Nematoda

Question 1

What is the phylum of unsegmented roundworms?

Answer 1

Phylum Nematoda

Unsegmented roundworms.

Question 2

What is the characteristic of nematodes’ digestive tract?

Answer 2

Has a two-hole digestive tract.

Advancements over flatworms.

Question 3

How many nematode species are there?

Answer 3

Nematodes are classified into about 16,000 species, but the actual number could be as high as 500,000.

Colorless, range in length from microscopic to several meters long, may be free-living or parasitic.

Question 4

What are the three cell layers of nematodes?

Answer 4

Nematodes have three cell layers: Ectoderm (outer tissue layer), Mesoderm (middle tissue layer), Endoderm (innermost tissue layer).

Known as pseudocoelomates, bilaterally symmetrical.

Question 5

What is the function of the cuticle in nematodes?

Answer 5

The cuticle is secreted by epidermal cells and functions to resist penetration, resist enzymatic digestion, and maintain internal hydrostatic pressure.

Usually molts 4 times during maturation.

Question 6

What is the body plan of nematodes?

Answer 6

Nematodes have a one way digestive system (mouth ➔ pharynx ➔ intestines ➔ rectum ➔ anus) and food is pushed through by hydrostatic pressure.

Linear progression.

Question 7

What type of muscles do nematodes have in their body wall?

Answer 7

Nematodes have only longitudinal muscles in their body wall that run lengthwise from the anterior to the posterior end of the worm.

Used for movement, lack circular muscles.

Question 8

What is the excretory system of aquatic nematodes?

Answer 8

Aquatic species have ventral glands called renettes that absorb waste from the pseudo-coelom and empties it through the excretory pore.

Parasitic nematodes have a more advanced tubular system.

Question 9

What is the nervous system of nematodes?

Answer 9

Nematodes have a nervous system that allows them to detect their environment, with aquatic nematodes having a pair of ocelli (eyes).

Central nervous system with a circular brain.

Question 10

Where do parasitic nematodes live?

Answer 10

Parasitic nematodes live within a host, while free-living nematodes live in marine, freshwater, or damp soil environments.

Free-living nematodes also live in the sea, fresh water, and soil.

Question 11

What are the key characteristics of parasitic nematodes?

Answer 11

1: Thick body wall for protection, 2: Vast numbers of resistant eggs for dispersal, 3: Microphagous habit pre-adapting to gut content diet, 4: Body design works well at small size.

Advantages for parasitic lifestyles.

Question 12

What is the life cycle of Ascaris lumbricoides?

Answer 12

Roundworm of man with 1.2 billion people infected worldwide, females lay 200,000 eggs a day, adults are 15-35 cm long.

Found in unsanitary soil.

Question 13

Adults - males are 15 to 30 cm long, with strongly curved tails; females are 20 to 35 cm long, with straight tails

Answer 13

ground (Night soil)

Unsanitary habits contaminate

Question 14

Life cycle: Ascaris lumbricoides

Answer 14

Humans ingest embryonated eggs containing infective larvae.

Larvae hatch from the eggs in the small intestine, penetrate the intestine wall, enter the bloodstream, migrate to the liver, travel to the lung via the blood stream.

Question 15

Life cycle: Ascaris lumbricoides (continued)

Answer 15

Larvae break out of lung capillaries and are coughed up to the pharynx.

They are swallowed and return to the intestine.

Molts twice to 4th stage larvae take place in alveoli.

Question 16

Life cycle: Ascaris lumbricoides (continued)

Answer 16

Larvae mature to adults in the small intestine.

Worms do not attach to the intestinal wall, but maintain their position by constant movement.

Worms have a life span of approximately 1 year.

Question 17

Enterobius vermicularis - the pinworm

Answer 17

Most common helminth infection in the U.S.A.

Transmission is direct, person-to-person.

Egg is infective immediately or within hours of being shed by the female.

