Hd Test 3 - Parasites

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parasite

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lives on/in an organism and draws nutrition directly from it

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definitive host

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host in which parasites complete sexual phase of their life cycle

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intermediate host

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parasites live here asexually

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vector

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organism that transmits parasite to host. A living fomite.

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reservoir

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natural host that serves as a source of parasites, allowing transmission.

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helminths

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multicellular worms; acquired via ingestion; larvae are usually the pathogenic form. burden related to #. pathology due to host immune response

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arthropods

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animals w/ segmented body and chitinous exoskeleton; can be vectors for other parasites or can act as ectoparasites. Include insects (6 legs) and Chelicerata (8 legs - mites and ticks)

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myiasis

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using human tissue as food source or place to lay eggs. Ex: flies

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Siphonaptera

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fleas; ectoparasites of warm-blooded animals; classic vectors of the plague

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Pediculus humanus

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Lice; have specific regions they like; vectors of typhus and trench fever

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Cimex lectularius

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bedbugs; not known to transmit disease

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Chelicerata

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ticks; vectors of rocky mtn spotted fever, lyme disease

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protozoans

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unicellular/eukaryotic; multiply rapidly asexually; potential for latency. No vaccines.

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transmission of protozoans

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fecal-oral route

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trophozoite

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motile stage, can multiply in host but die in outside enviro

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cyst

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enters this dormant stage when passing through the colon. tough outer wall that can survive in outside enviro.

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oocyst

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also a resistant stage but is formed by sexual reproduction and contains zygote

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protozoan life cycle

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ingestion of cyst or oocyst >> excyst into trophozoite form, multiply and remain in GI tract, potentially causing disease >> encyst into environmentally-resistant form, which can contaminate food/water and begin cycle again.

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Giardia

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most common intestinal parasite in world; flagellated; noninvasive organism w/ small ID

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sources of giardia

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found in water. cysts are chlorine resistant. cysts can be spread person-person, in food or from animals

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sx of giardia

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chronic submucosal inflammation; water diarrhea or steatorrhea. no blood/pus in stool.

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giardia life cycle

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adhere to intestinal epithelial cells via lectins >> multiply via binary fission >> impair epithelial absorption. Not migratory.

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Entamoeba histolytics

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very virulent EC pathogen that grows/multiplies in intestine

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troph form

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pathogenic multiplying stage; single nucleus w/ ingested erythrocytes. environmentally fragile

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cyst form

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excreted form, endures in enviro. has 1-4 nuclei and chromatoid body

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active disease

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troph form is excreted, which dies quickly in enviro. Less likely to spread disease

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pathogenesis of amebiasis

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degrades mucin layer and attaches to host cell; kills cell on contact and ingests it.

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outcomes of infection

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Most are non-invasive, troph stays in lumen and cyst is excreted. Some trophs invade mucosa >>intestinal disease; small # become extraintestinal and travel via bloodstream to brain/lung/liver.

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immune response to amebiasis

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largely involves cell-mediated immunity

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treatment considerations for amebiasis

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consider whether it is intestinal or has spread elsewhere.

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Cryptosporidiosis

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parvum (cattle/human) and hominis (humans only).

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Crypto sources/transmission

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recreational/drinking water, food, hands, daycare, cattle. not chlorine sensitive (must be filtered out)

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course of infection

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thick-walled oocyst is the infective form. In mammalian hosts it infects epithelial cells and reproduces sexually/asexually. No invasion beyond intestinal mucosa.

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cryptosporidiosis sx

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watery diarrhea; usually self-limiting. parasite is excreted for weeks after resolution of sx.

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Toxoplasma

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acquire by ingestion but does not cause intestinal disease. 90% infections are asymptomatic

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vulnerable populations

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newborns (congenital transmission) and immunocompromised

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toxoplasma life cycle

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definitive host is cat, which sheds oocysts in feces that mature in 48hrs. Can infect other vertebrate hosts that ingest the oocyst, which releases sporozoites that penetrate intestinal wall and emerge as trachyzoites in blood. Can infect any nucleated cell, form dormant tissue cyst and usually remain in body for life.

