Practical 16: Nematoda, Acantocephala

What is the common name for nematodes?

roundworms

What are the common names for Acantocephala?

thorny-headed worms or spiny-headed worms

Describe the basic morphology of nematodes

1. structurally simple organisms

2. body is not segmented

3. characterised as a tube within a tube

4. range from 0.3 mm to over 8 m

5. sexes are separate

Which body systems can be found in nematodes?

digestive system, nervous system, excretory system, reproductive system

What is the pseudocoelom?

fluid-filled body cavity

Which structure of nematodes is essential for movement?

pseudocoelom

What type of reproduction do nematodes undergo? (asexual/sexual)

sexual

Where can nematodes be found in the host?

digestive system, lymphatic system, nervous system, excretory system, reproductive system, respiratory system, body cavities, skin

What are the structures of the body wall of nematodes?

1. cuticle (pseudosegmentation)

2. hypodermis

3. pseudocoelom

What are the classes in phylum Nematoda?

Secernentea (Phasmida), Adenophorea (Aphasmidia)

What is the main difference between Secermentea (Phasmida) and Adenophorea (Aphasmidia)?

Secermentea (Phasmida) have phasmids and Adenophorea (Aphasmidia) don’t have phasmids

What are phasmids?

paired sensory organs at the posterior end around the anus or cloaca; chemoreceptors

What are the orders of nematodes found in class Adenophorea (Aphasmidea)?

Enoplida

What are the families of nematodes found in order Enoplida?

Trichuridae, Capillariidae, Trichinellidae

What are the orders of nematodes found in class Secementea (Phasmidea)

Rhabditida, Strongylida, Ascaridida, Spirurida, Camallanida

What are the main parts of the digestive system in nematodes?

1. mouth

2. oesophagus

3. intestine

4. anus/cloaca

Describe the mouth of nematodes

simple opening, may be surrounded by two or three lips, and leads directly into the oesophagus

What types of oesophagus are there in nematodes?

rhabditoid, strongyliform, filariform, trichuroid

Describe the rhabditoid oesophagus in nematodes

2 swellings (protubus and bulbus) separated by isthmus

Describe the strongyliform oesophagus in nematodes

bulbus in posterior part

Describe the filariform oesophagus in nematodes

simple and slightly thickened posteriorly

Describe the trichuroid oesophagus in nematodes

narrow with anterior muscular part and posterior glandular part with one or two rows of stichocytes

Describe the intestine of nematodes

straight tube; a valve separates the intestine from the rectum in some species

What are the possible food sources for nematodes in DH?

host tissues, host blood, mucus

What is the cloaca in nematodes?

1. opening in males, which functions as anus

2. where the vas deferens opens into

3. where the copulatory spicules may be extruded from

How many openings are there in the posterior end of female nematodes?

2 (anus, vulva)

Describe the excretory system of nematodes

primitive, consisting of a canal in each lateral cord, which join and open to the exterior in the oesophageal region as the excretory pore

Describe the main parts of the nervous system

nerve ring around the pharynx, large ventral nerve and smaller dorsal, or 2 or more lateral nerves

What are the sense organs in nematodes?

tactile (cephalic, cervical, caudal, peripheral) papillae, phasmids, amphids, pigment spots, ocelli

What are phasmids used for?

location of other male/female for copulation

Basic description of the reproductive system in nematodes

simple continuous tube; sexes are separate

What are the female reproductive organs in nematodes?

1. single tubular ovary

2. oviductus

3. uterus

4. receptacle seminis

5. vagina

Where can the vagina be found in nematodes?

laterally or medially in the first third of the body

What are the male reproductive organs in nematodes?

1. single tubular testis

2. vas deferens

3. seminal vesicle

4. cloaca

5. bursa copulatrix

What does the bursa copulatrix consist of?

1. numerous bursal rays (ventral, lateral, dorsal)

2. spicule

3. gubernaculum

What is the purpose of the spicule in nematodes?

helps with penetration

What is the purpose of the gubernaculum in nematodes?

helps with movement of spicules

What are the types of offspring of nematodes?

oviparous, ovoviviparous, viviparous

oviparous

unembryonated eggso

ovoviviparous

embryonated eggs

viviparous

live larvae

How many life stages are there in nematodes?

6 (4 juvenile, pre-adult, adult)

How many moultings does development of a nematode include?

4

What happens during the moulting of a nematode?

new cuticular layers are formed by hypodermis and old cuticle is detached

What are the ways of infection of DH of nematodes?

1. ingestion of egg with L3

2. direct infection of larvae by skin penetration

3. ingestion of infective larvae

4. ingestion of IH with infective larvae

5. inoculation of infective larvae with vectors

What is the infective stage of nematodes?

