Fungi, Algae, Protozoa, and Parasites

1

• Fungi, Algae, Protozoa, and Parasites

2

• I. FUNGI (Mycology)
• Diverse group of heterotrophs.
• Many are ecologically important saprophytes
  (consume dead and decaying matter)
• Others are parasites.
• Most are multicellular, but yeasts are
  unicellular.
• Most are aerobes or facultative anaerobes.
• Cell walls are made up of chitin
  (polysaccharide).
• Over 100,000 fungal species identified. Only
  about 100 are human or animal pathogens.
• Most human fungal infections are nosocomial
  and/or occur in immunocompromised individuals
  (opportunistic infections).
• Fungal diseases in plants cause over 1 billion
  dollars/year in losses.

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• CHARACTERISTICS OF FUNGI
• 1. Yeasts
• Unicellular fungi, nonfilamentous, typically oval
  or spherical cells. Reproduce by mitosis
• Fission yeasts Divide evenly to produce two new
  cells (Schizosaccharomyces).
• Budding yeasts Divide unevenly by budding
  (Saccharomyces).
• Budding yeasts can form pseudohypha, a short
  chain of undetached cells.
• Candida albicans invade tissues through
  pseudohyphae.
• Yeasts are facultative anaerobes, which allows
  them to grow in a variety of environments.
• When oxygen is available, they carry out aerobic
  respiration.
• When oxygen is not available, they ferment
  carbohydrates to produce ethanol and carbon
  dioxide.

4

• CHARACTERISTICS OF FUNGI (Continued)
• 2. Molds and Fleshy Fungi
• Multicellular, filamentous fungi.
• Identified by physical appearance, colony
  characteristics, and reproductive spores.
• Thallus Body of a mold or fleshy fungus.
  Consists of many hyphae.
• Hyphae (Sing Hypha) Long filaments of cells
  joined together.
• Septate hyphae Cells are divided by cross-walls
  (septa).
• Coenocytic (Aseptate) hyphae Long, continuous
  cells that are not divided by septa.
• Hyphae grow by elongating at the tips.
• Each part of a hypha is capable of growth.
• Vegetative Hypha Portion that obtains
  nutrients.
• Reproductive or Aerial Hypha Portion connected
  with reproduction.
• Mycelium Large, visible, filamentous mass made
  up of many hyphae.

5
Characteristics of Fungal HyphaeSeptate versus
Coenocytic
6
Mycelium Large, Visible Mass of Hyphae
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• CHARACTERISTICS OF FUNGI (Continued)
• Dimorphic Fungi
• Can exist as both multicellular fungi (molds) and
  yeasts.
• Many pathogenic species.
• Mold form produces aerial and vegetative hyphae.
• Yeast form reproduces by budding.
• Dimorphism in pathogenic fungi typically depends
  on temperature
• At 37oC Yeast form.
• At 25oC Mold form.
• Dimorphism in nonpathogenic fungi may depend on
  other factors Carbon dioxide concentration.

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• LIFE CYCLE OF FUNGI
• Filamentous fungi can reproduce asexually by
  fragmentation of their hyphae.
• Fungal spores are formed from aerial hyphae and
  are used for both sexual and asexual
  reproduction.
• 1. Asexual spores Formed by the aerial hyphae
  of one organism. New organisms are identical to
  parent.
• Conidiospore Unicellular or multicellular spore
  that is not enclosed in a sac.
• Chlamydospore Thick-walled spore formed within
  a hyphal segment.
• Sporangiospore Asexual spore formed within a
  sac (sporangium).
• 2. Sexual spores Formed by the fusion of nuclei
  from two opposite mating strains of the same
  species. New organisms are different from both
  parents.

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• IMPORTANT DIVISIONS OF FUNGI
• 1. Deuteromycota
• Not known to produce sexual spores.
• Reproduce asexually.
• Catch-all category for unclassified fungi
• Pneumocystis carinii Causes pneumonia in AIDS
  patients. Leading cause of death in AIDS
  patients. Originally classified as a protozoan.
• Candida albicans Causes yeast infections of
  vagina in women. Opportunistic infections of
  mucous membranes in AIDS patients.

