1. Chapter 15: Phylum Nematoda

2. General Characteristics
Bilateral symmetry
Unsegmented worms: not metemerised
Triploblastic: 3 germ layers
Complete mouth -> anus digestive tract
Located everywhere ( fresh water, open seas, and soil from the polar to the tropics)
No circulatory or respiratory tract

3. Where do nematodes live?
Image: Redrawn by Becky Westerdahl from Ayoub, S.M Plant nematology an agricultural training aid. Sacramento California Department of Food and Agriculture, Division
of Plant Industry. On the world wide web at

4. General Characteristics
Mode of nutrition
Can be free living- feeding on bacteria, yeast, fungus, and algae (can be harmful to plants)
Can be predatory- eating rotifers, small annelids and other nematodes
Can parasitize almost any animal and plant species
Pseudocoelomates: contains a body cavity called a pseudocoel but it lacks the peritoneal lining (mesodermal epithelium)

6. Benefits of a Pseudocoel
Even though it is not a true “coelomated” body cavity, having a pseudocoel is still an advancement over Platyhelminthes because:
It increases movement
Higher development and differentiation of digestive, excretory, and reproductive systems
Simple means of circulation (distribute O2 and nutrients)
Storage place for waste products
Acts as a hydrostatic organ

7. General Structure Tapered at both ends Cylindrical in shape
No cilia or flagella (except one species)
Has longitudinal muscles (no circular)
No protonephridia: excretory system can be:
1 or more gland cells
Canal system
Combination of gland cells and canal systems

8. General Structure
Outer Body is made of many layers of non-cellular cuticle (made mainly of collagen) that is secreted by the underlying layer called the hypodermis
Functions of the Cuticle
Serves to maintain the hydrostatic pressure
Made of crisscrossing fibers that give longitudinal elasticity but limits its ability to expand laterally

9. General Structure
Hypodermis: under the cuticle and secretes the cuticle
First true cellular layer
Longitudinal muscles located under the hypodermis
No circular muscles
Muscles are divided into 4 quadrants

10. General Structure Hydrostatic Skeleton
Accomplished by the fluid-filled pseudocoel located between the digestive tract and the body wall
Function is to transmit the force of the muscle contraction to the enclosed fluid
Nematodes do not have circular muscles to antagonize the longitudinal -> therefore, the cuticle serves that function

12. Hydrostatic Skeleton
As muscles on one side of the body contract they compress the cuticle on that side and the force of the contraction is transmitted by the fluid in the pseudocoel to the other side of the worm-> stretching the cuticle on that side (opposite side)
Stretching and compressing of the cuticle serve to antagonize the muscles and are forces that return the body to the resting position
Produces a thrashing motion for movement

13. Review of the Body Layers
Cuticle
Hypodermis
Longitudinal Muscles
Hydrostatic Skeleton (fluid in pseudocoel)

14. Digestive System Mouth (encircled by sense organs) Muscular Pharynx
Non-muscular intestine
Short Rectum
Anus (single opening)

15. Digestive System Steps of Ingestion
Food is sucked into the pharynx when muscles in the anterior portion contract and opens the lumen of the pharynx
Muscles anterior to the food relax and closes the lumen of the pharynx forcing food posterior toward the intestine
Food moves posterior by adding more food and body movements (hydrostatic pressure)
Feces formed and excreted by muscles that pull the anus open and push out feces by the force of the hydrostatic pressure that surrounds the gut

16. Nervous System
Composed of a nerve ring around the pharynx and 2 longitudinal nerve cords (1 dorsal and 1 ventral)
No nerve branches to the muscles , but processes from the muscles go to the nerve cords

17. Reproductive System Most are dioecious: separate male and female sexes
Structure of the male:
Males are usually smaller and has a curved posterior end with copulatory spicules (used for insemination of sperm against high hydrostatic pressure in the females body)
Structure of the female:
Females are longer and thicker than the male; no curved posterior end

