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Necator americanus and Ancylostoma duodenale Life Cycle

Diagnostic stage: eggs in feces and worms in intestinal biopsies
Embryo develops rapidly into rhabditiform
Infective stage is filariform larva
Method: penetration of the skins of human
Enters the lymphatics and the bloodstream
Travels to lung
Break out of lung
Coughed up and swallowed where they go to intestine
Mature to adults

Hookworm infection symptoms

Itching at penetration site
Abdominal pain


Egg: thin, smooth, colorless shell with two to eight cell cleavage
Buccal capsule is longer than strongyloides
Possess a bulbous esophagus

Strongyloides stercoralis

Diagnostic stage: first-stage larvae in feces
Eggs hatch in mucosa and noninfective rhabditiform larvae are observed in feces
Filariform larvae penetrate skin of host and move through the lymphatics and blood to the lung.
coughed up from the bronchioles to the pharynx and swallowed and return to the intestine


No male
Strongyloides stercoralis
Buccal cavity of this is much shorter than the other hookworms

Trichinella spiralis

Transmission: humans eat undercooked pork, deer, or bear contaminated with encysted larvae
Larvae mature in intestine and new larvae move to lymphatics, which then migrate to active, striated muscles and encyst
Diagnosis: extreme peripheral blood eosinophilia, muscle fiber biopsies with encysted larvae, serological tests.


Abdominal pain, headache, diarrhea, joint pain, periorbital edema

Dracunculus medinensis

Guinea worm
Consumption of contaminated water (copepod)
Forms papule, or painful blister
Typically observed on feet, legs, or ankle

Wuchereria bancrofti

most common filarial infection - endemic to tropical and subtropical areas
Migrate through lymphatics and mature as aduts
Transmitted by Anopheles mosquito
Symptoms: headache, feverm obstructive lymphadenopathy, elephantiasis
Diagnosis: ID of microfilaria in blood or skin

Loa Loa

African eye worm
chrysops fly
Calabar swellings is swelling around the eye
Diagnostic stage is microfilariae in blood

Onchocerca volvulus

Black fly
Produces nodules on the scalp
Diagnostic procedure is skin snips (parasite is walled off in a granuloma

Hymenolepis nana

Prevalence in Southeast US
Most common in US
Eggs in feces of infected mice and rats accidentally ingested by human host
Diganostic form is eggs in feces
Egg: filaments emerge from polar thickenings
- three pairs of hooklets
- hexacanth embryo

Taenia solium and saginata

Worldwide distribution
Transmission: inegstion of undercooked meat with encysted larvae - mature into adult worms that reside in small intestine
Diagnosis: proglottids or eggs in feces, biopsy for cystericercosis, serology tests


Abdonimal pain: ingestions of embryonated eggs or gravid proglottids causes cystercercosis - larvae migrate to brain, eye, muscle, etc.

T. saginata

15 - 30 lateral uterine brancehs

T. solium

<15 lateral unterine branches

Diphyllobothrium latum

Fish tapeworm
Intestional obstruction
Abdonminal pain, weight loss, weakness
B12 deficiency
Cultures and climates where raw fish are eaten
Pleurocercoid ingested by humans in raw or undercooked fish
Diagnostic stage is egg passed into the feces

Fish tapeworm

Egg is operculated
Terminal knob
Rosette shaped uterus

Echinococcus granulosus

human ingests eggs by close contact with dog or sheep - accidental host
Diagnostic stage is hydatid cyst in liver, lung or other organs
Complication is anaphylactic shock if cyst ruptures during biopsy or removal

Fluke life cycle

Eggs contaminate water and hatch in miracidium which penetrates snail
Miracidium develop into cercariae and emerge from snail and encyst on vegetation, fish, or shellfish and develop into metacercariae
Humans ingest the contaminated plant, fish, or shellfish
Metacercariae migrate to the appropriate site...lung, liver, intestine

Fasciola hepatica

Sheep liver fluke - worldwide
Transmission: ingestion of fresh-water vegetation
Larvae migrate through peritoneal cavity and penetrate liver and reside as adults in hepatobiliary ducts
Symptoms: headache, chills, fever, diarrhea, biliary obstruction, jaundice
Diagnosis: eggs in feces or bile; serological tests (ELISA, Western Blot)

Fasciolopsis buski

Large intestinal fluke
Ingestion of metacercariae from undercooked water plants
Associated with intestinal obstruction and malabsorption - eating bamboo
China, Vietnam, Malasia
Can have very large worm burden
Huge egg that is difficult to differentiate from hepatica

Clonorchi sinensis

Eggs in feces or entero-test capsule
Ingestion of metacercariae in undercooked fish
Operculated egg
Shoulders and small knob

Heterophyes heterophyes

Ingestion of metacercariae in undercooked fish
Eggs in feces
Similar to Clonorchis
Faint shoulders, small knob

Paragonimus westermani

Lung fluke
Ingestino of metacercariae in undercooked crabs or crayfish
Eggs in sputum
Operculated, terminal thickening


Only flukes with separate genders
Transmission: free-swimming larvae (fork tailed cercariae) penetrate human skin and migrate to organs
Blood flukes (mate in blood vessels)


Symptoms: inflamed site due to skin penetration, fever, abdominal or pelvic pain, diarrhea, cirrhosis
Urinary obstruction, urinary bladder squamous cell carcinoma
Diagnosis: eggs in stool or urine, eggs in tissue biopsies, serologic tests

Schistosoma haematobium

spike is on the bottom

Schistosoma japonicum

vestigial spine

Schistosoma Mansoni

Prominent sharp spike on the side

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