Introduction to Helminths

Question 1

What kind of organisms are helminths?

Answer 1

Worms

Question 2

Are most helminths parasitic?

Answer 2

No, they are free-living in the environment and only a minority are parasitic.

Question 3

A very significant proportion of expenditure on veterinary medicine is spent on what?

Answer 3

Anthelminthic drugs

Question 4

Parasite control programs for helminth diseases are based on what?

Answer 4

• Drugs
• Management measures such as keeping stocking densities down and understanding life cycles

Question 5

What are the categories of parasitic helminths?

Answer 5

• Nematodes (roundworms)
• Platyhelminthes (flatworms)

Question 6

What was the first complex organism to have its genome sequenced?

Answer 6

Cenorhabitis elegans

Question 7

Is C. elegans a parasitic helminth?

Answer 7

No

Question 8

What are the uses for Cenorhabditis elegans as a model helminth?

Answer 8

• Used in a wide variety of broad biological studies, including studies on developing new anthelminthic drugs
• Has 302 neurons and therefore used extensively in studies of neural networks

Question 9

How many hosts do parasitic nematodes have?

Answer 9

One host (definitive)

Question 10

Name 4 key facts about parasictic nematodes

Answer 10

1) They have separate sexes (di-ecious)
2) Females are often bigger
3) One egg = One adult
4) Organized body structure with cavities.

Question 11

How are infective larvae of parasitic nematodes are spread?

Answer 11

Via grass and plant material, which is contaminated by eggs in host species

More animal feces = more contamination.

Question 12

True or false: Infection by parasitic nematodes generally is only significant about a certain level.

Answer 12

True

Question 13

Control of parasitic nematodes works best by reducing _________ numbers.

Answer 13

Host; you have to break the cycle of infection.

Question 14

What are the 2 groups of flatworms?

Answer 14

• Trematodes (flukes)
• Cestodes (tapeworms)

Question 15

What are the major differences between nematodes and platyhelminthes?

Answer 15

• Nematodes: organs in the coelom, protective cuticle
• Platyhelminthes: organs in parenchyma, metabolically active tegument

Question 16

How many hosts do flatworms have?

Answer 16

At least 2 or more are needed to complete their life cycle.

Question 17

Flatworms body structure is more ________ than nematodes.

Answer 17

Primitive

Question 18

Which classification of helminths are often hermaphrodites?

Answer 18

Flatworms

Question 19

Describe the reproduction of flatworms.

Answer 19

Can be asexual or sexual, so one egg produces many adults.

Question 20

Taenia solium is what kind of helminth?

Answer 20

Flatworm

Question 21

What is the scientific name for the liver fluke?

Answer 21

Fasciola hepatica, which is a flatworm.

They live in the bile ducts of ruminant and other mammalian hosts

Anemia is a common sign of infection.

Question 22

What is the Life Cycle of Fasciola hepatica?

Answer 22

1) Adult liver flukes produce fertilizd eggs that leave the host via the common bile duct (CBD)iand intestinal tract feces.
2) If eggs fall into water, a ciliated miracidium develops over weeks or months depending on water temperature.
3) On hatching, they seek** lymnaeid snails** to develop 1 generation of sporocysts and 2 generations of rediae. No snail within 24 hrs = it dies.
4) It reproduces in the snail to become cercaria, tadpole-like larva and migrate above water level.
5) Cercaria mature, lose tadpole tail, become **metacercaria and climb up plants. **
6) **Metacercaria are infective to sheep and other grazing animals. **

Question 23

In Life Cycle Terminology, define a helminth definitive host.

Answer 23

Helminth reproductive stages in the host.

Question 24

In Life Cycle Terminology, define a helminth intermediate host.

Answer 24

Immature helminth stages occur here.

Question 25

In Life Cycle Terminology, define a paratenic host?

Answer 25

Optional extra host that is not required for life cycle completion.

Question 26

What is an example of a helminth organism with a paratenic host?

Answer 26

Toxocara cati

Question 27

In Life Cycle Terminology, define a direct life cycle?

Answer 27

Life cycle with only one required host.

Question 28

In Life Cycle Terminology, define an indirect life cycle?

Answer 28

Life cycle with more than one required host.

Question 29

How do helminths affect the immune response of their host?

Answer 29

Often 'dampen' it; which can be either bad or good. | dampen could mean "extra burden"

Question 30

What is the hygiene hypothesis?

Answer 30

The hypothesis that early exposure of a child/immature animal to particular microorganisms such as helminths protects against allergies by properly tuning the immune system.

Question 31

What is the "old friends" hypothesis?