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Opportunistic Infection by Candida albicans in an
AIDS Patient
Source Atlas of Clinical Oral Pathology, 1999
11

• IMPORTANT DIVISIONS OF FUNGI
• 2. Zygomycota (Conjugation Fungi)
• Also known as bread molds.
• Saprophytic molds with coenocytic hyphae (lack
  septa).
• Asexual Reproduction Used most of the time.
• Sporangiospore Asexual spore enclosed within a
  sporangium or sac at the end on an aerial hypha.
• Sexual Reproduction Occurs through conjugation,
  the joining of hypha of two different strains
  (plus and minus).
• Zygospores Sexual spores which are enclosed in
  a thick, resistant wall.
• Generally not pathogens.
• Rhizopus nigricans Common black bread mold. May
  cause opportunistic infections in diabetes
  patients

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Life Cycle of a Zygomycete Black Bread Mold
(Rhizopus)Reproduces Asexually and Sexually
13
Reproductive Structures of Zygomycete
(Rhizopus)Sporangia (asexual) and Zygospore
(sexual)
14

• IMPORTANT DIVISIONS OF FUNGI
• 3. Ascomycota (Sac Fungi)
• Molds with septate hyphae and some yeasts.
• Asexual Reproduction Conidiospores not enclosed
  in a sac. Become airborne easily. Form chains
  (broom-like structures).
• Sexual Reproduction Ascospores enclosed in a
  sac-like structure (ascus).
• Include common antibiotic producing fungi and
  yeasts, and several human pathogens.
• Penicillium notatum (Produces penicillin)
• Saccharomyces (Brewers yeast)
• Trychophyton (Athletes foot)
• Aspergillus (Carcinogenic aflatoxin in peanuts),
• Blastomyces (Respiratory infections)
• Histoplasma capsulatum (Respiratory and systemic
  infections)

15
Life Cycle of Eupenicillium (Ascomycete)Reproduce
s Asexually and Sexually
16
Severe nail infection with Trichophyton rubrum
in a 37-year-old male AIDS patient. Source
Intern. J. Dermatol. 31(1992) 453.
17
Disseminated Histoplasma capsulatum, skin
infection. Source Microbiology Perspectives,
1999.
18

• IMPORTANT DIVISIONS OF FUNGI
• 4. Basidiomycota (Club Fungi)
• Have septate hyphae.
• Include mushrooms, toadstools, rusts, and smuts.
• Sexual Reproduction Produce basidiospores
  Spores formed externally on a club shaped sexual
  structure or base called basidium.
• Asexual Reproduction Through hyphae.
• Examples
• Cryptococcus Causes opportunistic respiratory
  and CNS infections in AIDS patients.
• Amanita Mushroom produces lethal toxins to
  humans.
• Claviceps purpurea Produces ergot toxin in wheat
  and rye.

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Life Cycle of a BasidiomyceteMushrooms are
Produced Sexually
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• NUTRITIONAL ADAPTATIONS OF FUNGI
• Fungi absorb their food, rather than ingesting
  it.
• Fungi grow better at a pH of 5, which is too
  acidic for most bacteria.
• Almost all molds are aerobic. Most yeasts are
  facultative anaerobes.
• Fungi are more resistant to high osmotic pressure
  than bacteria.
• Fungi can grow on substances with very low
  moisture.
• Fungi require less nitrogen than bacteria to
  grow.
• Fungi can break down complex carbohydrates (wood,
  paper), that most bacteria cannot.

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• FUNGAL DISEASES
• Mycosis Any fungal disease. Tend to be chronic
  because fungi grow slowly.
• Mycoses are classified into the following
  categories
• I. Systemic mycoses Fungal infections deep
  within the body. Can affect a number if tissues
  and organs.
• Usually caused by fungi that live in the soil and
  are inhaled. Not contagious.
• Examples
• Histoplasmosis (Histoplasma capsulatum) Initial
  infection in lungs. Later spreads through blood
  to most organs.
• Coccidiomycosis (Coccidioides immites)
  Resembles tuberculosis.

22
Systemic Mycosis Histoplasmosis
Disseminated Histoplasma capsulatum, lung
infection. Source Microbiology Perspectives,
1999.
23

• FUNGAL DISEASES (Continued)
• II. Cutaneous mycoses Fungal infections of the
  skin, hair, and nails.
• Secrete keratinase, an enzyme that degrades
  keratin.
• Infection is transmitted by direct contact or
  contact with infected hair (hair salon) or cells
  (nail files, shower floors).
• Examples
• Ringworm (Tinea capitis and T. corporis)
• Athletes foot (Tinea pedis)
• Jock itch (Tinea cruris)

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Cutaneous Mycosis
Ringworm skin infection Tinea corporis Source
Microbiology Perspectives, 1999
25
Cutaneous Mycosis
Candida albicans infection of the nails. Source
Microbiology Perspectives, 1999.
26

• FUNGAL DISEASES (Continued)
• III. Subcutaneous mycoses Fungal infections
  beneath the skin.
• Caused by saprophytic fungi that live in soil or
  on vegetation.
• Infection occurs by implantation of spores or
  mycelial fragments into a skin wound.
• Can spread to lymph vessels.
• IV. Superficial mycoses Infections of hair
  shafts and superficial epidermal cells.
  Prevalent in tropical climates.

