Parasitology (extra practice, not made by ET) Flashcards
Painful keratitis & corneal ulcers following corneal trauma or association w/contact lens use
Acanthamoeba
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
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
Echinococcus
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
Trophozoite
- 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.
Patient presents with iron-deficient anemia
Ancylostoma duodenale or Necator americanus
Hookworm eggs have thin shells, are partially embryonated when passed, and measure 55 to 75 µm in length by 36 to 40 µm wide
In cases where more severe symptoms may occur, particularly in progressive anemia, what additional test procedure should be performed to determine the role that hookworm infection may play when ova are detected in stool specimens?
Make a quantitative count of the number of ova present.
*Increased egg counts of 20/mg or more are associated with symptoms indicative of heavy worm burdens.
Patient presents with iron-deficient anemia
Ancyclostoma duodenale
Patient presents with iron-deficient anemia
Necator americanus
70um ovum
Human infection is acquired through the ingestion of the intermediate hosts, usually grain or larder beetles.
Symptomatic infection, characterized by abdominal pain and diarrhea, may develop in patients with large numbers of worms.
Hymenolepsis diminuta
oval, thin-shelled eggs that measure 60 to 79 µm in diameter.
centrally located six-hooked embryo , which is separated from the outer shell by a clear space. This space does not contain polar filaments.
30-40 um ovum
Human infection is acquired through the ingestion of infectious eggs or through the ingestion of intermediate hosts (usually grain beetles). Symptomatic infection, characterized by abdominal pain and diarrhea, may develop in patients (usually children) with large numbers of worms.
Hymenolepsis nana “Dwarf tapeworm”
Hymenolepis nana eggs are oval, thin-shelled, colorless eggs that measure 30 to 49 µm in diameter. They contain a centrally located six-hooked embryo , which is separated from the outer shell by a clear space. This space contains polar filaments which arise from polar thickenings on the embryo wall .
Stool exam shows…
Iodamoeba butschlii. Non-pathogenic
Trophozoite -
- size from 8 to 20 µm
- single nucleus has a large, centrally located karyosome and lacks peripheral chromatin.
- The karyosome may appear to be within a muddy karyolymph space or halo.
- The cytoplasm may be vacuolated and usually contains debris.
Cyst -
- size from 5 to 20 µm
- single nucleus which is similar to that seen in trophozoites.
- The cyst has a prominent compact mass of glycogen that stains amber in iodine-stained wet mounts of fresh stool.
Diarrhea, steatorrhea, HA, F, abd pain, nausea, dehydration, weight loss
Isospora belli
- ovoid, acid-fast
- 20 to 33 µm in length.
- Immature oocysts are seen most frequently in freshly passed stool and contain one large undifferentiated sporoblast.
- Mature oocysts contain two sporocysts, each with four sporozoites.
zoonosis transmitted by blood-sucking sand flies that may present with cutaneous, mucocutaneous, or visceral symptoms.
Leishmania spp.
Amastigotes of Leishmania are found intracellularly in histiocytes and measure from 2 to 4 µm in diameter. The nucleus and characteristic kinetoplast stain prominently with Giemsa stain.
Imprint smears, aspirates, and tissue sections of skin (cutaneous and mucocutaneous leishmaniases) and other organs (visceral leishmaniasis) may be examined for the presence of amastigotes.
“Volcano” appearance (raised edge, central crater, scab)
Painless or painful
+/- lymphadenopathy near the sores
Look for satellite lesions surrounding the ulcer
Cutaneous Leishmaniasis (CL) by L. tropica/L. mexicana
90% of all cases are in Bolivia, Brazil & Peru
Granulomatous destruction that begins in nasal cavity
Mucocutaneous leishmaniasis (“Espundia”)
Mostly L. braziliensis
Fever, weight loss, discolored skin, and enlarged spleen and liver (usually the spleen is bigger than the liver)
Some with swollen glands (huge spleen/liver)
Frequently low RBC, WBC and platelet counts
visceral leishmaniasis (‘kala azar’)
Mostly Leishmania donovani
West african patient presents with indications of worms that move about in subcutaneous tissues producing migratory angioedema known as “fugitive” or “Calabar” swellings. There also appears to be something in their eye
Loa Loa
Loa loa microfilariae are sheathed and have nuclei that extend to the tip of the tail in a continuous row.
The sheath characteristically does not stain with Giemsa, but may be recognized as a ghost image.
DIURNAL PERIODICITY
Patients in Central and South America present with lymphadenopathy, pruritis, and urticaria.
Mansonella ozzardi
Mansonella ozzardi microfilariae are unsheathed and have a thin pointed tail without nuclei which may be difficult to visualize.