Answer 31

Observations of the potentially important role that helminth-driven suppression of our immune system responses has played in preventing or lessening our development of allergies and autoimmune diseases.

Question 32

What are the major clinical issues associated with helminths in general?

Answer 32

- Very limited number of drugs available - Few new drugs in development - Drug resistance has become a major problem; in Australia and NZ, some sheep roundworms are resistant to all available drugs.

Question 33

What are the aspects of future helminth control?

Answer 33

- New drug development - Development of vaccines - Anthelmintic stewardship - Prescriptions for food animals in EU

Question 34

In what kinds of animals are parasitic helminths found?

Answer 34

- All grazing animals - Cats, dogs, wildlife, and exotic pets

Question 35

What % of drug expenditures are spent on parasiticides?

Answer 35

23%

Question 36

Describe the importance of veterinary involvement in the control of helminth diseases.

Answer 36

Vets play a crucial role in the prevention measures, specifically those that do not involve the use of drugs, so as to minimize the rising levels of resistance.

Question 37

What 6 things make an animal at risk for a parasite?

Answer 37

1. age 2. immune status 3. genetics 4. nutritional status 5. pregnancy 6. hyperbiosis (ability of parasite to stay dorment inside the host, arrested development), common in livestock

Question 38

What 4 things make an environment at risk for a parasite?

Answer 38

1. parasite type 2. temperature 3. moisture 4. pasture composition

Question 39

What 5 things make an environment at risk for a parasite?

Answer 39

1. Grazing system 2. Housing system 3. Co-grazing 4. Alternate grazing 5. Anthelmintic regime

Question 40

Control is based on _____?

Answer 40

risk

Question 41

In the principles of parasite control, describe the susceptibiltiy of adults, compromised adults, and young stock.

Answer 41

1) Adults are mostly fine the majority of the time - Low susceptibility. 2) Compromised adults are pregnant, immunosupressed, or aged. Moderate susceptibility. 3) Young stock - Immature immune system. Highest susceptibility.

Question 42

Which grazing animals are at risk, high to low?

Answer 42

1) sheep **HIGH** 2) spring dairy cows 3) autumn dairy cows 4) beef calves **LOW**

Question 43

What 4 things to consider with pasture managment?

Answer 43

Avoid overuse of pastures and decrease pasture burden 1) Stocking densities - taking into account risk of stock 2) Mixed grazing -parasite cross over 3) Rotational grazing -between age cohorts (biological hoover) 4) Young stock pasture - turn out onto least contaminated pastures

Question 44

What is the 80/20 rule regarding parasites?

Answer 44

Most of the Parasites are in a minority of the population.

Question 45

Describe Ostertagia ostertagii.

Answer 45

- Anterior end has a mouth opening that feeds on the gut contents of the host - Lives in the abomasum of cows - Burrows into the mucosa of abomasum - Late summer and autumn

Question 46

What aspect of the posterior end of Ostertagia organisms was used to identify the organism prior to molecular ID?

Answer 46

Presence of 2 spicules.

Question 47

Describe Toxocara canis.

Answer 47

- Ascarid worm; long, spaghetti-like - Usually found in young animals - Live in small intestine - Produce very distinct eggs - Can survive a very long time in the environment - Infectious once larvae develop within the host.

Question 48

Describe cyathostomins.

Answer 48

- 'Small redworms' - Mostly white - Live in large intestine - Ubiquitous.

Question 49

True or false: Nematodes have separate sexes.

Answer 49

True; they are di-ecious.

Question 50

Which sex of nematodes are often bigger?

Answer 50

Females.

Question 51

One nematode egg gives rise to how many adults?

Answer 51

One.

Question 52

Describe the body structure of nematodes.

Answer 52

Organized with cavities.

Question 53

What allows nematodes to survive environmental conditions?

Answer 53

Cuticle.

Question 54

What allows nematodes to move?

Answer 54

Muscle layer.

Question 55

What kind of life cycle do flatworms have?

Answer 55

Indirect.

Question 56

Flatworms are what kind of parasite?

Answer 56

Obligate parasites.

Question 57

How do flatworms move?

Answer 57

Spikes on outside of tegument.

Question 58

Describe Taenia solium.

Answer 58

- 'Pork tapeworm' - Humans are definitive host, pigs are intermediate host - Causes space occupying lesions and epilepsy.

Question 59

Describe Fasciola hepatica.

Answer 59

- Mammalian species are definitive host - Intermediate host is very specific to snails - Causes serious economic losses in ruminants - Zoonotic.

Question 60

Describe the life cycle of Toxocara cati.

Answer 60

- Definitive host is cats - Paratenic host is rodents and birds.