Download Chapter 12: Fungi, Algae, Protozoa, and Parasites

I. FUNGI (Mycology)
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Diverse group of heterotrophs
heterotrophs..
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Chapter 12:
Fungi, Algae, Protozoa, and
Parasites
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Most are multicellular
multicellular,, but yeasts are unicellular.
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Most are aerobes or facultative anaerobes.
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Cell walls are made up of chitin (polysaccharide).
Over 100,000 fungal species identified. Only
about 100 are human or animal pathogens.
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CHARACTERISTICS O F FUNGI
1. Yeasts
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Unicellular fungi, nonfilamentous , typically oval or
spherical cells. Reproduce by mitosis:
CHARACTERISTICS O F FUNGI (Continued)
2. Molds and Fleshy Fungi
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Multicellular, filamentous fungi.
Multicellular,
Identified by physical appearance, colony characteristics,
and reproductive spores.
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Fission yeasts:
yeasts: Divide evenly to produce two new cells
( Schizosaccharomyces
Schizosaccharomyces).
).
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Budding yeasts:
yeasts: Divide unevenly by budding (Saccharomyces
(Saccharomyces)) .
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Candida albicans invade tissues through pseudohyphae
pseudohyphae..
Yeasts are facultative anaerobes, which allows them to
grow in a variety of environments.
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When oxygen is available, they carry out aerobic respiration.
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When oxygen is not available, they ferment carbohydrates to produce
produce
ethanol and carbon dioxide.
Characteristics of Fungal Hyphae:
Septate versus Coenocytic
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.
Budding yeasts can form pseudohypha
pseudohypha,, a short chain of
undetached cells.
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Many are ecologically important saprophytes (consume dead and
decaying matter)
Others are parasites.
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Thallus: Body of a mold or fleshy fungus. Consists of many
Thallus:
hyphae..
hyphae
Hyphae (Sing: Hypha
Hypha):
): Long filaments of cells joined together.
u Septate hyphae:
hyphae: Cells are divided by crosscross- walls (septa).
u Coenocytic ( Aseptate
Aseptate)) hyphae
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.
u Vegetative Hypha
Hypha:: Portion that obtains nutrients.
u Reproductive or Aerial Hypha
Hypha:: Portion connected with
reproduction.
Mycelium:: Large, visible, filamentous mass made up of many
Mycelium
hyphae..
hyphae
Mycelium: Large, Visible Mass of Hyphae
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CHARACTERISTICS O F FUNGI (Continued)
Dimorphic Fungi
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Can exist as both multicellular fungi (molds) and yeasts.
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Many pathogenic species.
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Mold form produces aerial and vegetative hyphae
hyphae..
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Yeast form reproduces by budding.
Dimorphism in pathogenic fungi typically depends on
LIFECYCLE
LIFE
CYCLE O F FUNGI
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Filamentous fungi can reproduce asexually by
fragmentation of their hyphae
hyphae..
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Fungal spores are formed from aerial hyphae and are
used for both sexual and asexual reproduction.
1. Asexual spores:
spores: Formed by the aerial hyphae of one organism.
New organisms are identical to parent.
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Conidiospore: Unicellular or multicellular spore that is not
Conidiospore:
enclosed in a sac.
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Chlamydospore: Thick- walled spore formed within a hyphal
Chlamydospore:
segment.
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Sporangiospore: Asexual spore formed within a sac
Sporangiospore:
(sporangium).
temperature:
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At 37o C: Yeast form.
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At 25o C: Mold form.
Dimorphism in nonpathogenic fungi may depend on other
factors: Carbon dioxide concentration.
IMPORTANT DIVISIONS OF FUNGI
1. Deuteromycota
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Not known to produce sexual spores.
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Reproduce asexually.
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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.
Opportunistic Infection by Candida
albicans in an AIDS Patient
Catch-- all category for unclassified fungi:
Catch
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Pneumocystis carinii
carinii:: Causes pneumonia in AIDS
patients. Leading cause of death in AIDS patients.
Originally classified as a protozoan.
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Candida albicans : Causes yeast infections of vagina in
women. Opportunistic infections of mucous
membranes in AIDS patients.
Source: Atlas of Clinical Oral Pathology, 1999
IMPORTANT DIVISIONS OF FUNGI
2. Zygomycota (Conjugation Fungi)
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Also known as bread molds.
