Infection with Cryptosporidium
sp. results in a wide range of manifestations, from asymptomatic infections to severe, life-threatening illness;
incubation period is an average of 7 days (but can range from 2 to 10 days).
Watery diarrhea is the most frequent symptom, and can be accompanied by dehydration, weight loss, abdominal pain, fever, nausea and vomiting.
In immunocompetent persons, symptoms are usually short lived (1 to 2 weeks); they can be chronic and more severe in immunocompromised patients, especially those with CD4 counts <200/µl.
While the small intestine is the site most commonly affected, symptomatic Cryptosporidium infections have also been found in other organs including other digestive tract organs, the lungs, and possibly conjunctiva.
Acid-fast staining methods, with
or without stool concentration, are most frequently used in clinical laboratories. For greatest sensitivity and specificity, immunofluorescence microscopy is the method of
choice (followed closely by enzyme immunoassays). Molecular methods are mainly a
Oocysts in stool specimens (fresh or in storage media) remain infective for extended
periods. Thus stool specimens should be preserved in 10% buffered formalin or sodium
acetate-acetic acid-formalin (SAF) to render oocysts nonviable. (Contact time with
formalin necessary to kill oocysts is not clear; we suggest at least 18 to
24 hours). In addition, the usual safety measures for handling
potentially infectious material should be adopted.
For more information on
safety, visit the website of the Centers for Disease Control
and Prevention to view
guidelines or the website of the Occupational
Safety and Health Administration (OSHA).
Stool specimens may be submitted fresh, preserved in 10% buffered formalin (see above,
Safety), or suspended in a storage medium composed of aqueous potassium
dichromate (2.5% w/v, final concentration). The use of mercuric chloride-containing
preservatives (e.g., polyvinyl alcohol, PVA) is not recommended due to incompatibilities
with some methodologies and the environmental hazards posed by the disposal of
mercury-containing compounds. Oocyst numbers can be quite variable, even in liquid
stools. Multiple stool samples should be tested before a negative diagnostic
interpretation is reported. To maximize recovery of oocysts, stool samples should be
concentrated prior to microscopic examination. Formalin-ethyl acetate sedimentation
is the recommended stool concentration method for clinical laboratories. Two
potential shortcomings of oocyst concentration techniques are:
- Sedimentation methods are
generally performed using low speed centrifugation. Given their small size and mass,
cryptosporidial oocysts may become trapped in the ether or ethyl acetate plug and fail to
sediment properly. Increased centrifugation speed or time (500 × g, 10
minutes) may be
warranted when attempting to recover cryptosporidial oocysts.
- Resolution of cryptosporidial
infections is accompanied by increasing numbers of non-acid-fast, oocyst
ghosts. Such oocysts may not float or sediment as expected, giving rise
to false-negative results.
There are currently no commercially available serologic assays for the detection
of Cryptosporidium-specific antibodies. However, immunoblots
for detecting the 17 and 27 kDa sporozoite antigens associated with recent
infection may be useful for epidemiologic investigations.
loss of fluids because of diarrhea can be managed by fluid and electrolyte
replacement. Infection in healthy, immunocompetent persons is self-limited.
Nitazoxanide has been approved for treatment of diarrhea caused by
Cryptosporidium in immunocompetent patients. Immunocompromised
persons and those in poor health are at highest risk for severe illness.
The effectiveness of nitazoxanide in immunosuppressed persons is
unclear. For persons with AIDS, anti-retroviral therapy, which
improves immune status, will also reduce oocyst excretion and decrease
diarrhea associated with cryptosporidiosis. For additional information,
see the recommendations in the Guidelines
for preventing opportunistic infections among HIV-infected persons --
- Kaplan JE,
Masur H, Holmes KK. Guidelines for preventing opportunistic infections
among HIV-infected persons. MMWR June 14, 2002; 51(RR08):1-46.
- Morgan-Ryan UM,
Fall A, Ward LA, Hijjawi N, Sulaiman I, Fayer R, et al. Cryptosporidium hominis n. sp. (Apicomplexa:
Cryptosporidiidae) from Homo sapiens. J Eukaryot Microbiol 2002;49:433-440.