Parasite biology Flashcards
What is the intermediate host of a digenean?
usually a snail
How do we know that parasites have specialised mechanisms to avoid immune responses of hosts?
That helminth infections are typically long-lived (i.e. chronic) infections, tells us that hosts typically are unable to remove parasites
What is the definitive / intermediate host of toxoplasma gondii?
cat
intermediate: bird, rodent, human
what is the lifecycle of Leucochloridium paradoxum?
- Bird definitive host - eggs in faeces.
- Snail eats bird faeces.
- Sporocysts have coloured spots and bands - they infect the eye stalks of snail host and pulsate.
- Snails can’t see properly í can’t hide from predators (can’t sense daylight so doesn’t hide under leaves + sometimes actually crawl into the view of the birds (which they never do w/out)
- The pulsating, brightly coloured eyestalks are conspicuous and resemble caterpillars so attract bird predators.
No release of cercaria: the snail is just predated with it inside it.
Evolution of nematode parasitism?
It is hypothesised that in the evolution of animal parasitism by nematodes, that nematodes developed increasingly intimate associations with hosts (evolved at least 5 times, more likely 12 times)
Heritability of infection traits (Ascaris infection): How much of that variation is due to genetic effects and what does that imply?
c. 40% of worm load variation is host genetics
Given that there is a significant effects of host genotype on Ascaris infection, this implies that Ascaris is a strong selective force on the host population.
what is an apicoplast? what does it do?
relict chloroplast(not fully functioning as in plants), present in plasmodium o Enzyme reactions: Chloroplast-type fatty acid biosynthesis o Possible drug target - could attack it using weedkillers?
How is anisakis acquired?
by eating raw fish containing larvae of anisakid nematodes such as anisakis complex or pseudoterranova decipiens.
Why are schistosomes an exception to typical digenean?
- Exception to being hermaphrodite: M+ F worms, copulating all their lives: F lives within a groove in the M body.
What is the differences between endo + ectoparasites?
end live in internal organs / tissues of host / ecto parasite: out of the body
Why is toxoplasma dangerous for pregnant women?
: can pass through the placenta to the developing embryo - you will be tested to see if you have antibodies for toxoplasma to see if already infected or not: if you get infected in pregnancy, you are mildly ill but developing foetus has severe abnormalities.
what type of lifecycle and transmission does Entamoeba have?
o Direct lifecycle: faeco-oral transmission - transmitted by cysts (thick wall, environmentally resistant)
Some facts about free living stages (in the environment, outside of host) and example
o Large numbers
o Environment resistant
o Targeted for (new) host acquisition
ASCARIS
o Large round worm
o Nematode
o 1 host lifecycle with free living larval stage
o Gastro-intestinal
Eggs require time external to the host before becoming infective. This process is temperature dependent such that, for example, with Ascaris infection of pigs, there is a peak of infective eggs present in the spring and summer, coinciding with the availability of Ascaris-naive piglets.
Ascaris eggs are resistant to desiccation and freezing and most disinfectants.
How does Dicrocoelium dendriticum modify the behaviour of its host?
host = sheep; Metacercariae encyst preferentially in ant neural ganglion so when temperature drops at night, walks up blades of grass + latches onto them with jaws ( infected ants cannot open jaws + get stuck on blades of grass)
- Normally ants go back to their nest at night.
- Parasite is in the NS controlling it’s BHV.
2 way of prasite-induced harm
o Parasites take nutrients / energy from hots in some way (competing for food with host/feeding off the host; Energetic cost of the immune response; Immunopathology)
o Intensity dependent (for marcoparasites especially, such as nematodes)
how does Plasmodium merozoite invade the red blood cell?
o Parasite binds & reorientates
o Enters into a parasitophorous vacuole, eeleasing proteins from apical organelles
o Parasite surface proteins are shed by proteases. Takes 30 seconds.
What is an example of a viviparous monogean?
Gyrodactylus “Russian doll parasite” - in any individual worm (hermaphrodite), you can see developing daughter.
What is the role of apical complex?
” Recognition. - of cell type to invade (RBC/ intestinal / nucleated cell) - cell to cell communication
“ Orientation. - the infective cell has to orient with apical complex forward to it can invade
“ Invasion - secreting proteases +structural proteins.
microparasites.
what is Apicomplexa? what is characteristic about them?
Parasitic Protozoa , all animal parasites
intracellular stages - get inside cells to survive (Characteristic of apicomplexan)
have apical complex.
Nematodes with direct transmission cycles
o Necator, Ancylostoma - human hookworms
o Ascaris lumbricoides, Toxocara canis - roundworms
o Enterobius - pinworm
What parasites can you get from eating undercooked food?
