Parasitology Week 6

in the clinical laboratory, parasite usually refers to _____ organisms

eukaryotic

eukaryotic organisms that are common clinical laboratory parasites

1. protozoa: one celled organism

2. helminths: worm like animals

morbidity 

rate of disease in a population 

where are parasitic disease less prevalent?

developed countries with good sanitation 

where are parasitic disease more common?

tropics and subtropics 

why are parasites less common in industrialized countries?

1. sanitation and good hygiene practices

2. temperate climate that don’t let dormant stages of parasites survive

3. less suitable vectors, less intermediate and reservoir hosts 

why have parasitic infections increased worldwide?

1. jet travel

2. wars

3. refugees

4. mosquitoes resistant to pesticides

5. drug resistance 

6. increased immunocompromised patients 

a successful parasite…

1. obtains part or all its nourishment from host

2. derives all the benefit of the association with host 

ectoparasite

lives outside the host’s body

endoparasite

lives inside the hosts’s body

facultative parasite

can live with and without the host

obligate parasite

cannot survive without the host

incidental parasite

can live in a host that is not ordinarily used 

pathogenic parasite

causes harm to the host

definitive host

host in which the parasite reaches sexual maturity and undergoes reproduction 

intermediate host

host in which some development of the parasite occurs but does not reach sexual maturity

accidental host

host in which the parasite can live, but is not required for its life cycle 

reservoir

host in which a parasite survives mostly without causing disease 

vector

carries parasite that can multiply within their body and be delivered to new hosts, usually by biting

what can be mistaken for a parasite?

pseudoparasites or artifacts

spurious parasite

does not infect humans and can pass through intestinal tract without causing infection 

what type of sample contains large amounts of debris that appear as artifacts and pseudoparasites?

fecal material 

white blood cells as pseudoparasites

1. can be confused with amoebas

2. human cells have a higher nuclear material to cytoplasm ratio

types of artifacts/pseudoparasites

1. yeast

2. plant cells and root hairs

3. oil droplets

4. pollen grains

5. diatoms

6. vegetable and muscle fibers

7. charcot-leyden crystals

charcot-leyden crystals

1. formed from the degradation of eosinophils

2. associated with inflammation 

three types of helminths (general categories)

1. nematodes

2. cestodes

3. trematodes 

round worms

nematodes

tape worms

cestodes

flukes

trematodes

nematodes shape, sexes, head end, alimentary canal, and body cavity

1. elongated cylindrical, unsegmented 

2. separate

3. no suckers, no hooks, well developed buccal cavity

4. present, complete anus

5. present 

cestodes shape, sexes, head end, alimentary canal, and body cavity 

1. tape-like, segmented

2. not separate

3. suckers often with hooks

4. absent

5. absent

trematodes shape, sexes, head end, alimentary canal, and body cavity 

1. leaf-like, unsegmented 

2. not separate, except Schisto

3. suckers, no hooks

4. incomplete, no anus

5. absent

species of intestinal nematodes

1. Enterobius vermicularis

2. Trichuris trichiura

3. Ascaris lumbricoides

4. Strongyloides stercoralis

5. Necator americanus

6. Ancylostoma duodenale 

7. Ancylostoma braziliense 

another name for Enterobius vermicularis

pinworm

disease caused by Enterobius vermicularis

enterobiasis 

most common intestinal helminthic infection in the US

enterobiasis

where does enterobiasis commonly occur geographically?

temperate climates

only known host of Enterobius vermicularis

humans

people most commonly isolated with enterobiasis

preschool children and in crowded places

diagnostic stage of Enterobius vermicularis

eggs on the perianal folds

infective stage of Enterobius vermicularis

embryonated eggs ingested by humans

how long does it take Enterobius vermicularis larvae inside the eggs to mature to infective stage?

4 to 6 hours

where do Enterobius vermicularis hatch into larvae?

small intestine

where do adult Enterobius vermicularis occupy?

lumen of cecum (colon)

where and when do female Enterobius vermicularis lay eggs?

crawling on the skin of the perianal area at night

how else can enterobiasis be contracted other than hands scratching the anus?

contaminated surfaces with pinworm eggs like carpets and bedding

general life cycle of Enterobius vermicularis

1. eggs laid on perianal folds

2. embryonated eggs ingested by humans

3. eggs hatch in small intestine

4. adults establish in colon 

5. females migrate to anus to lay eggs

common symptoms of enterobiasis

1. usually asymptomatic

2. perianal pruritus

3. vulvo vaginits

4. pelvic or peritoneal granulomas 

less common symptoms of enterobiasis

1. anorexia

2. irritability

3. abdominal pain 

lab diagnosis for enterobiasis

1. microscopic ID of eggs

2. adult worms found in perianal area during anorectal or vaginal examinations 

microscopic identification and testing method of Enterobius vermicularis eggs

1. scotch test/cellulose tape slide test

2. done in morning before defecation 

3. anal swabs 

enterobiasis is not diagnosed by microscopic examination of _______

fecal matter

Enterobius vermicularis egg morphology

1. colorless and smooth

2. thick shell flattened on one side

3. elongate-oval

4. can contain fully developed larvae

what species produces this egg?

