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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

2

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

3

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

4

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

5

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

8

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