Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (517 page)

   
Schistosoma haematobium
infection is seen in the Nile River valley. After infection, larvae migrate most commonly through the hemorrhoidal and pudendal veins to reside in the vesicle and pelvic plexuses. Eggs are most commonly embedded in the bladder and distal ureters, resulting in fibrosis and ulceration. Calcification, significant hematuria, obstructive uropathy, renal failure, chronic bacterial UTIs, and bladder carcinoma are complications of severe urologic disease. Genital involvement is common, manifesting with heavy egg deposition in the cervix, vagina, and vulva. Friable “sandy patches” are described in the lower genital tract. Bacteremic infections with
Salmonella
species are seen. Schistosomal appendicitis is well described with
S. haematobium
. Hepatosplenomegaly, due to portal fibrosis and pulmonary, CNS, and cardiac diseases, is described but uncommon.

   Laboratory Findings

Direct detection
: Eggs are seen but may be absent in the first several months after acute infection. Eggs are most commonly found in stool in
S. mansoni
and
S. japonicum
infections. For
S. haematobium
diagnosis, urine specimens, ideally collected between noon and 3 pm when egg excretion is highest, are used. The examination of multiple samples is recommended.

   Egg morphology is used as the basis for speciation, which is an important guide to therapy.

   Note:
Schistosoma haematobium
ova are sometimes found in stool, and
S. mansoni
eggs are sometimes found in urine, especially in heavy infection. Treated patients should have O&P examinations for at least 1 year to ensure sustained cure.

Histology
: Rectal or bladder biopsy is useful for diagnosis in light or inactive infections. Unstained rectal or bladder mucosa, examined microscopically, may show viable or dead ova when stools or urine O&P examinations are negative; granulomatous lesions may be present. Biopsy may identify eggs in affected organs.

Serology
: Serologic testing may be useful for diagnosis of infection in patients from nonendemic areas or to support a diagnosis in infection with low egg counts. A specific ELISA, confirmed by immunoblot, is recommended. Positive serology is not useful for distinguishing between acute and chronic infection.

Antigen detection
: May be more promising, but utility is hampered by low specificity and cross-reactions with other helminth parasites. Sensitive and specific methods have been described for
S. mansoni
,
S. japonicum,
and
S. haematobium
. An immunoblot assay to detect schistosome antigen is reported to have high sensitivity (approximately 95%) and specificity (approximately 100%).

Core laboratory
: Eosinophilia occurs in 20–60% of acute cases. ESR is increased. Hematuria is an important early sign of
S. haematobium
infection. Immunoglobulin levels, especially IgE, are elevated. Liver function tests are usually normal, even in chronic infection. Signs and symptoms related to inflammatory damage of other organs, like the lung (cough, hemoptysis, pulmonary hypertension), brain (seizures), and the spinal cord (myelopathy), may be present. Anemia, eosinophilia, increased serum globulin and decreased albumin, hematuria, proteinuria, hydronephrosis, azotemia, and squamous cell carcinoma of the bladder may occur.

STRONGYLOIDIASIS (
STRONGYLOIDES STERCORALIS
)

   Definition

The parasitic roundworm
Strongyloides stercoralis
has a global distribution in tropical and subtropical regions.

   Who Should Be Suspected?

   Strongyloidiasis should be considered in any patient who has traveled to an endemic area at any time in the past regardless of local disease prevalence. As in patients who host other successful intestinal parasites, most infected patients are asymptomatic or have minimal, nonspecific symptoms. Patients may complain of epigastric pain, bloating, dyspepsia, diarrhea (sometimes with blood), or constipation. Patients with chronic infection may develop urticarial rashes or the syndrome of larva currens, caused by migration of larvae in the dermal layer.

   The hyperinfection syndrome occurs in immunodeficient patients, including those with HIV and HTLV-1 infections. In the hyperinfection syndrome, severe, bloody diarrhea may result, with malnutrition and intestinal dysfunction. Septic complications may result from the damage to intestinal mucosa. Pulmonary complications, including pneumonia and pulmonary hemorrhage, are common in the hyperinfection syndrome. CNS involvement may result in gram-negative or mixed bacterial meningitis.

   Note that the morphology of larvae of
S. stercoralis
is similar to that of the larvae of hookworms, and care must be taken if endemic infection for both is possible.