Parasitology Flashcards Preview

M(ASCP) Prep COPY > Parasitology > Flashcards

Flashcards in Parasitology Deck (84)
Loading flashcards...

Painful keratitis & corneal ulcers following corneal trauma or association w/contact lens use


Trophozoites displaying acanthopodia may be seen in direct wet mount or from culture. A variety of permanent stains can be used including Giemsa, PAS, and trichrome.

Use of the fluorochrome calcofluor white is especially helpful in recognizing characteristic double-walled cysts.


Granulomatous amebic encephalitis (GAE)

Headaches, altered mental status and focal neurologic deficits, which progresses over several weeks to death

Mainly in immunoSUPPRESSED persons

Acanthamoeba/Balamuthia spp.

  • Acathamoeba spp. cysts have wrinkled fibrous outer wall + variable inner wall (endocyst)
    • Single nucleus with large karyosome
    • May be found in brain, eyes, skin, lungs, and other organs
  • Acanthamoeba spp. trophs have large nucleus/karyosome
    • Have spine-like processes called acanthapodia


Okay they're literally shitting worms during a high fever.

Ascaris lumbricoides

Fertile Ascaris eggs are round to slightly oval with a yellow-brown, irregular external mamillated layer (not always present) and a thick shell. 

Infertile eggs are elongate and measure from 85 to 95 µm.


Patient presents with fever after a tick bite


Babesia may be distinguished by the presence of tetrads (MALTESE CROSS IS A DEAD GIVEAWAY), vacuolated cytoplasm, and extracellular ring stages


Dysentery-like symptoms

Balantidium coli

Trophozoite - 

  • 50 -100 µm in diameter),
  • ovoid, and covered with cilia
  • two nuclei, one macronucleus and one micronucleus, although the latter is usually not seen.
  • A cytostome apears as a deep, curved depression.

Cyst - 

  • spherical or oval, being 50 to 70 µm in diameter
  • large macronucleus.
  • Cilia are often apparent underneath the thick cyst wall.


Blastocystis hominis

Central Vacuolar Form - 

  • 5 to 20 µm in diameter. 
  • usually spherical with a large central vacuole
  • two or more peripheral nuclei.

Ameboid Form - 

  • highly irregular in size, shape, and number of nuclei.
  • Crescent-shaped nuclear chromatin bands may be seen.


SE asian immigrant presents with lymphatic filariasis and early development of elephantiasis. Blood from a midnight draw shows...

Brugia malayi

Brugia malayi microfilariae have sheaths that generally stain well with Giemsa, and have two solitary nuclei (beyond the end of the contiguous nuclear column), the last of which extends to the tip of the tail.


42 yo male presents with abdominal pain and diarrhea after a visit to the Philippines

Capillaria philippinensis


After consuming sushi in a questionable venue, a patient complains of diarrhea. O&P reveals...

Capillaria philippinensis

C. philippinensis eggs resemble those of Trichuris trichiura, except that they usually measure 36 to 45 µm by 21 µm wide, and display thick, radially striated shells. Inconspicuous polar plugs are present at each end.


Chilomastix mesnili

Trophozoite - 

  • 6 to 24 µm in diameter and are pear- shaped.
  • The single nucleus has a centrally located karyosome and a ring of finely granular peripheral chromatin. 
  • prominent cytostome extending one-third to one-half the length of the body.

Cyst - 

  • lemon-shaped, have one nucleus, and vary from 6 to 10 µm in diameter.
  • An anterior hyaline knob and intra- cytoplasmic fibrils may be present.


infection is acquired by the ingestion of infected raw or uncooked freshwater fish.

Infections are often asymptomatic, although large numbers of flukes and repeated infections may produce inflammation of the bile ducts.

Clonorchis sinensis

small brown, embryonated, operculate eggs from stools. 

C. sinensis eggs measure 25 to 35 µm by 12 to 20 µm and have a prominent, seated opercula and a small knob at the abopercular end.


Typically in liver bile duct system Fluke.

Clonorchis sinensis


Mild to profuse watery diarrhea with cramps, N/V, weight loss, anorexia

Cryptosporidium parvum oocysts

  • spherical and range from 4 to 6 µm
  • acid-fast and appear deep fuchsia in color when stained with the modified Kinyoun's technique.
  • A characteristic internal wrinkling is noted. Similarly-sized and stained objects which lack foldings or wrinkling should be suspected of being artifacts. 
  • positive control material is mandatory when performing these stains.


mild-severe watery diarrhea, anorexia, weight loss, abdominal pain, nausea and vomiting, myalgias, low-grade fever, and fatigue

Cyclospora cayetanensis

  • spherical, acid-fast, and 8 to 10 µm
  • clear, round, and somewhat wrinkled objects on trichrome stained smears.
  • C. cayetanensis oocysts closely resemble those of C. parvum, but can be distinguished by their larger size and ability to autofluoresce when viewed on a microscope fitted with epifluorescence capability.


Dientamoeba fragilis

Trophozoite - 

  • 5 to 15 µm in diameter, are ameboid in shape
  • usually have two nuclei, although uninuclear forms are also common.
  • Nuclei often appear as clusters of small granules.

D. fragilis does not have a cyst form.


ID Tapeworm

Diphyllobothrium latum


Humans acquire these worms via ingestion of infected raw- or incompletely- cooked fish. Symptoms are rare, but may include varying degrees of abdominal discomfort and diarrhea and vitamin B12 deficient anemia.


This is a long-ass worm (30+ ft)

Diphyllobothrium latum

Eggs measure 58 to 76 µm by 40 to 51 µm and in addition to the operculum, have a small, round, knoblike projection on the abopercular end.