L3 (L1 in Enoplida)

What type of lifecycle does a geohelminth have?

direct

What type of lifecycle does a biohelminth have?

indirect

What types of life cycle can nematodes have?

direct (geohelminth), indirect (biohelminth), paratenic parasitism

Describe the life cycle of strongyles (fam. Trichostrongylidae)

1. LC: direct

2. eggs are passed with faeces; hatch on the ground releasing L1

3. moults to L2, and moults to infective L3

4. infection of by ingestion of L3

5. the host is infected by ingestion of L3 with herbage

6. L3 enter the mucosa of the small intestine, caecum, or colon; moult L4→L5→ adult

Which genus of Trichostrongylidae has larva which hatches from the egg as L3?

*Nematodirus*

Which genus of Trichostrongylidae has larva which hatches from the egg as L2?

*Marshallagia*

Describe the egg of *Nematodirus spp.*

1. extra large

2. eliptic, symmetrical

3. 2 thin shells

4. unembryonated (8 dark brown blastomeres)

5. light grey

Describe the male posterior end of *Nematodirus spp.*

bursa copulatrix without gubernaculum and long, slender spicules fused at the tip

Describe the female posterior end of *Nematodirus spp.*

tail spine

Describe the egg of *Chabertia ovina*

1. medium

2. oval, symmetrical

3. 2 thin shells

4. unembryonates (16-32 brown blastomeres)

5. light grey

Describe the anterior end of *Chabertia ovina*

1. large, bell-shaped buccal capsule

2. double ring of small cuticular teeth

3. sclerotisised plate at bottom of buccal capsule

Describe the male posterior end of *Chabertia ovina*

bursa copulatrix is well developed, the spicules are long with gubernaculum

Describe the life cycle of lungworms

1. LC: indirect

2. larvae or eggs with L1 are passes with faeces

3. the first 2 moults take place in IH to infective L3

4. DH is infected by ingestion of IH with L3

5. larvae migrate via the bloodstream to the lung, where they moult to L4, L5 in the bronchi and trachea

Describe the life cycle of *Syngamus trachea*

1. eggs produced by females pass from the trachea to the oral cavity, are swallowed and excreted in faeces

2. infection occurs by

   1. ingestion of L3 in egg, or free-living L3

   2. ingestion of paratenic host with L3

3. ingested larvae migrate from the intestines, via the blood, to the lungs, then the trachea

Describe the morphology of Trichuridae

1. thick, relatively short posterior end

2. long thread-like anterior end (whip-like in appearance)

3. posterior end is spirulated in males and straight in females

What is the common name for Trichuridae?

whipworms

Describe the life cycle of Trichuridae

1. LC: direct

2. unembryonated eggs are shed to the environment where infectious L1 develop inside the eggs

3. eggs with L1 are ingested by DH and hatch in small intestine or caecum and colon

4. invade mucosa of intestine and moult to L2

5. L2 migrate back to surface of mucosa (under epithelial layer) and complete moulting and development to adults

Describe the egg of *Trichuris spp.*

1. medium

2. lemon-shaped, symmetrical

3. 2 thick shells, bipolar prominent plugs

4. unembryonated

5. brown

Which genus of nematodes has males with a coiled tail?

*Trichuris*

Describe the male posterior part of *Trichuris spp.*

1. coiled

2. spinate spicular sheath is protruded with spines

Describe the life cycle of Rhabditidae (*Strongyloides spp.*)

1. LC: direct

2. host sheds embryonated eggs to environment, rhabditiform L1 develop and hatch

3. L1 moults twice to filariform L3 OR develop into free-living male or female adults, which undergo sexual reproduction (heterogonic life cycle)

4. L3 may infect DH by penetrating skin or by ingestion

5. larvae undergo systemic migration via tracheal or somatic route

6. only females in intestines undergo asexual parthenogenic reproduction to form eggs

What is rhabditiform?

non-infective, feeding form

What is filariform?

infective, non-feeding form

Describe the tracheal route of systemic migration

1. L3 migrate via subcutis of skin to lymphatic vessels or veins, penetrate to heart and lung, then to alveoli

2. from respiratory tract, migrate to pharynx, then small intestine

3. in small intestine, moult to form adults, penetrate mucosa of upper digestive tract, then migrate to trachea

Describe the somatic route of systemic migration

1. larvae pass in bloodstream to lungs, and via blood, penetrate to other organs, muscles, mammary glands, subcutaneous fat, etc.

2. larvae can remain in hypobiotic state in these organs for many months

3. become activated in peripartum period and lactation

4. migrate to mammary gland and are excreted in milk, infecting young animals (lactogenic infection)

Which organ systems do order Strongylida affect?

digestive system, respiratory system

What is the main morphological difference between *Ancylostoma caninum* and *Ancylostoma braziliense*?

