Laboratory Studies
Perianal and stool examinations can be performed. If worm infestation is suspected, first consider a stool examination for ova and parasites. This clearly is indicated for some of the cestodes that release eggs or worm segments directly into the stool (ie, T saginata, Diphyllobothrium species, D caninum). This is especially true of H nana infection, which is the most frequently diagnosed cestode infection in the United States.
Collecting 2-3 stool samples is necessary for detection of the parasite because eggs and parasite particles are released irregularly into the stool and may be periodically absent from stool during infection. Therefore, microscopy has been known to be relatively insensitive.
In T saginata infections, eggs may be observed in the perianal area and can be detected by using a cellophane tape swab. This method detects eggs in 85-90% of patients.
Eosinophil counts are not diagnostically reliable. Eosinophilia is sporadically present and does not correlate with the severity of the infection. Eosinophil counts also do not help in monitoring treatment modalities.
Imaging Studies
Neurocysticercosis
Imaging studies are not only useful in differential diagnosis and evaluation of neurocysticercosis, but they are important in identifying the number, the location, and the stage of the infestation.
The size of cysticerci varies according to location in the CNS. If located in the brain parenchyma, cysts are rarely larger than 10 mm in diameter because of physical space limitations. In contrast, cysts located in the cisterns of the cerebrospinal fluid may grow to 5 cm or greater in diameter.
Appearance of the cysticerci depends on the stage of development. On entering the CNS, the cysticerci are in a vesicular stage where the parasites are viable and surrounding tissue inflammatory changes are scant. After a variable time (maybe years), the host attacks immunologically and the process of degeneration occurs; this process changes the appearance of the cysticerci until ultimately complete degeneration leaves a nodular calcified cyst.
Generally, MRI is better than CT for the diagnosis of neurocysticercosis, detecting up to 60% of cases missed on CT. However, MRI is less sensitive than CT in identifying small calcifications, and many patients have parenchymal calcifications as the sole evidence of the disease (up to 40% of symptomatic patients). This along with cost-effectiveness lends to CT as the image study of choice and MRI for more inconclusive findings. Also see Cysticercosis and Cysticercosis, CNS.
Ultrasonography may be useful in evaluation of patients with orbital infestations.
Echinococcosis
As with most space-occupying lesions, imaging techniques are very useful. CT, MRI, and/or ultrasonography can assist in determining the extent and stage of the infestation and in evaluating the surrounding structures. CT is better in detecting calcified lesions, and MRI is better for visualizing necrotic or fibrotic noncalcified lesions and extrahepatic lesions of alveolar echinococcosis. Calcification occurs commonly in hepatic cysts but rarely in pulmonary cysts.
Ultrasonographic appearance of echinococcal cysts (Gharbi type I, World Health Organization [WHO] standardized classification CE1).
Radiographically, guided needle aspiration of a cyst is occasionally indicated for proper identification of cyst etiology without a need for concern of dissemination.
Other Tests
Immunologic testing
Although this type of testing may be useful for primary screening, it is most commonly used for confirmation testing for parasitic disease.
Complement fixation, hemagglutination, radioimmunoassay, enzyme-linked immunosorbent assay (ELISA), and immunoblot can be used for the detection of anticysticercal antibodies in serum, cerebrospinal fluid, and saliva.
Copro-Ag testing has been shown to acheive a sensitivity of 98% and specificity of 99% compared to the sensistity of 38% with direct microscopy. [8]
The immunoblot (Western blot = enzyme-linked immunoelectrotransfer blot assay) is the most effective, with sensitivity and specificity as high as 100% and 98%, respectively; however, the sensitivity decreases to about 70% in patients with a single cyst or in those with only calcified lesions. ELISA is more reliable when performed in cerebrospinal fluid than in serum, but the accuracy depends on the viability and location of the cysticerci. Stool antigen testing detects at least 2-3 times more cases of Taenia infection than stool microscopy. In echinococcosis, ELISA is positive in only 50% of patients with pulmonary hydatidosis and in more than 90% of patients with hepatic cysts.
Polymerase chain reaction
Polymerase chain reaction (PCR) of stool tests are also available for the detection of Echinococcus infection. [9]
Procedures
Although invasive, the subcutaneous edema of sparganosis and the space-occupying lesions of coenurosis and echinococcosis require surgery for diagnostic and therapeutic purposes.
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Adult tapeworm of Dipylidium caninum. Image courtesy of the Centers for Disease Control and Prevention (CDC).
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Ultrasonographic appearance of echinococcal cysts (Gharbi type I, World Health Organization [WHO] standardized classification CE1).
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Diagram of the Echinococcus life cycle. Image courtesy of the Centers for Disease Control and Prevention.
Tables
Cestode |
Primary Host |
Intermediate Host |
T solium |
Humans |
Pigs, humans, dogs, cats, sheep |
T saginata |
Humans |
Cattle |
Diphyllobothrium |
Humans |
Fish |
Hymenolepis |
Humans |
Hymenolepis nana: None; Hymenolepis diminuta: Rodents |
D caninum |
Humans, dogs, cats |
Fleas on dogs/cats |
Echinococcus |
Dogs |
Humans, sheep, cattle, goats, horses, camel |
Spirometra |
Humans |
|
T multiceps |
|
Hares, rabbits, squirrels, humans (rarely) |
