Nematoda Ascarids

Phylum Nematoda - Chapter 22

Nematodes or roundworms are among the most abundant animals on earth - over 500,000 species have been described.

Majority of nematodes are free-living in every conceivable habitat.

• free-living species are commonly microscopic in size

• importance? ____________________________

Phylum Nematoda

Two groups of nematodes are parasitic: (1) ___________________________________ - cause diseases of medical and veterinary importance - attract the attention of parasitologists (2) ___________________________________ - may destroy plants resulting in economic losses - attract the attention of plant pathologists

Characteristics of the Phylum Nematoda1. Body is non-segmented, elongate, and circular in cross-section (i.e. the name "roundworms").

2. Body wall consists of:

a) outermost noncellular ______________________________

b) underlying ___________________________ that secretes the cuticle

• is a cellular syncytium with nuclei lying in 4 thickenings

Characteristics of the Phylum Nematoda c) ____________________________________ lies below the

hypodermis

• contractile and noncontractile regions are present

• no circular muscle is present; worm cannot shorten or lengthen

• movement is due to undulating motion caused by contraction of the longitudinal muscles

Characteristics of the Phylum Nematoda

3. _____________________________________ is body cavity beneath the musculature.

- cavity is called a "pseudocoelom" as it is not lined internally with ______________________________

- pseudocoelom is filled with a fluid called pseudocoelomic fluid

- reproductive organs are suspended within the pseudocoelom


Pseudocoelomic fluid has two functions:

(1) serves as _________________________________________ giving the body rigidity

(2) serves as ________________________________________ transporting materials from cell to cell


4. Digestive tract is complete.

Mouth pharynx esophagus intestine anus

• Intestine possesses well-developed microvilli for absorption.

• Food - ___________________________________

___________________________________

• Little digestion occurs within the nematode intestine; it is dependent upon the host to digest food into an absorbable form.

Characteristics of the Phylum Nematoda 5. Nervous system consists of a

circumesophageal nerve ring and 2 or 4 longitudinal nerve trunks extending the length of the nematode.

Seen only with special staining

Characteristics of the Phylum Nematoda 6. Excretory system is primitive and

consists of 1 or 2 _____________________________ and excretory ducts

Excretory pore is anterior.

No flame cells are present.

Characteristics of the Phylum Nematoda 7. Nematodes are _______________________

Reproductive system consists of tubular organs lying in the pseudocoelom.

MALE nematodes are generally smaller in size. Posterior end is often curved due to presence of ____________________________________+.

Male system is a single tubule.

Inner end is _________________________

___________________________

___________________________

____________________________ supported by spicules


FEMALE nematodes are larger in size. The female reproductive organs are doubled.

2 threadlike ______________________

2 _________________________

2 _________________________

single ______________________

_________________________ (female opening)


In both the male and female systems, the tubular organs are continuous and increase in diameter as they extend to the genital opening.

When viewed in cross-section, the organs are histologically distinct.

Male Female


8. Nematode development is similar in all nematodes.

Consists of 4 larval (=juvenile) stages between the egg and adult. Each stage is separated by a molt of the cuticle.

M1 M2 M3 M4

Egg L1 L2 L3 L4 Adult

Larval stages may be passed within the egg, free-living in soil, parasitic in an intermediate host, or parasitic in definitive host.

Ascarid Nematodes – Chapter 26

Ascaris lumbricoides

Common parasite of humans. Disease is called ______________________________

Cosmopolitan in distribution.

- flourishes in warm, moist climates where the eggs may remain viable in warm soil for many years.

- use of ___________________________ to fertilize vegetables is common source of infection.

- Children are most likely to become infected by ingesting eggs by eating dirt or placing soiled fingers or toys into the mouth.


Human is the only definitive host of this parasite.

In the U.S. infections are most common in _________________________________

Parasite is endemic in Wisconsin - prevalence is low - 1.3% in 1976 and 0.5% in 1987.


ADULTS are the largest nematode parasites of humans.

Males are ______________ inches in length and 1/8 inch in diameter.

• posterior end is curved due to presence of spicules.