Patients from Africa, West indies and Central and South america rarely present with migratory angioedema caused by this organism…
Mansonella perstans
Mansonella perstans microfilariae are unsheathed and have nuclei that extend to the tip of the tail.
AIDS patient presents with diarrheal disease and stool exam shows this…
Microsporidia
Spores are small (up to 1.6 µm), elliptical and stain red against a faint green background on modified trichrome-stained smears. Some spores display a characteristic mid-body cross-band, which helps differentiate them from similarly-sized bacteria.
primary amebic meningoencephalitis
Naegleria fowleri
Diagnosis is usually made by identifying trophozoites in brain tissue at autopsy, although their presence has been occasionally detected in wet mounts, trichrome stains, and / or culture of cerebrospinal fluid. In wet mounts of CSF, trophozoites may display eruptive pseudopod formation, but must be distinguished from motile white blood cells.
Acquired by ingesting infected raw, incompletely cooked, or home-smoked salmon or trout.
The occurrence of symptoms is related to the number of worms present and may include abdominal pain and diarrhea.
Nanophyetus salmincola
Nanophyetus salmincola eggs are broadly ovoid, operculate, and yellowish brown and measure 60 to 80 µm by 34 to 50 µm. There is a thickening of the shell at the abopercular end, which should be differentiated from the knob seen on eggs of Diphyllobothrium.
Patient presents with heavily scarred cornea causing blindness. Examination reveals…
Onchocerca volvulus
River blindness
Symptoms, when present, may be caused by larvae migrating through tissues or by adults established in the lungs.
Infection is acquired via ingestion of infected uncooked, or marinated, freshwater crabs or crayfish in SE Asia.
Paragonimus spp (Lung Fluke)
The operculate, unembryonated eggs measure 80 to 120 µm by 45 to 70 µm and have a moderately thick, yellow-brown shell. The operculum is flattened and usually is set off from the rest of the shell by prominent shoulders. The abopercular end is somewhat thickened but does not have a knob.
100 um ovum
Paragonimus westermani
Differentiate from Fasciolopsis buski by the thick wall and shouldered operculum
Patient with 36-48 hr periodic fever, chills, headaches, nausea/vomiting, myalgias
Plasmodium falciparum
- 16-32 merozoites
- Only rings
- Appliqué forms
- Multi-ring/RBC
- Banana-shaped gametocytes
72 hour periodic fever, chills, headaches, nausea/vomiting, myalgias
Plasmodium malariae
- Band-form trophozoites
- Only ~8 merozoites per schizont (often in rosette)
- Recrudescing (in blood)
KEY THING- there’s also P. knowlesi, which is microscopically indistinguisable from P. malariae but more malignant than P. malariae due to 24 hr lifecycle (severe like P. falciparum)
Patient with 48 hour periodic fever, chills, headaches, nausea/vomiting, myalgias
Plasmodium ovale
- Up to 12 merozoites per schizont
- Infects young RBCs
- Ovale-shaped RBCs
- More compact trophozoites
- No req. for Duffy (>in W. Africa)
- Relapsing (hypnozoites)
Patient with 48 hour periodic fever, chills, headaches, nausea/vomiting, myalgias
Plasmodium vivax
- >12 merozoites
- Ameboid troph
- Schuffner’s dots
- Require Duffy receptor (
- Relapsing (hypnozoites)
muscle cysts; symptoms such as myalgia, muscle weakness and transitory edema may occur.
Sarcocystis hominis/suihominis
One of the earliest and most common symptoms of infection is hematuria. Chronic infection may cause pelvic pain and bladder colic with increased desire to urinate.
Schistosoma haematobium
S. haematobium eggs may be detected on examination of urine sediment. They are elongate, measuring 112 to 80 µm by 40 to 70 µm, and have a characteristic terminal spine.
Infection is acquired via skin penetration by infectious cercariae. Symptoms can include abdominal pain and dysentery, with abundant blood and mucus in the stool.
Chronic infection may result in liver fibrosis and portal hypertension, depending on the number of worms present
Schistosoma japonicum
S. japonicum eggs measure 75 to 90 µm by 60 to 68 µm. Eggs are broadly oval, with an inconspicuous lateral spine which may be difficult to demonstrate.
infection is acquired following skin penetration by waterborne cercariae.
Symptoms - abdominal pain and dysentery, with abundant blood and mucus in the stool.
Chronic infection may result in liver fibrosis and portal hypertension after many years, depending on the number of worms present.