Question 18

Enterobius vermicularis - the pinworm (continued)

Answer 18

Common worldwide but more prevalent in temperate climates.

It is a group infection especially common among children.

Very often associated with low sanitation and hygiene.

Question 19

Enterobius vermicularis - the pinworm (continued)

Answer 19

Adults - female: creamy white, ~ 8-13 mm long, with sharply pointed tails; Wing-like flaps (cervical alae) at head end; Male: small (2-5 mm) with strongly curved posterior.

Eggs - 50 to 60 x 20 to 32 microns, broadly oval. Compressed laterally. Normally are embryonated (contain a larva).

Question 20

Life Cycle of Enterobius Vermicularis

Answer 20

mature to adults.

Eggs are ingested, hatch in intestine, larvae

at night to lay eggs.

Gravid females migrate to the perianal area

Question 21

Trichuris trichiura - the whipworm

Answer 21

Infective, fully embryonated eggs are ingested, larvae hatch in small intestine, penetrate and develop in the intestinal villi and migrate to the area of the cecum.

Larvae mature and live in the colon. Worms embed their anterior portion (as much as two-thirds of the worm) into the mucosa.

Question 22

Trichuris trichiura - the whipworm (continued)

Answer 22

Barrel-shaped eggs are released into the stool.

Eggs must undergo development in the soil for approximately 10 days to 3 weeks before they become infective.

The worm’s life span is estimated to be 4 - 8 years.

Question 23

Hookworms

Answer 23

Anterior end hooks Necator americanus
Ancylostoma duodenale
Feed on blood Cause anemia

Hookworm rhabditiform larva

Question 24

Hookworms Morphology

Answer 24

Rhabditiform larvae - long buccal cavity, indistinct genital primordium. Filariform larvae lose oral structures & have sharp pointed tails.

Adults - males: 7 to 11 mm long with a copulatory bursa; females: 8 to 15 mm long.

Eggs - 55 to 70 x 35 to 40 microns; very thin shell; usually seen in the 8 - 32 stage of cleavage.

Question 25

Life Cycle of Necator Americanus

Answer 25

larvae (1st & 2nd stages).

Eggs shed in soil hatch within 48 hours, becoming r

Question 26

Hookworm egg

Answer 26

Eggs - 55 to 70 x 35 to 40 microns; very thin shell; usually seen in the 8 - 32 stage of cleavage.

Question 27

Hookworm rhabditiform larva

Answer 27

Filariform larvae lose oral structures & have sharp pointed tails.

Question 28

Onchocerca volvulus infections involve which tissues?

Answer 28

Infections involve the dermis and subcutaneous tissues, where adults gather within nodules.

The “blinding filaria.”

Question 29

What is the vector for Onchocerca volvulus?

Answer 29

Vector - Simulium flies (blackfly, or buffalo gnat).

Question 30

Where are microfilariae found in Onchocerca volvulus infections?

Answer 30

Diagnosis - microfilariae are found in skin scrapings from around nodules.

Microfilariae not sheathed; found only in skin, not in the blood stream.

Question 31

What is the major cause of blindness in Africa?

Answer 31

Blindness occurs due to the presence of microfilariae in ocular structures. This parasite is a major cause of blindness in Africa. Control is difficult because Simulium flies breed in running water.

Major pathology and symptoms -

Question 32

What is the vector for Loa loa?

Answer 32

Vector - Chrysops (mango fly), a large fly with biting mouthparts.

Question 33

How can the diagnosis for Loa loa be confirmed?

Answer 33

Diagnosis - Usually made from clinical symptoms, but if laboratory confirmation is required, blood should be drawn between 11 am & 1 pm.

Diagnosis - Microfilariae are sheathed, nuclear column extends to tip of tail.

Question 34

What type of edema is caused by Loa loa infections?

Answer 34

Infections cause a localized subcutaneous edema, particularly around the eye, because of larval migration and death in capillaries. Living adults cause no inflammation; dying adults induce granulomatous reactions.

Major pathology and symptoms -