Which statement about the rhabditiform larvae of Strongyloides stercoralis is correct?

• A. Are infective for humans
• B. Are the diagnostic form found in feces
• C. Are the diagnostic form found in blood
• D. Are found in the urine

Answer: (A)

In Strongyloides stercoralis, two larval forms matter for infection and diagnosis: rhabditiform and filariform. The rhabditiform larvae are the noninfective form that is shed in stool and is the usual diagnostic finding in clinical parasitology. Their presence in feces allows labs to identify the parasite and confirm infection. The actual infectious larvae are the filariform stage, which penetrate the skin from soil to initiate infection.

So the statement that rhabditiform larvae are found in feces and serve as the diagnostic form is the correct concept. They are not the form that causes new infections, which is why finding them in blood or urine is not typical, and the infective form is the skin-penetrating filariform larva rather than the rhabditiform larva.