Parasitology Flashcards
(128 cards)
1
Q
Why is parasitism considered a successful survival strategy?
A
Over 50% of animals are parasites and they’ve evolved in nearly every phylum.
2
Q
If an organism is not a parasite, what is it?
A
A host.
3
Q
What percentage of animals are parasites?
A
Over 50%.
4
Q
What does DALY stand for?
A
Disability-Adjusted Life Year.
5
Q
What does a DALY measure?
A
The burden of disease using years lost to death and years lived with disability.
6
Q
What are the two components of DALY?
A
YLL (Years of Life Lost) and YLD (Years Lost to Disability).
7
Q
Which kingdoms are traditionally studied in parasitology?
A
Animalia and Protista.
8
Q
What are the four main groups of parasites?
A
Protozoa, parasitic worms, arthropods, and chordates.
9
Q
What does parasitology overlap with?
A
Bacteriology, virology, and mycology.
10
Q
What is symbiosis?
A
A relationship where two organisms live together with varying degrees of dependence.
11
Q
What is phoresis?
A
A symbiotic relationship where one organism travels with another without interaction or harm.
12
Q
Give an example of phoresis.
A
Fierasfer spp. on sea cucumbers.
13
Q
What is mutualism?
A
Both organisms benefit without harming each other.
Not obligatory but some are dependent
14
Q
Give an example of mutualism.
A
Cleaner wrasse removing parasites from moray eels.
15
Q
What is commensalism?
A
Only one organism benefits, the other is unaffected.
16
Q
Give an example of commensalism.
A
Hermit crab with sea anemones.
17
Q
What is parasitism?
A
One organism benefits at the expense of the host.
- causes harm
- obligatory dependence
18
Q
How can oxpeckers be both mutualistic and parasitic?
A
They eat ticks (mutualism) but also feed on wounds (parasitism).
19
Q
How are parasites distributed in host populations?
A
They are over-dispersed or clustered.
Parasites have a higher reproductive rate than hosts
20
Q
Can parasites kill their host?
A
Yes, pathogenicity varies.
21
Q
Why is a parasite’s reproductive rate higher than the host’s?
A
To increase transmission chances.
22
Q
What is an obligate parasite?
A
A parasite that requires a host to complete its life cycle.
23
Q
What is a facultative parasite?
A
An organism that can live independently but may become parasitic under certain conditions e.g if ingested or enters a wound
24
Q
What’s the difference between permanent and temporary parasites?
A
Permanent stay in the host, temporary leave after feeding.
25
What are ectoparasites?
Parasites that live on the surface of the host.
26
What are endoparasites?
Parasites that live inside the host.
27
What is a definitive host?
The host where the parasite reaches sexual maturity.
28
What is an intermediate host?
A host where the parasite undergoes development but does not reach sexual maturity.
29
What is a paratenic host?
A host that carries the parasite without development.
- still infects but doesn't develop
30
What is a reservoir host?
A host that harbours a parasite and can transmit it to humans.
- the disease = zoonosis
31
What is the urban cycle?
Transmission involving domestic animals and humans.
32
What is the sylvatic cycle?
Transmission involving wild animals.
33
What is a mechanical vector?
A vector that carries the parasite without any development.
34
What is a biological vector?
A vector in which the parasite develops or multiplies.
35
How do microparasites and macroparasites differ in reproduction?
Microparasites reproduce at a high rate; macroparasites reproduce slowly.
36
How do infections differ between micro and macroparasites?
Microparasites cause epidemics (not always present); macroparasites cause chronic infections (endemic, continuous presence).
37
How does immunity differ between micro and macroparasites?
Microparasites trigger strong immunity; macroparasites trigger weak immunity.
38
How is transmission different in micro vs macroparasites?
Microparasites spread directly or via vectors, no transmission stages; macroparasites use life cycle/ transmission stages e.g larval stage.
39
What is a direct life cycle?
A life cycle that uses one host.
40
Give an example of a parasite with a direct life cycle.
Monogenean fish parasites.
41
What is an indirect life cycle?
A life cycle involving more than one host.
42
Give an example of a parasite with an indirect life cycle.
Schistosoma mansoni.
43
What is haemozoin?
A toxic waste product from malaria parasites that causes fever.
44
What triggers malaria parasite reproduction?
Synchronous bursting of red blood cells.
- have periods of wellness and then sickness due to bursting of rbcs and parasite infecting
45
What are the 2 cycles of malaria?
1. pre-erythrocytic cycle (liver)
- asexual
2. post-erythrocytic cycle (blood)
- gamete formation
- haemozin waste produced and released into blood
- rbcs get packed with parasite and lyse to release more of it
46
Name four types of microparasites.
Prions, viruses, bacteria, protozoa.
47
Name three types of macroparasites.
Platyhelminths, nematodes, arthropods.
48
Which monogenean platyhelminth (flat worm) infects flatfish?
Entobdella soleae.
