Post on 06-Apr-2015
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The Parasitesof
MedicalImportance
Protozoa
Life cycle Troph ⇔ Cyst
Entamoeba histolytica
• “Montezuma’s revenge”
Nagleria fowleri
• Occasional fatal infection of brain
• Swimming in natural waters
Ameba
• Advances rapidly—treatment futile
Acanthamoeba
Meningoencephalitis
Enters through broken skin,conjunctiva, lungs, urinary epithelia
Course of infection lengthy
At risk—traumatic eye injuries,contact lens wearers, AIDS
CiliatesBalantidium coli• Gastrointestinal disease• Normal flora in animals
Flagellates
Trichomonas vaginalis• Sexual transmission
Trichomonas tenax
• Normal oral flora
• Opportunist in gingival disease
Trichomonas hominis• Normal intestinal flora
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No cyst form
Giardia lamblia
• Contaminated water
• Diarrhea with flatulence
• Associated with camping
Trypanosoma
• Blood parasites
hemoflagellates
T. brucei—
Sleeping sickness
T. cruzi—Chagas disease
Leshmania
• Blood and tissue parasite
• Three species—Oriental sore or
visceral leshmaniasis
• Asia, Middle East
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Apicomplexans
no organelle for motility
Plasmodium• Blood parasite—malaria
• Four species—varying symptoms
and pathology
Pathology
• Cyclic fever when RBCs rupture
• Anemia from loss of RBCs
• Liver damage
• Kidney damage
Coccidians
no organelle for motility
• Live intracellularly
• Order (Coccidiorida) of the
Apicomplexa
Toxoplasma gondii
• Toxoplasmosis
• Mild disease in adults
• Severe to fatal disease in fetus and
individuals with AIDS
• Cats ⇔ Rats
• Humans ingest oocysts from cat
feces or pseudocysts from meat
• Dx—serology, symptoms, history
Sarcocystis
• Common in animals
• Rare in humans—ingest infected meat
Cryptosporidium
• Infects variety of animals• Contaminated food and water
• Mild to asymptomatic “stomach flu”
• Severe, chronic disease in AIDS• Immunofluorescent stain
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Isospora
• Contaminated food and water
• Self-limiting diarrhea, asymptomatic
Cyclospora• Emerging pathogen, Isospora
• Fresh produce, water with fecalcontamination
Babesia• Historical significance• Rare in humans, zoonosis
HelminthsHermaphroditic
Male and female sex organs in
same worm
Definitive hostHarbors sexual cycle
Intermediate host
Harbors asexual cycleTransport host
No development—link in life cycle
Epidemiology of Helminth Diseases
World-wide—3.8 million infections
Highest—children, rural areas,
tropics and subtropics
Fecal-soil contamination
Bare feet
Raw or undercooked meat
Pathology of Helminth Infestation
Mouth parts adapted for attachment
and feedingProcess food and reproduce
Many migrate through tissues—
inflammation
Set up housekeeping in various
tissues—trauma due to feeding,
toxins, blockages
Eosinophils produced in response
to infestation
Capable of destroying worms
Antibodies and T-cells also produced—limited ability to control
Immune system unable to eliminate
worms completely—size, migration,
inaccessibility
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Diagnosis
Eosinophils and serology
History of travel—even years ago
Evidence of worms or eggs in
various body fluids
Rx—antihelminthic drugs
Prevention—limit parasite-humancontact
Helminth lifeand
transmission
cycles
Helminth lifeand
transmission
cycles
Roundworms—Nematodes
Intestinal Nematodes
Some development in intestine
Tissue Nematodes
Live in soft tissues
Ascaris lumbricoides
• Large intestinal roundworm
• Ingest eggs
• Humans only host
• Larvae burrow through intestine
• Travel in blood to lungs
• Swallow to intestine
Intestinal Nematodes Adults do not
attach andmay migrate
to liver, gall
bladder oremerge from
mouth or nose
Allergic reactions can
occur
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Trichuris trichiura
• Whipworm
• Large intestine—rectal prolapse
• Ingest eggs
• Humans only host
Enterobius vermicularis
• Pinworm, seatworm
• Lives in appendix
• Female lays eggs in perianal area
• Ingest eggs
• Humans only host
Hookworms• Necator americanus
• Ancylostoma duodenale
• Eggs hatch in soil, larvae penetrateskin
Strongyloides stercoralis
• Thread worm
• Can complete life cycle in human
or in soil
• Eggs hatch in large intestine
• Larvae penetrate skin
• Can disseminate in immunocompromised host
disseminated Strongyloides infection
Trichinella spiralis
• Larva encysts in muscle
• Ingest cyst
• Associated with pork
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Tissue Nematodes
Require arthropod vector
Wuchereria bancrofti
• Elephantiasis
• Worms block lymphatics
Onchocerca volvulus
• Skin or eye—river blindness
Loa loa
• Skin or eye—nos blindness
• Calabar swellings
Dracunculus medinensis
• Longest—1 meter
• Pregnant female coils up under skin
• Releases eggs into water
• Eggs ingested by a copepod
• Humans ingest copepod
Trematodes—flukes
Schistosoma
• Blood flukes
• Invade blood vessels walls• Deposit eggs in intestine or bladder
• Eggs hatch in water
• Larva infects snail• Snails release infective larva—
penetrate skin
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Opisthorchis (Clonorchis) sinensis
• Chinese liver fluke
• Larva infect snail
• Larva from snail infect fish
• Humans eat fish
• Fluke migrates to liver
• Eggs in common bile duct
Fasciola hepatica
• Giant liver fluke
• Larva from snail encysts on plant
Paragonimus westermani
• Oriental lung fluke
• Second host (after snail) is crab
or crayfish
• Humans ingest infected crab or
crayfish
• Fluke migrates to lung
Cestodes—tapeworms
Head—scolex
Hooks or suckers for attachment
Body segments—proglottids
Uterus full of eggs
Further from scolex—more mature
scolex
chain of
proglottids
Eggs ingested by meat animal
Larva encyst in muscle
Humans ingest cyst
Tapeworm Life Cycle
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Taenia saginata
• Cows
Taenia solium
• Pigs
Diphyllobothrium latum
• Fish—Jewish mother’s disease
• Pernicious anemia
Cystocercosis• Human intermediate host for
T. solium
Arthropods as Disease Vectors
Ectoparasites—feed on blood and
tissue fluids
Biological vectors—part of diseasetransmission cycle
Many diseases vector specific—distribution of vector determines
disease distribution
Mosquitos—only female—spread
disease through anticoagulant
Fleas—spread from species to
species easily—regurgitate blood
Lice—infection through louse or
feces being crushed into wound
Ticks—broadest host range—
every vertebrate except fish