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Saprophytic molds with coenocytic hyphae (lack septa).
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Asexual Reproduction:
Reproduction: Used most of the time.
Life Cycle of a Zygomycete : Black Bread Mold (Rhizopus)
Reproduces Asexually and Sexually
Sporangiospore: Asexual spore enclosed within a
Sporangiospore:
sporangium or sac at the end on an aerial hypha
hypha..
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Sexual Reproduction:
Reproduction: Occurs through conjugation
conjugation,, the
joining of hypha of two different strains (plus and minus).
Zygospores: Sexual spores which are enclosed in a thick,
Zygospores:
resistant wall.
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Generally not pathogens.
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Rhizopus nigricans:
nigricans: Common black bread mold. May cause
opportunistic infections in diabetes patients
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Reproductive Structures of Zygomycete (Rhizopus)
Sporangia (asexual) and Zygospore (sexual)
IMPORTANT DIVISIONS OF FUNGI
3. Ascomycota (Sac Fungi)
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Molds with septate hyphae and some yeasts.
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Asexual Reproduction:
Reproduction: Conidiospores not enclosed in a
sac. Become airborne easily. Form chains (broom(broom-like
structures).
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Sexual Reproduction:
Reproduction: Ascospores enclosed in a sac
sac--like
structure (ascus
(ascus ).
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Include common antibiotic producing fungi and yeasts,
and several human pathogens.
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Penicillium notatum (Produces penicillin)
Saccharomyces(Brewer’s
Saccharomyces
(Brewer’s yeast)
Trychophyton (Athlete’s foot)
Aspergillus (Carcinogenic aflatoxin in peanuts),
peanuts),
Blastomyces(Respiratory
Blastomyces
(Respiratory infections)
Histoplasma capsulatum (Respiratory and systemic infections)
Life Cycle of Eupenicillium (Ascomycete)
Reproduces Asexually and Sexually
Severe nail infection with Trichophyton rubrum in
a 37-year-old male AIDS patient.
Source: Intern. J. Dermatol. 31(1992): 453.
IMPORTANTDIVISIONS
IMPORTANT
DIVISIONS O F FUNGI
4. Basidiomycota (Club Fungi)
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Have septate hyphae.
hyphae.
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Include mushrooms, toadstools, rusts, and smuts.
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Sexual Reproduction:
Reproduction: Produce basidiospores
basidiospores:: Spores
formed externally on a club shaped sexual structure or
base called basidium .
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Asexual Reproduction:
Reproduction: Through hyphae
hyphae..
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Examples:
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Disseminated Histoplasma capsulatum, skin infection.
Source: Microbiology Perspectives, 1999.
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Cryptococcus:: Causes opportunistic respiratory and CNS
Cryptococcus
infections in AIDS patients.
Amanita: Mushroom produces lethal toxins to humans.
Claviceps purpurea:
purpurea: Produces ergot toxin in wheat and rye.
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Life Cycle of a Basidiomycete
Mushrooms are Produced Sexually
NUTRITIONAL ADAPTATIONS O F FUNGI
Fungi absorb their food, rather than ingesting it.
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Fungi grow better at a pH of 5, which is too acidic for
most bacteria.
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Almost all molds are aerobic
aerobic.. Most yeasts are facultative
anaerobes.
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Fungi are more resistant to high osmotic pressure than
bacteria.
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Fungi can grow on substances with very low moisture.
moisture.
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Fungi require less nitrogen than bacteria to grow.
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Fungi can break down complex carbohydrates (wood,
paper), that most bacteria cannot.
FUNGAL DISEASES
Systemic Mycosis: Histoplasmosis
Mycosis: Any fungal disease. Tend to be chronic because
fungi grow slowly.
Mycoses are classified into the following categories:
I. Systemic mycoses
mycoses:: Fungal infections deep within the
body. Can affect a number if tissues and organs.
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Usually caused by fungi that live in the soil and are
inhaled. Not contagious.
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Examples:
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Histoplasmosis ( Histoplasma capsulatum):
capsulatum): Initial infection in
lungs. Later spreads through blood to most organs.
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Coccidiomycosis ( Coccidioides immites): Resembles tuberculosis.
FUNGAL DISEASES (Continued)
Disseminated Histoplasma capsulatum, lung infection.
Source: Microbiology Perspectives, 1999.