From eating raw/ undercooked meat or Fish - trichinella, Taenia (Solium + saginata), Anisakis, Diphyllobotrhium (fish tapeworm)
what are the routes by which toxoplasma gondii can be transmitted to humans?
o Ingestion of oocysts from soil or water contaminated with cat faeces
o Ingestion of tissue cysts in undercooked or cured meat
o Ingestion of infective parasites in unpasteurised milk
Body (strobila) and scolex (head) of cestodes (tapeworms)
o Made of individual segments = proglottids
o Each segment has male and female sex organs
o Skin allows absorption
o No mouth but suckers, grooves, hooks, spines to hold on to wall of vertebrate gut
what can schistosomes cause?
schistosomiasis or bilharzia
and “swimmer’s itch” when in wrong host e.g. bird schistosomes
What is the vector of Onchocerca volvulus
Blackflies Simulium damnosum. live in fast-flowing well oxygenated streams
what are obligate + facultative parasites?
obligate: always parasitic for at least part of lifecycle
Faculative: will be parasitic if opportunity arises (accidental infection)
How do schistosomes avoid the host immune response?
acquisition of host molecules: a dynamic process - the parasites are continuously renewing their surface (called the tegument). Overall, the worm strategy is to survive the host immune response by ‘disguising’ themselves as ‘host’. The tegument is a multi-layered membrane that is constantly renewed. Therefore, any immunological damage that occurs can be repaired by this tegmental renewal. Schistosomes also have glutathione peroxidase on their surface, which protects from free-radical damage.
what is the definitive intermediate host Nematodes Trichinella - causes trichinosis?
in the same animal (pigs / humans)
what is spontaneous cure.
a phenomenon in Nippostrongylus brasiliensis ( rat, like hookworms), In under two weeks from infection, the worms are lost from the host. In fact, the hosts have cured themselves from this infection.
This is a primary infection + primary response + kills and / or expels the worms.
If you give them a second infection, the infection is even more short-lived.
Differences between Protozoa and helmints?
Protozoa o Single cells o Often within host cells o Short-lived, infection stages short but infection might be long-lived (e.g. malaria) o Multiply within host
Helminths (trematodes, platyhelminths and cestodes) o Physically large & multi-cellular o Extracellular (too large) o Long-lived o Do not multiply within host
What is a definitive host?
a host in which the parasite undergoes sexual reproduction (meiosis for haploid gametes)
what are outbreaks of human Cryptosporidium associated with?
o Contamination of tap water/swimming pools with cysts from sewage. (outbreak in Lancashire in 2016)
o Contamination of ready-to-eat salad with cysts. (outbreak in Humberside , all adults + more women than men)
How does Giardia move?
o Creeps along the epithelial surface of the intestine + moves its flagella to hold its self in place, which create a current so they body becomes a suction cup, so it is stuck down by virtue of the suction power created by the movement of the fluid caused by the flagella.
o Feeds on the surface of the intestine.
what is the mechanism for worm killing / expulsion in Nippostrongylus brasiliensis
is immune mediated, T-cell dependent accompanied by high concentrations of IgE and an influx of mast cells to the intestine. Together, this suggests that there is an inflammatory response; more precisely a type I (immediate) hypersensitivity response. In this, histamine-containing mast cells, release their histamine via the action of IgE. Hay fever is a typical type I hypersensitivity response. In the N. brasiliensis infections, it looks like this type of response in the gut is responsible for the expulsion of the worms. This effect on the worms could come about directly (for example, by directly damaging and killing the worms); or, the histamine could alter the gut physiology, thereby making it an unsuitable environment for the worms; or, the histamine may allow the gut to become more permeable to other host effector molecules.
What is parasitism?
eating at your table, only the parasite benefits, intimate association, e.g. ascaris
Why was it difficult to eliminate Dracunculus medinensis completely? (once levels were ~26)
Because there was a reservoir host: some dogs can be infected which we didn’t know before the numbers of cases came to this level - this is a reason why it didn’t go to 0: animal reservoir kept the transmission cycle going.
what is Eimeria
A Coccidians important parasites of intensive farming
o Chickens, rabbits, calves, lambs , goats- several Eimeria species specific to each host
Parasite multiplies inside cells of gut wall; infective cysts pass out in faeces
direct lifecycle, feaco-oral transmission.
life cycle of Cryptosporidium?
1 thick walled- oocyst ingested, multiplication in the gut
Oocusts released in faeces
Oocysts contaminate water (used to wash salads / irrigate fields / swimming pools) and are then ingested.
Symptoms of helimthiasis?
o Negative relationship of helminth infection + cognitive performance (the more worms the less cognitive performance í Direct cost of parasitism)
o Deworming can: improve cognitive performance + school attendance.
