Transcript VI. HELMINTHS (Continued)

Chapter 12: Characterizing and
Classifying Eukaryotes
Protozoa, Fungi, Algae, and Parasites
CLASSIFICATION OF PROTOZOA

Unicellular, chemoheterotrophic, eucaryotic 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).
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.
Medically Important Protozoa
1. Amoebas (Phylum Sarcodina)
 Move and feed by extending projections (pseudopods)
 Engulf food with pseudopods and carry out phagocytosis
 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.
2. Flagellates (Phylum 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. Transmitted by Tse-Tse fly.
Trypanosoma cruzi: Hemoflagellate that causes Chaga’s disease, a
cardiovascular disease common in Texas and Latin America.
Transmitted by kissing bug living in mud houses or blood transfusions.
Can cause heart damage (heart failure, arrythmia over several years).
Medically Important Protozoa (Continued)
3. Apicomplexans (Phylum Sporozoa)

Not motile in their mature form.

Obligate intracellular parasites.

Have specialized organelles at tip (apex) of cells that
allow them to 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.
Medically Important Protozoa (Continued)
3. Apicomplexans

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.
Life Cycle of Plasmodium spp. the
Infectious Agent of Malaria
Medically Important Protozoa (Continued)
3. Apicomplexans

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.
Medically Important Protozoa (Continued)
4. 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.
Paramecium caudatum is a Ciliated Protozoan
Conjugation Between Opposite Mating Strains
CLASSIFICATION OF FUNGI (Mycology)

Diverse group of heterotrophs

Many are ecologically important saprobes or saproprophytes
(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 200 are human or animal pathogens


Most human fungal infections are nosocomial and/or occur in
immunocompromised individuals (opportunistic infections).
Fungal diseases in plants cause billions of dollars
a year in losses
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.
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.

Characteristics of Fungal Hyphae:
Septate versus Coenocytic
Mycelium: Large, Visible Mass of Hyphae
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.
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.
IMPORTANT DIVISIONS OF FUNGI
1. Division Zygomycota (Conjugation Fungi)



Over 1100 species known, most are saprophytes
Also known as bread molds
Molds with coenocytic hyphae (lack septa)

Asexual Reproduction: Used most of the time
Sporangiospore: Asexual spore enclosed within a sporangium or balloonlike 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 are enclosed in a thick wall.

Generally not pathogens

Rhizopus nigricans: Common black bread mold. May cause
opportunistic infections in diabetes patients
Life Cycle of a Zygomycete: Black Bread Mold (Rhizopus)
Reproduces Asexually and Sexually
Reproductive Structures of Zygomycete (Rhizopus)
Sporangia (asexual) and Zygospore (sexual)
2. Division Ascomycota (Sac Fungi)

Molds with septate hyphae and some yeasts.

Asexual Reproduction: Conidia means dust.
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 (Brewer’s yeast)
Trychophyton (Athlete’s foot)
Aspergillus (Carcinogenic aflatoxin in peanuts),
Blastomyces (Respiratory infections)
Histoplasma capsulatum (Respiratory and systemic infections)
Life Cycle of Eupenicillium (Ascomycete)
Reproduces Asexually and Sexually
Athlete’s Foot (Tinea pedis)
Source: Doctorfungus Corporation, 2000
Severe nail infection with Trichophyton rubrum in
a 37-year-old male AIDS patient.
Source: Intern. J. Dermatol. 31(1992): 453.
Disseminated Histoplasma capsulatum, skin infection.
Source: Microbiology Perspectives, 1999.
3. Division 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 neoformans: 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.
Life Cycle of a Basidiomycete
Mushrooms are Produced Sexually
IMPORTANT DIVISIONS OF FUNGI
4. Division Deuteromycota
 Most
are closely related to Ascomycota, division
abandoned by most taxonomists
 Not
known to produce sexual spores
 Reproduce
asexually
 Candida
albicans: Causes yeast infections of vagina in
women. Opportunistic infections of mucous
membranes in AIDS patients.
 Pneumocystis
carinii: Causes pneumonia in AIDS
patients. Leading cause of death in AIDS patients.
Originally classified as a protozoan.
Opportunistic Infection by Candida
albicans in an AIDS Patient
Source: Atlas of Clinical Oral Pathology, 1999
Other Fungi
Microsporans
 Reclassified as fungi in 2003.
 Obligate intracellular parasites, lack mitochondria
and microtubules.
 Discovered in 1984 to cause chronic diarrhea and
conjunctivitis, mainly in immunocompromised (AIDS,
cancer, etc.) patients.
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.
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.
Systemic Mycosis: Histoplasmosis
Disseminated Histoplasma capsulatum, lung infection.
Source: Microbiology Perspectives, 1999.
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)

