What is the disadvantage of mercuric chloride-based polyvinyl alcohol?
It contains mercury, it's poisonous and requires special handling and disposal
What guidline should be followed regarding the number and timing of stool specimens for routine O & P testing?
No more than 2/3 specimens per patient should be submitted and specimens should not be submitted from inpatients after the fourth day of hospitalization.
Recommended time limits for examination of formed, soft, and liquid stool specimens for O & P.
Liquid: within 30 min
Soft: within 1 hour
Formed: within 24 hours
What 3 exams are usually performed on fresh stool specimen submitted for O & P examination?
Direct wet preparation, a concentration, permanent stained smear.
What is the purpose of the saline direct smear in the ova and parasite examination?
Study the motility of trophozoites. If there is a significant delay between collection of the specimen and receipt in the lab.
What is the consistency of the stool specimen in which trophozoites are most likely to be found?
Liquid specimen. Troph are present in stool specimens when there is rapid evacuation of the bowel.
How concentrated should the saline direct smear be in the ova and parasite exam?
Be able to read newsprint through it
Why is iodine used in the direct smear in the ova and parasite exam?
Iodine stains the cysts and allows visualization of the nuclear structure. Trophs are killed by iodine, so a saline direct smear should be exam first.
What kind of iodine is used in the direct smear exam in the O & P procedure?
Dobell and O'Connor's
Gram stain is too concentrated
What is the purpose of the concentration technique in the O & P procedure?
Concentrates the parasites and separates them from the fecal debris so they are easier to find.
Which concentration technique is most widely used for O & P?
Sedimentation method. Easiest method and least subject to technical error.
What is the disadvantage of the formalin-ether sedimentation method?
Ether must be stored in an explosion-proof refrigerator.
What reagent is used for the floation concentration method?
33% zinc sulfate (SG 1.180)
What is the advantage of the zinc sulfate flotation method?
Results in a cleaner prep than the sedimentation method
What is the disadvantage of the zinc sulfate flotation method?
Unfertilized Ascaris eggs may be missed
Which form of protozoa is not recovered by a concentration?
Which parasites are best diagnosed by a permanent stained smear?
Permanent stained smear should be performed on all stools because interstinal protozoa may be missed in the concentration examination.
Name a fixative used for preparation of a permanent smear.
Specimen is smeared on a slide and while still wet, dipped in the fixative for 30 mins
Name two stains used for permanent stained slides in parasitology.
What is the Enterotest (string test)?
Method for recovering Giardia and Strongyloides from the duodenum when stool exams are negative. Gelatin capsule containing nylon string is used. Part of the string protrudes from the capsule and is taped to the patient's face. Patient is instructed to swallow the capsule.
After 4 hours the string is retrieved and the mucus clinging to the string is examined.
How can one determine the size of a parasite observed under the microscope?
Calibrated micrometer placed in one ocular of the microscope.
How is the ocular micrometer calibrated?
Exact distance between markings is determined by comparison with a stage micrometer with known calibration markings. An appropriate lens factor is determined for each objective. Ocular micrometers must be calibrated for the microscopes which are used.
Which intestinal ameba is pathogenic for man?
Name an ameba with cigar shaped chromatoidal bodies in the cyst.
Name an ameba whose trophozoite ingests RBCs.
Name an ameba whose nucleus has delicate, even, peripheral chromatin and a delicate, central karyosome.
Name an ameba whose cyst contains up to 8 nuclei.
Name an ameba whose cyst has a large glycogen vacuole.
Name an ameba whose cyst has only one nucleus.
Which ameba causes granulomatous amebic encephalitis (GAE) and ulcerative keratitis in contact lens wearers?
Contracted by swimming in contaminated water or by inadequate cleaning of contact lens.
Diagnosis: exam of the brain
Which ameba causes primary amebic meningoencephalitis (PAM)
Contracted by swimming in contaminated water. Trophs may be found in the CSF.
Name a flagellate that does not have a cyst.
Name a flagellate that has a lemon shaped cyst.
Name a flagellate whose trophs always has two nuclei
Name a flagellate that can be seen in a blood smear.
Cause sleeping sickness and Chagas disease
Name a flagellate that can be seen in urethral discharge.
Spread by sexual contact.
Name a flagellate which resembles an ameba because its flagella can only be seen with electron microscope.
Name a common intestinal protozoan whose troph usually has 2 nuclei and which does not have a cyst stage.
Name a flagellate whose cyst has two or four nuclei at the anterior end, parabasal bodies, an axostyle, and cytoplasm that shrinks away from the cell wall.
Name a flagellate that looks like an old man with glasses.
Name the most common intestinal protozoan infection in the US
Name a flagellate that can be diagnosed from duodenal aspirates or the Enterotest capsule
Name a protozoan that is ciliated and has a large kidney shaped macronucleus and a small micronucleus
Which is the largest protozoan to infect man?
Which parasites can be found in the blood?
Plasmodium, Babesia, Trypanosoma, and microfilariae
Name two parasites that live inside erythrocytes.
Plasmodium and Babesia
Name a protozoan that infects reticuloendothelial cells.
Cause kala azar and cutaneous and mucocutaneous leishmaniasis
Name the parasite that causes sleeping sickness.
What causes Chagas disease?
Which sporozoan causes maliaria?
Which parasite has killed more people worldwide than any other?