19. Female Reproductive Tract
Females contain:
Ovaries-> Oviduct->Uterus->Vagina-> Genital Pore
Eggs of the female are produced by the ovaries and travel through tubes called oviducts where they are fertilized by the male sperm
The fertilized eggs develop in the uterus of the female until it is expelled out through the genital pore

20. Male Reproductive Tract
Males contain:
Testes-> Vas Deferens-> Seminal Vesicles-> Ejaculatory Duct
Sperm are produced in the testes and travel through a system of tubules to get expelled into the female
Sperm lack flagella (once inside the female they move by pseudopodia)

21. Reproduction Fertilization is internal
Eggs are stored in the uterus until deposition
Following Deposition is embryonation-> Juvenile worm (4 stages) each stage is separated by a shedding of the cuticle

22. Nematoda Examples
We will be looking at the following Nematoda parasitic examples:
Ascaris lumbricoides
Necator americanus (Hookworm)
Trichina worm-Trichinosis
Pinworms
Filarial Worms
Wuchereria bancrofti- Elephantiasis
Onchocerciasus
Dirofilaria immitis- Dog Heartworm

23. Ascaris lumbricoides
Large round worm of humans (live in small intestine and lung)
Infection occurs when parasite eggs are eaten with uncooked or poorly washed food (fruits or veggies) or when soiled fingers (feces) are put into mouth (Passive Transmission)
Most damage is done when they migrate around bodily tissues then return to gut to reach maturity
Females lay up to 200,000 eggs/day
Males grow to 30 cm and female 40 cm
Can also infect dogs, cats, pigs, and horses

24. Distribution of Ascaris
Highly adapted for high temperatures and sunlight
64% of the south-eastern U.S. is infected and 1.2 billion world-wide
High prevalence in tropical and subtropical areas with inadequate sanitation and where human feces are used as fertilizer

25. Ascaris lumbricoides Causes: Prevention:
Allergic reaction (release of waste or molting)
Intestinal blockage/perforation
Abdominal pain
Peritonitis
Pulmonary symptoms (coughing)
Can emerge from anus or throat
Can travel to trachea, Eustachian tube or middle ear
Prevention:
Sanitary habits
Washing agricultural products

26. 9.8
Male (top) and female Ascaris lumbricoides

27. Ascaris lumbricoides Female Male
Ascaris unfertilized egg.
Ascaris egg containing a larva, which will be infective if ingested.
Ascaris fertilized egg.

29. Ascaris lumbricoides

30. Class Nematoda - The Roundworms
Ascaris lumbricoides - Large Intestinal Roundworm
Life cycle: (complex, involves a heart-lung cycle)
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.
Larvae break out of lung capillaries into alveoli, travel to the bronchioles, and are coughed up to the pharynx. They are swallowed and return to the intestine. Two molts to 4th stage larvae take place in alveoli.

31. Class Nematoda - The Roundworms
Life cycle: (continued)
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.
Undeveloped eggs are passed in the feces. These eggs develop in soil and are infective after two weeks to one month. The egg shell is very thick and resistant to environmental changes.
Eggs can remain infective for up to 5 years if protected from direct sunlight and desiccation.

32. Ascaris Lifecycle Highlights
Mode of Infection
Egg location
Larvae location
Adult location
Symptoms
Treatment
Prevention
Passive: unsanitary habits; eating eggs off fingers or contamin-ated food
Soil->small intesti-ne
Hatch in small intestine->migrate to liver->travel to lung via blood stream-> get coughed up and swallowed
Larvae-> adults in small intestine
Site of sexual reprodu-ction
Eggs are excreted out in feces
-blockage
-coughing
-cramping
-allergic RXN
Medication
-wash hands
-wash fruits and veggies

33. Intestinal roundworms
Ascaris lumbricoides
Image: Courtesy of Richard Cyr. On the world wide web at

34. Another “NASTY NEMATODE” – THE HOOKWORM

35. Hookworm Named for the dorsal curve in their anterior end
Mouth has teeth/plates for grasping and cutting the intestinal lining of the host
Smaller in size than Ascaris
The parasite pumps blood through its gut, partially digesting it before excreting it
Do not permanently attach to one spot-> they move around intestine and reattach when they are ready to feed
Have anti-clotting factors that keep blood from clumping while feeding