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toxoplasma transmission

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ingestion of feline feces; ingestion of tissue cysts from infected animal meat; transmission from mom to baby; tainted transplant or transfusion

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acquisition of helminths

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ingestion if egg/larvae; skin penetration by larvae; accidental infection of unintended host

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nematodes

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unsegmented roundworms

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cestodes

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flatworms

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trematodes

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flukes

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Pinworms

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intestinal nematodes transmitted by ingestion. Eggs are directly infective

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Pinworm life cycle

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Ingest eggs and hatch in SI; Females live in LI and emerge @ night to lay eggs on perineum. Eggs cause itching >> reinfection occurs easily and can also spread person-person.

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reinfection

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through the skin or by anus/mouth contact

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pinworm treatment

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scotch tape prep to look for eggs. Treat entire family, wash linens/pajamas

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Ascaris lumbricoides

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longest human intestinal roundworm

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Ascaris life cycle

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Adults live in SI and females produce 200,000 eggs per day >> eggs must mature for 2 weeks in soil >> ingested >> invade intestinal mucosa >> travel via portal system to systemic circulation to lungs >> mature in lungs and penetrate alveolar walls >>ascend bronchial tree and are swallowed >> develop into mature adult in SI

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eggs

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need 2-4 weeks in mature soil to mature. Aren't infectious, otherwise

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sx

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may produce respiratory sx while maturing in lungs; mature worms can produce abdominal discomfort, physical irritation or block intestines if worm burden is very high

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worm characteristics

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must move to stay in place; can be aggravated by fever, surgery, steroids.

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Trichuris

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aka whipworm. Roundworms. Ingested eggs hatch in SI and migrate to colon, where they mate and lay eggs that need 3 weeks in soil to mature.

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Trichuris sx

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Sx range from asymptomatic to diarrhea and abdominal pain/distension, to profuse bloody diarrhea; dependent on worm burden. Associated w/ vitamin A deficiency

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Trichina

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Infectious encysted larvae ingested in undercooked pork that hatches in SI, migrates through bowel wall and enters circulation and disseminates into tissues. Rare in US. public health measure have broken life cycle

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Nector americanus and ancylostoma duodenale

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Hookworms

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Hookworm life cycle

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Eggs shed in stool, hatch and larva become infectious. Can penetrate human skin and travel via blood to lungs. Penetrate alveoli, ascend bronchial tree and are swallowed. Use teeth to bite mucosa in SI and can live there for years

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hookworm pathogenesis

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blood loss can lead to anemia and stunt growth in children

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hookworm cycle broken by

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wearing shoes, proper waste disposal, treatment of infected

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Strongyloides stercoralis lifecycle

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similar to hookworm but eggs hatch in intestine and motile larvae passed in feces. Mature in soil to infective stage, which can penetrate intact skin

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free-living life cycle

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molt 2x in soil and become infective larvae or 4x and become free-living adults that mate and produce eggs

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parasitic life cycle

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penetrate human skin and go to lungs > stomach >> molt 2x in SI and attach, produce eggs, which hatch there.

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autoinfection

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can penetrate skin of perineum or mucosa and reinfect. source of persistent infection

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hyperinfection

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life-threatening condition in immunosuppressed. Must screen transplant recipients for this.

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larva curens

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itching due to migration

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accidental infection

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egg or larva of dog/cat/raccoon parasite infects human, where it can't complete lifecycle and may migrate through tissues

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cutaneous larva migrans

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dog hookworm enters human skin and causes creeping erruption

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visceral larva migrans

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when kids ingest soil w/ eggs of pet's roundworms. larva often migrate to liver/eye/brain.

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beef and pork tapeworms

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Taenia; infect humans who eat undercooked meat from IM host. humans are the only definitive host.

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lifecycle

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cows/pigs eat eggs that hatch in SI and migrate to muscle and other tissues and form cysticerus. If eaten by human, it can attach in SI wall, mature and release eggs.

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cysticercosis

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human can be IM host to pork worm if they ingest EGGS. Migrate to brain and muscle

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neurocysticerosis

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cysts migrate to brain and cause inflammation when they die years later

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C echinococcus granulosus

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definitive host is dog; sheep/humans are IM host. surgery needed to remove hydatid cyst. Rupture could lead to anaphylaxis

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dwarf tapeworm

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most common in humans; eggs are immediately infective, so reinfection is possible