Lecture PowerPoint to accompany
Foundations in
Microbiology
Sixth Edition
Talaro
Chapter 23
The Parasites of Medical
Importance
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Parasitology
• The study of eucaryotic parasites, protozoa
and helminths
• Cause 20% of all infectious diseases
• Less prevalent in industrialized countries;
increasingly common in AIDS patients
2
Typical Protozoan Pathogens
• Single-celled, animal-like microbes, most
having some form of motility
• Estimated 100,000 species, approximately 25
are important pathogens
• Life cycles vary
– Most propagate by simple asexual cell division of
the active feeding cell (trophozoite).
– Many undergo formation of a cyst.
– Others have a complex life cycle that includes
asexual and sexual phases.
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4
Infective Amebas
5
Entamoeba histolytica and Amebiasis
• Alternates between a large trophozoite, motile
by means of pseudopods and a smaller
nonmotile cyst
• Trophozoite has a large nucleus and lacks most
other organelles.
• Humans are the primary hosts.
• Ingested
• Carried by 10% of world population
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Entamoeba histolytica
• Cysts are swallowed and arrive at the small intestine;
alkaline pH and digestive juices stimulate cysts to
release 4 trophozoites.
• Trophozoites attach, multiply, actively move about and
feed.
• Asymptomatic in 90% of patients
• Ameba may secrete enzymes that dissolve tissues and
penetrate deeper layers of the mucosa.
• Causing dysentery, abdominal pain, fever, diarrhea and
weight loss
8
Entamoeba histolytica
• Life-threatening manifestations are:
hemorrhage, perforation, appendicitis, and
tumorlike growths, amebomas.
• May invade liver and lung
• Severe forms of disease result in 10% fatality
rate.
• Effective drugs are iodoquinol, metronidazole,
and chloroquine.
9
Amebic Infections of the Brain
• Caused by Naegleria fowleri and Acanthamoeba
• Ordinarily inhabit standing water
• Primary acute meningoencephalitis is acquired
though nasal contact with water or traumatic eye
damage.
• Infiltration of brain is usually fatal.
10
An Intestinal Ciliate: Balantidium coli
• An occupant of the intestines of domestic animals
such as pigs and cattle
• Acquired by ingesting cyst-containing food or water
• Trophozoite erodes intestine and elicits intestinal
symptoms.
• Healthy humans are resistant.
• Rarely penetrates intestine or enters blood
• Treatment – tetracycline, iodoquinol, nitrimidazine
or metronidazole
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12
The Flagellates
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Trichomonads: Trichomonas species
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•
Small, pear-shaped
4 anterior flagella and an undulating membrane
Exist only in trophozoite form
3 infect humans:
– T. vaginalis
– T. tenax
– T. hominis
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15
Trichomonas vaginalis
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Causes an STD called trichomoniasis
Reservoir is human urogenital tract
50% of infected are asymptomatic.
Strict parasite, cannot survive long outside of host
3 million cases yearly, a top STD
Female symptoms – foul-smelling, green-to-yellow
discharge; vulvitis; cervicitis; urinary frequency and
pain
• Male symptoms – urethritis, thin, milky discharge,
occasionally prostate infection
• Metronidazole
16
Giardia lamblia and Giardiasis
• Pathogenic flagellate
• Unique symmetrical heart shape with concave
ventral surface that acts like a suction cup
• Cysts are small, compact, and multinucleate.
• Reservoirs include beavers, cattle, coyotes,
cats, and humans.
• Cysts can survive for 2 months in environment.
• Usually ingested with water and food
• ID 10 to 100 cysts
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18
• Cysts enter duodenum, germinate, travel to
jejunum to feed and multiply
• Causes giardiasis – diarrhea, abdominal pain
• Diagnosis is difficult because organism is shed
in feces intermittently.
• Treatment: quinacrine or metronidazole
• Agent is killed by boiling, ozone, and iodine.