Athlete’s foot (Tinea pedis)

Jock itch (Tinea cruris)
Cutaneous Mycosis
Ringworm skin infection: Tinea corporis
Source: Microbiology Perspectives, 1999
Cutaneous Mycosis: Jock Itch
Organsim: Tinea cruris
Source: DermNet.com
Cutaneous Mycosis
Candida albicans infection of the nails.
Source: Microbiology Perspectives, 1999.
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.
FUNGAL DISEASES (Continued)
Opportunistic mycoses: Caused by organisms that are
generally harmless unless individual has weakened
defenses:


AIDS, cancer, transplant, and diabetic 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.
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.

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.
Saccharomyces boulardi: Used as probiotic because it kills other
yeast.
II. ALGAE

Most are simple eucaryotic 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.
II. ALGAE

Vegetative Structures of multicellular algae:
 Thallus:
Body. Lacks conductive tissue.
 Holdfasts:
 Stipes:
Anchor alga to rock.
Hollow, stem-like structures. Does not support
weight.
 Blades:
Leaf-like structures.
 Pneumatocyst:
Floating, gas-filled bladder.
Comparison of Algae and Plant Structure
DIVISIONS OF ALGAE

Green algae (Chlorophyta): May be unicellular or
multicellular.
Have cellulose cell walls, contain chlorophyll a and b, and
store sugar and starch like plants. Most are microscopic.
Live close to water surface. Believed to be the ancestors
of terrestrial plants.

Brown Algae or Kelp (Phaeophyta): Macroscopic (up to
50 m long). Most are found in coastal waters, at
intermediate depths. Rapid growth. Can be harvested
regularly.
Seaweed is a Multicellular Brown Alga (Laminaria)
DIVISIONS OF ALGAE

Red Algae (Rhodophyta): 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.

Source of gel-like polysaccharides agar and carragean.

Golden, Yellow-Green Algae, and Diatoms (Chrysophyta)

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.

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 (Alexandrium spp.) that produce
neurotoxin.

Red Tide: Caused by large concentrations of Alexandrium. Avoid
harvesting mollusks and fish during red tide.
Euglenoids: Unicellular, flagellated algae. Semi-rigid
plasma membrane (pellicle). Most have anterior red eye
spot. Frequently studied with protozoa, because lack a
cell wall.
Euglenoids are Flagellated, Unicellular Algae
Pathogenic Algae
 Oomycota
(Water Molds): Most are decomposers.
Form cottony masses on dead animals in water.
 Previously
classified as fungi (zygomycetes).
 Phytophthora
infestans: Caused great potato famine in
mid-1800s. Over 1 million people died from starvation
in Ireland; many immigrated to the U.S.
Also infects soybean, potatoes, and cocoa.
http://de.wikipedia.org/wiki/Phytophthora_infestans
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 earth’s 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.
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).
Lichens: Combinations of Fungi and Green
Algae (or Cyanobacterium)
IV. SLIME MOLDS

Have both fungal and animal characteristics.

