Chapter 15:
Phylum Nematoda:
The Roundworms
Cryptosporidium
Protozoan pathogen
 Drinking contaminated water
 Diarrhea/ Severe in immune-compromised

Elephantiasis
Filarial worm (Nematode)
Transmitted by mosquitoes
Swelling of lymphatic system
Anisakis
Nematode
 Ingesting fish/marine mammals

Tapeworm
Parasitic flatworm
 Ingestion of contaminated/undercooked
meat
 Malnutrition/ neurological damage

Giardia
Protozoan parasite
 Ingestion of contaminated food, water,
soil
 Intestinal infection, diarrhea, abdominal
pain

Roundworms
The common name for phylum Nematoda is
roundworms. They are among the most
numerous of all animals.
 Roundworms are pseudocoelomates

Nematode = Thread?

In Greek, ”nematos” actually means thread,
hence why they are called nematodes.
What is a Roundworm?
Roundworms are slender, unsegmented
worms with tapering ends. They can be
microscopic or up to a meter in length.
 Most species of roundworms are free-living,
inhabiting soil, salt flats, aquatic sediments,
and water from polar to tropical regions.
 Still others are parasitic and live in hosts
that include almost every kind of plant and
animal.

What is a Roundworm?
Nematodes parasitize virtually every type of
animal and many plants.
 Almost all species of vertebrates and many
invertebrates serve as hosts for one or more
types of parasitic nematodes.

What is a Roundworm?

Nematodes have a digestive tract with two
openings. This body plan is often called a
“tube-within-a-tube.” The outer tube is the
body wall and the inner tube is the digestive
tract.
Form and Function in Roundworms
Roundworms have specialized tissues and
organ systems that carry out essential body
function.
 In general, the body systems of free-living
roundworms tend to be more complex than
those of parasitic forms.

Feeding
Many free-living roundworms are carnivores
that use grasping mouthparts and spines to
catch and eat other small animals.
 Some soil-dwelling and aquatic forms eat
algae, fungi, or pieces of decaying matter.
 Other nematodes digest the bacteria and
fungi that break down dead animals and
plants.

Response
Nematodes have simple nervous systems,
consisting of several ganglia.
 Several nerves extend from ganglia in the
head and run the length of the body. These
nerves transmit sensory information and
control movement.
 Roundworms have several types of sense
organs.

Reproduction
Roundworms reproduce sexually, and most
species of roundworms are dioecious
(male/female)
 They reproduce using internal fertilization:
the male usually deposits sperm inside the
female’s reproductive tract.
 Parasitic nematodes often have complex life
cycles that involve two or three different
hosts or several organs within a host.

Nematode Parasites

Many nematodes are very important
pathogens of humans and domestic
animals. Some of the nematodes we will
discuss:




Roundworms
Hookworms
Pinworms
Filarial Worms
Roundworm

Ascaris lumbricoides occurs in up to 64% of
people in some areas of the southeastern
U.S. More than 1.2 billion are affected
worldwide.
Roundworm

A female roundworm can lay 200,000 eggs
per day, passing out through the host’s
feces.

Viable eggs remain after signs of fecal
matter have disappeared. Eggs can survive
long periods in the soil.
Roundworm
When a host swallows the eggs, juveniles
hatch and burrow through the intestinal wall.
 The juveniles then are carried through the
heart to the lungs. When at the lungs, they
break into the alveoli and are carried up to
the trachea.
 Juveniles are coughed up and swallowed,
then mature in the intestine two months
after they were swallowed.
 They feed on intestinal contents and may
block or perforate the intestines.

Hookworms
Hookworms are so named because the
anterior (head) end curves dorsally,
resembling a hook.
 Necator americanus is most common
species.
 They have large plates in their mouths that
cut into the intestines so that they can suck
on the host’s blood.

Hookworms
Hookworms pump more blood than they can
digest. A heavy infection can cause anemia.
 Eggs pass in feces and juveniles hatch in soil
where they can live off of bacteria.
 If human skin comes in contact with the soil,
infective juveniles burrow through the skin to
blood.
 Their life cycle is similar to that of Ascaris.

Pinworms
Pinworms are the most
common worm parasite
in the U.S., but causes
little disease.
 It is estimated that
30% of children and
16% of adults in the
U.S. have them.
 Adults live in the large
intestine and cecum.

Pinworms

Females, about 12 mm in length, migrate to
the anal region at night and lay eggs,
causing itching. Scratching the anal region
contaminates hands and bedclothes.
Scotch Tape Method
Doctors usually diagnose pinworms by fecal
examinations and finding the eggs, but eggs
are often not found in feces.
 Many times the female pinworm will deposit
her eggs on the skin around the anus.
Doctors have started using the “scotch tape
method.”

Scotch Tape Method
1. The scotch tape method consists of placing
the sticky side of cellulose tape onto the
anus overnight.
2. The next morning the tape is
umm...harvested and placed under a
microscope to search for eggs.
Several drugs are effective against it,
and all members of the family should be
treated at the same time because the
worms spread easily through a
household.
Pinworms
Eggs develop rapidly and become infective
within six hours at body temperature.
 When swallowed, these eggs hatch in the
anterior end of the small intestine (the
duodenum) and mature in the large
intestine.
 Members of this order have haploid (one set
of chromosomes) males from unfertilized
eggs and diploid females from fertilized
eggs. This is known as haplodiploidy.

Filarial Worms
There are eight species of filarial nematodes
that infect humans. Some cause major and
serious diseases.
 About 250 million people in tropical countries

Filarial Worms

Females can be as long as 100 mm and
can release live young into the blood and
lymph.
Filarial Worms

Mosquitoes ingest the microfilariae when
they feed. The worms develop to the
infective stage while inside the mosquito and
move into the mosquito bite wound when it
feeds.
Filarial Worm Diseases

Filarial worms cause three main
diseases in their hosts:
 Elephantiasis
 River
blindness
Elephantiasis
Elephantiasis
symptoms are
apparent after long
and repeated exposure
to filarial worms.
 It is marked by
excessive growth of
connective tissue and
enormous swelling of
affected parts, such as
the legs and arms.

Onchocerciasis: River blindness
River blindness is caused by a filarial
worm that is carried by black flies.
 It infects more than 30 million people in
parts of Africa, Arabia, Central America,
South America, and virtually all other
tropical areas.