19
Hemoflagellates: Vector-Borne Blood
Parasites
• Obligate parasites that live in blood and tissues of
human host
• Cause life-threatening and debilitating zoonoses
• Spread in specific tropical regions by bloodsucking insects that serve as intermediate hosts
• Have complicated life cycles and undergo
morphological changes
• Categorized according to cellular and infective
stages
20
21
Trypanosoma species and
Tropanosomiasis
• Distinguished by their infective stage;
trypomastigote is an elongate, spindleshaped cell with tapered ends, eel-like
motility
• 2 types of trypanosomiasis:
– T. brucei – African sleeping sickness
– T. cruzi – Chagas disease – endemic to
Central and South America
22
Trypanosoma brucei and African
Sleeping Sickness
• Spread by tsetse flies
• Harbored by reservoir mammals
• Two variants of disease caused by 2 subspecies:
– T.b.gambiense – Gambian strain; West Africa
– T.b. rhodesiense – Rhodesian strain; East Africa
• Biting of fly inoculates skin with
trypomastigotes, which multiplies in blood and
damages spleen, lymph nodes and brain.
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• Chronic disease symptoms are sleep
disturbances, tremors, paralysis and coma.
• Trypanosomes are readily demonstrated in
blood, spinal fluid or lymph nodes.
• Treatment before neurological involvement
melarsoprol, eflornithine
• Control involves eliminating tsetse fly.
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Trypanosoma cruzi
• Causes Chagas disease
• Reduviid bug (kissing bug) is the vector.
• Infection occurs when bug feces is inoculated into a
cutaneous portal.
• Local lesion, fever, and swelling of lymph nodes,
spleen, and liver
• Heart muscle and large intestine harbor masses of
amastigotes.
• Chronic inflammation occurs in the organs
(especially heart and brain).
• Treatment nifurtimox and benzonidazole
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Leishmania species and Leishmaniasis
• Leishmaniasis - zoonosis transmitted among
mammalian hosts by female sand flies that require
a blood meal to produce eggs
• Endemic to equatorial regions
• Promastigotes are injected with sand fly bite,
convert to amastigote and multiply; if macrophage
is fixed the infection is localized; systemic if
macrophage migrates.
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• Cutaneous-oriental sore, Baghdad boil localized ulcerated sore
• Espunda – skin and mucous membrane
infection of the head; chronic infection
• Systemic-visceral - high intermittent fever;
weight loss, enlarged spleen, liver, and
lymph nodes
– Kala azar is the most severe and fatal form if
untreated.
30
Apicomplexan parasites
• Sporozoans
• Lack locomotor organelles in the trophozoite state
• Alternate between sexual and asexual phases and
between different animal hosts
• Most form specialized infective bodies that are
transmitted by arthropod vectors, food, water, or
other means.
– Plasmodium
– Toxoplasma
– Cryptosporidium
31
Plasmodium: The Agent of Malaria
• Dominant protozoan disease
• Obligate intracellular sporozoan
• 4 species: P. malariae, P. vivax,
P. falciparum and P. ovale
• Female Anopheles mosquito is the primary vector;
blood transfusions, mother to fetus
• 300-500 million new cases each year
• 2 million deaths each year
32
2 distinct phases of malarial parasite development:
• asexual phase – human host
– Infected female mosquito injects asexual sporozoite
which localizes in liver; it then undergoes
schizogony generating 2,000-40,000 merozoites
which enter circulation in 5-16 days depending on
species.
– Merozoites attach to and enter red blood cells,
convert to trophozoites and multiply; red cell bursts
releasing merozoites that differentiate into gametes.
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• Sexual phase – mosquito host
– Mosquito draws infected RBCs; gametes
fertilize forming diploid cell which forms
sporozoites in stomach.
– Sporozoites lodge in salivary glands; available
to infect human host
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Plasmodium
• Symptoms include episodes of chills-fever-sweating,
anemia, and organ enlargement.