Females are ______________ inches in length and 1/4 inch in diameter.


Anterior end is composed of ___________________ which surround the mouth.


EGGS are __________________________________________ _____________________________________________.

Eggs are unembryonated when passed in the feces.

Embryonation occurs in the soil.

Unembryonated egg in feces Embryonated egg in soil

Life Cycle of Ascaris lumbricoides

1. Adult males and females live in _______________________

2. Female releases 200,000 eggs/day which are passed in the feces.

3. Eggs embryonate in warm, moist shady soil and __________________stages are passed within the egg.


4. ____________________ is the infective stage and is ingested by a human.

5. L3 hatches from egg in the duodenum, penetrates the duodenum, enters the circulation, travels through the heart, and reaches the ____________________ via the pulmonary circulation.

6. In the lungs, the L3 molts to the L4 stage.


7. L4 break into the alveoli, move up the respiratory tree to the pharynx, and __________________________ 8. L4 move into the _________________________where they molt to theadult stage. Become mature in 2 months. Migratory phase (time from ingestion of the L3 in egg untilL4 reach the small intestine) is about 25 days.


Adults typically live a year.

Why is there this migratory phase?

Pathology of Ascaris lumbricoides

Adults cause:

(1) _________________________ (due to toxemia from Ascaris waste products)

(2) __________________________(due to loss of monosaccharides and amino acids absorbed by the worms)

(3)__________________________________by large numbers of tangled worms (may be fatal).

Pathology of Ascaris lumbricoides

Larvae cause problems in the lungs when they break through the lung capillaries to enter the respiratory tree.

(1) small hemorrhages are produced causing plasma to enter alveoli resulting in ________________________

(2) inflammatory response to this damage occurs and __________________ _________________________________________ resulting in pneumonia-like symptoms

The more eggs ingested, the more migrating larvae, the greater the pathology.

larva

Inflammatory cells


DIAGNOSIS - ID eggs in feces

Eggs have thick, rough outer shell.

Size:

There is no diagnostic method for migrating larvae.

Treatment of Ascaris lumbricoides

TREATMENT - drug called _____________________________ is effective against adults.

No drug treatment is available against migrating larvae.

Ascaris suum

___________________________ is the single greatest cause of economic loss in the swine industry.

Adults of A. suum are nearly identical to A. lumbricoides in morphology (differences are visible only with scanning EM).

Parasitologists believe that a single species of Ascaris infected both humans and pigs at one time but has now evolved into two separate species - one infecting humans and one infecting pigs.

Ascaris suum

LIFE CYCLE, PATHOLOGY, DIAGNOSIS, AND TREATMENT of A. suum is identical to that of A. lumbricoides except that pigs are the only hosts.

Larval migration in lungs

Egg with L3 infective stage

Adults in small intestine

Unembryonatedd eggs in feces (identical to A. lumbricoides)

Ascaris suum

Question? Can Ascaris suum develop into adults in humans?

Difficult to find a volunteer for this experiment but we did find out an unusual way.

Ascaris suum

Ascaris suum

What did we find out from infections in these “volunteers’?

1. If eggs of A. suum are ingested by a human, the ___________ larvae will hatch from the egg and undergo _______________________________.

2. The migration is abnormal and greater pathology occurs in the human lungs resulting in severe ____________________. A near-fatal pneumonia occurred in the roommates

3. Adults? _____________________________________

Toxocara canis and Toxocara cati

Common ascarids in the ______________________________________________

Prevalence in dogs and cats is estimated to be 20 to 100%.

These parasites are enzootic in Wisconsin dogs and cats.

Adults are much smaller than Ascaris.

- males are about ____ inches in length

- females are _____________inches in length

Toxocara canis Life Cycle

4 aspects to the life cycle:

1. Normal cycle in the dog

Dogs are infected by ingestion of ______________________

Larvae undergo migration through the ___________and are swallowed

Reach adulthood in dog _______________________

1. Normal cycle in dog L3

L3


2. Addition of a paratenic host (mouse) If a mouse ingests an infective egg, the ________hatches and migrates to

many internal organs. It develops no further. If mouse is eaten by a dog, the ________ penetrates the dog’s intestine

and undergoes normal migration.