Enterobius vermicularis 

another name for Trichuris trichiura 

whipworm

infection caused by Trichuris trichiura

trichuriasis 

route of trichuriasis

fecal-oral route, no intermediate host

where do Trichuris trichiura ova mature?

external environment

where is trichuriasis mostly seen geographically?

tropical climates and areas with poor sanitation, sometimes southern US

diagnostic stage of Trichuris trichiura

unembryonated eggs passed in feces

infective stage of Trichuris trichiura

embryonated eggs that are ingested

when do Trichuris trichiura eggs become infective after deposited in soil via feces?

10-14 days

where do Trichuris trichiura eggs hatch into larvae?

small intestine

where do adult Trichuris trichiura mature and occupy?

cecum (colon)

general life cycle of Trichuris trichiura

1. undeveloped eggs in feces

2. eggs embryonate in soil by 1 month

3. ingested eggs hatch in small intestine

4. larvae mature into adults in colon 

how do Trichuris trichiura live in the intestines?

they bury their threadlike anterior half into the intestinal mucosa to feed on tissue secretions

symptoms of heavy infections with Trichuris trichiura

1. abdominal pain

2. nocturnal loose stools 

3. dysentery

4. rectal prolapse

5. stunted growth

who is more at risk for severe cases of trichuriasis?

children

endoscopy and microscopy lab diagnoses of trichuriasis

1. endoscopy: showing adult whipworms attached to bowel mucosa

2. microscopy: ova and parasites in stool samples

formalin ethyl acetate sedimentation FAS technique

recommended for light infections of trichuriasis

Trichuris trichiura egg morphology

1. football shaped

2. bipolar colorless plugs

3. thick shell 

4. unembyronated in feces 

5. yellow or brown shell 

what species produces this egg?

Trichuris trichiura

distinctive morphology of female whipworms

long pointed tail

distinctive morphology of male whipworms

blunted posterior ends 

what is the largest intestinal nematode parasite to humans?

Ascaris lumbricoides

disease caused by Ascaris lumbricoides

ascariasis

source of transmission for ascariasis 

contaminated soil and vegetation 

where is ascariasis most common geographically?

tropics and subtropics, rural areas of southeastern US

diagnostic stages of Ascaris lumbricoides

1. fertilized and unfertilized eggs

2. adult worm

infective stage of Ascaris lumbricoides

fertilized eggs that are ingested

how long does the whole life cycle of Ascaris lumbricoides take?

2-3 months

where do Ascaris lumbricoides eggs hatch into larvae?

small intestine

where do Ascaris lumbricoides larvae mature into adults?

small intestine

where do adult Ascaris lumbricoides occupy?

lumen of small intestine

general life cycle of Ascaris lumbricoides 

1. fertilized eggs are ingested

2. eggs hatch in small intestine

3. larvae invade gut into blood vessels

4. liver

5. lung capillaries 

6. alveoli

7. bronchioles

8. coughed up to pharynx

9. swallowed back down to small intestine 

10. mature to adults in small intestine 

symptoms of ascariasis

1. diarrhea, vomiting, fever

2. stunted growth

3. abdominal pain and intestinal obstruction 

symptoms of migrating Ascaris lumbricoides

1. migrating adult worms cause occlusion of biliary tract or oral expulsion 

2. migrating larvae in lung cause cough, dyspnea, hemoptysis, eosinophilic pneumonitis (Loeffler’s syndrome)

samples taken for ascariasis diagnosis

1. stool

2. sputum

3. gastric aspirate 

laboratory diagnosis of ascariasis

1. microscopic identification of eggs

2. presence of larvae 

3. presence of adult worms 

4. direct wet mounts with heavy infections

morphology of unfertilized Ascaris lumbricoides eggs

1. elongated

2. larger than fertile eggs

3. thinner shell 

4. with or without mammillated layer 

5. refractile granules 

morphology of fertilized Ascaris lumbricoides eggs

1. round and thick shell 

2. mammillated layer 

3. decorticated eggs lack outer layer

4. fully developed larva in developed eggs

what species produces this egg, and is it fertilized or unfertilized?

Ascaris lumbricoides, unfertilized

what species produces this egg, and is it fertilized or unfertilized?

Ascaris lumbricoides, fertilized 

what is shown here?

Ascaris lumbricoides has three lips with teeth to help attach to intestinal wall 

what is Strongyloides stercoralis also called?

threadworm

what disease does Strongyloides stercoralis cause?

strongyloidiasis 

where is strongyloidiasis most common geographically?

tropics and subtropics

which intestinal nematode species alternates between free-living and parasitic cycles?

Strongyloides stercoralis 

where does reproduction occur with Strongyloides stercoralis?

natural environment and host

diagnostic stage of Strongyloides stercoralis

rhabditiform larvae