Clinical Overview of Strongyloides

Key points

  • Strongyloides infection can range from subclinical to fatal.
  • Patients using high-dose corticosteroids may have severe illness.
  • Serial stool examination is the gold standard for diagnosis.

Clinical features

The symptomatic spectrum of Strongyloides infection ranges from subclinical in acute and chronic infection to severe and fatal in hyperinfection syndrome and disseminated strongyloidiasis.

Hyperinfection syndrome and disseminated strongyloidiasis have case-fatality rates that approach 90%. In disseminated strongyloidiasis, patients' symptoms are a result of the parasite's larval form migrating through various organs of the body.

Acute strongyloidiasis

The initial sign of acute strongyloidiasis, if noticed at all, is a localized pruritic, erythematous rash at the site of skin penetration. Patients may then develop tracheal irritation and a dry cough as the larvae migrate from the lungs up through the trachea.

After the larvae enter the gastrointestinal tract, patients may experience diarrhea, constipation, abdominal pain, and anorexia.

Chronic strongyloidiasis

Chronic strongyloidiasis is generally asymptomatic, but in patients with clinical disease gastrointestinal and cutaneous manifestations are the most common.

Of the gastrointestinal complaints, epigastric pain, postprandial fullness, heartburn, and brief episodes of intermittent diarrhea and constipation are the most frequent. Less commonly, patients may present with fecal occult blood, or massive colonic and gastric hemorrhage.

Rarely, presentations resembling inflammatory bowel disease, specifically ulcerative colitis, can occur. Also rare, but documented, are endoscopic exams revealing pathology similar to pseudopolyposis.

Cutaneous symptoms include chronic urticaria and larva currens—a recurrent serpiginous maculopapular or urticarial rash along the buttocks, perineum, and thighs due to repeated auto-infection. It has been described as advancing as rapidly as 10cm/hr.

Rarely, patients with chronic strongyloidiasis have complained of arthritis, cardiac arrhythmias, and signs and symptoms consistent with chronic malabsorption, duodenal obstruction, nephrotic syndrome, and recurrent asthma.

Up to 75% of people with chronic strongyloidiasis have mild peripheral eosinophilia or elevated IgE levels.

Hyperinfection syndrome and disseminated strongyloidiasis

Hyperinfection syndrome and disseminated strongyloidiasis are most frequently associated with subclinical infection in patients receiving high-dose corticosteroids for the treatment of asthma or chronic obstructive pulmonary disease (COPD) exacerbations. Subsequent impaired host immunity leads to accelerated autoinfection and an overwhelming number of migrating larvae. In chronic strongyloidiasis and in hyperinfection syndrome the larvae are limited to the GI tract and the lungs whereas in disseminated strongyloidiasis the larvae invade numerous organs. Left untreated, the mortality rates of hyperinfection syndrome and disseminated strongyloidiasis can approach 90%.

The following signs and symptoms can be seen with hyperinfection syndrome and disseminated strongyloidiasis:

Gastrointestinal manifestations

  • Abdominal pain, nausea, vomiting, diarrhea
  • Ileus, bowel edema, intestinal obstruction
  • Mucosal ulceration, massive hemorrhage, and subsequent peritonitis or bacterial sepsis

Pulmonary manifestations and findings

  • Cough, wheezing, dyspnea, hoarseness
  • Pneumonitis
  • Hemoptysis
  • Respiratory failure
  • Diffuse interstitial infiltrates or consolidation on chest radiographs

Neurologic findings

  • Aseptic or gram-negative meningitis
  • Larvae have been reported in the CSF, meningeal vessels, dura, epidural, subdural, and subarachnoid spaces

Systemic signs and symptoms

  • Peripheral edema and ascites secondary to hypoalbuminemia from protein losing enteropathy
  • Recurrent gram negative bacteremia or sepsis from larvae carrying bacteria that penetrate mucosal walls
  • Syndrome of inappropriate secretion of anti-diuretic hormone (SIADH)
  • Peripheral eosinophilia is frequently absent

Cutaneous manifestations

  • Recurrent maculopapular or urticarial rash that can be found anywhere on the skin but is most commonly found along the buttocks, perineum, and thighs due to repeated auto-infection
  • Larva currens—serpiginous or urticarial rash that advances as rapidly as 10cm/hr.


The gold standard for the diagnosis of Strongyloides infection is serial stool examination. However, traditional stool examinations are insensitive and can require up to seven exams to reach a sensitivity of 100%.

Specialized stool exams include:

  • Baermann concentration
  • Horadi-Mori filter paper culture
  • Quantitative acetate concentration technique
  • Nutrient agar plate cultures

Duodenal aspirate is more sensitive than stool examination.

Duodenal biopsy may reveal parasites in the gastric crypts, in the duodenal glands, or eosinophilic infiltration in the lamina propria.

Frequently, larvae can be seen by a simple wet-mount in fluid from a bronchoalveolar lavage (BAL).

Serologic tests

Many of the serologic tests that are available are quite sensitive. But they cross-react with other filarial parasites, schistosomes, and Ascaris lumbricoides, decreasing their specificity. Furthermore, since antibodies can persist for some time, it can be difficult to distinguish between active cases and historical cases.

A significant proportion of people become antibody negative within 6 months after successful treatment. More sensitive and specific serologic tests using recombinant antigens have been developed.

Note: CDC performs reference serologic testing only to confirm test results, which are occasionally difficult to interpret or equivocal.