L3

L3

L3

1. Normal cycle in dog

2. Paratenic host

3. Transplantal transmission

If a bitch becomes infected, the migrating L3 can cross the placenta to infect the fetal puppies.

When the puppies are born, they are already infected with adult worms.

Prevalence rates in puppies can reach 100% because of the efficiency of transplacental transmission.

3. Transplacental transmission

L3

L3

L3


4. Human infection

L3

L3

L3

L3

L3

4. Human infection

Human infections of Toxocara cause ______________________________________________

This disease results when eggs with L3 are accidentally ingested by humans.


4. Human infection

L3

L3

L3

L3

L3

L3 hatch in the human small intestine, penetrate the intestine, and enter the circulation.

L3 are carried throughout the visceral organs where they wander randomly - hence, the name "visceral larva migrans".

further development? ___________________________

___________________________


Eventually, the human immune system recognizes the parasite, encapsulates it with ______________________________, and the L3 is killed.

Pathology of Visceral Larva Migrans

PATHOLOGY - dependent upon which organs are invaded by the L3

1. ______________________ is commonly invaded - hepatomegaly & cirrhosis may occur

2. __________________________ invasion results in a severe tissue reaction that can result in death

3. _____________________________may be invaded - scar tissue deposition in the retina can result in blindness

Scar tissue in retina

L3 in retina

Tragically, most human cases involve children due to their close association with pets.

Diagnosis and Treatment of Toxocara in Dogs & Cats

DIAGNOSIS:

Adults in dog - Identify egg in feces

Diagnostic features –

____________________________

____________________________

____________________________

TREATMENT -

Diagnosis and Treatment of Human Visceral Larva Migrans

DIAGNOSIS:

Larvae in human are very difficult to ID

- only way is to ____________________________________

____________________________________________

TREATMENT - _____________________________has recently been reported to be successful.

Prevention of Human Infection

1. _______________________________________________

2. _______________________________________________

• many cities have enacted "pooper scooper" laws that require owners to clean up after their pets

• especially important in parks where pet owners take animals for walks and children are playing

3. ________________________________________________

Baylisascaris procyonis

Raccoon ascarid - common parasite in the small intestine of raccoons

This parasite has recently been found to cause ________________________________________________ in HUMANS

Baylisascaris procyonis

Raccoons are infected by ingestion of ____________________________

Larvae undergo migration through the __________________________, are swallowed, and reach adulthood in raccoon __________________________ .

Egg with L3

Human Infections of Baylisascaris procyonis

Result from the accidental ingestion of eggs with L3

L3 hatch in small intestine, penetrate intestine, and enter circulation

L3 have preference for invading the ___________________________________ where they cause a severe tissue reaction - often fatal.

Egg with L3


Four human fatalities - in Pennsylvania (1983), Illinois (1985), and two in 2002 in Minnesota

• occurred in children who had associations with raccoons.


This parasite is a POTENTIAL HEALTH HAZARD IN WISCONSIN

Wisconsin DNR survey indicated that 51% of our raccoons are infected. Highest prevalence is in the southern half of the state.

Juvenile raccoons have heavy infections

What might this suggest?


Having a young raccoon as a pet could be a fatal mistake!

Raccoon hunters and trappers should be aware of this dangerous parasite.

Anisakis spp.

Anisakis is parasitic in the stomach and small intestine of ______________ ____________________________________________________________.

____________________________are 1st intermediate hosts of this parasite.

Many species of __________________________serve as 2nd intermediate hosts of these ascarids - Pacific salmon, Atlantic cod, haddock, herring, & mackeral

Egg with L2

L2 in copepod or krill

L3 in marine fish

Anisakis spp.

Egg with L2

L2 in copepod or krill

L3 in marine fish

If marine fish containing Anisakis L3 are eaten in raw or poorly cooked fish (i.e. sushi, cerviche, etc.), HUMANS CAN SERVE AS ACCIDENTAL HOSTS.

