Parasitology Exam 2: Nematodes Flashcards
What is another name for nematodes?
Roundworms
Describe nematodes as a whole.
Nonsegmented
Elongate
Cylindrical
Well-developed digestive tract and reproductive system
How do nematodes reproduce?
Sexually; there are separate nematode sexes (males and females).
- Males smaller than females
List the intestinal nematodes:
Ascaris lumbricoides
Enterobius vermicularis (pinworm)
Strongyloides stercoralis (threadworm)
Trichuris trichiura (whipworm)
Ancylostoma duodenale (old world hookworm)
Necator americanus (new world hookworm)
What is a general name for E. vermicularis? What type of helminth is this?
Pinworm
Intestinal nematode
What is a general name for S. stercoralis? What type of helminth is this?
Threadworm
Intestinal nematode
What is a general name for T. trichiura? What type of helminth is this?
Whipworm
Intestinal nematode
What is a general name for A. duodenale? What type of helminth is this?
Old World hookworm
Intestinal nematode
What is a general name for N. americanus? What type of helminth is this?
New World hookworm
Intestinal nematode
What is the most common and largest roundworm?
Ascaris lumbricoides
Describe the life cycle of A. lumbricoides including the transmission, hosts, any important facts
Eggs are ingested and hatch in duodenum, penetrate intestinal wall, migrate to hepatic portal circulation, adult worms live and reproduce in the lumen of the small intestine
*Indirect life cycle because transmission is not via a direct route from one host to the next
Transmission: Fecal-oral route
What disease does A. lumbricoides cause?
Can cause Loffler syndrome (accumulation of eosinophils in the lungs) or Hepatic ascariasis (hepatic abscesses, obstructive cholangitis)
Laboratory diagnosis of A. lumbricoides
ID of eggs or adult worms in feces
What is the infective/diagnostic stage of A. lumbricoides?
Infective stage: Ingestion of eggs
Diagnostic stage: ID of eggs in stool
Standout features/morphology of A. lumbricoides eggs
Fertile eggs have a thick mamillated shell
Infertile eggs have a thin decorticated shell
Describe the life cycle of E. vermicularis
At night, female worm migrates out of anus and lays eggs in perianal region, eggs mature, larvae develop
**Direct life cycle because transmission occurs from an infected host to another individual
How is E. vermicularis transmitted?
Ingestion or inhalation of eggs
Which worm discussed most commonly affects school aged children?
E. vermicularis
Most common complaint of E. vermicularis
perianal itching
Retroinfection of E. vermicularis
May occur when eggs hatch and third-stage larvae return to intestine (anus to colon)
Autoinfection of E. vermicularis
Embryonated eggs released into the air or hands and are placed into the mouth and swallowed by an already infected patient (anus to mouth)
Infective/diagnostic stage of E. vermicularis
Infective: eggs ingested by humans
Diagnostic: eggs on perianal folds
Lab diagnosis of E. vermicularis
Microscopic ID of the egg; best obtained using the Scotch tape method
E. vermicularis egg/worm
Female has pin shaped tail
Egg is transparent and flat on one side
Gravid = entire body is filled with eggs
Transmission of S. stercoralis
Direct penetration of larvae, or person to person
Differentiate filariform vs rhabditiform larvae
Filariform: infective larvae that penetrate skin
Rhabditiform: noninfective larvae that can develop into filariform larvae
Describe the life cycle of S. stercoralis
Can have a direct, indirect, or autoinfection life cycle. They typically penetrate skin of humans
What is pathenogenesis?
A mechanism in which female produces eggs as a form of asexual reproduction in which growth and development occur without fertilization
**Associated with S. stercoralis
What is hyperinfection?
Increased worm burden in lungs and intestines, can lead to damage to those organs
What disease does S. stercoralis cause?
Strongyloidiasis, urticarial or serpiginous rash
Lab diagnosis of S. stercoralis?
Rhabditiform larvae (noninfective form) in stool
What organism is associated with “short and sexy”?
S. stercoralis because of the short buccal cavity and large genital primordium
Which organisms may be identified by their rhabditiform larvae forms? How are they differentiated?
