Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (512 page)

Direct detection
: Most diagnoses are made by examination of thin and thick blood smears. Multiple smears should be examined to rule out infection. Parasites may be seen inside or outside of erythrocytes.

Serology
: Antibody detection is limited by poor overall sensitivity and specificity; serologic tests are not widely available but are rarely needed or used for diagnosis.

Core laboratory
: Hemolytic anemia may last days to months; most patients have thrombocytopenia. Concurrent infection with
B. burgdorferi
(Lyme disease) and
A. phagocytophilum
(HGA) should be considered. Patients should be monitored closely for complications of primary babesiosis, with coagulation, renal, liver, and pulmonary function tests.

BEEF TAPEWORM (
TAENIA SAGINATA
)

   Definition

Beef tapeworm disease is caused by ingestion of viable metacestodes (cysticerci) of
Taenia saginata
.

   Who Should Be Suspected?

Most beef tapeworm infections are asymptomatic, but intestinal, biliary, or pancreatic obstruction may occur in heavy infection.

   Laboratory Findings

Direct detection
: Detection is usually achieved by identification of ova, proglottids, strobila, or scolices from feces. Tapeworm ova are detected in the stool in 50–75% of patients but cannot be distinguished from those of
Taenia solium
(see below for specific discussion). Definitive identification is usually achieved by examination of the uterine morphology of gravid proglottids. Because
T. saginata
proglottids actively migrate though the anus to deposit eggs on the perianal skin, proglottid segments may be available for examination, significantly improving species identification.

Core laboratory
: Eosinophils may be slightly increased.

CRYPTOSPORIDIOSIS AND OTHER COCCIDIA INFECTIONS

   Definition

Coccidia infections are caused by protozoon parasites, including
Cryptosporidium parvum
,
Isospora belli
, and
Cyclospora cayetanensis.
These parasites are capable of causing severe diarrheal illness in patients with AIDS. These organisms infect microvillus epithelial cells of the GI tract.

   Cryptosporidiosis is very infectious, and diarrheal disease occurs in most infected patients. Outbreaks linked to day care centers and recreational water activities are well described. Springtime is the season of peak incidence.

   Humans serve as the only known reservoir for infection with
Isospora belli
. There is global distribution, but the highest prevalence is in tropical and subtropical areas. The oocytes of
Isospora
mature to infectious forms in the environment several days after excretion, so person-to-person transmission is less efficient.

   
Cyclospora
infection is probably acquired by ingestion of contaminated water. Because the oocysts of
Cyclospora
must mature to infectious forms in the environment for several days after excretion, direct person-to-person transmission is uncommon.
Cyclospora
may cause endemic disease during the rainy season in developing countries. Epidemic disease is well described in developed countries; consumption of fecally contaminated foods is usually implicated.

   Who Should Be Suspected?

Coccidial infections manifest with watery diarrhea, crampy abdominal pain, and anorexia. Nonspecific systemic symptoms are common. RBCs and WBCs are typically absent from stool. Chronic and intermittent diarrheal illness may occur in immunocompromised patients.

   Laboratory Findings

Direct detection
: Routine O&P examination is insensitive for detection of coccidian protozoan pathogens. All are acid-fast and are detected in stool using an acid-fast stain modified for staining stool smears for parasites. Multiple stool samples should be examined to rule out infection. Sensitivity of staining may be increased by concentration techniques. Staining of
Cyclospora
may be variable, but
Cyclospora
may be detected by its characteristic autofluorescence.

Histology
: Biopsy of the duodenal or proximal jejunal mucosa may demonstrate
Isospora
when stool acid-fast stains are negative.

Serology and immunology
: DFA staining techniques have been described and may improve detection compared to acid-fast staining. Commercially available EIA methods also provide sensitive and specific diagnosis. Kits combining reagents for multiple intestinal parasites, like
Cryptosporidium
,
Giardia
, and
E. histolytica
, are available.

Core laboratory
: Eosinophilia may be seen in patients with
Isospora
infection.