Schistosoma mansoni
S. mansoni eggs measure 116 to 180 µm by 45 to 58 µm and are oval, with a large distinctive lateral spine that protrudes from the side of the egg. If the spine is not visible, the egg may be rotated by gently tapping the coverslip.
Movement of flame cells in the miracidium may be evident in unfixed material and indicates active infection.
Patient presents with abd pain, watery diarrhea, dyspnea, cough following a respiratory illness.
Strongyloides stercoralis
S. stercoralis rhabditiform larvae (180 µm to 380 µm in length) must be differentiated from those of hookworms and are characterized by having a short buccal cavity and a prominent genital primordium.
S. stercoralis filariform larvae (approximately 500 µm in length) have a notched tail and an esophagus approximately half the length of the body. Either stage of larvae are readily seen in fresh saline wet mounts under low power.
Immunosuppressed patients are at risk for hyperinfection!
Taenia saginata (Beef Tapeworm)
T. saginata (cattle) has four large suckers with no rostellar hooks
T. saginata has >14 branches
Taenia solium “Pig tapeworm”
T. solium has four suckers with rostellar hooks
T. solium proglottid has 7-13 branches
T. solium will develop cystocerci preferentially in the brain and eye or can have muscular cystocerci
Taenia spp.
Eggs of all Taenia species are indistinguishable. Eggs are spherical and measure 31 to 43 µm in diameter. The shell of the egg is thick, radially striated, and contains a six-hooked embryo. Species identification may be made on recovery of proglottids, or, more rarely, the scolex.
Immunosuppressed (AIDS) patient presents with encephalopathy (ring-enhancing lesions)
Toxoplasma gondii
Chronic toxoplasmosis has cysts with bradyzoites. These develop once the organisms have reached an equilibrium with the immune system.
Acute toxoplasmosis shows tacyhzoites in tissues, typically in rosettes of elongated tachyzoites
Patient presents with eosinophilia of 90% after eating undercooked pork chops
Trichinella spiralis
inflammation, itching, vaginal discharge and, occasionally, dysuria.
Trichomonas vaginalis
Trichomonas vaginalis is a pear-shaped flagellate which displays four anterior flagella and an attached undulating membrane. A rod-like structure known as the axostyle runs the length of the organism and protrudes posteriorly. On Gram-stained smears, T. vaginalis can resemble epithelial cells.
Trichostrongylus spp
Trichostrongylus eggs resemble those of hookworms but are longer and narrower, measuring 78 to 98 µm by 46 to 50 µm, and are slightly tapered at one end.
Tropical medicine doctor sees patient with bloody diarrhea, rectal prolapse, weakness, pallor, anorexia, dehydration, and weight loss. O&P reveals…
Trichruis trichiura (Whipworm)
T. trichiura eggs are barrel-shaped with refractile plugs at both ends and usually measure 50 to 55 µm by 22 to 24 µm wide.
Adult worm –> half thin string, half thicker section (male is curled)
Patient presents with muscle pain, neurological disorders (esp. kids <2 yrs old), and Romaña’s Sign (swelling around bite site) after travel to South America. Blood examination reveals…
Trypanosoma cruzi
The diagnostic stage of Trypanosoma cruzi is the trypomastigote, which often assumes a “C” or “U” shape in thick or thin stained blood smears. Large kinetoplasts.
Must differentiate from commensal T. rangeli(andTR/TG)
- Key is large, subterminal/terminal kinetoplast in T. cruzi
- Rangeli has small kinetoplast like African trypanosomes
Patient presents with sleeping sickness. Blood examination reveals…
Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense
Trypomastigotes of Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense are morphologically identical.
Unlike Trypanosoma cruzi, these species display graceful curves and a small kinetoplast.
After a tropical vacation, patient presents with bancroftian or lymphatic filariasis which may progress to elephantiasis after many years duration. A blood smear made from a midnight draw revealed…
Wuchereria bancrofti
Wuchereria bancrofti microfilariae are sheathed, which is most evident with hematoxylin stains and rarely evident with Giemsa stain, and have nuclei that do not extend to the tip of the tail.
Microfilariae are sheathed and nocturnally periodic, appearing in the peripheral blood between 10 p.m. and 4 a.m.
Trematode fluke 30-70mm. Resides primarily in the small intestine
Faschiolopsis buski
Key is the large size and smooth, round cephalic end without a protrusion
Presumptive ID of rhabditiform nematode larvae
Hookworm.
I guess we’re calling this a long buccal cavity. Strongyloides will have a shorter buccal cavity (1/3)
ID
Plasmodium ovale
Key is enlarged erythrocytes
Small 8-10um amoebic cysts with owl-eye nuclei beneath the outer membrane
Endolimax nana