• Symptoms occur at 48-72 hour intervals as RBCs
rupture; interval depends on species.
• P. falciparum most malignant type; highest death rate
in children
• Diagnosis by presence of trophozoite in RBCs,
symptoms
• Increasing drug resistance
• Therapy is chloroquine, quinine, or primaquine.
36
Coccidian Parasites
• Zoonotic in domestic animals and birds
37
Toxoplasma gondii and Toxoplasmosis
• Intracelllular apicomplexan parasite with extensive
distribution
• Lives naturally in cats that harbor oocysts in the GI
tract
• Acquired by ingesting raw meats or substances
contaminated by cat feces
• Most cases of toxoplasmosis go unnoticed except in
fetus and AIDS patients who can suffer brain and
heart damage.
• Treatment: pyrimethamine and sulfadiazine
38
39
Sarcocystis and Sarcocystosis
• Sarcocystis – parasites of cattle, swine, and sheep
• Domestic animals are intermediate hosts; they pick
up infective cysts while grazing on grass
contaminated with human feces.
• Humans are infected when the meat is consumed.
• Symptoms include diarrhea, nausea, and abdominal
pain.
• No specific treatment
40
Cryptosporidium: A Newly
Recognized Intestinal Pathogen
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An intestinal pathogen
Infects a variety of mammals, birds, and reptiles
Exists in tissue and oocyst phases
1990s – 370,000 cases in Milwaukee, WI due to
contaminated water; filtration required for removal
Ingestion of oocysts which give rise to sporozoites
that penetrate intestinal cells
Causes gastroenteritis, headache, sweating, vomiting,
abdominal cramps, diarrhea
AIDS patients may suffer chronic persistent diarrhea.
No effective drugs
41
Isospora belli and Coccidiosis
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Intracellular intestinal parasite with oocyst stage
Transmitted in fecally contaminated food or drink
Infection usually asymptomatic or self-limited
Symptoms include malaise, nausea and vomiting,
diarrhea, fatty stools, abdominal cramping, and
weight loss.
• Treat with sulfadiazine and pyrimethamine, when
required
42
Cyclospora cayetanensis and
Cyclosporiasis
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Emerging protozoan pathogen; causes cyclosporiasis
Oral-fecal transmission; fresh produce and water
Oocysts enter small intestine and invade the mucosa.
Symptoms of watery diarrhea, stomach cramps,
bloating, fever, muscles aches
• Diagnosis can be complicated.
• Treatment: trimethoprim and sulfamethoxazole
43
Babesia species and Babesiosis
• First protozoan found to cause a disease –
redwater fever of cattle
• First protozoan found to be associated with
a vector - tick
• Human babesiosis - relatively rare zoonosis
• Associated with infected rodents
• Infection resembles malaria.
44
A Survey of Helminth Parasites
• Adults are large, multicellular animals with specialized
tissues and organs.
• Adult worms mate and produce fertilized eggs that
hatch; larvae then mature in several stages to adults.
• The sexes may separate or are hermaphroditic.
• Adults live in the definitive host.
• Eggs and larvae may develop in the same host, the
external environment of the intermediate host.
• A transport host experiences no parasitic
development.
• Four basic patterns of life and transmission
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Helminths
• Pathology arises from worms feeding on and
migrating through tissues, accumulation of worms and
worm products.
• Diagnosis based on blood cell count (eosinophilia),
serological tests; eggs, larvae, or adult worms in feces;
sputum, urine, blood, or tissue biopsies.
• Antihelminthic drugs suppress a helminthic metabolic
process that differs from the human process, inhibit
the worm’s movement, prevent it from holding
position, and act locally in the intestine.
