PArasitology

Question 1

what are parasites

Answer 1

disadvantageous to the host, one-way relationship
very diverse
can be divided into macro and micro parasites - visible or not to the eye

Question 2

what are microparasites

Answer 2

small, multiply inside the host, cause transient infection, result in sterile immunity
eg virus, ebola, bacteria, salmonella. Protozoa, giardia, covid-19

Question 3

what are macroparasites?

Answer 3

large, don’t multiply inside the host, cause chronic infection, concomitant community, vary in length from micrometres to many metres
eg helminths, ectoparasites, ascaris, ticks

Question 4

what is concomitant immunity?

Answer 4

when a parasite inside a host gives a degree of protection against superinfection - results in chronic infection and density dependent disease

Question 5

eradication of malaria

Answer 5

bill and melinda gates challenged world to eradicate in their lifetime
1960s - WHO wanted to eradicate in 10 yers
semi-effective vaccine but still major cause of infant mortality and most deadly parasitic infection

Question 6

why are parasites difficult to control?

Answer 6

diverse - present in every branch of evolutionary tree
many are eukaryotic - sexual stages allow chromosome mixing, much bigger genome, similarities to host metabolism and structure
large and complex - difficult to find suitable target molecule out of thousands
complex life cycles - hard to regulate from outside, obligate parasites
immune evasion - parasite and host proteins have structural overlap

Question 7

what are obligate parasites?

Answer 7

have to go through a certain mammalian host and invertebrate vector to complete their life cycle

Question 8

how are parasites adapted to live in their host?

Answer 8

survive phagocytosis by host
some adapted to survival in macrophages
some vary their antigens preventing host to develop effective immunity - chronic invasion
some hide in host cells in immunopriveledged sites eg muscle eye brain (immune system doesnt reach)

Question 9

what are amoebas?

Answer 9

entamoeba - human pathogen
naegleria - soil amoeba - opportunistic human parasite

Question 10

what is entamoeba?

Answer 10

human pathogen
directly transmitted host to host
causes gut infection - amoebic dysentry
can escape into liver and cause fatal liver disease

Question 11

what is the life cycle of entamoeba?

Answer 11

cyst ingested with faecally contaminated food/water
excyst in small intestine -> trophozoites reproduce in large intestine
may invade large intestine lining -> symptoms - diarrheoa, dysentry
- cysts pass in faeces
- or trophozoites invade blood vessels in large intestine transported around body - fatal unless treated with metronidazole

Question 12

how is etamoeba adapted to colonise human gut tissue?

Answer 12

upregulated adhesion
increased phagocytosis
proteins associated with virulence identifies:
- lectin - mediates adherence to epithelial cells
- pore-forming peptide lysing host cells
- secreted proteases degrading host tissues

Question 13

what is naegleria? naegleria fowleri

Answer 13

facultative pathogen
lives for many generations without infecting host
present in soil and warm water all over globe
enters nose during swimming in warm water
attaches to olfactory nerves and enters brain by locomotion and destruction of neurones
almost always fatal
- becoming more common with global warming

Question 14

why did the Bath baths shut down in 1979?

Answer 14

girl in Bath died due to meningitis-related disease - naegleria fowleri
soil contamination

Question 15

what are the advantages of a parasitic lifestyle?

Answer 15

unlimited food - host supplies all the nutrients needed
protection - from other predators
transportation - travel further inside the host than it would without

Question 16

what are the challenges of a parasitic lifestyle?

Answer 16

immune evasion - need to get around host immune system
removal - systems in host will try to remove parasite
transmission - movement in between hosts to complete life cycle

Question 17

what are some examples of parasites avoiding removal?

Answer 17

giardia - concave shape acts as suction to host’s epithelial cells in intestine
malaria - changes shape of red blood cells but avoid filtering removal by adherence of RBCs to capillary wall
hookworm - teeth clamp onto intestinal tract
lice - attach themselves to hair

Question 18

how are parasites transmitted?

Answer 18

direct - host to host
indirect - intermediate host (vector)

Question 19

what is trichomonas?

Answer 19

sexually transmitted
inhabits urogenital tract
has flagella
infection effects 1.3% US women, 13% african american women
6000 cases per year UK
- example of directly transmitted parasite

Question 20

what are some examples of synchronised host and parasite life-cycles? - direct

Answer 20

Nematodirus battus - delayed hatching until spring when susceptible lambs begin grazing
Hookworm - synchronises with host environment
dormant in host during dry season - migrates to intestine matures during rainy season - lay eggs. Eggs in faeces hatch - larvae survive much better in rainy season
- 1000mil people in trop and subtrop regions
Trichenella
- pigs
- embeds in muscle and forms rings
- passage by carnivorism

Question 21

what are some examples of indirect life cycles?

Answer 21

schistosomes
- infect humans and snails
Toxoplasma gondii
- complete life cycle in cats where sexual stages occur, cause an infection in many animals

Question 22

what are some examples of how parasites effect hosts?

Answer 22

malaria - effect host through the genetic selection of sickle cell anaemia
- anopheles mosquito vector increased feeding when infected
Toxoplasma gondii - infected rats become attracted to cat odours - enhance transmission - cat required for life cycle completion
Trypanosome - tsetse fly vector more active when infected
Gypsy moth - when infected with virus gene, climb to top of tree, virus finishes infection burst over tree infecting other caterpillars
isopods - turned from clear to more visible so more likely to be eaten by next host

Question 23

how are parasites classified?