Name a parasite that requires the Anophles mosquito for its sexual cycle.
Which species of Plasmodium is associated with enlarged RBC?
P. vivax and P. ovale
Which species of Plasmodium has sausage-shaped or cresent-shaped gametocytes?
Which species of Plasmodium commonly has multiple ring forms within on RBC?
Which species of Plasmodium is most malignant?
With which species of Plasmodium does one see rings and gametocytes only?
Which species of Plasmodium is characterized by band-shaped troph?
With which species of Plasmodium does one see Schuffner's dots?
P.vivax and P.ovale
When is the best time to draw blood for malaria smears?
Shortly after a paroxysm (shaking chills and fever). Blood should be taken at 6-8 hour intervals so different stages of the parasite can be studied to identify the species.
How is thick malaria smear prepared?
3 drops of blood are placed on a slide, allowed to dry, and placed directly into Giemsa stain without fixation.
Concentrates the parasites and removes hemoglobin from the RBCs so that the parasites are easier to see.
Only used for screening because the parasites are distorted and the species cannot be determined.
Name a protozoan that can be found in municipal water supplies, causes a profuse watery diarrhea, is a serious risk to immunocompromised patients, and appears as red spherical structures approx. 6 microns in diameter on a modified AFS.
Name a protozoan that is round to ovoid, 6-40 u in diameter, with a large central body and peripheral granules.
Organism used to be considered a nonpathogenic yeast. It is now considered a protozoan and is thought to be an intestinal pathogen when present in large numbers in the stool.
Which protozoan can be spread by infective oocysts in cat feces?
Which protozoan can cause neurologic problems if contracted by the fetus after the first trimester?
Which protozoan is the major cause of encephalitis in AIDs patients?
How is toxoplasmosis diagnosed?
Name a roundworm that has a barrel shaped egg with a clear plug at either end.
Trichuris trichiura, whipworm
What is the most common helminth infection in the US?
Pinworm. Enterobius vermicularis
Name a roundworm that is diagnosed by the scotch tape prep.
Enterobius vermicularis, pinworm
When is the best time to collect a scotch tape prep?
First thing in the morning, before bathing or defecation.
Name a roundworm whose egg resembles a loaf of Italian bread-flat on one side and rounded on the other.
Name a nematode whose diagnostic stage is the rhabditiform larva.
Name the most common helminth infection in the world.
Name the roundworm that looks like an earthworm.
Name a roundworm that can pass from the anus, nose, or mouth.
Which intestinal parasite is not diagnosed by an O & P prep?
Pinworm. Diagnosed by scotch tape prep
Which intestinal roundworm infection is contracted by skin penetration by the filariform larva or sexually, includes larval migration through the lungs, and can be fatal in an immunocompromised host?
Name an intestinal roundworm in which diagnostic stage is not the ovum.
Diagnostic stage is rhabditiform larva
Name two hookworms.
Necator americanus (American hookworm)
Ancylostoma duodenale (Old world hookworm)
How are hookworm infections contracted?
Skin penetration by the filariform larva
Larva may also be ingested
Which intestinal roundworms can lead to anemia?
Necator and Ancylostoma
Which parasitic infections cause marked eosinophilia?
Those that have a migratory cycle through the lungs, such as Necator, Strongyloides, Ascaris
Which nematode is contracted from undercooked pork and is found in encysted in the host's skeletal muscle?
Name the beef tapeworm.
Name the pork tapeworm.
Name the fish tapeworm.
How are Taenia saginata and Taenia solium differentiated?
By the scolex or the number of lateral uterine branches.
T. solium, has hooklets around the rostellum, 7-13 uterine branches per side with regularly alternating genital pores.
T. saginata, 15-30 uterine branches per side with irregularly alternating genital pores.
Describe Taenia eggs
Spherical, approximately 35 microns
Yellow-brown, have thick radially-striated shell.
Name the tapeworm that causes cysticercosis.
Taenia solium, contracted by ingestion of eggs. Man serves as the intermediate host and larvae can migrate to any organs.
What is the most common tapeworm in the US?
Hymenolepsis nana (dwarf tapeworm)
Does not require intermediate host
Causes growth retardation in children and autoinfective.
Which tapeworm has an almond-shaped scolex with lateral grooves on each side and central rosette- shaped uterus?
Which tapeworm has an operculated ovum?
Name the tapeworm that causes hydatid disease.
Man is an accidental host
Following ingestion of fecal material from an infected dog.
Diagnosis is from ID of scoleces in needle biopsy material from the cyst
Which tapeworm can cause a Vitamin B12 deficiency?
Which group of parasites requires a snail in its life cycle?
Which fluke is one of the most frequent infections seen in Asian refugees?
Ovum of C. sinensis one of smallest passed by man.
Bulb shaped with opercular shoulders and small comma shaped protuberance at the posterior end.
Name the only parasite that lives in the excretory system and whose eggs can be found in urine sediment.
Name a fluke whose egg can be found in sputum?
Ovum resembles a Chinese vase
Which trematode has an elongated ovum, approximately 155 microns by 65 microns, with a pronounced lateral spine?
Which is the largest trematode to infect man?
Which parasite ova could be infectious to the lab tech?
Describe Charcot-Leyden crystals and explain their significance
Slender crystals with pointed ends which vary in size and stain red-purple with the trichome stain. Represent breakdown products of eosinophils and are sometimes seen with the parasitic infections.