Leptospirosis – identifying pathogenic species Among the following Leptospira options, which represents the pathogenic group responsible for human disease (as opposed to saprophytic species)?

Introduction / Context:
Leptospirosis is a zoonotic disease caused by pathogenic Leptospira. Diagnostic algorithms and public health messaging depend on distinguishing pathogenic versus saprophytic species.

Given Data / Assumptions:

• Leptospira spp. are divided into pathogenic (e.g., L. interrogans sensu lato) and saprophytic (e.g., L. biflexa) groups.
• Clinical human disease is associated with the pathogenic group.
• Nomenclature historically included serovars within species complexes.

Concept / Approach:
L. interrogans is the classic pathogenic complex linked with human leptospirosis (Weil’s disease), maintained in animal reservoirs such as rodents and transmitted via urine-contaminated water. By contrast, L. biflexa is typically free-living and nonpathogenic. Leptospira parva is described among saprophytes and is not considered a primary human pathogen.

Step-by-Step Solution:
Separate pathogenic from saprophytic species.Identify L. interrogans as the pathogenic group causing human disease.Select “Leptospira interrogans.”

Verification / Alternative check:
Clinical references and WHO guidance list L. interrogans serovars (e.g., Icterohaemorrhagiae, Canicola) among the major human pathogens, whereas L. biflexa is nonpathogenic.

Why Other Options Are Wrong:

• L. biflexa: saprophytic, nonpathogenic.
• L. parva: saprophytic, not a recognized human pathogen causing leptospirosis.
• All of these: incorrect because not all listed are pathogenic.
• None: incorrect because L. interrogans is pathogenic.

Common Pitfalls:
Assuming all Leptospira are pathogenic; environmental isolates are common and do not equate to disease risk.

Final Answer:
Leptospira interrogans.