Cutaneous Mycosis
II. Cutaneous mycoses
mycoses:: Fungal infections of the skin, hair,
and nails.
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Secrete keratinase
keratinase,, an enzyme that degrades keratin.
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Infection is transmitted by direct contact or contact with
infected hair (hair salon) or cells (nail files, shower
floors).
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Examples:
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Ringworm (Tinea capitis and T. corporis
corporis))
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Athlete’s foot ( Tinea pedis)
pedis)
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Jock itch ( Tinea cruris)
cruris)
Ringworm skin infection: Tinea corporis
Source: Microbiology Perspectives, 1999
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Cutaneous Mycosis
FUNGAL DISEASES (Continued)
III. Subcutaneous mycoses
mycoses:: Fungal infections beneath the
skin.
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Caused by saprophytic fungi that live in soil or on
vegetation.
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Infection occurs by implantation of spores or mycelial
fragments into a skin wound.
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Can spread to lymph vessels.
IV. Superficial mycoses:
mycoses: Infections of hair shafts and
superficial epidermal cells. Prevalent in tropical climates.
Candida albicans infection of the nails.
Source: Microbiology Perspectives, 1999.
FUNGAL DISEASES (Continued)
Opportunistic mycoses:
mycoses: Caused by organisms that are
generally harmless unless individual has weakened
ECONOMIC IMPORTANCE OF FUNGI
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25 -50% of harvested fruits and vegetables are damaged
25by fungi.
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Fungal infections of plants are commonly called rots,
defenses:
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AIDS and cancer patients
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Individuals treated with broad spectrum antibiotics
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Very old or very young individuals (newborns).
Examples:
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Aspergillosis:: Inhalation of Aspergillus spores.
Aspergillosis
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Yeast Infections or Candidiasis
Candidiasis:: Caused mainly by Candida
albicans.. Part of normal mouth, esophagus, and vaginal flora.
albicans
rusts, blights, wilts, and smuts.
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Beneficial fungi:
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Candida oleophila:
oleophila: Prevents fungal growth on harvested fruits.
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Saccharomyces cerevisiae:
cerevisiae: Used to make bread and wine.
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Genetically engineered yeast strains are used to make proteins
(Hepatitis B vaccine).
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Taxomyces: Produces anticancer drug taxol
taxol..
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II. ALGAE
Phytophthora infestans:
infestans: Caused great potato famine in midmid1800s. Over 1 million people died from starvation in Ireland.
Many immigrated to the U.S.
Trichoderma:: Produces cellulase . Used to make fruit juice.
Trichoderma
II. ALGAE
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Simple eucaryotic photosynthetic autotrophs .
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Unicellular or multicellular
multicellular.. Kingdom Protista
Protista..
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Thallus : Body. Lacks conductive tissue.
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Most are found in the ocean or other bodies of water.
Need water for support, reproduction, and nutrition.
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Holdfasts: Anchor alga to rock.
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Stipes: Hollow, stemStipes:
stem-like structures. Does not support
weight.
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Vegetative Structures of multicellular algae:
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Absorb nutrients from the water over entire surface.
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Reproduction: All reproduce asexually. Some can also
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Blades: Leaf -like structures.
reproduce sexually.
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Pneumatocyst:: Floating, gasPneumatocyst
gas-filled bladder.
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Most are not pathogens. A few produce toxins that are
harmful to humans.
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Comparison of Algae and Plant Structure
DIVISIONS OF ALGAE
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Green algae:
algae : May be unicellular or multicellular
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.
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Brown Algae or Kelp:
Kelp: Macroscopic (up to 50 m long).
Most are found in coastal waters, at intermediate depths.
Rapid growth. Can be harvested regularly.
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Red Algae:
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.
Seaweed is a Multicellular Brown Alga (Laminaria)
DIVISIONS OF ALGAE (Continued)
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Diatoms:: Unicellular or filamentous algae with complex
Diatoms
cell walls with silica or calcium.
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Two parts of cell wall fit together like Petri dish.
Distinctive patterns are used for identification. Store
energy in form of oil.
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Some diatoms can cause neurological disease (memory
loss and diarrhea) in people who eat mussels, due to
domoic acid intoxication.
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Fossil deposits of diatoms (diatomaceous earth) are
used as filtering agents and abrasives in several
industries.
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Dinoflagellates (Plankton)
(Plankton):: Unicellular freefree-floating
algae. Rigid structure due to cellulose in plasma
membrane.