49
Macroparasite Entobdella soleae details
Macroparasite in fish
Ectoparasite which moves from fish to fish with transmission stages
- the adult feeding on the outside of the fish produced pyramidal shaped eggs which hatch after 3 weeks into pre-living larva
- repeat with new hosts
- direct life cycle - only 1 host
- kills the fish
50
Name two trematodes.
Schistosoma, Fasciola.
51
Microparasite Schistosomiasis details
Caused by Trematoda platyhelminth (flat worm)
- infects humans in liver and colon
- definitive host (parasite reaches sexual maturity on host)
- dimorphic - male and female at same time
- mate in blood vessels and eggs are released in faeces then hatch in water
- first larval stage intermediate host is a snail and then goes back into humans from water (2nd larval stage)
- indirect life cycle bc has more than one host
- has to have a vertebrate host and a snail host
52
Name two cestodes.
Taenia, Echinococcus.
53
Name two nematodes.
Ascaris, Trichinella.
54
What arthropods act as parasites?
Lice, fleas, mites, and ticks.
55
What is Trichinella spiralis?
A nematode that causes Trichinosis.
56
What are the two transmission cycles of Trichinella spiralis?
Urban (pigs/rats) and sylvatic (wild carnivores).
57
Where do Trichinella larvae encyst?
In the muscle tissue, they take over and create nurse cells in gut
58
What type of parasite is Trichinella spiralis?
Endoparasite (in gut), obligate, permanent, macroparasite.
59
What type of host is a human in Trichinella infection?
Definitive and reservoir host.
60
What type of life cycle does Trichinella spiralis have?
Direct life cycle.
- cycles between same species
61
What is the key difference between epidemic and endemic diseases?
Epidemic rises and falls quickly (micro); endemic persists over time (macro).
62
What is the most common lifestyle on Earth?
Parasitism – approximately 50% of species are parasitic.
63
What are three major benefits parasites get from hosts?
Habitat, mobility, and energy efficiency.
64
What are the four key challenges parasites face?
Spatial gaps, temporal gaps, immune defenses, host evolution.
65
What is the body plan of Platyhelminthes?
Acoelomate (no body cavity), solid body, tegument instead of a cuticle.
- monogeneans, digeneans and cestodes
66
What is the body plan of Nematodes?
Pseudocoelomate with a cuticle and fluid-filled cavity.
- nematodes
67
What are the key steps in a parasite's life cycle?
Find host, enter host, locate site, survive, reproduce, disperse.
68
How did parasitism likely evolve?
From free-living forms through phoresis and facultative parasitism to obligate parasitism.
69
How many times did parasitism evolve in nematodes?
At least 18 times independently across different host groups.
70
Origins of platyhelminths
Freeliving, then became facultative parasites then obligate ectoparasites or endoparasites by accidental ingestion then accumulated more hosts
71
What is a benefit of complex life cycles in parasites?
They offer more reproductive niches and increased transmission opportunities.
72
What are three influences on host-parasite evolution?
Co-evolution with host, host-switching, biogeography - physical separation like continental drift.
73
Name the oldest known parasite traces.
Traces in trilobites dating to 570 million years ago.
74
What organism is considered the oldest symbiont?
Mitochondria – evolved from a parasitic α-proteobacterium.
- rickettsia is closest relative to the proto-mitochondria
75
How do Symsagittifera roscoffensis flatworms survive?
By ingesting algal chloroplasts for photosynthesis (kleptoplasty) to get nutrients
- symbiosis
76
What is the Red Queen Hypothesis?
Hosts and parasites must constantly evolve to maintain their relationship and prevent extinction
77
What evidence supports Red Queen dynamics?
Oscillating allele frequencies in host populations under parasite pressure.
78
What other pressures influence parasite evolution?
Environmental conditions, host evolution, and control measures like drugs.
79
Can parasites have beneficial effects?
Yes – some modulate the immune system or treat diseases like Crohn’s.
80
How are maggots used medicinally?
They clean wounds and secrete antimicrobial compounds; genetically modified ones produce growth factors.
81
What parasite is explored for immune modulation?
Whipworm (Trichuris suis) – used in Crohn’s disease research.
82
What hypothesis links parasites to allergy suppression?
Hygiene hypothesis – suggests helminth exposure reduces allergy risk.
83
What is the function of parasite attachment structures?
To anchor the parasite to the host and resist dislodgement.
84
What structure do Monogeneans use to attach to hosts?
A posterior opisthaptor with hooks, clamps, and suckers.
85
What structures do Digeneans use for attachment?
Oral and ventral suckers.
86
What is a scolex?
The anterior attachment organ in cestodes, often with hooks or suckers.
- embeds into gut wall to absorb nutrients directly
87
What is the trade-off between complex and simple parasite attachment?
Complex structures provide strong anchorage but reduce mobility.
88
How do microparasites get nutrition?
Absorb nutrients via cell surface
89
Name four feeding strategies of macroparasites.
1. Surface browsing e.g entobdella
2. blood feeding e.g schistosoma
3. bulk tissue feeding
4. absorption across the body wall e.g cestodes
90
What is surface browsing?
