2.2 Intro to Nematodes - Roundworms

What phylum do nematodes belong to?

Nematoda.

How diverse are nematodes?

They contain millions of species and are the most numerous and diverse group of animals on Earth.

What mnemonic helps remember taxonomy order?

Kings, Play, Cards, On, Fat, Green, Stools.

Why are nematodes important in veterinary medicine?

They are the largest and most diverse group of parasites that infect animals.

Where are nematodes found?

Everywhere.

Are nematodes multicellular or unicellular?

Multicellular.

Describe the body structure of nematodes.

Unsegmented, tubular, bilaterally symmetric.

What type of digestive tract do nematodes have?

A complete digestive tract.

What is the rectum in nematodes?

The terminal part of the female digestive tract.

What is the cloaca in nematodes?

The terminal part of the male digestive and reproductive tract.

What does dioecious mean?

Nematodes have separate sexes (male and female).

How many eggs can female nematodes produce?

Several thousand eggs (or larvae) per day.

What is the nematode "superfamily" Ascarids?

A group of roundworms between order and family level.

What are the three main ascarids of dogs and cats?

Toxocara canis, Toxocara cati, Toxascaris leonina.

Which species does Toxocara canis infect?

Dogs.

Which species does Toxocara cati infect?

Cats.

Which species does Toxascaris leonina infect?

Dogs and cats.

In which animals are Toxocara species most common?

Puppies and kittens.

What is a common physical sign of Toxocara infection in young animals?

"Wormy belly."

Why should all puppies and kittens be checked for Toxocara?

They are commonly infected at initial visits.

Where are Toxocara adults found in the host?

Small intestine.

Can Toxocara migrate to other tissues?

Yes, they may migrate elsewhere in the body.

What do Toxocara worms feed on?

Body fluids and intestinal contents of the host.

What GI signs can Toxocara cause?

Vomiting and diarrhea.

Where might adult Toxocara worms be seen?

In feces or vomit.

How is Toxocara spread?

Ingestion of eggs, transplacentally, or transmammary.

How do dogs under 6 months typically acquire Toxocara canis?

In utero or through milk.

How do dogs over 6 months typically acquire Toxocara canis?

Direct ingestion of eggs or ingestion of an infected mouse/rabbit (paratenic host).

Is Toxocara canis zoonotic?

Yes.

What is the infectious stage of Toxocara canis?

L3 larval stage.

What is the PPP (prepatent period) of Toxocara canis?

21-35 days.

What medications can treat Toxocara canis?

Pyrantel, Ivermectin, Milbemycin, Febantel (converted to fenbendazole).

What are key prevention steps for Toxocara canis?

Monthly preventatives, cleaning feces, discouraging feces ingestion, washing hands.

Does Toxocara cati have the same life cycle as T. canis?

Yes.

How do Toxocara cati eggs differ microscopically?

They are smaller.

Is treatment for Toxocara cati the same as for T. canis?

Yes.

How does Toxascaris leonina differ from Toxocara spp.?

L3 develops faster (within 1 week) and there is no lung migration.

What is the PPP of Toxascaris leonina?

74 days.

What do Toxascaris leonina eggs look like?

Smoother outer shell with a hyaline central portion.

Is treatment for Toxascaris leonina the same as Toxocara spp.?

Yes.

What are the definitive hosts of Toxascaris leonina?

Wild and domestic canines and felines.

What is the paratenic host of Toxascaris leonina?

Rodents.

What is visceral or ocular larval migrans?

Human infection caused by ingesting Toxocara canis eggs.

What happens after humans ingest Toxocara eggs?

Eggs hatch, larvae penetrate the intestinal wall, and migrate through various tissues.

What is the taxonomy order

Kingdom, Phylum, Class, Order, Family, Genus, Species

What family is roundworms?

Ascarids

External features of nematodes

cuticle and muscles

What is the cuticle of nematodes and what is it made of?

Exoskeleton

- Protective barrier to the environment

- Protein, lipids and carbohydrates

What do the muscles of nematodes do?

Allow the nematode to move, feed and reproduce

Typical life cycle of nematodes

1. Adult female produces an egg (within the female)

2. 1st stage larva

3. First 3 stages (Juvenile)

- 3rd stage larva

- 4th and 5th stage larva (within host)

- 5th stage larva

Explain the 1st part of a nematode life cycle

Female egg produces an egg

Unicellular

Original cell divides multiple times within eggshell

- morula, tadpole, larval stages

Explain 1st stage larva

1. Hatches from eggshell in environment

2. Molts and develops = 2nd stage larva

3. Molts again = 3rd stage larva = infective stage

What happens during the first 3 stages of a nematodes (juvenile) cycle

can develop in external environment or within intermediate host, intermediate host is the transmission to definitive host

What if there is no intermediate host for a nematode

direct lifecycle

explain 3rd stage larva

must return to definitive host

explain 4th and 5th stage larva

once in the host

explain 5th stage larva

migrates to most common site for specific parasite where it develops into a mature adult, breeding begins

what is an ascarid

roundworm

Toxocara canis Life Cycle

1. eggs shed in feces

2. direct ingestion of infective L3 stage larva via paratenic host or from environment

3. L3 hatch once inside definitive host and migrate to the lungs - in young dogs

4. Adults undulate within small intestine and do not attach to host

What happens after toxocara canis are inside definitive host and in lungs

they are coughed up and swallowed where they grow into adults within the small intestine

what can happen when toxocara canis get to small intestine

they can migrate to other organs and remain dormant for years eating our nutrients