Euglenoids are Flagellated, Unicellular Algae
Some dinoflagellates produce neurotoxins, which kill fish,
marine mammals, and humans.
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Paralytic shellfish poisoning:
poisoning: Consumption of clams and mussels
that have eaten dinoflagellates (Gonyaulax
Gonyaulax)) that produce
neurotoxin.
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Red Tide : Caused by large concentrations of ( Gonyaulax
Gonyaulax).
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Euglenoids : Unicellular, flagellated algae. SemiSemi-rigid
plasma membrane (pellicle). Most have anterior red eye
spot. Frequently studied with protozoa, because lack a
cell wall.
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Ecological Importance of Algae
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III. LICHENS
Important part of the food chain in aquatic ecosystems
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because they fix carbon dioxide into organic molecules
that can be used by heterotrophs .
Combination of a green alga (or cyanobacterium ) and a
fungus.
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Mutualistic relationship in which each partner benefits.
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80% of the earth’s oxygen is believed to be produced by
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planktonic algae.
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Algal blooms are indicators of water pollution.
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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.
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Grow very slowly, secreting acids that break down rocks.
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Accumulate nutrients needed for plant growth.
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Sensitive to air pollution.
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Major food source for tundra herbivores (caribou and
reindeer).
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.
Lichens: Combinations of Fungi and Green
Algae (or Cyanobacterium)
IV. SLIME MOLDS
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Have both fungal and animal characteristics.
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Amoeboid stage
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Produce spores like fungi
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Eucaryotes,, classified as protists
Eucaryotes
protists..
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Cellular and plasmodial (acellular
acellular)) slime molds.
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Life Cycle of Cellular Slime Molds:
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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
Acellular)) Slime Molds
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Life Cycle of a Cellular Slime Mold
Alga: Provides nutrients by photosynthesis to fungus.
Alga:
Fungus:: Provides attachment and protection from desiccation.
Fungus
Mass of protoplasm with many nuclei (plasmodium
(plasmodium).
).
Capable of sexual reproduction.
V. PROTOZOA
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Unicellular, chemoheterotrophic
chemoheterotrophic,, eucaryotic organisms of
kingdom Protista (3
(3--2000 µ m).
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Protozoan means “first animal”.
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20,000 species, only a few are pathogens.
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Most are freefree-living organisms that inhabit water and
soil. Some live in association with other organisms as
parasites or symbionts
symbionts..
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Reproduce asexually by fission, budding, or schizogony
schizogony..
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Some exhibit sexual reproduction (e.g.: Paramecium
Paramecium)).
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Trophozoite: Vegetative stage which feeds upon bacteria
Trophozoite:
and particulate nutrients.
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Cyst: Some protozoa produce a protective capsule under
Cyst:
adverse conditions (toxins, scarce water, food, or oxygen).
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Medically Important Protozoa
V. PROTOZOA (Continued)
Nutrition
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Most are heterotrophic aerobes. Intestinal protozoa can
grow anaerobically
anaerobically..
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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.
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Some transport food across the membrane.
Others have a protective covering (pellicle
(pellicle)) and required
specialized structures to take in food.
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Digestion takes place in vacuoles.
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Waste may be eliminated through plasma membrane or
an anal pore.
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Ciliates take in food through a cytostome
cytostome..
1. Amoeboflagellates (Phylum Sarcomastigophora
Sarcomastigophora))
Move using pseudopods (false feet) or flagella.
A. Amoebas (Subphylum Sarcodina )
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(pseudopods ).
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u Several species cause amoebic dysenteries of varying
degrees of severity.
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Entamoeba hystolytica:
hystolytica: Feeds on red blood cells. Produces
dysentery and extraintestinal cysts.
Dientamoeba fragilis:
fragilis: Found in 4% of humans. Usually
commensal.. Can cause chronic, mild diarrhea.
commensal
Other diseases include:
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Meningoencephalitis: Caused by Naegleria fowleri.
Meningoencephalitis:
fowleri. Penetrate
nasal mucosa of swimmers in warm waters. Mortality rate
almost 100%.
Keratitis:: Caused by Acanthamoeba
Keratitis
Acanthamoeba.. Can cause blindness.
Associated with use of contact lenses.