What is Lymphatic filariasis?
Lymphatic filariasis, also known as elephantiasis, is a human disease caused by parasitic worms known as filarial worms. Most cases of the disease have no symptoms. Some people, however, develop a syndrome called elephantiasis, which is marked by severe swelling in the arms, legs, breasts, or genitals.
why do we know that spontaneous cure doesn’t happen in all hosts?
it did, these parasites would be extinct (and most worm infections are long-lasting, chronic infections).
why is malaria more dangerous than eimeria?
b. The cycle of schizogony is uncontrolled (unlike in eimeria where there is ¾ cycles then gametocytes); this can just continue dangerously í once you’re infected the cycle just continues in the RBC.
c. Single infected liver cell can give 1000s of parasites
What are the diffs/ similarities in the structures of monogeneans and digeneans?
both have uterus, ovavries + testies, a mouth and a pharynx that leads to two blind ending guts.
Digenea: 2 suckers in ventral + oral region (instead of posterior haptor)
Monogenean have haptor on posteria,
Why is the teste fly both bad. + good for Africa?
Vector of Trypanosoma brucei. Distributions of tsetse and cattle in Africa are mutually exclusive: stopped development of agriculture
saviour: Trypanosomiasis in vast areas of tsetse-infested land stopped agricultural exploitation - legacy of National Wildlife reserves and preservation of large wild animal
Why is the 3rd larval stage in nematode importnant?
For animal parasitic nematodes whose host infective stage is larval, it is always a third larval stage, either ensheathed or not.
The other similarities between dauer larvae of free-living nematodes and the infective larvae of parasitic nematodes is that they are both non-feeding, they are long-lived, and they are developmentally arrested, and will only resume development (to the L4 stage) when:
(a) for free-living nematodes, environmental conditions improve, such as more food is available or
(b) for parasitic nematodes, when a suitable host is encountered and infected. Biologically dauer larvae and infective larva are fulfilling the same role of dispersal.
why is Cryptosporidium bad for people who are immune-compromised people?
o In lifecycle: Autoinfection is possible. Two types of oocyst are produced: thin (allows autoinfection) and thick-walled (goes into environment) (this is all you need to see from the more complicated lifecycle)
o í if you are immunocompromised with a Cryptosporidium infection you will reinfect yourself (autoinfection)
o Trophozoites take place at surface of epithelial cell: bubbles on epithelial cell are the Schizonts of Cryptosporidium
o This means the gut won’t be able to absorb food í become v. thin
what are the defintive+ intermediate hosts of schistosomes?
definitive: humans
intermediate: aquatic snail
What are 2 theories for why parasite infection ‘tickles’ into the host?
1) One possibility is that this lower rate of worm delivery, gives the worms opportunities to adapt to the host immune response.
2) An additional possibility is that the parasites are able to (immuno)modulate the host immune response, thereby prolonging their survival.
3 types of platyhelminthes
Monogenea - mostly ectoparasites of fish and amphibia
Digenea - flukes or trematodes
Eucestoda - cestodes or tapeworms
How do filarial worms interfere with the immune response?
Parasites immunomodulate the host immune response. Adult worms interfere with T cell function, such that T cells are less likely to be stimulated into action.
There are changes in the sub-sets of T cells that are activated.
Very recent evidence suggests that worms are secreting molecules that directly affect the control of the host immune response.
What are microfilariae worms?
an early stage in the life cycle of certain parasitic nematodes in the family Onchocercidae.[2] In these species, the adults live in a tissue or the circulatory system of vertebrates (the “definitive hosts”). They release microfilariae into the bloodstream of the vertebrate host. The microfilariae are taken up by blood-feeding arthropod vectors (the “intermediate hosts”). In the intermediate host the microfilariae develop into infective larvae that can be transmitted to a new vertebrate host.
How can humans become infected with trichinella?
if ingest undercooked pork (larval worms encysted in the muscle will be released + most to become adults + release eggs in intestinal mucosa)
What kind of ‘immunity’ can be developped against Schistosoma mansoni infection?
o Concomitant immunity (worms in blood vessels but resistant to new infections, IgG and IgE: complement cascade).
Schistosomulae are attacked by IgE and IgG, which will stimulate the complement cascade. These antibodies will also attract esosinophils and induce ADCC.
what Taenia solium - pork tapeworm cause?
Infection with larvae in the human brain which can cause epilepsy (neurocysticercosis)
what are the species of malaria vectors in humans?
plasmodium (parasitic protozoans)
o 5 species in humans: Plasmodium falciparum, P.vivax, P.ovale, P. malariae, P. knowlesi
