Chapter 15: Phylum Nematoda: The Roundworms

Chapter 15:Phylum Nematoda:The Roundworms

1CryptosporidiumProtozoan pathogenDrinking contaminated waterDiarrhea/ Severe in immune-compromised

ElephantiasisFilarial worm (Nematode)Transmitted by mosquitoesSwelling of lymphatic system

AnisakisNematodeIngesting fish/marine mammals

TapewormParasitic flatwormIngestion of contaminated/undercooked meatMalnutrition/ neurological damage

GiardiaProtozoan parasiteIngestion of contaminated food, water, soilIntestinal infection, diarrhea, abdominal pain

RoundwormsThe common name for phylum Nematoda is roundworms. They are among the most numerous of all animals.Roundworms are pseudocoelomates

8Nematode = Thread?In Greek, nematos actually means thread, hence why they are called nematodes.

9What 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.

10What 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.

11What 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.

12Form and Function in RoundwormsRoundworms 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.13FeedingMany 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.14ResponseNematodes 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.

15ReproductionRoundworms reproduce sexually, and most species of roundworms are dioecious (male/female)They reproduce using internal fertilization: the male usually deposits sperm inside the females reproductive tract.Parasitic nematodes often have complex life cycles that involve two or three different hosts or several organs within a host.16Nematode ParasitesMany nematodes are very important pathogens of humans and domestic animals. Some of the nematodes we will discuss:RoundwormsHookwormsPinwormsFilarial Worms

17RoundwormAscaris lumbricoides occurs in up to 64% of people in some areas of the southeastern U.S. More than 1.2 billion are affected worldwide.

18RoundwormA female roundworm can lay 200,000 eggs per day, passing out through the hosts feces.

Viable eggs remain after signs of fecal matter have disappeared. Eggs can survive long periods in the soil.

19RoundwormWhen 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.20

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22HookwormsHookworms 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 hosts blood.23

24HookwormsHookworms 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.25

27PinwormsPinworms 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.

28PinwormsFemales, 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.

29Scotch Tape MethodDoctors 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.

30Scotch Tape Method1. 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.

31Several 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.

PinwormsEggs 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.33Filarial WormsThere are eight species of filarial nematodes that infect humans. Some cause major and serious diseases.About 250 million people in tropical countries

34Filarial WormsFemales can be as long as 100 mm and can release live young into the blood and lymph.

Filarial WormsMosquitoes 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.

36Filarial Worm DiseasesFilarial worms cause three main diseases in their hosts:ElephantiasisRiver blindness37ElephantiasisElephantiasis 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.

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39Onchocerciasis: River blindnessRiver 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.40

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