Parasite e.g entobdella moves over surface of fish and eats epithelial and surface cells
- also causes damage from opisthahaptor
91
What does neoteny mean?
Reaches sexual maturity but still retains larval characteristics
92
What issues do blood-feeding parasites face?
Coagulation - clotting agents,
toxicity - waste products,
vitamin depletion - lack of B vitamins,
and immune exposure.
93
How do parasites handle coagulation?
By producing anticoagulants to prevent clotting.
94
What morphological adaptations do parasites have?
1. increase body surface area
2. modified mouthparts
95
What physiological and behavioural adaptations do parasites have?
1. Symbiotic micro-organisms to counteract vit B deficiency e.g human body louse
2. Production of anticoagulants e.g nematodes
3. Release of endogenous (parasite) enzymes and binding of exogenous (host) enzymes
4. Acidification of hosts gut through secretion of H+
5. Migration along the hosts gut
96
What is antigenic variation?
A process by which parasites change surface proteins to evade immune detection.
97
What is antigen disguise?
Parasites coat themselves with host-like molecules to avoid detection.
98
What is cross immunity?
immunity between species
99
What is a susceptible host?
Cannot eliminate the parasite
100
What is a resistant host?
Prevents establishment and survival of parasite
101
What is concomitant immunity?
Host is protected from reinfection but carries the existing parasite as not affected by immune response
e.g schistosomes
102
What is premunition?
Partial resistance allowing low-level parasite persistence and reproduction e.g malaria
103
How do parasites evade the hosts immune response?
1. inaccessibility by hiding in host tissue or in macrophages
2. antigen mimicry or disguise - host like antigens bound to the surface of the parasite
3. antigen polymorphism - antigen changes shape if immune system starts to recognise it
4. immunomodulation - alters host immune response like inhibiting wbc activation or destroying cytokines
5. anticomplementary activity - stops complement system
104
are parasites r-strategists or k-strategists?
r-strategists - high reproductive rate
105
What is hermaphrodites?
Both sexes in same individual
106
What is sequential hermaphrodites?
One sex matures before other
107
What is the benefit of hermaphroditism in parasites?
Ensures reproduction even when mates are scarce.
Increases egg output
Potential for self-fertilisation
108
What is protandry?
A form of sequential hermaphroditism where male organs mature before female organs.
109
What is protogyny?
Female organs develop before male
110
What are oviparous parasites?
Parasites that lay eggs which develop outside the body.
111
What are viviparous parasites?
Parasites that give birth to live young without egg laying.
112
What are ovoviviparous parasites?
Parasites whose eggs hatch inside the parent before birth.
113
What is parthenogenesis?
Asexual reproduction from unfertilized eggs.
114
How does Polystoma integerrimum synchronize with its host?
It times reproduction with frog spawning and can mature on tadpole gills.
Switches dependent on the age of the tadpole it attaches to to increase success of parasite transmission
- it is a neotenic parasite
- feeds on blood
- has a dimorphic life cycle
115
4 methods of transmission in parasites?
1. Contact transfer
2. Ingestion of intermediate and/or paratenic hosts
3. Release of egg/spores/cysts - survive outside host
4. Free living larvae
116
What is contact transmission in parasites?
Direct movement from one host to another, e.g., via skin contact.
- ectoparasite
- opisthaptors can be used to jump from fish to fish and hold on
117
What is intermediate host ingestion?
Parasites reach their definitive host when the intermediate host is consumed.
- passive when ingested
- then becomes active which results in transmission
118
How does Dicrocoelium dendriticum manipulate ants?
Infected ants cling to grass tips to be eaten by grazing animals.
119
How does Toxoplasma gondii alter rodent behavior?
Infected rodents lose fear of cats, increasing predation.
- is a reservoir host
- reproduces in cats
- definitive host - only cats
120
How is Toxoplasma transmitted to humans?
Via undercooked meat, contaminated water, cat feces, or placental transfer.
121
What does Toxoplasma gondii produce that may affect human behavior?
Tyrosine hydroxylase, which increases dopamine levels.
Makes females nicer but opposite for males
More likely to get into car crashes and develop schizophrenia
122
Toxoplasma transmission summary
Horizontal: faeces, cat, humans
Vertical: through placenta
123
What types of taxis can free-living larvae show?
- Phototaxis ( light)
- Geotaxis (gravity)
- Rheotaxis (water currents)
- Chemotaxis (chemicals) e.g entobdella
124
What is phototaxis in parasites?
Movement toward or away from light, used by larvae to find hosts.
125
What is rheotaxis?
Movement in response to water currents, aiding host location.
126
What is chemotaxis?
Movement in response to chemical stimuli to locate a host.
127
Why do parasites produce large numbers of offspring?
To increase the chance of transmission to new hosts.
128
List five traits of a successful parasite.
Strong attachment, efficient feeding, immune evasion, high reproduction, and effective transmission.
