1. Eukaryotic Microorganisms: The Parasites
Chapter 18
Eukaryotic Microorganisms: The Parasites

2. 18.1 Protists Exhibit Great Structural and Functional Diversity
most protists are unicellular and nutritionally diverse
Many are free-living, thriving in water.
Green algae have chloroplasts for photosynthesis.
Some dinoflagellates cause red tides.
Radiolarians have silica plates that form deposits on the ocean floor.
© M. I. Walker/Photo Researchers, Inc.
© M I (Spike) Walker/Alamy Images
Figure 18.03B: Radiolarians.
Figure 18.03A: Green algae.

3. Figure 18.03C: White chalk cliffs.
Foraminiferans have chalky, snail-shaped skeletons.
Diatoms have two-part silica walls, they photosynthesize and are part of the phytoplankton in fresh and marine waters.
© Mark Bond/ShutterStock, Inc.
Figure 18.03C: White chalk cliffs.
Figure 18.03D: Diatoms.
Courtesy of Eduardo A. Morales, Ph.D., The Academy of Natural Sciences of Philadelphia

4. Protozoans encompass a variety of parasitic lifestyles.
Figure 18.04A: Trichonympha.
© Wim van Egmond/Visuals Unlimited/Getty
Protozoans encompass a variety of parasitic lifestyles.
Supergroup Excavata are single-celled and have flagella
Some parabasalids like Trichonympha live mutualistically in termite guts.
Trichomonas vaginalis is an STD
Diplomonads, including Giardia intestinatlis, is found as cysts in water in lakes and rivers
Kinetoplastids include Trypanosoma causing sleeping sickness and Leishmania that causes a skin disease.
Figure 18.04B: Giardia intestinalis.
© Michael Abbey/Visuals Unlimited

5. Figure 18.05A: An Amoeba and a Ciliate.
Supergroup Unikonta have amoeboid motion
Amoebas are mostly free-living single cells.
Amoeboid motion occurs by the formation of pseudopods.
Pseudopods also form food vacuoles for ingestion through phagocytosis.
Entamoeba causes amoebic dysentery, the third leading cause of death due to parasite infection
Figure 18.05A: An Amoeba and a Ciliate.
© M I (Spike) Walker/Alamy Images

6. Figure 18.06: Conjugation and Reproduction in Paramecium.
Supergroup Chromalveolata includes dinoflagellates, diatoms and ciliates
18.05B: Paramecium.
© Roland Birke/Phototake/Alamy Images
Ciliates are covered with rows of hair-like cilia.
The pellicle provides cell structure and stores calcium ions.
Contractile vacuoles
eliminate excess water.
Ciliates have two types
of nuclei:
macronuclei.
micronuclei.
Have sexual reproduction through conjugation
Figure 18.06: Conjugation and Reproduction in Paramecium.

7. Figure 18.07: The Life Cycle of Plasmodium.
Apicomplexans – most don’t have cilia or flagella
Parasites include Plasmodium that causes malaria and Toxoplasma seen in AIDS patients.
The sexual cycle occurs in the definitive host (mosquito).
The asexual cycle occurs in the intermediate host (human).
Figure 18.07: The Life Cycle of Plasmodium.

8. Figure 18.08A: Light micrograph of Leishmania cells.
© Dennis Kunkel Microscopy, Inc./Phototake/Alamy Images
18.2 Protists and Parasites Attack the Skin, and the Digestive and Urinary Tracts
Figure 18.08A: Light micrograph of Leishmania cells.
Leishmania can cause a cutaneous or visceral infection.
L. major causes cutaneous disease with ulcerative sores.
L. donovani causes a visceral disease (kala azar) affecting:
white blood cells.
spleen.
liver.
It is transmitted by sandflies of the genus Phlebotomus.
Figure 18.08C: skin lesion.
© Medical-on-Line/Alamy Images
Courtesy of WHO/CDC
Figure 18.08B: Sand fly.

9. Figure 18.09: The Course of Amoebiasis Due to Entamoeba histolytica.
Several protozoal parasites cause diseases of the digestive system.
Amoebiasis is the second leading cause of death from parasitic disease caused by Entameoba histolytica.
Cysts enter the body through food or water contaminated with feces.
Trophozoites cause loose stools, stomach cramping and pain.
Lesions may form, causing amoebic dysentery with pain, bloody stools, and fever.
Figure 18.09: The Course of Amoebiasis Due to Entamoeba histolytica.

