Helminths

Question 1

Helminths

Answer 1

Helminths = Worms
Most helminths are NOT parasitic - they are free living in the environment
A minority of helminths are parasitic, a minority are relevant to vet med and pub health
Large expenditure on vet med is spent on anthelmintic drugs

Question 2

What are the two categories of parasitic helminths?

Answer 2

Nematodes (roundworms)
Platyhelminths (flatworms)

Question 3

What is a model helminth?

Answer 3

Cenorhabdytis elegans - NOT a parasite, was the first complex organism to have its genome sequenced

Has 302 neurons - used extensively in studies of neural networks

Question 4

How many sexes do parasitic nematodes have?

Answer 4

They have two separate sexes (di-ecious)

Question 5

Are male or female parasitic nematodes generally larger?

Answer 5

The females are often bigger

Question 6

What does one parasitic nematode (roundworms) egg give rise to?

Answer 6

One egg gives rise to one adult

Question 7

What is the general structure of parasitic nematodes?

Answer 7

Organized body structure, with cavities

Question 8

Nematodes (roundworms) of Grazing Animals:

Answer 8

Often have only one host (definitive host)
Infective larvae are spread via grass/plant material that is contaminated by eggs in host feces
Eggs mature, releasing larvae which become infective
More hosts = more eggs = more larvae = more infection
Generally, infection only significant above a certain level
Reducing the host number does work!

Question 9

Platyhelminths (flatworms) are split into which two categories”

Answer 9

Trematodes (flukes)
Cestodes (tapeworms)

Question 10

Nematode vs Flatworm

Answer 10

Nematode - organs in coelum, protective cuticle
Flatworm - organs in parenchyma, metabolically active tegument

Question 11

How many hosts do Platyhelminths (flatworms) require to complete their life cycle?

Answer 11

Two or more

Question 12

What is the Platyhelminths body structure like?

Answer 12

They have more primitive body structures than the nematodes (roundworms), organs directly embedded in a solid parenchyma

Question 13

What is the outer surface of the Platyhelminths like?

Answer 13

The tegument is metabolically active, unlike the nematode cuticle

Question 14

Are flatworms (Platyhelminths) hemaphrodites?

Answer 14

Often, but not always

Question 15

What type of sexual reproduction does Platyhelminths have?

Answer 15

There is asexual as well as sexual reproduction, one egg produces many adults

Question 16

Definitive host:

Answer 16

Helminth (worm) reproductive stages in this host

Question 17

Intermediate host:

Answer 17

Immature helminth stages here

Question 18

Paratenic host:

Answer 18

Optional extra host (not required for lifecycle completion)

Question 19

Direct lifecycle:

Answer 19

One host only required

Question 20

Indirect lifecycle:

Answer 20

More than one host species required

Question 21

Other facts of helminths (worms):

Answer 21

Dampen the immune responses of their host

Question 22

What are some current problems with helminths?

Answer 22

We have a very limited # of drugs available
Drug resistance
Few new drugs in development

Question 23

Who do parasitic helminths infect?

Answer 23

All grazing animals - control is mostly based on keeping #s below production/disease/welfare levels

Question 24

Parasitic helminths are common in:

Answer 24

Dogs, cats, wildlife and exotic pets

Question 25

Is zoonotic transmission a concern?

Answer 25

YES, relevant to food safety and other aspects of public health

Question 26

What must veterinarians do in response?

Answer 26

Must be competent to advise on helminth control, while minimizing use of anthelmintics and preserving drug efficacy

Question 27

What is the future of worm control?

Answer 27

New drugs - rare and slow
Vaccines - difficult
Anthelmintic stewardship
Prescription only for food animals in Europe