B. Flagellates (Subphylum Mastigophora
Mastigophora))
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Move by one or more whiplike flagella. Some parasitic
flagellates have up to eight flagella.
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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
cytosotome..
Important pathogens:
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Trichomonas vaginalis:
vaginalis: Causes genital and urinary infections.
Has undulating membrane. Lacks a cyst stage. Transmitted
sexually or by fomites
fomites..
Giardia lamblia:
lamblia: Causes a persistent intestinal infection
( giardiasis
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:
cruzi: Hemoflagellate that causesChaga’s
causesChaga’s disease, a
cardiovascular disease common in Texas and Latin America.
Medically Important Protozoa (Continued)
2. Apicomplexans (Phylum Apicomplexa )
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Medically Important Protozoa (Continued)
2. Apicomplexans (Phylum Apicomplexa )
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Not motile in their mature form.
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Obligate intracellular parasites.
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Have specialized organelles at tip (apex
(apex)) of cells that
penetrate host tissues.
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Complex life cycles. May have more than one host.
Definitive host:
host: Harbors sexually reproducing form.
Intermediate host:
host: In which asexual reproduction
occurs.
Life Cycle of Plasmodium spp. the
Infectious Agent of Malaria
Important pathogens:
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Plasmodium vivax and falciparum
falciparum:: Cause malaria in humans
(intermediate host).
Initially treated with quinine, drug resistance is a major problem
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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Medically Important Protozoa (Continued)
2. Apicomplexans (Phylum Apicomplexa )
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Important pathogens:
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Toxoplasma gondii:
gondii: Causes toxoplasmosis in humans. Causes
Medically Important Protozoa (Continued)
3. Ciliates (Phylum Ciliophora
Ciliophora))
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Move and obtain food using cilia.
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Only known human pathogen is Balantidium coli,
coli, which
blindness and lymphatic infections in adults. Dangerous to
causes a severe intestinal infection in pigs and humans.
pregnant women, causes severe neurological defects in unborn
children. Cats are part of life cycle, oocysts excreted in feces.
4. Microsporans (Phylum Mycrospora
Mycrospora))
Contact with infected feces or meat are means of transmission.
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Cryptosporidium:: Causes respiratory and gallbladder infections
Cryptosporidium
mammals and water. Major cause of death in AIDS patients.
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Obligate intracellular parasites, lack mitochondria and
microtubules.
in immunosuppressed individuals. Found in intestines of
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Cyclospora cayetensis:
cayetensis: New parasite (1996) caused diarrhea
Discovered in 1984 to cause chronic diarrhea and
conjunctivitis, mainly in AIDS patients.
associated with raspberries.
Paramecium caudatum is a Ciliated Protozoan
Conjugation Between Opposite Mating Strains
VI. HELMINTHS (WORMS)
Characteristics
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Eucaryotic, multicellular animals that usually have
Eucaryotic,
digestive, circulatory, nervous, excretory, and
reproductive systems.
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Worms with bilateral symmetry, head and tail, and tissue
differentiation (endoderm, mesoderm, and ectoderm).
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Parasitic helminths spend most or all of their lives in host
and usually have the following specializations:
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May lack a digestive system.
system. Absorb nutrients from host’s food,
body fluids, or tissues.
Have a reduced nervous system.
system.
Means of locomotion is reduced or absent.
Complex reproductive system. Individuals produce many eggs
that can infect another host.
VI. HELMINTHS (Continued)
VI. HELMINTHS (Continued)
Two main groups (phyla)
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Platyhelminths (Flatworms)
Nematoda (Roundworms)
Life Cycle
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I. Platyhelminths (Flatworms)
Flattened from front to back.
Include:
1. Trematodes or Flukes
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Intermediate hosts harbor larval (developmental) stage.
Definitive host harbors adult stage.
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Sexual reproduction strategies:
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Dioecious: Male and female reproductive organs are found in
Dioecious:
separate individuals.
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Monoecious (Hermaphroditic): One animal has both male and
female sex organs. Most hermaphrodites copulate with other
animals, a few copulate with themselves.
Leaf shaped bodies
Ventral and oral suckers for attachment and sucking
fluids from host.
Some can absorb nutrients through their cuticle
cuticle..
Named for host tissues in which adult lives.
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Blood Fluke ( Schistosoma spp.
