Cestodes Flashcards
1
Q
What are cestodes?
A
Ribbon like Platyhelminthes.
2
Q
Are there any free-living cestodes?
A
NO there are only parasitic cestodes.
3
Q
Where do the cestode larval stages occur?
A
In the tissues of vertebrates and invertebrates.
4
Q
How do cestodes attach to the intestine?
A
Through the scolex on the head.
5
Q
What is contained in the neck region? What is contained in the body region?
A
Neck- germinal region.
Body- proglottids.
6
Q
Are cestodes hermaphrodites or dioecious?
A
All are hermaphrodites.
7
Q
How do cestodes absorb nutrients? How does the layout of their body plan facilitate this?
A
No mouth, no intestine, no anus, they absorb nutrients!
8
Q
What is a rostellum?
A
A knob-like protrusion on the extreme anterior end of the cestode. When protruding, it is a globular, spiny structure. When it is retracted, it is a circular, hollow pit. Composed of a concentric rows of hooks. .
9
Q
What is the strobila?
A
The body which is made up of proglottids. (The segmented part of the tapeworm).
10
Q
What is the operculum?
A
On eggs, some are operculated. (Lid that flips open to reveal larvae).
11
Q
What is a protoscolex?
A
A juvenile scolex formed from the germinal layer of a hydatid metacestode.
12
Q
What is a hydatid?
A
Can be a hydatic cyst which is a fluid-filled cyst containing the larvae of the cestode.
13
Q
What is a hexacanth embryo?
A
A six hooked larvae inside eggs which uses the hooks to attach to intestines.
14
Q
What is an oncosphere?
A
The larval stage once it is ingested by the intermediate host.
15
Q
What are the two groups that cestodes are split into?
A
-Suckers and hooks or grooves: cyclophylidae and pseudophylidae respectively.
16
Q
What is a hexacanth embryo?
A
An embryo characterised by three pairs of hooks used for penetration through the gut of an intermediate host.
17
Q
Where do worms grow from and what does this mean about cutting worms in half?
A
Grow from the neck (as this contains the germinal region) so cutting in half means it will simply regrow!
18
Q
What makes up one proglottid?
A
The ovary, uterus and sperm duct.
19
Q
What is the function of the tegument?
A
Is a spongey like covering over the whole body that allows them to import nutrients straight from the environment into the segments.
20
Q
How do cestodes excrete without an anus?
A
Excrete directly through the tegument.
21
Q
How do cestodes move inside the intestine?
A
Have muscles and a nervous system to allow them to move.
22
Q
What are the differences between pseudophyllids and cyclophyllids in terms of
- Scolex
- Uterus
- Proglottids
- Eggs
A
Pseudophyllids:
- Slit like grooves
- No branching of uterus, colvoluted uterine tubules forming rosettes
- Eggs released FROM proglottids, eggs in faeces
- Operculated eggs, ciliated larvae
Cyclophyllids:
- Suckers and/or hooks
- Branching, may or may not have convoluted uterine tubules
- Proglottids containing eggs released from adult worm so both eggs and proglottids found in stool
- Unoperculated, no ciliated larvae
23
Q
What are the names for the most common human cestodes that are the beef tapeworm and the dwarf tapeworm?
A
- Taenia saginata
- Htmenolepis nana
24
Q
What is the drug of choice for most platyhelminth infections?
A
Praziquantel. also niclosamide and albendazole (for tissue stages) for some.
25
How long is echinococcus and where does it have its adult form?
Less than a cm long, in fox or dog intestine.
26
How is PZQ thoght to have its antihelminthic effects?
By causing Ca influx which causes muscle contractions and surface modifications, ending in paralysis.
27
How large is taenia and where does it have its adult form?
From 2-10m long but up to 25 m long in human intestines.
28
What is diphyllobothrium? Where is it found? What are the three most common species (and where are they found and which species are they found in)?
A broad tapeworm/fish tapeworm.
Latum- Found in freshwater fish in Europe and America.
Diphyllobothrium pacificum- in pacific South America and East Asia in salt water fish.
Diphyllobothrium nihonkaiense- in Japan and US pacific coast and is found in Pacific salmon.
29
What is the most common diphyllobothrium that we study? How big are they? What is their lifespan?
Latum. Is the fish/ broad/ broad fish tapeworm.
3-10m long, reports of up to 25m.
5-15 year lifespan (reported up to 25).
30
What are the intermediate hosts for diphyllobothrium latum? HOw do humans get infection? Where is D latum still very prevalent?
Copepods (crustaceans) (first intermediate host) and fresh water fish (second intermediate host).
By eating raw or undercooked fish?
In Europe, especially in the Alps.
31
Describe the lifecycle of D latum.