Segments are wider than they are long.


Infection occurs as a result of accidental ingestion of adult fleas containing cysticercoid larvae.

Human infections produce few symptoms, and generally cause concern only on detection of the actively moving proglottids in diapers or underclothing.

Dipylidium caninum

Spherical eggs, each containing a six-hooked embryo, measure from 24 to 40 µm in diameter and occur either singly or in packets.

Species identification may be made on recovery of proglottids, or, more rarely, the scolex.


Enlarging cysts --> symptoms in affected organs

Liver cyst --> abdominal pain/biliary tract obstruction

Lungs --> chest pain/cough…esp of blood


Cysts produced by E. granulosus and E. vogeli infection usually contain hydatid sand, a mixture of protoscoleces, disintegrating brood capsules, hooklets, and calcareous corpuscles.


Stool exam reveals...

Endolimax nana

Trophozoite - 

  • smallest ameba found in the human intestine (6 to 12 µm in diameter).
  • Trophozoites have a single nucleus with a prominent karyosome
  • A clear halo surrounds the karyosome.
  • Peripheral chromatin is lacking.

Cyst - 

  • 5 to 10 µm in diameter.
  • Cysts usually contain four or fewer nuclei. The nuclei have centrally located karysomes surrounded by a small halo.


This parasite observed in stool. Do we freak out?

Entamoeba coli

No. It's non-pathogenic.

Trophozoite - 

  • Size = 15 to 50 µm in diameter.
  • large, often eccentrically located, karyosome and coarsely granular peripheral chromatin that is unevenly distributed.
  • Cytoplasm usually stains darkly and contains numerous vacuoles.

Cyst - 

  • 8-16 nuclei
  • size = 10 to 35 µm.
  • Glycogen may be present as a large mass, especially in immature cysts. 
  • E. coli chromatoid bodies are irregular in shape with splintered or pointed ends.


Stool exam shows this...

Entamoeba hartmanni. Non-pathogenic

Trophozoite - 

  • maximum diameter of 12 µm.
  • Nucleus- small, usually centrally located karyosome with a finely granular ring of peripheral chromatin.
  • E. hartmanni is distinguished from E. histolytica primarily on the basis of its smaller size, although sizes may overlap.

Cyst - 

  • maximum diameter of 10 µm 
  • four nuclei, although immature cysts containing one or two nuclei are seen more commonly. 
  • E. hartmanni cysts are essentially identical to those of E. histolytica and are differentiated solely on the basis of size using the ocular micrometer.


Brown stuff "Chocolate pus" oozing out of abscess.

Entamoeba histolytica

Trophozoite - 

  • E. histolytica trophozoites vary from 10 to 60 µm in diameter
  • single nucleus- evenly distributed peripheral chromatin and a small karyosome which is often centrally located.
  • Cytoplasm is finely granular.
  • The presence of ingested erythrocytes is considered diagnostic for E. histolytica.

Cyst - 

  • E. histolytica cysts are spherical and measure 10 to 20 µm in diameter.
  • Mature cysts have four nuclei; immature cysts may have one or two.
  • Nuclei are similar to those found in trophozoites.
  • Cyst cytoplasm may contain glycogen vacuoles, especially in young cysts, and elongate chromatoid bodies which have rounded or blunt ends.


Child presents with perianal skin irritation. Scotch tape preparation reveals...

Enterobius vermicularis eggs (Pinworm)

Eggs measure from 50 to 60 µm, are characteristically flattened on one side, and each contains a developing larva


The best time for a scotch-tape test to detect Enterobius ova is...

Immediately after waking

Females exit the anus during sleep to deposit the eggs in the peri-anal area


Blocks bile duct, leading to gallstone-like disease

Possible liver damage if wastes cannot be broken down and excreted

Associated with ingestion of watercress and fresh-water plant-fed animals (sheep) with human contact

Fasciola hepatica (sheep liver fluke) in Europe, Middle, Asia

F. gigantica Asia, Africa, and Hawaii


Infection is acquired by ingestion of infectious metacercariae on aquatic food plants in SE Asia. Symptoms including diarrhea, epigastric pain, and nausea may develop if sufficient worms are present to produce ulceration of the superficial intestinal mucosa.

Fasciolopsis buski

Diagnosis is made by finding the large (130 to 140 µm by 80 to 85 µm), brown, oval, and thin-shelled eggs. The operculum may be inconspicuous, and the eggs are passed unembryonated.


Genera of Coccidia

Cryptosporidium, Cyclospora, and Isospora

Acid-fast and auramine-O stains are sensitive and cost-effective for detection of coccidian oocysts, but they lack specificity.


Acute = water stools…floating/fatty because the stool is full of the fat that you fail to absorb

Chronic = fat malabsorption syndrome, loss of fat soluble vitamins (A/D/E/K) 

Giardia lamblia


  • Bilaterally symmetrical, pear-shaped
  • two nuclei with centrally located karyosomes.
  • eight flagella not always seen on smears.
  • Length varies from 10 to 20 µm.
  • The concave "sucking disc" may be apparent with proper staining and organism orientation.

Cyst - 

  • size from 8 to 19 µm, are oval or ellipsoidal in shape
  • usually have 4 nuclei.
  • Characterisitc intracytoplasmic fibrils are usually visible.


Infections are acquired by ingestion of infected raw or incompletely cooked freshwater fish. Most infections are self-limited but may produce diarrhea and abdominal pain.

Heterophyes/Metagoninus spp.

Diagnosis is established by finding the embryonated operculate eggs, which measure 20 to 30 µm in length by 15 to 17 µm in width. Eggs of these species may be difficult to differentiate from those of Clonorchis sinensis.