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Y3 Parasitology > Flukes > Flashcards

Flukes Flashcards

1
Q

Name the two most common fluke species

A
  • Fasciola hepatica

- Fasciola gigantica

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2
Q

Give examples of typical fluke characteristics

A
  • Indirect lifestyle
  • Dorso-ventrally flattened
  • Hermaphrodite
  • No body cavity
  • Branches of the gut are visible
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3
Q

What are the major impacts of fluke on animal production?

A
  • Growth rate
  • Milk yield
  • Wool and fibre
  • Liver condemnation
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4
Q

How can you tell apart the eggs of Fasciola hepatic and Fasciola gigantics?

A

Fasciola gigantica eggs are larger and paler in colour

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5
Q

Describe the host cycle of Fasciola hepatica

A
  • Indirect (includes more than one host)
  • Definitive mammalian host where sexual reproduction occurs – where the adults reside
  • Snail intermediate host is where asexual reproduction occurs
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6
Q

Give examples of the definitive mammalian host of Fasciola hepatica

A
  • Ruminants
  • Camelids
  • Horses
  • Humans (zoonosis)
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7
Q

Name and describe the intermediate host of Fasciola hepatica in the UK

A

Mud snail - Galba truncatula

- 5mm in size, burrow in mud so hard to find

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8
Q

Describe the eggs of F.hepatica when they are passed in the faeces

A

Undifferentiated so have a golden appearance with a very thin egg shell

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9
Q

Over how many weeks does the F.hepatica develop in the eggs on pasture?

A

2-4

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10
Q

When the F.hepatica eggs hatch, what happens, and how does it reach the snail?

A

The operculum on the egg opens up and the miracidium is released and it is covered in a ciliated outer surface, these cilia help it swim to come into contact with the snail

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11
Q

Describe how the miracidium are adapted to reach and infect the snail?

A
  • Miracidium are motile, photosensitive and they can detect the chemical signature of the snail
  • The miracidium are short lived (24hrs) so they have to rapidly swim to the snails to infect them
  • They burrow into the foot of the snail to gain access to the body cavity
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12
Q

What happens to the miracidium when they have infected the snail?

A

They lose the outer ciliated surface – they are now called sporocysts

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13
Q

Describe the reproduction of sporocysts

A

From one sporocyst we can get multiple rediae (asexual reproduction, clonal expansion), which are genetically identical

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14
Q

Further asexual reproduction of the rediae produces?

A

Cercariae

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15
Q

How do cercariae continue the life cycle?

A
  • This stage burrows out of the snail

- When they come into contact with a solid surface e.g. vegetation, they encyst

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16
Q

What is involved in the encystation of a cercariae?

A

Lose their tail, surround themselves with a carbohydrate and protein rich coating which protects the parasite when its out on pasture – now named a metacecariae

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17
Q

Name the stage of the F.hepatica that is infective to the mammalian host

A

Metacecariae

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18
Q

How do metacecariae infect the mammalian host, and which tissues do they migrate to?

A
  • ingested with vegetation
  • exist as juveniles in the gut
  • there is a cap on the metacecariae that opens up and releases the parasite – they exist within the intestine in the duodenum, they pass through the peritoneal cavity in search of the liver, where they migrate
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19
Q

How long does it take the metacecariae to migrate to the liver?

A

6-8 days

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20
Q

Once the metacecariae have reached the liver, what happens next?

A
  • By secreting proteolytic enzymes they make holes in and migrate through the liver
  • After 10-12 weeks the parasites are continuing to grow in size, once they are adults they migrate into the bile ducts- they are sexually mature adults producing eggs at this point
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21
Q

What is the name of the diseases caused by migrating fluke?

A

Fasciolosis

22
Q

What are the two forms of Fasciolosis?

A

Acute

Chronic

23
Q

The type of Fasciolosis disease is determined by?

A

The number of metacercariae ingested and the time period over which they are ingested

24
Q

Describe the pathogenesis of Acute fasciolosis

A
  • Large numbers of immature flukes migrating through the liver, cause lots of damage
  • Multifocal necrotic or haemorrhagic tracts throughout the liver
  • Inflammation, liver enlargement, fibrosis
25
Q

At what time of the year would you see acute fasciolosis?

A

October - December

26
Q

What are the clinical signs of acute fasciolosis?