27

• FUNGAL DISEASES (Continued)
• Opportunistic mycoses Caused by organisms that
  are generally harmless unless individual has
  weakened defenses
• AIDS and cancer patients
• Individuals treated with broad spectrum
  antibiotics
• Very old or very young individuals (newborns).
• Examples
• Aspergillosis Inhalation of Aspergillus spores.
• Yeast Infections or Candidiasis Caused mainly
  by Candida albicans. Part of normal mouth,
  esophagus, and vaginal flora.

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• ECONOMIC IMPORTANCE OF FUNGI
• 25-50 of harvested fruits and vegetables are
  damaged by fungi.
• Fungal infections of plants are commonly called
  rots, rusts, blights, wilts, and smuts.
• Phytophthora infestans Caused great potato
  famine in mid-1800s. Over 1 million people died
  from starvation in Ireland. Many immigrated to
  the U.S.
• Beneficial fungi
• Candida oleophila Prevents fungal growth on
  harvested fruits.
• Saccharomyces cerevisiae Used to make bread and
  wine.
• Genetically engineered yeast strains are used to
  make proteins (Hepatitis B vaccine).
• Taxomyces Produces anticancer drug taxol.
• Trichoderma Produces cellulase. Used to make
  fruit juice.

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• II. ALGAE
• Simple eukaryotic photosynthetic autotrophs.
• Unicellular or multicellular. Kingdom Protista.
• Most are found in the ocean or other bodies of
  water. Need water for support, reproduction, and
  nutrition.
• Absorb nutrients from the water over entire
  surface.
• Reproduction All reproduce asexually. Some can
  also reproduce sexually.
• Most are not pathogens. A few produce toxins
  that are harmful to humans.

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• II. ALGAE
• Vegetative Structures of multicellular algae
• Thallus Body. Lacks conductive tissue.
• Holdfasts Anchor alga to rock.
• Stipes Hollow, stem-like structures. Does not
  support weight.
• Blades Leaf-like structures.
• Pneumatocyst Floating, gas-filled bladder.

31
Comparison of Algae and Plant Structure
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• DIVISIONS OF ALGAE
• Green algae May be unicellular or
  multicellular.
• Have cellulose cell walls, contain chlorophyll a
  and b, and store starch like plants. Most are
  microscopic. Live close to water surface.
  Believed to be the ancestors of terrestrial
  plants.
• Brown Algae or Kelp Macroscopic (up to 50 m
  long). Most are found in coastal waters, at
  intermediate depths. Rapid growth. Can be
  harvested regularly.
• Red Algae Live at greater ocean depths than
  other algae. Red pigments allow them to absorb
  blue light that penetrates deepest into ocean.
  Agar is extracted from many red algae. Some
  produce lethal toxins.

33
Seaweed is a Multicellular Brown Alga (Laminaria)
34

• DIVISIONS OF ALGAE (Continued)
• Diatoms Unicellular or filamentous algae with
  complex cell walls with silica or calcium.
• Two parts of cell wall fit together like Petri
  dish. Distinctive patterns are used for
  identification. Store energy in form of oil.
• Some diatoms can cause neurological disease
  (memory loss and diarrhea) in people who eat
  mussels, due to domoic acid intoxication.
• Fossil deposits of diatoms (diatomaceous earth)
  are used as filtering agents and abrasives in
  several industries.

35

• Dinoflagellates (Plankton) Unicellular
  free-floating algae. Rigid structure due to
  cellulose in plasma membrane.
• Some dinoflagellates produce neurotoxins, which
  kill fish, marine mammals, and humans.
• Paralytic shellfish poisoning Consumption of
  clams and mussels that have eaten dinoflagellates
  (Gonyaulax) that produce neurotoxin.
• Red Tide Caused by large concentrations of
  (Gonyaulax).
• Euglenoids Unicellular, flagellated algae.
  Semi-rigid plasma membrane (pellicle). Most have
  anterior red eye spot. Frequently studied with
  protozoa, because lack a cell wall.

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Euglenoids are Flagellated, Unicellular Algae
37

• Ecological Importance of Algae
• Important part of the food chain in aquatic
  ecosystems because they fix carbon dioxide into
  organic molecules that can be used by
  heterotrophs.
• 80 of the earths oxygen is believed to be
  produced by planktonic algae.
• Algal blooms are indicators of water pollution.
• Grow rapidly in water with high concentrations
  of organic material (sewage or industrial waste).
• Petroleum and natural gas reserves were formed
  primarily from diatoms and plankton.
• Many unicellular algae are symbionts in animals.

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• III. LICHENS
• Combination of a green alga (or cyanobacterium)
  and a fungus.
• Mutualistic relationship in which each partner
  benefits.
• Alga Provides nutrients by photosynthesis to
  fungus.
• Fungus Provides attachment and protection from
  desiccation.
• 20,000 species of lichens occupy unique habitats,
  in which either fungi or algae could not survive
  alone rocks, cement, rooftops, trees, and newly
  exposed soil.
• Grow very slowly, secreting acids that break down
  rocks.
• Accumulate nutrients needed for plant growth.
• Sensitive to air pollution.
• Major food source for tundra herbivores (caribou
  and reindeer).