Fish is eaten and worms mature in intestine--> eggs are released from the proglottid --> eggs come out unembryonated in stool --> eggs embryonate in water --> corocidia hatch from eggs --> corocidia are eaten by copepods --> --> develop in copepod into procircoid larvae --> infected copepod eaten by fish --> plerocoid larvae (infective form) develop inside fish --> fish is eaten by a bigger fish, larvae moves into the flesh --> humans eat this and become infected.
32
Define bothria.
Longitudinal grooves on the scolex of cestoda.
33
What is the main clinical feature of D latum infection?
Vitamin B12 deficiency because they absorb this in the intestine, they absorb up to 80%.
34
Describe the scolex of D latum.
Scolex with two sucking grooves (bothrias)
35
Describe the uterus of D latum.
Characteristic rosette-shaped uterus which is central.
36
Describe the features of the ova of D latum
```
~60 um
• Shed in large numbers in faeces
• Oval
• Does not float in salt solutions
• Abundant granules
• Operculum at one end
• Small knob at other end
• Not infective to humans
```
37
How long after D latum eggs hatching in water does it take for them to become larvae? What emerges from the egg?
About 12 days. The operculum/ lid releases L1 cilliated larvae called coracium.
38
What happens/ which stages are where the L2 and L3 D latum larvae occur?
L2 is ingested by fish. L3 occurs in fish tissue and when it is infective it is called plerocercoid.
39
What is the infective D latum stage called?
Plerocercoid.
40
HOw do we diagnose and treat D latum?
Diagnose: expect intestinal disturbance and B12 deficiency. Eggs in stool to diagnose.
Treat with PZQ and possibly supplement with vitamin B12.
41
What is L1 of latum called?
Ciliated coracidium.
42
How do we control for D latum?
* Cooking fish (63oC)
| * Freezing fish, -20oC, 24h to a week (depending on size of fish)
43
What is L3 D latum larvae called?
Procercoid.
44
See notes for spirometra (don't need to know, mainly just for interest).
-
45
What is (one of) the most common tapeworm infections seen in humans?
Hymenoleptis nana. Dwarf tapeworm.
46
What are the definitive and intermediate hosts for hymenoleptis nana? What is interesting about this?
Definitive: humans and rodents
Intermediate: insects and arthropods
The intermediate host is OPTIONAL. IT is the only human tapeworm that can complete its lifecycle without the intermediate host!
47
Which is the only human tapeworm that does not REQUIRE an intermediate host?
Hymenoleptis nana.
48
How do humans acquire hymenoleptis nana infection?
Ingesting infected embryonated eggs from rodent faeces or ingesting infected arthropod containing larval stages.
49
how can we get amplification of hymenoleptis nana infection in humans?
Autoinfection if eggs within adult proglottids hatch inside the human.
50
How long does development of hymenoleptis nana take in the human intestine?
2-3 weeks.
| Short lived in the intestine but as they multiply, there can be large numbers!
51
Describe the lifecycle of hymenoleptis nana.
Eggs hatch in intestine --> develop into adults in 3 weeks --> eggs are passed, they develop into adults (autoinfection) or pass into faeces --> can either enter intermediate host or infect humans or rats (definitive hosts) directly.
52
Describe the scolex of hymenoleptis nana.
Has a crown of hooks on the rostellum with 4 suckers.
53
Describe the eggs of hymenoleptis nana.
They are 40-60µm and are slightly oval. Oncosphere found inside which forms an oncophere.
Eggs have hooks to attach to the intestinal wall.
54
What are the clinical symptoms of hymenoleptis nana?
Usually, light infections are asymptomatic. Heavy infections may give non-specific abdominal symptoms.
It is more of a clinical problem in children who may get more severe anorexia type symptoms.
55
How do we diagnose hymenoleptis nana?
-Eggs in stoo
56
How is hymenoleptis nana treated?
Praziquantel for adults and larvae.
57
How do we control for hymenoleptis nana?
- Rodent control (because humans AND rodents are the definitive hosts)
- Insect control (e.g. insect control in grain stores)
- Sanitation
58
What are the two most important taenias?
Solium and saginata
59
Which factor is responsible for most of the distribution of taenia saginata? Therefore, how is infection acquired?
In most countries in the world where there is cattle and beef is eaten.
Eating undercooked meat infected with larvae.
60
What are the definitive and intermediate hosts for taenia?
Humans are definitive.
| Cattle (and other ruminants such as water buffalo) are intermediate hosts.
61
Describe the lifecycle of taenia solium.
The human gut releases tapeworms and tapeworm eggs--> these infect pastures and contaminate grassland --> ruminants ingest the eggs --> larvae hatch in intestine and penetrate the intestine walls --> form the cyst stage in tissues (cysticercus) --> humans become infected by eating this meat.
62
How long does development of adults of taenia saginata take in the intestine? How long do they grow up to?