10. Figure 18.10: Giardia intestinalis.
Giardiasis is caused by Giardia intestinalis.
The most common intestinal parasitic infection in the US
Transmission occurs through food or water contaminated with sewage containing cysts.
Trophozoites emerge and attach to the intestinal lining.
Symptoms appear after about 7 days.
Nausea
Cramps
Flatulence
Diarrhea
Figure 18.10: Giardia intestinalis.
© Jerome Paulin/Visuals Unlimited

11. Figure 18.11: Cryptosporidium Oocysts.
Cryptosporidiosis is caused by Cryptosporidium.
It is transmitted through contaminated water and physical contact.
Diarrhea lasts 1-2 weeks.
In immunocompromised patients, cholera-like diarrhea can occur.
Cyclosporiasis is caused by Cyclospora cayetanensis.
Transmission occurs through contaminated fresh produce and water.
Symptoms are diarrhea, nausea, cramping, bloating and vomiting
Figure 18.11: Cryptosporidium Oocysts.
Reproduced from Ma, P. and R. Soave, J Infect Dis. 147:5 (1983): With permission from University of Chicago Press.

12. Figure 18.12: Trichomonas vaginalis.
A protozoan parasite also infects the urinary tract.
Trichomoniasis is often transmitted through sexual contact.
It is caused by Trichomonas vaginalis.
Physical and chemical factors can encourage establishment in the female vagina and male urethra and prostate.
Females experience:
itching.
burning.
discharge.
Males may be asymptomatic.
Figure 18.12: Trichomonas vaginalis.
© Dr. Dennis Kunkel/Visuals Unlimited

13. Figure 18.01: Malaria Cases (per 100,000) by Country – 2008.
18.3 Many Protozoal Diseases of the Blood and Nervous System Can Be Life Threatening
Plasmodium can be a deadly blood parasite
Malaria affects million people.
Spread by the Anopheles mosquito
Four species of Plasmodium cause malaria:
P. vivax
P. ovale
P. malariae
P. falciparum
Figure 18.01: Malaria Cases (per 100,000) by Country – 2008.
Source: Data from the WHO/Malaria Department.

14. Figure 18.13: Plasmodium Life Cycle.
Death can occur due to:
loss of RBCs.
anemia.
RBC clustering in small vessels, causing clots in the brain, kidneys, heart and liver.
Quinine is used for treatment.
Figure 18.13: Plasmodium Life Cycle.

15. Human African sleeping sickness is caused by T. brucei.
The Trypanosoma parasites can cause life-threatening systemic diseases.
Trypanosomiasis is the name for 2 diseases caused by species of Trypanosoma.
Human African sleeping sickness is caused by T. brucei.
It is transmitted by the Tsetse fly.
A chancre forms at the bite site.
Parasites invade the bloodstream
and then central nervous system.
Figure 18.14B: Tsetse fly.
Courtesy of Peggy Greb/USDA ARS

16. Figure 18.14A: SEM of trypanosomes.
T. brucei var. gambiense causes a chronic form characterized by:
bouts of fever
headaches
changes in sleep patterns
and behavior
wasting
when parasites enter the brain, coma ensues
T. brucei var. rhodesiense causes a more acute form, with high fever and rapid coma preceding death.
Figure 18.14A: SEM of trypanosomes.
Courtesy of Dr. Mae Melvin/CDC

17. American trypanosomiasis (Chagas disease) is found in Mexico, and Central and South America.
It is caused by T. cruzi.
Transmission occurs through reduvid bug bites, called the “kissing bug” as it bites on the face or arms at night.
Parasites reproduce in the blood, while the patient may remain asymptomatic.
A chronic, irreversible disease may appear in years causing heart failure.

18. Figure MM08: Babesia microti.
Babesia is an apicomplexan parasite.
Babesiosis is a malaria-like disease caused by Babesia microti.
It is transmitted by ticks.
Parasites invade RBCs, causing:
anemia.
headache.
occasionally meningitis.
Figure MM08: Babesia microti.

19. Figure 18.16: The cycle of Toxoplasmosis in Nature.
Toxoplasma causes a relatively common blood infection.
Toxoplasmosis is caused by Toxoplasma gondii.
Parasites invade all mammalian cells except RBCs.
Transmission can occur via contaminated beef, pork, and lamb.
It can also occur via domestic cats .
They pick up cysts from soil, birds, or rodents.
Can be severe in AIDS patients
Figure 18.16: The cycle of Toxoplasmosis in Nature.

