Page 517 - Small Animal Internal Medicine, 6th Edition

CHAPTER 31 Disorders of the Intestinal Tract 489

a laboratory experienced in diagnosing cryptosporidiosis. patients. In cats there may be an association between shed-
The laboratory must be warned that the feces may contain ding giardial oocysts and shedding either cryptosporidial or
VetBooks.ir C. parvum, a potential zoonosis. coccidian oocysts.

Diagnosis
Treatment and Prognosis
Nitazoxanide and paromomycin (both potentially toxic in Giardiasis is diagnosed by finding motile trophozoites (Fig.
the cat) are used to treat cryptosporidiosis in people. Tylosin 31.6) in fresh feces or duodenal washes, finding cysts with
has been suggested to be effective, but this is dubious. fecal flotation techniques or IFA, or finding giardial antigens
Azithromycin (7-10 mg/kg PO q12h) might be safe and in feces using ELISA or PCR methodology. Zinc sulfate solu-
effective. Immunocompetent persons and cattle often spon- tions are the best for demonstrating cysts (especially when
taneously eliminate the infestation, but whether small centrifugal flotation is performed); other flotation solutions
animals do so is unknown. Any time cryptosporidiosis is may distort them. At least three fecal examinations should
diagnosed one should look for causes of immunosuppres- be performed over the course of 7 to 10 days before discount-
sion in the host. Most young dogs with diarrhea associated ing giardiasis. However, there can be false-positive results
with cryptosporidiosis die or are euthanized. Many cats have due to particles in the feces (e.g., pollen) that resemble giar-
asymptomatic infestations, and those with diarrhea have an dial cysts. Fecal ELISA techniques (e.g., SNAP Giardia Test,
uncertain prognosis. Idexx Laboratories) have high sensitivity and are easier than
centrifugal fecal flotation examinations, but none offers
GIARDIASIS 100% sensitivity. The ELISA is better at ruling out giardiasis
than ruling it in. Some asymptomatic patients are repeatedly
Etiology ELISA positive even though oocysts cannot be demonstrated
Animals are infected with the protozoan Giardia when they on fecal examination. ELISA is not useful in determining
ingest cysts shed from infected animals, often via water. efficacy of therapy because the antigen often persists for 4+
Organisms are principally found in the small intestine, where weeks after successful therapy. PCR of feces is very specific
they interfere with digestion through uncertain mechanisms. but is too insensitive to be reliable. Therefore IFA testing of
In people Giardia organisms may occasionally ascend into feces is believed to be more specific than ELISA, but it
the bile duct and cause hepatic problems. requires sending feces to a diagnostic laboratory. Testing
asymptomatic patients that are not in close contact with a
Clinical Features known infected patient is of dubious value.
Patients may be asymptomatic or have mild to severe diar-
rhea, which may be persistent, intermittent, or self-limiting. Treatment
Diarrhea can begin 5 days after exposure, before cysts appear Treatment of giardiasis consists of (1) decontaminating the
in the feces. Typically the diarrhea is “cow patty”–like without environment, (2) bathing the patient to remove cysts from
blood or mucus, but there is substantial variation. Some the hair, and (3) administering drugs to eliminate the intes-
animals experience weight loss; others do not. Diarrhea tinal infection. Because of the difficulty in finding Giardia
caused by Giardia can mimic large bowel diarrhea in some organisms, therapeutic trials are often used (see Table 28.7).

FIG 31.6
Giardia trophozoites (arrows) in a canine fecal smear that has been stained to enhance
internal structures (×1000). (Courtesy Dr. Tom Craig, Texas A&M University.)