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MCB55 > 37-38: Parasites > Flashcards

37-38: Parasites Flashcards

1
Q

definitive hosts

A

hosts in which the adult form matures

typically where sexual reproduction takes place

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2
Q

intermediate hosts

A

hosts which have larval or cyst form

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3
Q

parasitic worm infection statistics

A

1.5B people infected with soil-transmitted helminths worldwide

10-20% of the population infected with worms at any given time

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4
Q

human-human transmission vs zoonoses

A

some worm infections have high human-human transmission and are found primarily in humans
- humans as definitive or intermediate hosts

other helminths are zoonoses with distinct animal reservoirs and limited transmission to and between humans

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5
Q

soil-transmitted nematodes

A

ascaris, trichuris and hookworm

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6
Q

what are helminths divided into?

A

nematodes
- round worms

cestodes
- flat worms

trematodes
- flukes

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7
Q

how are soil-transmitted nematodes transmitted?

A

fecal-oral

lack of good sanitation

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8
Q

where do parasitic worms live?

A

mostly intestine
- ability to release eggs into the feces
- also a constant source of food

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9
Q

worms that have evolved to live outside the intestine

A

schistosoma worms
- blood flukes that reside in blood vessels

guinea worms
- peripheral tissues

intestinal worms
- traffic through lungs or other tissues as part of the life cycle

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10
Q

pinworm (nematode)

A

1 worm in the US

most common worm infection in the US
- prevalence in children can be as high as 50%

doesn’t cause harmful disease/cyst

no animal reservoir
- fecal-oral even with good sanitation

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11
Q

pinworm transmission

A

not a zoonosis

people infected by ingesting egg on fingers, clothing and other surfaces

childcare centres as common sites of outbreaks

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12
Q

how do we diagnose pinworms?

A

itching and examining for eggs by tape test

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13
Q

ascaris lumbricoides (nematode)

A

most common worm infection in the world
- more than 1B infections at any given time

human-only worm found everywhere

large round worms living in the small intestine

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14
Q

ascaris lumbricoides life cycle

A

larvae mature in liver, travel out capillaries into lungs where they are coughed up and swallowed to enter intestine (9 days after initial infection)

mature over 8-12 weeks into adults

eggs come out in the feces

can be prevented with good sanitation

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15
Q

ascaris lumbricoides statistics

A

807M-1.2B people infected
- most don’t get disease but just infection

<5% have disease

<0.5% have death or mortality
- still a lot with 1B infections
- more people die from ascaris infection then ebola

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16
Q

diagnosis of ascaris lumbricoides

A

finding eggs in stool or worms expelled

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17
Q

hookworms (nematodes)

A

parasites are transmitted through contaminated feces or from contact with larval form in soil
- can penetrate unbroken skin and doesn’t have to be swallowed

hook onto intestinal wall with teeth

ingest RBCs for nutrition

18
Q

ancylostoma hookworms

A

can digest its way through human skin which is uncommon

19
Q

hookworms eating

A

penetrate the intestine, find a blood vessel then suck in blood from the blood vessel

leads to a higher symptomatic rate because people have symptoms from anemia

20
Q

trichinella (nematodes)

A

classic larval cyst

larvae make cysts in muscle that can be transmitted to humans when they eat undercooked pork

21
Q

trichinella life cycle

A

rodents which are carnivorous

pigs interact with feces or eat the cyst, so the pig has cysts and then the human eats the pig

mostly, humans don’t go back and infect rodents

zoonosis from a pig/rodent or rodent/rodent cycle

22
Q

filarial worms (nematode)

A

mosquito-born worm transmitted by mosquitos

humans are definitive hosts

23
Q

filarial worms can cause lymphatic filariasis also known as elephantiasis

A

microfilariae secreted by adults into blood for uptake by mosquitos
- small larval forms which serve the purpose of eggs

microfilariae can build up in lymphatic vessels and block fluid uptake along with other infections
- creates hardened tissue

24
Q

filarial worms as high on the list of neglected tropical diseases

A

100M infected, most problematic in SE Asia and Indonesia

worm infections can last for months or even years

25
Q

guinea worm (nematode)

A

caused by ingestion of drinking water with copepods

primarily a zoonosis but humans can pass it to copepods who pass it to other humans

26
Q

guinea worm infection

A

female worm extends anterior end through skin and forms a painful lesion up to 1 year after infection

burning sensation so you try to relieve it with water

water is a trigger for the guinea for to extend and release larvae into water

27
Q

guinea worm removal

A

worm twisting

removal has to be gradual to prevent breaking off worm under skin

28
Q

guinea worm is close to eradication

A

millions of infections in the 1980s down to 9 in 2022

still 490 infections in animals
- still has potential to infect humans

29
Q

cestodes

A

flat segmented worms

primarily intestinal dwelling tapeworms

true parasites in that they lack a mouth, alimentary (intestinal/digestive) tract, circulatory system, body cavity and major metabolic pathways

absorb nutrient molecules through their body surface (tegument)

30
Q

tapeworm anatomy

A

scolex is the anterior-most portion of the worm
- head

scolex armed with large hooks that alternate with small ones

neck followed by a chain of flat, ribbon-like segments
- proglottids

31
Q

tænia life cycle

A

human agricultural disease

not a zoonosis

two species
- one passed through cows, other through pigs
- most common through pigs

cysts form in animal meat so if not cooked well enough, larval form and cyst are activated to become adult form

32
Q

tapeworm infections cause taeniasis and worms are found worldwide

A

cysts take over muscle cells and form an inter-larval form that is like sleeping larvae

taeniasis occurs when raw/undercooked beef or pork is eaten

humans are definitive hosts but can also be intermediate hosts if infected with cysts

33
Q

taenia sodium and cysticercosis

A

cysticercus in the brain can lead to neurological damage

cysts can go into a muscle cell and stay there forever

34
Q

neurocysticercosis and epilepsy

A

when people have worms or are exposed to eggs, and there are cysts in the brain, this can be the greatest cause of acquired epilepsy

cysts in the brain can cause neurocysticercosis

35
Q

neurocysticercosis and epilepsy

A

when people have worms or are exposed to eggs, and there are cysts in the brain, this can be the greatest cause of acquired epilepsy

cysts in the brain can cause neurocysticercosis

36
Q

neurocysticercosis statistics

A

2.5-8.3M

37
Q

trematodes (schistosomes)

A

blood flukes

life cycle includes a replication stage in water snails
- snails as intermediate hosts or animal vectors

38
Q

schistosoma species

A

2 major forms of schistomiasis (intestinal and urogenital) caused by 5 main species of blood fluke

most common is the schistosome mansoni found in most of the world

39
Q

schistosome life cycle

A

worm that can penetrate skin, lose their tail, go through circulation, go to the blood and live in the blood vessels of the liver or intestine

female lays egg, male fertilises the eggs which then have to get from the blood stream, penetrate through intestines and cell walls to the feces or urine

40
Q

schistosoma disease

A

adult worms do not cause disease
- eggs released into tissues cause disease

eggs cause damage to the tissue and leak fluid from the blood into the peritoneum so the abdomen is filled with fluid

41
Q

schistosoma granulomas

A

trap everything and form a granuloma around the egg

or the egg is successful, digests through the tissue and its released

inflammation causes tissue damage, but even if we try to get the worm out, it doesn’t do anything for adult worms which we have no immune response to

MCB55 (30 decks)

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