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Lichens Combinations of Fungi and Green Algae
(or Cyanobacterium)
40

• IV. SLIME MOLDS
• Have both fungal and animal characteristics.
• Amoeboid stage
• Produce spores like fungi
• Eukaryotic, classified as protists.
• Cellular and plasmodial (acellular) slime molds.
• Life Cycle of Cellular Slime Molds
• Amoeba stage Germinate from a spore.
• Slug stage Many amoebas aggregate and sheath
  forms. Migration.
• Fruiting body Releases spores which germinate
  into amoebas.
• Plasmodial (Acellular) Slime Molds
• Mass of protoplasm with many nuclei (plasmodium).
• Capable of sexual reproduction.

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Life Cycle of a Cellular Slime Mold
42

• V. PROTOZOA
• Unicellular, chemoheterotrophic, eukaryotic
  organisms of kingdom Protista (3-2000 mm).
• Protozoan means first animal.
• 20,000 species, only a few are pathogens.
• Most are free-living organisms that inhabit water
  and soil. Some live in association with other
  organisms as parasites or symbionts.
• Reproduce asexually by fission, budding, or
  schizogony.
• Some exhibit sexual reproduction (e.g.
  Paramecium).
• Trophozoite Vegetative stage which feeds upon
  bacteria and particulate nutrients.
• Cyst Some protozoa produce a protective capsule
  under adverse conditions (toxins, scarce water,
  food, or oxygen).

43

• V. PROTOZOA (Continued)
• Nutrition
• Most are heterotrophic aerobes. Intestinal
  protozoa can grow anaerobically.
• Some ingest whole algae, yeast, bacteria, or
  smaller protozoans. Others live on dead and
  decaying matter. Parasitic protozoa break down
  and absorb nutrients from their hosts.
• Some transport food across the membrane.
• Others have a protective covering (pellicle) and
  required specialized structures to take in food.
• Ciliates take in food through a cytostome.
• Digestion takes place in vacuoles.
• Waste may be eliminated through plasma membrane
  or an anal pore.

44

• 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.

45

• 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.

46

• 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.

47

• 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.

48
Life Cycle of Plasmodium spp. the Infectious
Agent of Malaria
49

• 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.

50

• 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.

51
Paramecium caudatum is a Ciliated
ProtozoanConjugation Between Opposite Mating
Strains
52

• 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.

53

• 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.

54

• 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.

55
Free-Living Flatworm Life Cycle of Blood
FlukePlanaria (Schistosoma)
56

• 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.

57
Asian Liver Fluke (Clonorchis sinensis)
Source http//www.biosci.ohio-state.edu/parasit
e/a-h.html
58

• 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.

59
Cestode (Tapeworm) Body StructureScolex and
Proglottids
60

• 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.

61

• 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.

62
Comparison of Body Organization of Flatworms,
Roundworms, and Earthworms
Flatworm
Roundworm
Earthworm
63

• 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.

64
Pinworm (Enterobius vermicularis)
Source http//www.biosci.ohio-state.edu/parasit
e/a-h.html
65
Pinworm Eggs (Enterobius vermicularis)
Source http//www.biosci.ohio-state.edu/parasit
e/a-h.html
66
Ascaris (Ascaris lumbricoides)
Source http//www.biosci.ohio-state.edu/parasit
e/a-h.html
67
Head of Ascaris (Ascaris lumbricoides)
Notice three lips characteristic of
Ascaris Source www. soton.ac.uk/djab/ascaris.ht
ml
68

• VII. Arthropods as Vectors
• Segmented bodies, hard exoskeleton (chitin), and
  jointed legs.
• Largest phylum in animal kingdom, over 1 million
  species.
• Several classes of arthropods
• Arachnida (8 legs) Spiders, mites, and ticks.
• Crustacea (4 antennae) Crabs, crayfish. Most
  are aquatic.
• Insecta (6 legs) Largest group of living
  organisms on earth. Include bees, flies, lice,
  cockroaches, mosquitoes, and fleas.
• Arthropods that transmit microbial diseases are
  called vectors.
• How do arthropod vectors transport microbes?
• Mechanically Houseflies and cockroaches.
• Hosts Tick vectors of Lyme disease.
• Mosquito vectors of malaria and encephalitis.

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Arachnids are Arthropods with Eight Legs
Lyme Disease Vector Spotted Mountain Fever
and Tularemia Vector
Source www. soton.ac.uk/djab/ascaris.html
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Insects are Arthropods with Six Legs
Tse-tse Fly Host Vector of African Sleeping
Sickness
Source www. soton.ac.uk/djab/ascaris.html
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Crustaceans are Arthropods with Four Antennae