A
  • Occurs in sheep most commonly
  • Sudden death
  • Weakness/dull
  • Abdominal pain
  • Anaemia
27
Q

Describe the pathogenesis of chronic fasciolosis

A
  • Sheep and cattle
  • Low numbers of metacercariae ingested over longer period of time
  • Adult flukes in bile ducts feed on blood
  • Spines on the tegument irritate bile duct walls
  • Hyperplasia of the bile ducts to accommodate the number of parasites
  • Inflammation of the bile duct system
28
Q

At what time of the year would you see chronic fasciolosis?

A

late winter/early spring – January-March

29
Q

What are the clinical signs of chronic fasciolosis?

A
  • progressive weight loss
  • anaemia
  • sub-mandibular oedema
  • ascites
30
Q

Describe spring in a year in the life of a British fluke

A
  • low snail population
  • eggs on pasture
  • eggs develop following an increase in temperature
  • miracidia infect snails
31
Q

Describe summer in a year in the life of a British fluke

A
  • Summer infection of snails
  • Asexual reproduction
  • sporocyst – rediae - cercariae
32
Q

How can the weather in summer cause acute disease?

A

Three warm, wet months cause large numbers of cercariae released on pasture in September

  • Large numbers of metacercariae on pasture, ingested by sheep
  • Acute disease 2-6 weeks later
33
Q

How can the weather in summer cause chronic disease?

A

A cool dry summer:

  • Fewer metacercariae produced – cause chronic disease
  • Released gradually from snails between September and November
  • Chronic disease in winter and early spring the following year
34
Q

How can fluke be diagnosed at an individual level?

A
  • Clinical signs (sudden death, weight loss, anaemia)
  • Season (autumn & winter)
  • Farm history
  • Post-mortem exam
35
Q

How can fluke be diagnosed at a farm level?

A
  • Composite faecal egg counts (10 animals/group)
  • Bulk tank milk ELISA
  • Abattoir returns
36
Q

Describe some fluke control methods

A
  • Disease forecasting: used to predict the levels of disease at different times of the year based on the weather previously had
  • Grazing management
  • Elimination of snail habitat
  • Drug prophylaxis
37
Q

Which drug can be used in the prophylaxis of fluke?

A

Triclabendazole - effective against all stages of fluke

- resistance in the UK

38
Q

Which 2 drugs can be used to treat fluke in dairy herd and why?

A

Albendazole
Oxyclozanide
- Short withdrawal periods

39
Q

What are paramphistomes?

A

Rumen fluke

40
Q

Name the predominant species of rumen fluke in the UK

A

Calcicophoron daubneyi

41
Q

Describe clinical disease of Calcicophoron daubneyi

A

Acute infection when large numbers of metacercariae excyst en masse in the duodenum
- stay within the rumen and intestine

42
Q

How can Calcicophoron daubneyi be treated?

A
  • Cloantel: affective but only as an oral drench

- Oxyclozanide

43
Q

The life cycle of Dicrocoelium dendriticum involves which two intermediate hosts?

A

Garden land snails

Brown ants

44
Q

How does Dicrocoelium dendriticum go from the snail to the ant?

A

Released from the respiratory pore of the snail in a slime ball which is ingested by the ant

45
Q

Name the blood fluke spp

A

Schistosoma spp

46
Q

state three characteristics of trematodes

A
  • Dorsoventrally flattened
  • Solid parenchyma body (no body cavity)
  • Hermaphrodite
  • Indirect life cycles.
47
Q

How long does it take for the development of (a) the egg and (b) the stages in the snail of F. hepatica during a typical UK summer?

A

(a) 2-4 weeks.
(b) 6-8 weeks.
Development only occurs if temps above 10oC, warmer the temperature, the more
rapid the development

48
Q

What is the PPP for F. hepatica?

A

10-12 weeks

49
Q

What drug(s) could you use to treat acute fasciolosis?

A

Triclabendazole but check for resistance, or closantel

50
Q

What drug(s) could you use to treat chronic fasciolosis?

A

Ideally not triclabendazole or closantel to reduce selection pressure on fluke populations, so use nitroxynil, clorsulon, albendazole (increased dose cf nematode dose) or oxyclozanide.

Y3 Parasitology (13 decks)

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