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Nematode (Roundworm) Infestations
• Most abundant animal groups; 50 species that
affect humans
• Enlongated, cylindrical worms with protective
cuticles, circular muscles, a complete digestive
tract, and separate sexes
• Ascaris lumbricoides, Trichuris trichiura,
Enterobius vermicularis, hookworms,
Strongyloides stercoralis, Trichinella spiralis,
filarial worms
49
Ascaris lumbricoides
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A large intestinal roundworm
Most cases in the U.S. occur in the southeastern states
Indigenous to humans
Ascaris spends its larval and adult stages in humans;
release embryonic eggs in feces, and are spread to other
humans; food, drink, or contaminated objects
• Ingested eggs hatch into larvae and burrow through the
intestine into circulation and travel to the lungs and
pharynx and are swallowed.
• Adult worms complete cycle in intestines and reproduce
– 200,000 eggs/day.
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Ascaris lumbricoides
• Worms retain motility, do not attach.
• Severe inflammatory reactions mark the
migratory route.
• Allergic reactions can occur.
• Heavy worm loads can retard physical and
mental development.
51
Trichuris trichiura and Whipworm
Infection
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Whipworm
Humans sole host
Trichuriasis has its highest incidence in the tropics.
Eggs hatch in intestines, larvae attach, penetrate the
outer wall and develop into adults.
• Females lay 3,000-5,000 eggs daily.
• Worms can pierce capillaries, cause localized
hemorrhage, and allow bacteria to leave intestine.
• Heavy infestations can cause dysentery, rectal
prolapse – can be fatal in children.
52
Enterobius vermicularis and
Pinworm Infection
• Pinworm or seatworm
• Enterobiasis most common worm disease of children in
temperate zones
• Eggs are picked up from surroundings and swallowed.
• After hatching in the small intestine, they develop into
adults.
• Anal itching occurs when mature females emerge from
intestine to release eggs.
• Self-inoculation is common.
• Tape test
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Hookworms
• Characteristic curved ends and hooked mouths
• Necator americanus and Ancylostoma duodenale
• Humans shed eggs in feces, which hatch into
filariform larvae and burrow into the skin of the
lower legs.
• Larvae travel from blood to lungs, proceed up
bronchi and throat and are swallowed.
• Worms mature and reproduce in small intestine
and complete, the cycle.
• May cause pneumonia, nausea, vomiting, cramps
and bloody diarrhea
• Blood loss is significant – anemia.
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Strongyloides stercoralis and
Strongyloidiasis
• Threadworm
• Tiny roundworms completes life cycle in humans
or moist soil.
• Larvae penetrate skin and migrate to lungs, are
swallowed and complete development in the
intestine.
• Can reinfect the same host without leaving the
body
• Heavy worm loads can cause pneumonitis and
eosinophilia, bloody diarrhea, liver enlargement,
bowel obstruction and malabsorption.
56
Trichinella spiralis and Trichinosis
• Life cycle entirely within mammalian host
• Acquired from eating undercooked pork or bear
meat
• Larvae migrate from intestine to blood vessels,
muscle, heart, and brain, where it forms cysts
• First symptoms –flulike, diarrhea
• Second symptoms – muscle and joint pain, shortness
of breath, pronounced eosinophilia
• No cure after larva have encysted
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Tissue Nematodes
• Complete their life cycle in human blood,
lymphatics, or skin
• Filarial worms; elongate, filamentous
bodies, spread by biting arthropods
• Cause chronic, deforming disease
• Wuchereria bancrofti – elephantiasis
• Onchocerca volvulus – river blindness
• Loa loa – eye worm
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Wucherereia bancrofti and
Bancroftian Filariasis
• Tropical infection spread by mosquitoes
• Vector deposits larvae which move into
lymphatics and develop into adults.
• Chronic infection causes blockage of
lymphatic circulation and elephantiasis,
massive swelling in the extremities.
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Onchocerca volvulus and River
Blindness
• Transmitted by biting black flies
• Larvae develop into adults in subcutaneous
tissues.
• Adult females migrate via the blood to the
eyes, provoking inflammatory reactions.
