Medically Important Protozoa

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• Medically Important Protozoa
• 1. Amoeboflagellates (Phylum Sarcomastigophora)
• Move using pseudopods (false feet) or flagella.
• A. Amoebas (Subphylum Sarcodina)
• Move by extending blunt, lobelike projections
  (pseudopods).
• Amoebas engulf food with pseudopods and
  phagocytize it.
• Several species cause amoebic dysenteries of
  varying degrees of severity.
• Entamoeba hystolytica Feeds on red blood cells.
  Produces dysentery and extraintestinal cysts.
• Dientamoeba fragilis Found in 4 of humans.
  Usually commensal. Can cause chronic, mild
  diarrhea.
• Other diseases include
• Meningoencephalitis Caused by Naegleria
  fowleri. Penetrate nasal mucosa of swimmers in
  warm waters. Mortality rate almost 100.
• Keratitis Caused by Acanthamoeba. Can cause
  blindness. Associated with use of contact
  lenses.

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• B. Flagellates (Subphylum Mastigophora)
• Move by one or more whiplike flagella. Some
  parasitic flagellates have up to eight flagella.
• Most are spindle shaped with flagella projecting
  from anterior end.
• Outer membrane is a tough pellicle. Food is
  ingested through an oral groove or cytosotome.
• Important pathogens
• Trichomonas vaginalis Causes genital and
  urinary infections. Has undulating membrane.
  Lacks a cyst stage. Transmitted sexually or by
  fomites.
• Giardia lamblia Causes a persistent intestinal
  infection (giardiasis) with diarrhea, nausea,
  flatulence, and cramps. In U.S. most common
  cause of waterborne diarrhea. About 7 of U.S.
  population are healthy carriers.
• Trypanosoma brucei gambiense Hemoflagellate
  (blood parasite). Causes African sleeping
  sickness.
• Trypanosoma cruzi Hemoflagellate that causes
  Chagas disease, a cardiovascular disease common
  in Texas and Latin America.

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• Medically Important Protozoa (Continued)
• 2. Apicomplexans (Phylum Apicomplexa)
• Not motile in their mature form.
• Obligate intracellular parasites.
• Have specialized organelles at tip (apex) of
  cells that penetrate host tissues.
• Complex life cycles. May have more than one
  host. Definitive host Harbors sexually
  reproducing form. Intermediate host In which
  asexual reproduction occurs.

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• Medically Important Protozoa (Continued)
• 2. Apicomplexans (Phylum Apicomplexa)
• Important pathogens
• Plasmodium vivax and falciparum Cause malaria
  in humans (intermediate host).
• Initially treated with quinine, drug resistance
  is a major problem today.
• Major cause of worldwide mortality Kill 3
  million people/year and infect 500 million.
• Transmitted by Anopheles mosquito (definitive
  host).
• DDT was used extensively in 1960s in an attempt
  to eradicate the mosquito vector.
• Successful vaccine not available yet.

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Life Cycle of Plasmodium spp. the Infectious
Agent of Malaria
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• Medically Important Protozoa (Continued)
• 2. Apicomplexans (Phylum Apicomplexa)
• Important pathogens
• Toxoplasma gondii Causes toxoplasmosis in
  humans. Causes blindness and lymphatic
  infections in adults. Dangerous to pregnant
  women, causes severe neurological defects in
  unborn children. Cats are part of life cycle,
  oocysts excreted in feces. Contact with infected
  feces or meat are means of transmission.
• Cryptosporidium Causes respiratory and
  gallbladder infections in immunosuppressed
  individuals. Found in intestines of mammals and
  water. Major cause of death in AIDS patients.
• Cyclospora cayetensis New parasite (1996)
  caused diarrhea associated with raspberries.

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• Medically Important Protozoa (Continued)
• 3. Ciliates (Phylum Ciliophora)
• Move and obtain food using cilia.
• Only known human pathogen is Balantidium coli,
  which causes a severe intestinal infection in
  pigs and humans.
• 4. Microsporans (Phylum Mycrospora)
• Obligate intracellular parasites, lack
  mitochondria and microtubules.
• Discovered in 1984 to cause chronic diarrhea and
  conjunctivitis, mainly in AIDS patients.

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Paramecium caudatum is a Ciliated
ProtozoanConjugation Between Opposite Mating
Strains
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• VI. HELMINTHS (WORMS)
• Characteristics
• Eukaryotic, multicellular animals that usually
  have digestive, circulatory, nervous, excretory,
  and reproductive systems.
• Worms with bilateral symmetry, head and tail, and
  tissue differentiation (endoderm, mesoderm, and
  ectoderm).
• Parasitic helminths spend most or all of their
  lives in host and usually have the following
  specializations
• May lack a digestive system. Absorb nutrients
  from hosts food, body fluids, or tissues.
• Have a reduced nervous system.
• Means of locomotion is reduced or absent.
• Complex reproductive system. Individuals produce
  many eggs that can infect another host.

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• VI. HELMINTHS (Continued)
• Two main groups (phyla)
• Platyhelminths (Flatworms)
• Nematoda (Roundworms)
• Life Cycle
• Extremely complex
• Intermediate hosts harbor larval (developmental)
  stage.
• Definitive host harbors adult stage.
• Sexual reproduction strategies
• Dioecious Male and female reproductive organs
  are found in separate individuals.
• Monoecious (Hermaphroditic) One animal has both
  male and female sex organs. Most hermaphrodites
  copulate with other animals, a few copulate with
  themselves.

