Direct and molecular methods

Illustrated in the photomicrograph are acid-fast stained mounts of a 5 µm oocyst of Cryptosporidium (top) and a 10 µm oocyst of Cyclospora (bottom). Knowing the clinical suspicion of what disease would alert the laboratory scientist that a preparation of an acid fast stain should be made on the submitted stool specimens?

AIDS

In the formalin-ethyl acetate sedimentation procedure, four layers will occur. Out of the layers, where does the formalin layer occur?

Between the bottom layer and the debris/fat layer

The avoidance of laboratory diagnosis techniques that utilize water is recommended for the identification of which of these parasites?

Blastocystis hominis

In hookworm cases where progressive anemia is present, what additional test procedure should be performed to determine infection in stool specimens?

Concentration technique

This intestinal parasite, which measures 5 µm, is usually not visible in samples processed using standard permanent stains. Special staining, as indicated by the coloring here, is helpful in its identification.

Cryptosporidium oocyst

The addition of iodine to a direct and indirect wet prep is used to detect which of the following protozoan stages?

Cysts

All of the following represents an organism with an appropriate form of diagnostic procedure, EXCEPT:

Echinococcus granulosus - routine ova and parasite examination

The 20 µm in diameter cyst illustrated in the photograph had been observed microscopically in a trichrome stained mount prepared from a stool specimen of a patient with low grade, intermittent diarrhea. What is the presumptive identification?

Entamoeba coli

In the performance of which of the following procedures may eggs with opercula be difficult to recover from or detect in stool specimens?

Zinc sulfate flotation

Which of the following is considered the technique of choice for isolating the oocysts of Isospora belli and Cryptosporidium parvum?

Zinc sulfate flotation

Xenodiagnosis has historically been used to identify:

Trypanosoma cruzi

The 6 µm in diameter cyst illustrated in the trichrome-stained photomicrograph was inadvertently observed a stool specimen that was being examined for reasons not clinically related to parasitic diseases. Further history revealed that the patient for whom the stool examination was being performed had only rare bouts of mild diarrhea. Based on the characteristics in the illustration and the patient information, the most likely identification is:

Entamoeba hartmanni

Illustrated in the image shown is a 20 µm amoebic trophozoite that was observed in a random stool specimen from a patient who had no symptoms of a parasitic infection. Several molecular based studies have found that in the analysis of stable DNA polymorphisms, several differences in DNA zymodeme patterns were found to encode for genetically different strains of Entamoeba histolytica. As some of these strains were found to be non-pathogenic, it has been recommended that the laboratory report be altered to draw attention to this possibility. Select from the choices below the report that should be issued.

Entamoeba histolytica/dispar

Which of the following specimen processing techniques is based on the principle that parasites are heavier than sample debris and will be present in the sediment after being processed?

Ethyl acetate concentration

A large number of antigen detection procedures and assays are available to diagnose clinically suspected parasitic diseases in the absence of finding ova or other forms of parasites in stool preparations or other body fluids. Illustrated in the photograph are antigen positive-staining green dots at sites where small drops of duodenal aspirated fluid had been applied to the test reagents. Trophozoites of this protozoan occupy the upper gastrointestinal tract and the excreted ova may not find the way down the long stretch of bowel to be excreted in stool specimens. From the list of multiple choice selections, indicate the genus/species in which antigen detection may be required to make a diagnosis.

Giardia duodenalis

The Entero-Test or string test may be helpful in diagnosing an infection with which of the following parasitic organisms?

Giardia duodenalis

The Enterotest may be used to recover which of the following parasites?

Giardia duodenalis

When parasites are observed in clinical stool specimens, antigen detection is the preferred method for identification, providing increased sensitivity over more common microscopy techniques. Several commercial products (DFA, EIAs, and rapid tests) are available. The H & E - stained tissue section of duodenum illustrates the presence of an intra-luminal intestinal trophozoite in which an antigen assay might be helpful in making a definitive identification. Select the presumptive identification from the choices listed.

Giardia duodenalis

Illustrated in this image is a field of view microscopically observed on a Scotch-tape preparation. Based on the morphology and presentation of these ova, an identification of Enterobius vermicularis can be made. The optimum time to obtain Scotch-tape samples of peri-anal skin to recover these ova is:

Immediately after waking up

The cyst as illustrated in the photograph was observed in a permanently stained smear of a stool specimen. Making a presumptive identification would be difficult because of the poor quality of the stain and the lack of internal detail. From the multiple-choice answers listed below, select the most likely cause for the poor staining quality observed in this cyst.

Inadequate stool fixation

A 27-year-old male submitted a stool for culture and parasite study. The culture revealed no enteric pathogens. The suspicious form in the photograph was seen on the permanent trichrome stain. It measured 10 µm. Which of the following is the most likely identification?

Iodamoeba butschlii

Amoebae stained with this substance may be readily distinguished, since it enhances nuclear and structural detail.

Iodine

The Knott technique serves as a means of identifying:

Loa loa

Illustrated in the photomicrograph is a high-power view of the elements within a duodenal aspirate preparation using a Weber Stain (Chromotope 2R, Fast Green, phosphotungstic acid). This stain is used to identify the tiny 1.5 µm pink-red staining spores, many with central transverse septa as:

Microsporidium species

Which of the following steps is the first step of the ethyl acetate concentration procedure?

Mix fresh stool specimen with 10% formalin and strain to obtain a sediment

Which of the following is considered the best fixative for maintaining specimen integrity during and following permanent staining of ova and parasites?

Polyvinyl alcohol (PVA)

The ideal stool sample for parasitic examination is one that is freshly collected and submitted to the laboratory at:

Room temperature (approximately 22° C)

The ability to detect and identify human parasites is directly linked to the following, EXCEPT:

The genus and species of the parasite

A stool specimen was received in the laboratory for an O & P examination. The medical laboratory scientist performed a direct wet mount and found suspicious forms. A formalin ethyl acetate concentration procedure was performed and the top layer was examined with no suspicious forms observed. A slide made from the top layer was stained with Trichrome and again no suspicious forms were noted. Which of the following is the most likely explanation for these discrepant results?

The wrong layer was examined following the formalin ethyl acetate concentration procedure.

Methods of detecting and identifying intestinal parasites include all of the following except:

Thin and think Giemsa smear

Which type of stain is recommended to speciate Plasmodium species?

Thin-stained Giemsa smears

All of the following characteristics should be observed for and noted in the macroscopic examination of a stool sample for parasites EXCEPT?

Time that last meal occurred

Illustrated in the photomicrograph is a 10 µm in diameter, trophozoite observed in a trichrome-stained vaginal smear from a 39-year-old female experiencing a frothy vaginal discharge along with vaginal discomfort and pain on urination. What is the name of the invasive parasite?

Trichomonas vaginalis