Amoeboid stage

Produce spores like fungi

Eucaryotes, 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.
Life Cycle of a Cellular Slime Mold
VI. HELMINTHS (WORMS)
Characteristics

Eucaryotic, 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 host’s 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.
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.
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.
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): 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.
Asian Liver Fluke (Clonorchis sinensis)
Source: http://www.biosci.ohio-state.edu/~parasite/a-h.html
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.
Cestode (Tapeworm) Body Structure:
Scolex and Proglottids
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. May cause
cysticercosis.

Echinococcus granulosus: Dogs and coyotes are definitive
hosts. Humans may become infected by contact with dog feces
or saliva.
Cysticercosis: Pork Tapeworm
http://www.biosci.ohio-state.edu/~parasite/cysticercosis.html
http://www.thamburaj.com/cysticercosis.htm
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.
Comparison of Body Organization of Flatworms,
Roundworms, and Earthworms
Flatworm
Roundworm
Earthworm
II. Nematodes (Roundworms) Continued
Infectious eggs
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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
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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.
Pinworm (Enterobius vermicularis)
Source: http://www.biosci.ohio-state.edu/~parasite/a-h.html
Pinworm Eggs (Enterobius vermicularis)
Source: http://www.biosci.ohio-state.edu/~parasite/a-h.html
Ascaris (Ascaris lumbricoides)
Source: http://www.biosci.ohio-state.edu/~parasite/a-h.html
Head of Ascaris (Ascaris lumbricoides)
Notice three lips characteristic of Ascaris
Source: www. soton.ac.uk/~djab/ascaris.html
VII. Arthropods as Vectors
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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.
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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?
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Mechanically: Houseflies and cockroaches.
Hosts: Tick vectors of Lyme disease.
Mosquito vectors of malaria and encephalitis.
Arachnids are Arthropods with Eight Legs
Lyme Disease Vector
Spotted Mountain Fever and
Tularemia Vector
Source: www. soton.ac.uk/~djab/ascaris.html
Scabies (Sarcoptes scabiei)
Infestation of the skin by microscopic mite (arachnid).
Transmission: Prolonged skin to skin contact and fomites
(e.g.: clothing and bedding). Common during water shortages.
Symptoms: Appear between 1 day to 6 weeks after exposure.
• Vesicular or pimple like lesions and rashes of the skin
• Intense itching worse at night
• Allergic reaction to mites
• Bleeding and scabbing from scratching
• Sores on body caused by scratching may become infected
• Norwegian scabies may occur in immunocompromised individuals
with extensive scaling and crusting
Treatment: Several creams and lotions have been approved by
FDA to treat mite infestations. Risky for pregnant women.
SCABIES (Sarcoptes scabiei)
Scabies rash
Source: www. stanford.edu
Scabies mite in human skin (SEM)
Insects are Arthropods with Six Legs
Tse-tse Fly: Host Vector of
African Sleeping Sickness
Source: www. soton.ac.uk/~djab/ascaris.html
Head Lice (Pediculosis)
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Caused by a parasitic insect Pediculus humanus capitis.
Transmission: Head-to-head contact or sharing personal
items (clothing, brushes, towels). Most common in
children ages 3-11 and their families.
Symptoms: Tickling sensation on scalp, itching,
irritability, sores, and scratching.
Life Stages

Egg/Nit: Yellow or white, oval shaped, firmly attached to hair
shaft. Females lay eggs near scalp (1/4 inch). Hatch in 8 to 9 days.

Nymph: Looks like a small louse and feeds on blood. Matures in
9 to 12 days.
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Adult: Has six legs with claws, size of sesame seed, tan to gray
color. Feed on blood. Females can lay up to 100 eggs and live up
to 30 days on head. Lice die within 1-2 days after falling off head.
Treatments: Fine tooth combs, chemical treatments,
shaving hair, and hot air treatment (blow dryer device).
Head Lice (Pediculus humanus capitis)
Egg/Nit, Nymph, and Adult
Adult louse claws
Source: www. cdc.gov/NCIDOD/PARASITES/lice
Crustaceans are Arthropods with
Four Antennae