S. stercoralis
What organism is associated with tracks on agar plates seen as an incidental finding in respiratory specimens?
S. stercoralis
Trichuris trichiura coinfections can occur with _______ or _______
A. lumbricoides or hookworm
Transmission of trichuris trichiura
Ingestion of eggs
Life cycle of T. trichiura
Ingestion of eggs –> larvae released into intestine –> mature into adult worms –> eggs passed in feces
NO tissue or pulmonary migration stage, unlike other intestinal nematodes
Lab ID of T. trichiura
ID of eggs in feces
Describe T. trichiura egg (standout words)
Barrel shaped, hyaline polar plugs at each end
What is the second most common helminthic infection in humans?
Hookworms
What are the two most common hookworm species and how are they differentiated?
A. duodenale (old world hookworm) - well developed mouth parts (looks like teeth)
N. americanus (new world hookworm) - cutting plates
Cannot differentiate species by ID of eggs
How are hookworms transmitted?
Direct skin penetration by filariform larvae
Lab diagnosis of hookworms?
Presence of eggs or rhabditiform larvae in stool. Cannot distinguish species by eggs, only know that they are hookworm eggs
How to differentiate hookworms from S. stercoralis?
Hookworm has a longer buccal cavity and smaller genital primordium
S. stercoralis has a short buccal cavity and large genital primordium
List the types of tissue nematodes discussed:
Trichinella spp.
Toxocara canis (causes VLM)
Toxocara cati (causes OLM)
A. braziliense/A. caninum (causes CLM)
D. medinensis (Guinea worm)
Transmission of Trichinella spiralis
Eating undercooked meat, typically pork
Key factor of Trichinella spiralis life cycle
Parasite remains in striated muscle
Pigs involved in life cycle (ingestion of undercooked pork containing parasite)
Trichinosis
Disease of the muscle caused by Trichinella infection
How is Trichinella spiralis diagnosed in the lab?
Encysted larvae via muscle biopsy
Most common way is detection of Ab to Trichinella antigen
Infective/diagnostic stage of Trichinella sp.
Infective: ingestion of undercooked meat
Diagnostic: larva in striated muscle
What disease does T. canis and T. cati cause?
Toxocariasis (includes VLM, OLM, CT, NT described on different flashcards)
Transmission of T. canis and T. cati
Ingestion of eggs
Definitive hosts of T. canis and T. cati
T. canis = dogs
T. cati = cats
Which species states that they CANNOT mature in human host, so wander throughout the body and cause migratory syndromes?
T. canis and T. cati
What is VLM?
Visceral (tissue) larva migrans - may see high eosinophilia
Seen with T. canis/T. cati infections in children
What is OLM?
Ocular larva migrans - development of granulomatous reaction in retina seen in children with T. canis/T. cati infections
What is Covert/common toxocariasis? (CT)
Nonspecific symptoms, eosinophilia, positive Toxocara serology (children and adults affected)
What is neurotoxocariasis? (NT)
Invasion of Toxocara larvae to the brain and spinal cord (seen in childrens and adults)
Lab ID of Toxocara infections
Visualization of migrating larvae in tissue biopsy, CSF, or ocular fluids
What is the diagnostic/infective stage of Toxocara?
Diagnostic: larvae in tissues
Infective: ingestion of eggs
What are common hookworms of cats and dogs? (aka zoonotic hookworms)
A. braziliense and A. caninum
What disease does A. braziliense and A. caninum cause, the zoonotic hookworms?
CLM (cutaneous larva migrans) aka creeping eruption
Definitive host of Toxocara and Ancylostoma
Cats and dogs
Infective and diagnostic stage of A. caninum and A. braziliense
Infective: Skin penetration of worm
Diagnostic: larvae in skin
Lab ID of Ancylostoma braziliense and Ancylostoma caninum
Evidence of visible tracks and a patient history of possible exposure is usually sufficient
What disease does D. medinensis cause and what is another name for it?
Guinea Worm
Causes dracunculiasis, blisters caused by gravid female leading to burning and itching
Transmission of D. medinensis?
Ingestion of freshwater from stagnant ponds containing larvae-infected copepods
Lab ID of D. medinensis
ID of larvae or adult worms in clinical specimens
