Leptospira interrogans: Pathogenesis, Lab Diagnosis

By Acharya Tankeshwar •  Updated: 05/05/22 •  4 min read

Leptospira interrogans is a member of the class Spirochaetes order Spirochaetales and the family Leptospiraceae. There are two species of Leptospira; L. interrogans are the pathogenic species and are the causative agents of leptospirosis or Weil’s disease whereas L. biflexa is sprophytic in nature.

Morphological Characteristics


3R’s: The three important epidemiological determinants for leptospirosis include exposure to rodents, rainfall, and rice field.

First Phase: Acute or bacteremic/septicemic phase

Second Phase (Immune Phase)

After seroconversion Spirochetes start to disappear from the blood but they may colonize in kidney: Leptospira become adherent to the proximal tubular brush border and is excreted in the urine.

Clinical Manifestations

Incubation period: 5-14 days

Two distinct clinical syndromes:

Weil’s Syndrome:

Laboratory Diagnosis

Laboratory diagnosis of leptospirosis infection can be done by detecting L. interrogans in a clinical specimen (urine, blood, or CSF) by immunofluorescence, impregnation stains such as Fontana stain, and modified Steiner technique or by using dark-ground microscopy or phase-contrast microscopy.

(a) Growth from blood in EMJH semisolid media Leptospira is forming subsurface colonies in the tube on the left and no growth in the tube on the right; (b) dark field microscopy image of the culture showing spirochetes with morphology compatible with Leptospira; (c) Conventional PCR targeting lipL32 gene  (Image source: Christopher Ryan Larson)

It can be isolated in the lab by using Fletcher’s or EMJH (Ellinghausen, McCullough, Johnson, Harris) medium.

Antibodies may be detected in the blood within 5–7 days of symptom onset which can be demonstrated by the microscopic agglutination test (MAT). Molecular diagnosis includes amplification and detection of various genes such as 16S or 23S rRNA or IS1533 insertion sequence.

Find details about the laboratory diagnosis of leptospirosis in this post of microbeonline.

References and Further Readings

Acharya Tankeshwar

Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. As an asst. professor, I am teaching microbiology and immunology to medical and nursing students at PAHS, Nepal. I have been working as a microbiologist at Patan hospital for more than 10 years.

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