetic change?
Parasite - E.coli has new generation every 20 minutes
What is the red queen hypothesis?
A species must adapt not only for reproductive advantage, but because other organisms are also evolving
What are 2 ways hosts can get around the fast parasitic generation times?
- Sex -> multiple copies of genes so if parasite becomes resistant to phenotypic gene our next generation has a backup (parasite resistant phenotype)
- Adaptive immunity -> evolve in real time to new pathogens
What are two options for the host when dealing with parasites?
Resistance - coevolution between host and parasite
Tolerance - no immune response brought on
What is host switching?
Ability of a parasite to survive in a new host species
What is host adding?
Addition of extra hosts that expands distribution and aids transmission
Each additional host needs new set of parasite adaptations
What is a protist?
eukaryoite, single cell organism
Nuclei, organelles, mitochondria and can have flagella
What 2 lineages show a predisposition for evolving into parasites?
Apicomplexans and kinetoplastids
What are the 3 major groups of protists?
Metamonda
Apicomplexan
Kinetoplastida
What are the 3 types of Metamonada?
Diplomonads
Trichomonads
Histomonas
What are 2 types of diplomonads and what do they do?
Giardia - anaerobic, flagella, faecal oral transmission, prevents nutrient and water absorption in small intestine causing diorrhoea
Spironucleus + hexamita -> found in intestine of vertebrates - recognised disease of king parrots
What are 3 types of tritrichomonads?
Trichomonas gallinae
Tritrichomonas and tetratrichomonas
What is tritrichomonas gallinae? (where does it live, who does it infect, how does it transmit)
Metamonada
Pigeons and doves
Lives in upper GIT or repro tract
Oral-oral transmission (feeding young)
What do tritrichomonas and tetratrichomonas do?
Tritrichomonas foetus is veneral of bovine and causes diarrhoea in cats
Tetratrichomonas -> found in vertebrates as GIT parasites
What does histomonas Meleagridis do?
Intestinal parasites of poultry
Cause histomoniasis - invasion of caecal wall and liver
Larvae come out and eaten by earthworms, then poultry again
What defines a kinetoplastida?
Has insect vectors
Heteroxenous -> need multiple host species for lifecycle, veterbrates are intermediate hosts (sexual reproduction here)
What are two types of kinetoplastida?
Leishmania
Trypanosoma -> indirect life cycles with insect vectors
What are two groups of trypanosoma?
Salivarian - transmitted in saliva of insect
Stercorarian -> transmitted in faeces of haematophagous insect, excreted onto skin of host. penetrate wound and re-enter insect through blood meal
What defines an apicomplexan?
Complex life cycles with multiple stages involving animal hosts, vectors and intracellular life stages
Schizonts
What are 3 types of apicomplexans?
Piroplasms
Malarial parasites
Coccidians
What do piroplasms do? (definitive hosts, intermediate stage location, reproduction site)
Tick parasites are definitive host - sexual reproduction here
Intermediate stages in vertebrates (cattle) causing tick fever
Reproduce in blood/endothelium by clonal reproduction (schizonts)
What are vectors, definitive hosts and where does reproduction occur in Malarial parasites?
Vectors -> biting dipteran insects
Definitive host -> dipteran insects (sporogony here - asexual spore production)
Merogony in hepatocytes and blood/endothelial/macrophages
Coccidians - host, what do they cause, examples of species
Hepatozoon -> infect invertebrates and can infect vertebrates as intermediate hosts
One host species, blood diarrhoea
Neospora, toxoplamsa -> infects vertebrates without insect life stages
Toxoplasma, neospora life cycle type
Monoxenous or limited host range with no intermediate host
Reproduction of coccidians
- Oocytes shed in faeces
- Sporulate
- After ingestion, release sporozoites that invade intestinal epithelial cells
- Reproduce by binar y fission
- Cell ruptures + releases merozoites which infect other cells
Which host is sexual reprocution completed in?
definitive host
What is an adverant host?
Dead end host
What is a paratenic host?
Ends up in host, not ideal, but can develop in it
What is a metazoan?
Multicellular eukaroyte
What are the 3 groups of metazoans?
Nematodes - roundworms
Platyhelminths - flatworms
Arthropods
How many animals are nematodes?
80%
How are nematodes described?
Free-living
Microscopic to over 1m
Have GIT and anus
Feed on host or GIT nutrients
What are the nematode life stages?
Dioecious adults
Lay eggs or are ovoviviparous
Larvae hatch from eggs and moult through stages (L1, L2, L3)
Have to get to L3 to infect
What hosts do nematodes have?
Some have multiple intermediate hosts
Where do filarial nematodes live? Do they have vectors or intermediate hosts?
Pleural + peritoneal space, heart, joints
Produce larvae (microfilaria)
Intermediate hosts ingest these and transmit by biting another defintiive host
Insect vectors
What are 3 groups of platyhelminths?
Cestodes (tapeworms)
Trematodes (flukes)
Monogeneans
what is the structure of platyhelminths?
No body cavity, no GIT
No ciruclartory or respiratory organs
Flat -> allow nutrients to diffuse through
Dont feed on host, only GIT nutrients
Where is liver fluke found?
Cattle and sheep
Only grow where grass is wet (embryonate in water)
What are 2 types of arthropods?
Insects (flies, mosquito, lice)
Arachnids - ticks and mites
How are arthropods described and what do they cause?
Important vectors for other parasites
Associated with production losses, hypersensitivities (flee allergy dermatitis)
Tick paralysis, queensland itch, flystrike
What things can change to cause an emerging infectious disease?
New host demographic Changed distribution in space and time Changes in virulence Cycle of behaviour Increase in incidence, fatality
What are 6 emerging infectious diseases?
FMD Lumpy skin disease JEV Hendra African swine fever Highly pathogenic avian influenza
What is spillover?
Infectious disease reaches new species
Rarely leads to host switch
What are 7 steps of spillover?
- Need reservoir species in place and time where spillover occurs
2, Need infectious agent present - Host needs to be shedding
- Environmental contamination
- Survival outside host
- New host exposure
- Infectability of new host (right receptor for spike protein? can innate immunity stop it?)
What is spillback?
Spilt over to new host then back into reservoir again with new attributes
What is a reservoir?
Co-evolves with
What is R0?
Average number of individuals a person will infect
Cant survive long term if this is 1 or less than
Higher the value -> more infectious
