HUMAN PARASITES

INTRODUCTION

A parasitic symbiotic relationship is one in which an organism benefits by taking something away from another organism and possibly hurting it in the process. Many parasitic relationships kill the host. Fortunately, in the U.S., our public health laws provide for an environment where parasites, at least deadly ones, have a hard time becoming established. That doesn’t mean they are not present! As you will discover in this activity, some are closer than you think.

OBJECTIVESStudents will be able to:

  • Explain the life cycles of several parasites
  • Identify the advantages or disadvantages of being an internal or external parasite
  • Describe several ways to avoid becoming infected with parasites

in order to examine structures of cellular and multi-cellular organisms and explain their function in maintaining life.

MATERIALSMicroviewerPrepared micrographs- Slide sets 74 & 75

PROCEDURE

  1. Observe each of the human parasites listed above using the proper technique described by your teacher.
  2. Make a biological drawing of each of the parasites (make sure to follow all of the rules for making a biological drawing).
  3. After viewing each organism and reading about its lifestyle and impact on humans, answer the analysis questions usingcomplete sentences.

ANALYSIS (complete sentences)

  1. Lyme disease is on the increase in the Baltimore area. From reading about the habits of the tick can you tell why this may be happening? How can you avoid becoming infected with this disease?
  2. Why do you think it would be difficult to know if someone had a tapeworm? If you find a small, white, “sesame seed–looking” structure in or near your cats litter box, what problem might they have?
  3. Explain why mosquitoes are able to spread disease so well and so quickly.
  4. Protists (unicellular animal–like organisms) divide by a process called binary fission. What does this mean and would this allow a protist like trypanosome to spread quickly in humans or would it take a long time for the disease to spread? Explain your answer.
  5. As we have discovered some parasites are external and like to attach to the outside of an animal and some are internal and find some way to enter the host. Give 2 advantages to being an external or internal parasite? Give 2 disadvantages to being each type of parasite.

Internal ParasiteExternal Parasite

AdvantagesAdvantages

1.1.

2.2.

DisadvantagesDisadvantages

1.1.

2.2.

  1. As we have discovered, eating raw or undercooked meat can lead to major health problems. Identify the two parasites we have studied that can infect people who have eaten raw meat and describe how they are transmitted and what diseases they can cause.

PARASITEDESCRIPTIONBIOLOGICAL DRAWING

1. Wood TickSlide Set 75 Image 8 Tick Larva

Dermacentor variabilis

Large deer ticks carry a disease called

Rocky Mountain spotted fever. Small deer ticks carry Lyme disease that causes pain around joints if not identified early. Deer carrying these ticks are abundant on the east coast because they do not have any predators. If you see a round rash on your body, go to the doctor right away. Ticks are external parasites that live off of the blood of various organisms. They are able to drop off when they are filled with blood or feel threatened by their host.

Internal or External? ______

2. Tapeworm(scolex)Slide set 75 Image 6 Tapeworm Scolex

Taenia pisiformis

An internal parasite that attaches to the

intestines of its host and absorbs nutrients that have already been broken down by the host in which it is living. The head has tiny hooks and suckers to attach to the intestinal wall and hold on. Parts of the worm can break off and be deposited in feces, where they will remain until eaten by another animal. Some tapeworms can reach a length of over 20 feet.

Internal or External? ______

3. Malarial ParasiteSlide set 75 Image 5 Malarial Parasite

Anopheles

One of the world’s most dangerous animals.

Mosquitoes carry microorganisms that cause diseases in other organisms. These carriers are called “vectors”. Malaria is one of the diseases passed by female mosquitoes as they stab an unwilling host to gather food for egg development. Malaria causes flu-like symptoms and can be fatal. Some countries have a major problem with malaria and travel to these countries is restricted.

Internal or External? ______

4. Trichina WormSlide set 75 Image 1 Trichina Worms

Trichinella spiralis

Have you ever been told to cook your pork

chops or bacon well before you eat them, or not to eat pink pork? The reason is because it may contain roundworm larvae. The larvae burrow into the hosts’ muscles then these coiled up worms spread muscles apart and cause nausea, diarrhea, fatigue, fever, abdominal discomfort, muscle swelling, pain, and weakness. People who have a heavy infection my experience heart problems and trouble breathing and even death. This fatal disease is called Trichinois and can be avoided by cooking your pork to 170°F.

Internal or External? ______

5. Liver FlukeSlide set 74 Image 7 Chinese Liver Fluke

Clonorchis sinesis

The fluke is a close relative of the tapeworm.

The fluke lives in the bile duct of the liver and, unlike the tapeworm it causes death. Eggs are passed out with the feces and are eaten by snails where they start to develop. Fish then eat the snails with the now mobile flukes in them. The flukes tunnel into the muscle of the fish and take up residence. When you eat raw fish the fluke then enters your body. The liver fluke is a good reason to think twice before eating sushi.

Internal or External? ______

6. Trypanosoma Slide set 74 Image 3 Trypanosoma Lewisi

Trypanosoma lewisi

Trypanosoma causes African Sleeping Sickness. The parasites are protozoa belonging to the Trypanosoma genus. They are transmitted to humans by tsetse fly (Glossina genus) bites which have acquired their infection from human beings or from animals harboring the human pathogenic parasites. The parasite can cause changes in behavior and the sleeping cycle. Without treatment, the disease can be fatal.

Internal or External? ______

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