Takes about 2-3 months to develop. Are 4-8 metres but reports of up to 25m.
63
What is the lifespan of taenia saginata in the human?
About 10 years.
64
How often are proglottids of taenia saginata released and where do they oviposit?
5-10 times per day.
| Are motile and can crawl to the anus where they oviposit in the perianal region.
65
To whom are the eggs of taenia infectious to? (aka in which species can cysticercosis occur)?
To ruminants only. Taenia saginata does not cause cysticercosis in humans.
66
How can we tell the difference between the proglottids of saginata and solium?
The proglottid uterus has branches. If more than 15 branches, it is saginata, if less than 15 it is solium.
67
Describe the scolex of saginata
Scolex is very small with 4 suckers and no hooks. Does not have a rostellum. These features identify it from the other taenia.
68
Describe taenia eggs (at this point cannot distinguish between solium and saginata).
- 45 microns
- Circular
- Thick striated shell
69
What is a cysticercus?
A fluid filled cyst with protoscolex inside which eventually grows to be the adult tapeworm.
The shape looks like a bladder and is because the protoscolex is invaginated and can exvaginate (pop out) so that it is no longer inverted and from this the adult head develops.
70
What are the symptoms of saginata?
Mild gastrointestinal issues. Anal priritis from the exit of gravid proglottids to the anus.
71
How do we diagnose taenia spp?
Eggs or proglottids in faeces.
72
How could we control for saginata?
Meat inspection, cooking meat, sanitation and hygiene are hard to control and can spread wiely through wind or birds.
73
How do we treat saginata?
PZQ or niclosamide.
74
What are the definitive and intermediate hosts for solium? (definitive NOT in cysticercosis)
Humans- direct
| Pigs- intermediate
75
What are the two types of infection seen with solium?
- Intestinal infection with the adult worm through eating uncooked pork infected with larval form
- Tissue infection by the larval form (cysticercosis) by the ingestion of infected eggs from the environment. When cysticercosis occurs in the humans, we become the intermediate hosts
76
To whom is the solium egg infectious?
BOTH the pig and the human.
77
How large are solium worms? How long do they live for?
A lot smaller than saginata, about 2-8m. Live about 25 years. This may explain the greater severity of the symptoms produced by saginata.
78
What are the clinical symptoms of solium? How do we diagnose? How do we treat?
Asymptomatic or mild. Eggs or proglottids in faeces. PZQ or niclosamide.
79
How do we control for solium?
- Meat inspection
- Cooking meat
- General sanitation and hygiene
- Antihelminthic treatment of pigs to break the transmission cycle with oxfendazole.
- Pig vaccines e.g. TSOL18, cysvax)
80
Describe the scolex of solium
4 suckers AND a crown of hooks.
81
What is cysticercosis? How is it transmitted? Which tissues are affected?
The larval form of the disease. It is not associated with eating meat as eggs can be carried on hands. Is transmitted through the faecal-oral route from human to human. This means autoinfection is possible.
Any tissues can be affected
82
What occurs to the cysts in cysticercosis over time?
OVer time they can die off. THey calcify over time and the death of them produces an immune response.
83
What is the most important clinical manifestation of cysticercosis (i.e. affecting WHICH tissue may be the most dangerous)?
Neurocysticercosis. A high proportion of cases result in death (50,000 deaths per year). It is the most frequent preventable cause of epilepsy in the world.
84
Which locations can cysticercosis (caused by solium) affect? Do infections in these locations cause problems?
- Muscle- usually asymptomatic depending on the site. Muscle can expand so little or no disease symptoms
- Brain- brain cannot expand like muscle so this causes disease
- Eye- treatment with antihelminthics causes inflammatory response which is a problem if the infection site is the eye
85
How do we diagnose solium cysticercosis?
- Imaging (CT, MRI, x ray)
- Serology (immunoblots)
- If neurocystocercisis: look for CNS lesions, focal lesions, convulsions and intracranial hypertension (from inabilityof brain to expand when the cysts form there)
86
What are the stages of the cysts in cysticercosis?
- Alive cysts
| - Dying cysts produce strong inflammatory reaction and calcify
87
How do we treat cysticercosis?
Dependent on the site, number of cysts and symptoms.
| -Albendazole, PZQ (combinations), steroids, surgery, antiepileptics, analgesics.
88
How do we control for solium?
Human sanitation as we are the only source of eggs.
89
What is another name for echinococcus? What is it?
The hydatid worm.
| Is the hyper tapeworm or the dog tapeworm.
90
What are the two echinococcus species we concentrate on?
E. granulosus and multilocularis
91
What are the two species of echinococcus that are more rate and are found in south america?
Vogeli and oligarthrus. Are polycystic echinococci
92
Describe the common cycle for echinococcus granulosis (what are the definitive hosts).