Answer 23

protozoa: 4 groups
worms: flatworms, roundworms
parasitic arthropods: fleas, flies, lice, mites

Question 24

what are the 4 groups of protozoan parasites?

Answer 24

Amoeboid protozoa: Entamoeba histolytica, Giardia lamblia
Flagellates: Trypanosomes, Trichomonas vaginalis
Ciliated: Balantidium coli
Sporozoa: Plasmodium

Question 25

what are zoonosis?

Answer 25

disease transmissible between animals and humans

Question 26

what are examples of zoonosis?

Answer 26

toxoplasma, swine flu, avian flu, COVID-19, ebola, Giardia, Trypanosomes

Question 27

what is ebola?

Answer 27

zoonotic parasite, virus
minus single stranded RNA

Question 28

what pathology does ebola infection cause?

Answer 28

very dangerous viral infection in humans 90% fatal
- low incidence but high fatality rate
rapidly leads to death - poorly evolved
ability to turn internal organs to soup
symptoms appear rapidly 2-21 days high fever, chill, muscle pain. Later vominting, diarrhoea, chest pain, cough - often confused with malaria, typhoid fever

Question 29

how is ebola transmitted? (initially and now)

Answer 29

unclear how first transmitted to humans - maybe fruit bats sold in markets in western Africa
not transmitted until late stage when bodily fluids carry virus - early isolation prevents
direct transmission in funeral ceremonies - touching body - transmission

Question 30

how does ebola behave inside the body?

Answer 30

single-stranded RNA bound up by proteins
coded RNA fuses with cell membrane - allows release of viral RNA into host cell cytosol
dependent RNA polymerase converts strand into coding (+ve) strand
some -ve RNA becomes template for more
packaged, released, lyses cell in process

Question 31

how is ebola being controlled? whats its history?

Answer 31

first recorded outbreak 1976
2014 - major outbreak in western africa contained:
- banning corpse transportation, bat meat regulation, nationwide test centres, health workers trained in ebola containment, support for isolated patients, anti-stigmatization campaign, whole genome sequencing for surveillance - nanopore DNA sequencing
recombinant ebola vaccine found effective - keeps numbers down
2018 - ebola crisis in DRC hard to control during civil war
2019 - WHO supported ebola vaccine

Question 32

How does COVID-19 work inside the body?

Answer 32

(+)ssRNA virus
binds to receptors on cell surface - taken into vesicle inside cell
uncoated, releases RNA, directly translated to proteins
proteins passed through golgi bodies, repackages
RNA replicated several times also
Virus released

Question 33

how was COVID-19 first transmitted to humans?

Answer 33

unknown intermediate host but can infect pangolins, cats, ferrets, rhesus macaques, hamsters, farmed mink
likely passed through intermediate animal and evolving before infecting humans
similar virus to SARS-CoV-2 found in bats - suspected host
- determined by sequencing virus RNA

Question 34

what is Giardia?

Answer 34

single-celled flagellated protozoa
suction cup - sticks to inside of intestinal tract where it resides
takes nutrients directly through its plasma membrane
comes out in faeces
many species
considered to be an ancient parasite form
considered an archaeozoa

Question 35

what is the life cycle of Giardia?

Answer 35

cyst (7-14 micrometres) resistant transmission stage
cysts picked up from environment - excyst and trophozoites colonise small intestine
trophozoites (10-15 micrometres, four flagella pairs, two nuclei one dormant, ventral suction disc) divide in gut causing infection
cysts pass in faeces - can pass through different reservoirs including beavers

Question 36

does Giardia have mitochondria?

Answer 36

no - but it is mitochondrial
it has a mitochondria-like organelle - mitosomes
involved in iron-sulphur synthesis - so parasite can take in iron
still anaerobic

Question 37

what is giardia pathology?

Answer 37

although majority of infections are asymptomatic
Giardiasis - ‘beaver fever’
usually self-limiting lasting 5-20 days
significant infection can occur in infants, young mammals and immunocompromised individuals
symptoms don’t always coincide with excretion of cysts

Question 38

is giardia a common infection?

Answer 38

yes
humans 1.2-32%
dogs 1.6-53%
sheep 7-35.6%
beaver 9.2%-18%
wild rat 10-98%

Question 39

which giardia species infect which species?

Answer 39

G. duodenalis (G. intestalinis, G. lamblia) - mammals, humans, domestic animals, pets
G. muris - mice
G. microti - voles, muskrats
G. psicatti - budgerigars
G. ardeae - heron, ibis
G. argilis - frogs
- all present a zoonotic potential

Question 40

what is the prevalence of giardia in the USA?

Answer 40

2.5 million cases per year
very high incidence
1000 conc in swimming pool
10 minimum needed to contract giardiasis

Question 41

what are Trypanosomes?

Answer 41

Trypansomes (technically called kineoplastids)
zoonotic parasite
several species eg T. cruzi
kinetoplast at terminal end containing nucleic acid
flagellum starting at terminal end near kinetoplast and running along edge, moves in corkscrew fashion

Question 42

what is Trypanosoma cruzi?

Answer 42

found particularly in new world in south america
originally though to be a rare disease
- studies suggest infection rate 60%`