Foundations in Microbiology...7 Entamoeba Histolytica and Amebiasis •Alternates between a large...
Transcript of Foundations in Microbiology...7 Entamoeba Histolytica and Amebiasis •Alternates between a large...
Foundations in
Microbiology Seventh Edition
Chapter 23
The Parasites of
Medical Importance
Lecture PowerPoint to accompany
Talaro
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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23.1 Parasitology
• The study of eukaryotic parasites, protozoa,
and helminths
• Cause 20% of all infectious diseases
• Less prevalent in industrialized countries;
increasingly common in AIDS patients
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23.2 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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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
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Entamoeba Histolytica
• Life-threatening manifestations are: hemorrhage, perforation, appendicitis, and tumorlike growths, amoebomas
• May invade liver and lung
• Severe forms of disease result in 10% fatality rate
• Effective drugs are iodoquinol, metronidazole, and chloroquine
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Amebic Infections of the Brain
• Caused by Naegleria fowleri and Acanthamoeba
• Ordinarily inhabit standing water
• Primary acute meningoencephalitis is acquired
through nasal contact with water or traumatic eye
damage
• Infiltration of brain is usually fatal
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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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Trichomonads: Trichomonas Species
• 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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Trichomonas Vaginalis
• 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
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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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• 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
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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 blood-sucking insects that serve as intermediate hosts
• Have complicated life cycles and undergo morphological changes
• Categorized according to cellular and infective stages
Hemoflagellates
• Amastigote: the form lacking a free
flagellum
• Promastigote: the stage bearing a single,
free, anterior flagellum
• Epimastigote: the flagellate stage
• Trypomastigote: large, fully formed stage
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Trypanosoma Species and
Tropanosomiasis
• Distinguished by their infective stage; trypomastigote is an elongate, spindle-shaped 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
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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
Trypanosoma Brucei and African
Sleeping Sickness
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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
does not migrate the infection is localized;
systemic if macrophage migrates
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• Cutaneous-oriental sore, Baghdad boil –
localized ulcerated sore
• Espundia – 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
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23.3 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
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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
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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 numerous 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, mefloquine
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Toxoplasma Gondii and Toxoplasmosis
• Intracellular 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
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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
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Cryptosporidium: A Newly
Recognized Intestinal Pathogen
• 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 gives 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
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Isospora Belli and Coccidiosis
• 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
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Cyclospora Cayetanensis and
Cyclosporiasis
• 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
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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
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23.4 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 hermaphroditic
• Adulthood and mating occur in the definitive host
• Larval develop occurs in 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
• Elongated, cylindrical worms with protective cuticles, circular muscles, a complete digestive tract, and separate sexes
• Divided into intestinal nematodes, and tissue nematodes
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Ascaris Lumbricoides
• 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
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Trichuris Trichiura and Whipworm
Infection
• 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
• Heavy infestations can cause dysentery, rectal prolapse – can be fatal in children
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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 bare feet
• 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
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Trichinella Spiralis and Trichinellosis
• 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 (Clonorchis) sinensis – cycles between mammals and snails and fish; humans are infected by eating inadequately cooked fish containing cercariae, 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
• 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
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23.5 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
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Insects
• Mosquitoes – require an aquatic habitat; females take blood meal transmitting disease: malaria, filariasis, Dengue fever
• 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
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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 or ixodid ticks – small compact, rigid bodies; transmit bacterial, rickettsial, and viral diseases
– Soft or argasid ticks – flexible outer bodies; transmit relapsing fever