20. Figure 18.17: Naegleria fowleri.
Naegleria Can Infect the Central Nervous System.
Primary ameobic meningoencephalitis (PAM) is caused by species of Naegleria, especially N. fowleri.
Parasites enter the body through the nose when swimming in contaminated warm water.
Symptoms are similar to
other forms of encephalitis
and meningitis.
95% of victims die within 4-5 days.
Figure 18.17: Naegleria fowleri.
Courtesy of Dr. Govinda S. Visvesvara/CDC

21. 18.4 Parasitic Helminths Cause Substantail Morbidity Wordwide
Flatworms (Phylum Platyhelminthes) do not have respiratory or circulatory structures, or a digestive tract.
Trematodes, including flukes, have complex life cycles and often 2 hosts.
Eggs develop into larvae (miracidia) in water, which invade snails.
Trematodes evade the immune system by having a surface similar to host cells.
Figure 18.18A: Light micrograph of a liver fluke.
© Sinclair Stammers/Photo Researchers, Inc.

22. Cestodes, including tapeworms, have a head region called a scolex.
Fertilized eggs are produced in proglottids distal from the scolex, which break off and spread eggs.
Tapeworms generally live in the host’s intestine, absorbing nutrients.
They have limited host range, but usually at least 2 hosts.
Humans become infected from undercooked meat
Beef and pork tapeworm disease are caused by Taenia saginata and T. solium, respectively.
© Dennis Kunkel Microscopy, Inc./Phototake/Alamy Images
Figure 18.18C: T. saginata showing the suckers and hooks.
Figure 18.18B: Beef tapeworm.
© Medical-on-Line/Alamy Images

23. Several trematodes can cause human illness.
Roundworms (Phylum Nematoda) live in every habitat on Earth.
Damage to the host often occurs by large worm burdens in vessels or intestines.
Figure 18.19: Roundworms.
Several trematodes can cause human illness.
© R.F. Ashley/Visuals Unlimited

24. Figure 18.20: The Life Cycle of the Blood Fluke Schistosoma mansoni.
Schistosomiasis is caused by several species of blood flukes.
Eggs can cause damage in the liver, intestines and bladder.
Miracidia in snails convert to cercariae, which leave the snail and attach to human skin.
They infect the blood and mature, causing fever and chills.
Certain species cause swimmer’s itch
Figure 18.20: The Life Cycle of the Blood Fluke Schistosoma mansoni.

25. Figure 18.22: Diagnosing Pinworm Disease.
Pinworm disease is caused by Enterobius vermicularis.
Infection of the intestines leads to diarrhea and anal itching.
Reinfection can occur if contaminated hands contact food or the mouth.
Worms die in a few weeks, even without treatment.
Figure 18.22: Diagnosing Pinworm Disease.

26. Figure 18.23: Trichinella spiralis.
Trichinellosis is caused by Trichinella spiralis.
T. spiralis lives in pig intestines and can encyst in skeletal muscles.
Transmission to humans occurs by eating raw or poorly cooked pork.
Symptoms include:
pain
vomiting
nausea
Constipation
Larvae can migrate to the tongue, eyes, and ribs.
Figure 18.23: Trichinella spiralis.
Courtesy of CDC

27. Ascariasis is caused by Ascaris lumbricoides.
Females produce a large number of eggs that can remain viable in soil for months.
Transmission occurs by consuming contaminated food or water.
Worms mature in the intestine, causing blockage and perforation.
Larvae can move to the lungs.
This causes pneumonia and reinfection if coughed up larvae are swallowed.
They can grow up to cm long

28. Figure 18.25: Life Cycle of Hookworms.
Hookworms have a set of hooks or suckers to attach to the upper intestine.
Hookworms suck blood from intestinal capillaries.
This causes blood loss and anemia.
Humans are the only host.
Larvae in soil penetrate the skin of bare feet and enter the bloodstream.
Figure 18.25: Life Cycle of Hookworms.
Figure 18.24: A Hookworm.
© Dennis Kunkel Microscopy, Inc./Phototake/Alamy Images

29. Figure 18.26: Elephantiasis.
Filariasis is caused by Wuchereria bancrofti.
It is transmitted by mosquitoes.
Larvae infect the lymphatic system.
They damage vessels and glands.
After years of infestation, arms, legs, and scrotum swell and distort.
a.k.a. elephantiasis, lymphedema
Figure 18.26: Elephantiasis.
© John Greim/Photo Researchers, Inc.