Disease is called ________________________________________

Human ingests raw fish

Anisakis spp.

Anisakis L3 from marine fish are about 1 inch long. L3 normally occur in the fish intestine but migrate to the musculature when the fish __________________________ and warm up during transportation.

Pathology of Anisakis in humans

PATHOLOGY:

1. Larval Anisakis (an L3) burrows into the wall of the stomach or small intestine

- _______________________is produced around larva

- causes _________________________________

2. Larva eventually dies (humans are abnormal hosts) resulting in a _______________________________________________ to the dead worm

- this response mimics an ulcer or acute apppendicitis

- fatalities have occurred.

Human Cases of Anisakis spp.

U.S. has ~12 cases/year - mostly in west coast and Hawaii

Japan has about 1,000 cases/year

DIAGNOSIS and TREATMENT - find L3 by ______________________________ and remove it

PREVENTION -

Enterobius vermicularis - Chap. 27

____________________________________ - Humans are the only host of this parasite.

Cosmopolitan distribution - common in temperate and tropical climates.

In Wisconsin?

Enterobius vermicularis

Almost anybody can become infected with this parasite. No social class is exempt. These parasites soon become "family affairs".

Once one person, usually a child becomes infected, other family members will undoubtedly also become infected.

Adults of Enterobius vermicularis

Adults live in the _______________________________________________ (ileum, cecum, appendix, and colon).

They feed on bacteria and dead intestinal cells - they do not invade tissue.

Pinworms are recognized by 2 structures:

1. ____________________________- winglike extensions of the cuticle at the anterior end

2. _______________________________- muscular bulb at end of esophagus


Males: _______________________________________________________

______________________________________________________________

Females: ______________________________________________________

______________________________________________________________

______________________________________________________________

female

male


Female showing esophageal bulb & cephalic alae Male with curved posterior end

Life Cycle of Enterobius vermicularis

1. Adults copulate in the human digestive tract. Male dies after copulation.

2. Female migrates at night to the perianal folds of the anus and deposits eggs (commonly over 10,000) in the skin of the ____________________. Female dies after all eggs have been laid.


3. Eggs contain L1 larvae when laid, but within 6 hours larvae molt twice in the egg to the ______ stage.

4. ____________________ are infective and when ingested by a human, the L3 hatch in the small intestine.

5. L3 molt twice to the adult stage as the worms move into ileum and large intestine.


METHODS OF HUMAN INFECTION:

1. Infective eggs may be transmitted _____________ ______________________________________________ Deposition of eggs by the female causes _______________________

2. Bed clothing and bedding are contaminated with infective eggs and ingested.

3. _____________________ - eggs are inhaled and ingested.


METHODS OF HUMAN INFECTION cont:

4. Infective eggs can become ______________________ (sweeping in a bedroom) and can be inhaled and swallowed.

5. _____________________ - if the perianal region is not cleaned for some time, infective eggs may hatch and the L3 wander into the large intestine and molt to adults.

Pathology of Enterobius vermicularis

1. Pinworms are generally considered to be harmless as they do not invade any tissue. They may cause ___________________ __________________________________________________.

2. They do cause irritation of the anal region resulting __________________________________________________. Secondary bacterial infection in areas scratched raw may occur.

3. Pinworms also cause ______________________________ - mental anguish and embarrassment of parents whose kids have "worms" - this often leads to frantic efforts to eliminate the parasite and its eggs.

Diagnosis of Enterobius vermicularis

DIAGNOSIS - ______________________is commonly used.

Use of double-stick tape on a tongue depresser.

This is pressed against the perianal folds where eggs will stick to the tape.

Tape is then stuck onto a microscope slide and examined for eggs.

Diagnosis of Enterobius vermicularis

DIAGNOSIS - Eggs are distinct.

• football-shaped with one side flattened

• eggshell is smooth

• size -

Treatment of Enterobius vermicularis

TREATMENT - pinworms are easily killed with drugs - _________________________________________________

To prevent re-infection, treat the whole family.

Wash all bed clothes and bedding in hot water to kill infective eggs.

Documents

Nematoda Ascarids