• Coinfection with Wolbachia bacteria causes
river blindness.
• Treatment: tetracycline and ivermectin
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Loa loa: The African Eye Worm
• Spread by bite of small flies
• Temperature-sensitive worm migrates
around/under the skin and may enter the
eye.
• Treatment – pull worm from a small hole in
conjunctiva or diethylcarbamazine
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Trematodes or Flukes
• Flatworms with ovoid leaflike bodies
• Have digestive, excretory, neuromuscular, and
reproductive systems
• Lack circulatory and respiratory systems
• Animals such as snails or fish are usually the
intermediate hosts and humans are the
definitive hosts.
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Blood Flukes: Schistosomes
• Schistosomiasis - prominent parasitic disease
• Schistosoma mansoni, S. japonicum,
S. haematobium
• Adult flukes live in humans who release eggs into
water; early larva (miracidium) develops in
freshwater snail into a 2nd larva (cercaria).
• This larva penetrates human skin and moves into the
liver to mature; adults migrate to intestine or bladder
and shed eggs, giving rise to chronic organ
enlargement.
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Liver and Lung Flukes
• Zoonotic
Liver flukes:
• Opisthorchis (Chlonorchis) sinesis - cycles between
mammals and snails and fish; humans are infected by
eating inadequately cooked fish containing cercaria,
larvae crawl into bile duct, mature and shed eggs into
feces; snail are infected.
• Fasciola hepatica-cycles between herbivores, snails,
and aquatic plants; humans are infected by eating
raw aquatic plants; fluke lodges in liver.
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Lung fluke:
• Paragonimus westermani – cycles between
carnivorous animals, snails, and
crustaceans; humans infected by eating
undercooked crustaceans; intestinal worms
migrate to lungs.
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Cestode (Tapeworm) Infestations
• Flatworms
• Long, very thin, ribbonlike bodies composed of
sacs (proglottids) and a scolex that grips the
intestine
• Each proglottid is an independent unit adapted to
absorbing food and making and releasing eggs.
• Taenia saginata
• Taenia solium
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Taenia saginata
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Beef tapeworm
Very large, up to 2,000 proglottids
Humans are the definitive host.
Animals are infected by grazing on land contaminated
with human feces.
• Infection occurs from eating raw beef in which the
larval form has encysted.
• In humans, larva attaches to the small intestine and
becomes an adult.
• Causes few symptoms; vague abdominal pain and
nausea; proglottids in stool
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Taenia solium
• Pork tapeworm
• Infects humans through ingesting cysts or
eggs
• Eggs hatch in intestine, releasing tapeworm
larva that migrate to all tissues and encyst.
• Most damaging if they lodge in heart muscle,
eye, or brain
• May cause seizures, psychiatric disturbances
70
The Arthropod Vectors of Infectious
Disease
• Arthropods – exoskeleton and jointed legs;
includes arachnids and crustaceans; many
must feed on blood and tissue fluid of host
during life cycle; ectoparasites
• Those of medical importance transmit
infectious microbes in the process of
feeding – biological vectors
71
Insects
• Mosquitoes – require an aquatic habitat; females
take blood meal transmitting disease: malaria,
filariasis, zoonoses
• Fleas – highly motile, flattened bodies; feed on
warm-blooded animals; carry zoonotic diseases:
plague, murine typhus
• Lice – small, soft; attach to head and body hair
feeding inconspicuously on blood and tissue fluid;
release feces that contaminate wound; epidemic
typhus, relapsing fever
• Flies – tsetse fly, sand fly
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Arachnids
• Ticks – cling on vegetation and attach to
host on contact; larvae, nymph and adults
get blood meal by piercing skin of host
– hard ticks – Dermacentor, Ixodes – small
compact, rigid bodies; transmit rickettsial,
borrelial, and viral diseases
– soft or argasid ticks – Ornithodoros- flexible
outer bodies; transmit relapsing fever
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