Cycle in domestic dogs and pigs and sheep/ livestock as definitive hosts. (Australia has wild cycles with wallabies and dingos).
Strongly associated with sheep farming.
93
What are the intermediate hosts for Echinococcus multilocularis?
Foxes are the definitive hosts and rodents are intermediate hosts, humans can be accidental intermediate hosts by ingesting eggs from foxes and cats.
94
Descrive the transmission cycle of e granulosis
Adult in the dog intestine sheds eggs into the faeces --> eggs are ingested by sheep where oncospheres hatch in their intestine --> oncosphere penetrates the intestine -->hydatid cyst forms in the tissues -->proliferation of new larval stages within the cyst.
95
Describe the transmission cycle of multilocularis
Adult in the fox intestine sheds eggs into the faeces --> eggs are ingested by rodents where oncospheres hatch in their intestine --> oncosphere penetrates the intestine -->hydatid cyst forms in the tissues -->proliferation of new larval stages within the cyst.
96
What is the definitive host of e granulosis? Intermediate hosts?
Definitive: Canids: dogs, jackals, wolves, fox etc.
Intermediate: sheep, humans, cattle, horse etc.
97
How can echinococcus granulosis be transmitted?
Dogs eating offal from sheep, humans accidentally ingesting dog faeces.
Eggs may also be dispersed by wind, rain, herbivores and insects etc.
98
Describe the egg of e granulosis.
Ovoid and resembles taenia but NOT found in human faeces.
99
To whom is the egg of echinococcus granulosis infective?
Humans, cattle, sheep and other herbivores.
100
Describe the events occurring post ingestion of egg of e granulosis.
Egg is ingested and hatches --> oncosphere penetrates intestinal wall --> migrates to tissues --> hydatid cyst forms containing larvae which are proliferating to produce new larval stages (protoscolices) from the germinal layers inside the cyst --> cyst grows slowly but steadily --> BROOD CAPSULES develop inside the cyst and may contain thousands of scolices (hydatid sand)
101
What is a brood capsule?
One of the secondary scolex-containing cysts that are proliferated from the lining of a hydatid and constitute the infective agent when eaten by a suitable host (such as a dog) --> cysts within the cyst!
102
What is hydatid sand? Describe its most important property.
The fluid within the hydatid cyst containing scolices. It is produced by the germinal layer in the cyst. This fluid is VERY allergenic and if the cyst ruptures, severe anaphylaxis can occur.
103
What are calcareous corpuscles?
Calcium bodies which are found in all cestodes. Thought to provide some form of osmoregulation.
104
Describe pathogenesis of e granulosis. What causes it?
Caused by the slow growing developing larval cyst, symptoms vary depending on the infected organ.
Most common is liver but can occur anywhere.
-Abdominal pain
-Hepatic mass
-Bile duct obstruction (if in liver)
-May be asymptomatic for years, only presenting if a cyst ruptures to release highly immunogenic hydatid sand, causing anaphylaxis.
105
How do we diagnose e granulosis?
Imaging or serology.
106
How do we treat e granulosis?
Dependent on size, stage and site.
- Albendazole (sometimes combined with praziquantel)
- Surgery to remove cysts
107
Describe the surgical procedure to remove hydatid cysts (e granulosis).
- PAIR
| - Puncture, Aspiration (of fluid), Injection (of alcohol or salt solution to kill germinal layer) Re-aspiration.
108
How do we control for hydatids?
Control dogs: carcass removal to prevent dog scavenging, cooking dog food, deworming dogs, controlling stray dog populations, education.
109
Describe the transmission of e multilocularis. What are the definitive and intermedaite hosts.
Definitive: canids, dogs, foxes etc.
Intermediate: rodents, humans.
Humans accidentally ingest eggs from faeces.
110
Describe the pathogenesis of e multilocularis. What are the symptoms?
Similar to granulosis but much slower growing (5-15 years) and cysts are tumour like, mainly in the liver.
- Abdominal pain
- Weightloss
- General malaise
- Hepatic symptoms (jaundice)
- Larval metastases to new tissues to form cysts (brain,
111
How is multilocularis treated?
- Hard to catch early as is asymptomatic for years
- Radical surgery, then long term albendazole
- Palliative care for later stages
112
How do we control multilocularis?
Harder as cycle contains wild animals. Deworming of domestic cats and dogs. lacing chicken carcases with albendazole and leaving in the forest.
113
How do the cysts of multilocularis present in tissues?
Not defined, lots of small cysts in a honeycomb pattern. Do NOT have a collagen capsule. As they are proliferating, they have no germinal layer inside- instead, there is a budding off of cysts with germinal layers when they metastasie.
114
Which cestode species do not have adult stages in humans?
Echinococcus (hydatid) and spirometra.
115
Which cestode species do not have larval stages in humans?
Saginata, diphyllobothrium, and hymenoleptis.