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
Planaria
Life Cycle of Blood Fluke
(Schistosoma )
VI. HELMINTHS (Continued)
I. Platyhelminths (Flatworms)
1. Trematodes or Flukes
Asian Liver Fluke (Clonorchis sinensis)
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Asian Liver Fluke ( Clonorchis sinensis)
sinensis) : Infests gallbladder, bile
ducts, pancreatic ducts, causes biliary cirrhosis and jaundice.
Cannot be transmitted in U.S. because intermediate hosts are not
available.
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Lung Fluke (Paragonius
(Paragonius westermani):
westermani): Lives in bronchioles of
humans and other animals. 12 mm long. Infection from eating
undercooked crayfish.
VI. HELMINTHS (Continued)
I. Platyhelminths (Flatworms)
2. Cestodes or Tapeworms
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Long flat bodies
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Intestinal parasites
Lack a digestive system, absorb food through cuticle.
Body Organization:
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Head or scolex has suckers for attachment.
Body is made up of segments called proglottids .
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Each proglottid has both male and female reproductive organs.
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Proglottids farthest from head are mature and contain many
fertilized eggs.
Source: http://www.biosci.ohio-state.edu/~parasite/a-h.html
Cestode (Tapeworm) Body Structure:
Scolex and Proglottids
VI. HELMINTHS (Continued)
I. Platyhelminths (Flatworms)
Cestodes or Tapeworms (Continued)
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Beef Tapeworm ( Taenia saginata)
saginata): Human is definitive host.
Can reach up to 6 meters in length, scolex is 2 mm long with
hundreds of proglottids
proglottids.. Infection occurs by ingestion of
contaminated, undercooked beef (“measly beef”).
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Pork Tapeworm ( Taenia solium)
solium) : Human is definitive host.
Infection can occur from eating infected undercooked pork
(rare in the U.S.) or from human to human contact.
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Echinococcus granulosus:
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)
Comparison of Body Organization of Flatworms,
Roundworms, and Earthworms
II. Nematodes (Roundworms)
u Cylindrical body tapered at each end.
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Have a complete digestive system:
system: mouth, intestine, and
anus.
Body is covered by tough cuticle that resists drying and
crushing.
Most species are dioecious : separate males and females.
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Males are smaller than females and have one or two spicules on
posterior end.
Over 90,000 known species. Most are freefree-living. Only
about 50 are human parasites.
Life cycle of parasitic nematodes is simpler than that of
flatworms.
Flatworm
Roundworm
Earthworm
Infections can be caused by eggs or larvae.
II. Nematodes (Roundworms) Continued
Infectious eggs
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Pinworm (Enterobius
(Enterobius vermicularis)
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
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.
time.
Pinworm (Enterobius vermicularis)
Infectious larvae
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Adult Hookworm (Necator
(Necator americanus
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.
sputum.
Avoided by wearing shoes.
Trichinosis (Trichinella
(Trichinella spiralis):
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.
Pinworm Eggs (Enterobius vermicularis)
Source: http://www.biosci.ohio-state.edu/~parasite/a-h.html
Source: http://www.biosci.ohio-state.edu/~parasite/a-h.html
Ascaris (Ascaris lumbricoide s)
Source: http://www.biosci.ohio-state.edu/~parasite/a-h.html
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Head of Ascaris (Ascaris lumbricoides)
VII. Arthropods as Vectors
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Notice three lips characteristic of Ascaris
Source: www. soton.ac.uk/~djab/ascaris.html
Arachnids are Arthropods with Eight Legs
Segmented bodies, hard exoskeleton (chitin), and jointed
legs.
Largest phylum in animal kingdom, over 1 million
species.
Several classes of arthropods:
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Arachnida (8 legs): Spiders, mites, and ticks.
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Crustacea (4 antennae): Crabs, crayfish. Most are aquatic.
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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..
vectors
How do arthropod vectors transport microbes?
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Mechanically: Houseflies and cockroaches.
Mechanically:
Hosts:: Tick vectors of Lyme disease.
Hosts
Mosquito vectors of malaria and encephalitis.
Insects are Arthropods with Six Legs
Tse-tse Fly: Host Vector of
African Sleeping Sickness
Lyme Disease Vector
Spotted Mountain Fever and
Tularemia Vector
Source: www. soton.ac.uk/~djab/ascaris.html
Source: www. soton.ac.uk/~djab/ascaris.html
Crustaceans are Arthropods with
Four Antennae
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