*A. caninum*: 3 pairs of teeth

*A. braziliense*: 1 pair of long teeth

Which *Ancylostoma spp.* affect humans?

*A. braziliense, N. americanus*

What do *Ancylostoma spp.* cause in humans?

dermatitis = larva migrans cutanea

Describe the egg of *Ancylostoma spp.*

1. medium

2. ovoid, symmetrical

3. 2 thin shells

4. unembryonated (4-8 brown blastomeres)

5. grey

What is the cause of pathology of *Ancylostoma spp.*?

bite microvilli of small intestine, ingest mucosa of microvilli, opening up for secondary bacterial infections

Describe the life cycle of *Ancylostoma caninum*

1. LC: direct

2. unembryonated eggs are shed in the faeces; L1 forms in egg in environment

3. L1 hatches, and moults → L2 → L3

4. L3 is ingested or penetrates through the skin

5. some larvae remain in small intestine and develop to adults; somatic or tracheal migration

What is the tracheal migration route of *Ancylostoma*?

1. L3 penetrate subcutaneous veins, transported to lungs, where they migrate via trachea and oesophagus to small intestine

2. moult → L4 → L5 and adult

What is the somatic migration route of *Ancylostoma*?

1. migration starts from the intestine, subcutis, or lungs, leads through body tissues or cavities to different organs

2. larvae invade striated muscle or fat cells and become hypobiotic

3. some are reactivated in the final stages of pregnancy and migrate to the mammary glands and are excreted in milk (lactogenic transmission)

Describe the posterior end of male *Ancylostoma duodenale*

ends in bursa copulatrix with bursal rays and spicules

Describe the posterior end of female *Ancylostoma duodenale*

straight, pointed end

Describe the anterior end *Ancylostoma duodenale*

buccal capsule having 2 pairs of teeth and 2 dental plates

What is characteristic about order Ascaridida?

three large, rounded lips

Describe the life cycle of *Toxocara canis*

1. LC: direct

2. females release unembryonated eggs which are passed in the faeces

3. L3 develops in the egg in the environment

4. L3 egg (or L3 in paratenic host) is ingested by DH

5. L3 hatch from egg and migrate via tracheal or somatic migration

What type of migration do *Toxocara spp.* have?

entero-hepatic-pulmonary (and somatic)

What are the ways of infection of *Toxocara spp.*?

1. orally

2. transplacental

3. lactogenic

4. carnivorous (paratenic host)

What is the tracheal migration of *Toxocara spp.*?

1. after ingestion, L3 hatch from eggs, penetrate the intestinal wall, enter the bloodstream, and migrate to the liver

2. they are then transported to the lungs, where they invade the alveoli, moult to L4 and migrate to trachea and pharynx to small intestine

3. moult to L5 in small intestine and mature to adult

What is somatic migration of *Toxocara spp.*?

1. after infection of older dogs

2. L3 invade gut wall, enter blood circulation and are taken to the lungs, where they are trapped in capillaries, penetrate the walls, migrate through the tissue to re-enter the bloodstream

3. migrate to various organs (muscles, liver, kidney, etc.) where they can survive for years in hypobiotic state

4. reactivated and can cause transplacental and lactogenic transmission

Describe the egg of *Toxocara canis* and *Toxocara cati*

1. medium

2. subspherical

3. 3 thick shells, pitted shell

4. unembryonated (1 blastomere)

5. dark brown

Describe the egg of *Toxascaris leonina*

1. medium

2. spherical

3. 3 thick shells

4. unembryonated (1 blastomere of light colour)

5. colourless

Describe the cervical alae of *Toxocara canis*

long and narrow

Describe the cervical alae of *Toxocara cati*

short and broad

Describe the cervical alae of *Toxascaris leonina*

long and narrow

What types of migration is there in *Toxocara canis* in humans?

1. larva migrans ocularis

2. larva migrans visceralis

3. brain, heart

Where are species of family Oxyuridae found in DH?

large intestines

What is the common name of family Oxyuridae?

pinworms

What happens to female Oxyuridae species when ready to lay eggs?

crawls out of the anus and deposits the egg on the perianal skin

What are important families of order Spirurida?

Spiruridae, Filariidae

Describe the life cycle of *Dirofilaria immitis*

1. LC: indirect

2. microfilariae (larvae) released by female into the blood are ingested by blood-sucking mosquiotes (Culicidae)

3. microfilariae → “sausage form” → L2 → L3 (infective stage)

4. L3 migrates to proboscis and invades DH when mosquito feeds

5. L3 moults to L4 in subcutaneous tissue, then migrates between muscle fibres

6. L4 moults to L5, then penetrates the wall of a vein and arrives in the arteria pulmonalis or right heart

7. in dogs: adult females produce microfilariae

8. in cats: only 50% of infected cats become microfilaraemic