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• VI. HELMINTHS (Continued)
• I. Platyhelminths (Flatworms)
• Flattened from front to back.
• Include
• 1. Trematodes or Flukes
• Leaf shaped bodies
• Ventral and oral suckers for attachment and
  sucking fluids from host.
• Some can absorb nutrients through their cuticle.
• Named for host tissues in which adult lives.
• Blood Fluke (Schistosoma spp.) Cause
  schistosomiasis which affects over 400,000
  immigrants in U.S. and 200 million people
  worldwide.
• Cause damage to blood vessels, liver, and many
  other organs.
• Live in waters contaminated with feces, burrow
  through skin of human and enter the circulatory
  system, particularly abdominal and pelvic veins.

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Free-Living Flatworm Life Cycle of Blood
FlukePlanaria (Schistosoma)
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• VI. HELMINTHS (Continued)
• I. Platyhelminths (Flatworms)
• 1. Trematodes or Flukes
• Asian Liver Fluke (Clonorchis sinensis)
  Infests gallbladder, bile ducts, pancreatic
  ducts, causes biliary cirrhosis and jaundice.
  Cannot be transmitted in U.S. because
  intermediate hosts are not available.
• Lung Fluke (Paragonius westermani) Lives in
  bronchioles of humans and other animals. 12 mm
  long. Infection from eating undercooked crayfish.

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Asian Liver Fluke (Clonorchis sinensis)
Source http//www.biosci.ohio-state.edu/parasit
e/a-h.html
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• VI. HELMINTHS (Continued)
• I. Platyhelminths (Flatworms)
• 2. Cestodes or Tapeworms
• Long flat bodies
• Intestinal parasites
• Lack a digestive system, absorb food through
  cuticle.
• Body Organization
• Head or scolex has suckers for attachment.
• Body is made up of segments called proglottids.
• Each proglottid has both male and female
  reproductive organs.
• Proglottids farthest from head are mature and
  contain many fertilized eggs.

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Cestode (Tapeworm) Body StructureScolex and
Proglottids
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• VI. HELMINTHS (Continued)
• I. Platyhelminths (Flatworms)
• Cestodes or Tapeworms (Continued)
• Parasitic human tapeworms
• Beef Tapeworm (Taenia saginata) Human is
  definitive host. Can reach up to 6 meters in
  length, scolex is 2 mm long with hundreds of
  proglottids. Infection occurs by ingestion of
  contaminated, undercooked beef (measly beef).
• Pork Tapeworm (Taenia solium) Human is
  definitive host. Infection can occur from eating
  infected undercooked pork (rare in the U.S.) or
  from human to human contact.
• Echinococcus granulosus Dogs and coyotes are
  definitive hosts. Humans may become infected by
  contact with dog feces or saliva.

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• VI. HELMINTHS (Continued)
• II. Nematodes (Roundworms)
• Cylindrical body tapered at each end.
• Have a complete digestive system mouth,
  intestine, and anus.
• Body is covered by tough cuticle that resists
  drying and crushing.
• Most species are dioecious separate males and
  females.
• Males are smaller than females and have one or
  two spicules on posterior end.
• Over 90,000 known species. Most are free-living.
  Only about 50 are human parasites.
• Life cycle of parasitic nematodes is simpler than
  that of flatworms.
• Infections can be caused by eggs or larvae.

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Comparison of Body Organization of Flatworms,
Roundworms, and Earthworms
Flatworm
Roundworm
Earthworm
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• II. Nematodes (Roundworms) Continued
• Infectious eggs
• Pinworm (Enterobius vermicularis) Spends entire
  life in human host. Adults live in large
  intestine. Female lays eggs in perianal region
  which causes itching. Up to 90 of children are
  infected through contaminated clothes or bedding.
  Infection usually disappears after a few years.
• Ascaris (Ascaris lumbricoides) Large nematode,
  up to 30 cm. Dioecious with sexual dimorphism.
  Live in small intestines of humans, horses, and
  pigs. Eggs can survive in soil for long time.
• Infectious larvae
• Adult Hookworm (Necator americanus) Live in
  small intestine of humans, eggs are excreted in
  feces. Enter host by penetrating skin. Enters
  bloodstream, travels to lungs, swallowed in
  sputum. Avoided by wearing shoes.
• Trichinosis (Trichinella spiralis) Reproduce
  sexually in small intestine of humans. Obtained
  from eating undercooked pork. Larvae enter blood
  vessels and form cysts throughout body.
• Anisakines (Wriggly worms) Infected fish and
  squid. Killed by freezing and cooking.

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Pinworm (Enterobius vermicularis)
Source http//www.biosci.ohio-state.edu/parasit
e/a-h.html
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Pinworm Eggs (Enterobius vermicularis)
Source http//www.biosci.ohio-state.edu/parasit
e/a-h.html
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Ascaris (Ascaris lumbricoides)
Source http//www.biosci.ohio-state.edu/parasit
e/a-h.html
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Head of Ascaris (Ascaris lumbricoides)
Notice three lips characteristic of
Ascaris Source www. soton.ac.uk/djab/ascaris.ht
ml
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