37. Hookworms: Symptoms
Hookworms suck more blood than they use-> causing anemia in host
Stunt growth and development (physical and mental) in children
Lack of energy
Respiratory problems

38. Hookworm: Life Cycle
Eggs pass out of feces and juveniles hatch in soil
If human skin comes in contact with soil, infective juveniles burrow (ACTIVE TRANSMISSION) through skin to blood
Juveniles travel in blood to lungs, are coughed up to be swallowed, and mature in the intestine

40. Hookworm life cycle

41. Hookworm Lifecycle Highlights
Mode of Infection
Egg location
Larvae location
Adult location
Symptoms
Treatment
Prevention
Active: walking in contaminated areas
- Parasite burrows into skin
Feces
-> soil
Hatch in soil and burrow into skin ->travel to lung via blood stream-> get coughed up and swallowed
Larvae-> adults in small intestine
Site of sexual reprodu-ction
Eggs are excreted out in feces
-Anemia
-coughing
-delayed growth
Medication
-Protect exposed skin in contaminated areas

42. Trichinella spiralis
Encysted larvae of Trichinella in pressed muscle tissue. 
Larvae of Trichinella, freed from their cysts, typically coiled.

43. Trichina Worm Responsible for the disease Trichinosis
Humans become infected eating undercooked or raw pork
Located almost anywhere (China, Spain, France, Italy); not prevalent in U.S. due to meat inspection programs (only 100 cases/year)
It is a parasite of carnivorous and omnivorous animals(foxes, wolves, bears, raccoons, rats, skunks)-> common in rats and swine fed uncooked garbage and scraps in slaughterhouse

44. Trichina Worm: Life Cycle
Infected larvae cysts are ingested (passive transmission) in meat products
Hatches from cyst in host’s gut and travel to small intestine where they mature and undergo sexual reproduction (adult expelled by immune system)
Newborn larvae travel in blood and enters skeletal muscle where the larvae matures in the muscle and manipulates the hosts muscle DNA (lose striations) -> it recruits a blood supply to provide food to the cell and produce collagen to form a cyst and turns into a nurse cell complex
This juvenile awaits ingestion by another host

48. Trichina Worm Symptoms based on phases:
Intestinal: small intestine swelling, nausea, vomiting, abdominal pain, diarrhea, fever
Migrational: High fever, swelling, cough, lung pain
Muscle: acute, localized swelling and pain

49. Trichina Worm Lifecycle Highlights
Mode of Infection
Egg location
Larvae location
Adult location
Symptoms
Treatment
Prevention
Passive- eating raw / undercooked pork and ingesting the encysted juveniles
None-
Larval stage is directly produced
Encysted in pork-> ingested -> small intestine -> new larvae travel to skeletal muscle of host
Larvae-> adults in small intestine
See previous slide
-fever
-pain
Medication
-Cook pork completely

50. Enterobius vermicularis: Pinworms
Most common worm parasite in the U.S.
Causes little disease
Infects 30% of children and 16% of adults in the U.S.
Adults (females about 12mm long)live in the large intestine and cecum
Females migrate to anal region at night and lay eggs-> causes itching
Scratching anal region contaminates hands and bedclothes
Eggs develop rapidly and become infective within 6 hours at body temperature
When swallowed, hatch in small intestine and mature in large intestine

51. Enterobius vermicularis

52. Female pinworm from intestine Group of Pinworm eggs released from anus

53. GOT PINWORMS? Pinworm Symptoms
Perianal itching
Children can have behavioral changes; restlessness, irritability, and insomnia
Women-> pinworm can enter vagina and cause additional irritation

