number of organisms are packed in the cell (see chapters 7 and 19). The amastigotes may resemble Histoplasma capsulatum if the kinetoplast bar structure is not easily seen (Fig. 10.9).
Figure 10.9 (Left) Histoplasma capsulatum. (Right) Leishmania donovani. Note that the Leishmania amastigotes have the bar structure while the Histoplasma amastigotes do not; Histoplasma also has a “halo” around the organisms. doi:10.1128/9781555819002.ch10.f9
Any laboratory using staining reagents must use good quality control measures to ensure that the solutions do not become contaminated with artifacts or free-living organisms. Bits of cotton fiber, lint, and other components of dust can mimic microfilariae in wet mounts or when stained. However, the artifacts do not contain any internal nuclei. Rarely, nonhuman parasites can also be confused if they appear on the stained blood smears. One laboratory used to dry the blood films upright, leaning against a fish tank (many years ago, before more stringent safety measures were instituted). Examination of one of the stained blood films suggested that the patient had a filarial infection. Since the patient history did not support this diagnosis, further studies were performed. When samples of the fish tank water were centrifuged and examined, the “microfilariae” were found! This is just one example of the many unusual sources of artifact contamination (Fig. 10.10).
Figure 10.10 Fungal spores (Helicosporium type). Artifacts that can resemble microfilariae in stained blood films; these structures are not parasites but instead are some type of thread. Note that there is little to no internal structure visible. (Left) Courtesy of the CDC Public Health Image Library. (Middle and right) Photographed at a higher magnification than the image on the left. doi:10.1128/9781555819002.ch10.f10
Body Fluids: Ciliated Epithelial Cells
Detached ciliary tufts (ciliocytophthoria) have been seen in a variety of body fluids (especially peritoneal and amniotic fluids; also respiratory specimens). These tufts are the remnants of ciliated epithelium that are found as a part of normal cellular turnover in a number of sites: respiratory tract and sinuses, ventricles of the brain, central canal of the spinal cord, and epithelia of the male and female reproductive tracts. The tufts are motile, measure 10 to 15 µm in diameter, and can be confused with ciliated or flagellated protozoa. However, when they are carefully examined on a stained smear, there is no internal structure like that seen in protozoa (4–6). Ciliated epithelium cells can be seen in Fig. 10.11; ciliocytophthoria are anucleate remnants of these ciliated cells. However, in some cases, the cell nuclei are clearly visible. The ciliated tufts can be seen on the cells in this figure.
Figure 10.11 Bronchial epithelium cells. When these cells disintegrate, the ciliary tufts may be visible and may be confused with protozoan flagellates or ciliates (detached ciliary tufts = ciliocytophthoria). doi:10.1128/9781555819002.ch10.f11
These cells have been found in many clinical specimens, including peritoneal fluid (7). Recognition of these uncommon structures can be important in avoiding a misdiagnosis with a suspect protozoan infection. This has also been recognized as a potential problem in the virology laboratory (5). The difference between ciliocytophthoria and ciliated or flagellated parasites becomes very important during examination of specimens submitted for cytologic testing. Also, in performing immunofluorescence assays (direct fluorescent antibody [DFA] tests) used in the virology laboratory for the rapid detection of viruses, assessment of the cellularity of specimens is required for the most effective use of the DFA assay.
Plant or root hairs, such as the fuzz on peaches, may resemble nematode larvae. The root hairs tend to be clear and refractile, while the larvae pick up stain (iodine) which reveals internal structures (Fig. 10.12). It is important to recognize this potential error when examining formalin-fixed specimens submitted as proficiency testing specimens. In fecal specimens from patients with diarrhea, partially digested plant material, such as bean sprouts or other vegetable material, can mimic adult nematodes or tapeworm proglottids. Also, all stages of free-living nematodes can occur in feces or as contaminants of the water used in making fecal suspensions.
Figure 10.12 (Top) Root hair. (Middle) Root hair. Note that there is no internal structure visible within the root hairs. (Bottom) Strongyloides stercoralis rhabditiform larva. Note the short buccal cavity at the head end of the larva and the genital primordial packet of cells within the curved portion of the body (arrow). doi:10.1128/9781555819002.ch10.f12
Hairworms (often called horsehair worms) belonging to the phylum Nematomorpha can be confused with human parasites (8). These adult worms are slender, measuring 10 to 50 cm long, and have a blunt, rounded anterior end. “The caudal end of the male is bifurcate or has a dorsoventral groove; that of the female is entire or trilobate” (8) (Fig. 10.13). The adult worms are free living in water, while the larvae are parasites of insects. Human infection is quite rare and accidental, although in the past literature, serious health problems were attributed to “hair snakes” in the human body. Generally, human infection occurs through ingestion of free-living adult worms or adolescent worms within their insect hosts in drinking water or food. Worms have been reported as passing from the urethra in several cases. They have been identified as being in the genera Gordius, Chordodes, Parachordodes, Paragordius, Pseudogordius, and Neochordodes. Worms have been recovered in vomitus, urine, and feces; often, the stated origin of the worms in the body was not well documented. In spite of the reported cases, no evidence of pathogenicity has been demonstrated (8). Often symptoms were attributed to other causes or were psychological.
Figure 10.13 Gordius worms. (Upper) Adult worms (called hairworms or horsehair worms), which measure 20 to 50 cm long and are very slender. (Lower) Characteristic structure of Gordius worms. (A) Diagram of anterior end; (B) diagram of posterior end of a male worm in the genus Gordius; (C) whole worm. Bar, 1 cm. (Illustration by Sharon Belkin.) doi:10.1128/9781555819002.ch10.f13
In some cases, very large objects are recovered in patient stools. One structure resembled a trematode, but was actually a slug. These objects can be very confusing, particularly when