54. Pinworm Detection Look for eggs or worms on the perianal skin
Will not find eggs or worms in feces
Detection can be done by examining the perianal region with a flash light to locate worms (during night/early morning hours)
Eggs on perianal skin can also be detected by using “the Scotch tape method”

56. Enterobius vermicularis Enterobius vermicularis eggs
Female
Male
Enterobius vermicularis egg
Enterobius vermicularis eggs

57. Pinworm Lifecycle Highlights
Mode of Infection
Egg location
Larvae location
Adult location
Symptoms
Treatment
Prevention
Passive- eating eggs off fingers
-unsanitary habits
-auto-infection
Perianal region->fingers-> ingestion
Hatch in small intestine
Larvae travel to large intestine where they mature in the large intestine and cecum
-Perianal itching
-behavior changes
Medication
-Sanitary habits

58. Filarial Worms Thread-like nematodes
Located in tropical regions (primarily)
Humans are usually the definitive host
250 million people worldwide are infected
Spread by an insect vector
Microfilariae: modified eggs (juvenile) live in definitive host but cannot develop further until ingested by and intermediate host (mosquito in this case)
3 Type of Filarial Worms (actually there are 8)
Wuchereria bancrofti-> Elephantiasis
Onchocerciasus-> African River Blindness
Dirofilaria immitis-> Dog Heartworm

59. Wuchereria bancrofti Transmitted by mosquito bite
Microfilariae: sucked up by mosquito
Very tiny worms but reproduce to block lymphatic vessels and cause edema (swelling)
Repeated exposure can cause Elephantiasis: excessive growth of connective tissue leading to swelling of body parts (usually seen in extremities and scrotum)

60. Wuchereria bancrofti: Symptoms
Swelling-> allergic reaction and reproduction of worms
Obstruction of lymphatic vessels
Elephantiasis
Connective tissue swelling

63. Elephantiasis of leg
caused by filarial worms
9.12

64. Surgery in elephantiasis
Diagnosis: Demonstration of microfilaria in blood molecular diagnosis using PCR
Wuchereria bancrofti
:iethylcarbamazine,
Surgery in elephantiasis

65. Wuchereria bancrofti Lifecycle Highlights
Mode of Infection
Egg location
Larvae location
Adult location
Symptoms
Treatment
Prevention
Mosquito bite
Produced in humans (micro-filariae) sucked up by mosquito
Micro-filariae develop further in mosquito and advanced form gets injected into humans
Lymph vessels- make more micro-filariae
-Swelling of C.T. in arms and legs
-elephantiasis
Some medication
-not reversible
-protection from bites

66. Onchocerca volvulus Vector is a small black fly
Affects 30 million people in Africa, Central America, and South America
Also called the “blinding filaria”
Causes:
African River Blindness: due to presence of microfilariae in ocular structures (ocular lesions can lead to blindness)
When parasite dies the immune system produces a severe reaction resulting in inflammation->blindness
Progressive allergic skin reaction-dermatitis and lizard skin

68. Black flies of the genus Simulium.
Onchocerca volvulus
Black flies of the genus Simulium.
Nodules containing Onchocerca volvulus on the head of a man in Guatemala

69. Onchocerca volvulus Lifecycle Highlights
Mode of Infection
Egg location
Larvae location
Adult location
Symptoms
Treatment
Prevention
Black fly bite
Produced in humans (micro-filariae) sucked up by black fly
Micro-filariae develop further in black fly and advanced form gets injected into humans (under skin)
Sub-cutaneous tissue and blood -> reproduce and the larvae produced can travel all over including the eye
-Skin rash
-blindness (ARB)
Some medication
-blindness not reversible
-protection from bites

70. Dog Heartworm Most common filarial worm in the U.S.
Causes heartworm in dogs
Live in dogs heart and lungs
Can do damage to the dogs heart-> often leads to death for the dog
Killing the worm is difficult and dangerous for the dog
Prevention of infection by regular dosing of a dog with drugs that kill circulating larvae is a better strategy

71. Diriofilaria immitis
Dog heartworm
9.13