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.
- Tightly coiled fine spirochete:
- L. interrogans have a size of 6-12 μm length x 0.1 μm width which allows them to pass through filters used to sterilize the culture medium.
- They are tightly and regularly coiled, with characteristic hooked ends (hence the species name interrogans resembling interrogation or question mark).
- Spirals have a wavelength (interval between spirals) of 0.5μm and an amplitude of 0.1μm.
- They possess a single endoflagellum attached at the pole and are highly motile exhibiting spinning and translational movements.
- Not Stained with dyes
- Antigenically complex: Divided into serogroups which were further divided into serovars. On the basis of agglutination testing with specific antisera against the surface LPS antigens, Leptospira is divided into:
- Leptospira interrrogans: Comprises of 250 serogroups which further consists of over 250 serovars.
- L. biflexa: 65 serovars arranged in 38 serogroups.
- Source: Although more than 100 animals can be infected; but important sources of infection are rats dogs, cattle, and pigs. Even asymptomatic animals can transmit the infection via urine (persistent colonization of renal tubules of carrier animals.)
- Zoonotic: Humans can become infected through direct or indirect contact with the urine (or other body fluids, except saliva) of infected animals.
- Person to person transmission rare
3R’s: The three important epidemiological determinants for leptospirosis include exposure to rodents, rainfall, and rice field.
- Risk factors:
- Lower socioeconomic status
- Urban and rural slum areas
- Rainfall and floods
- Occupational exposure to animal urine, e.g. rice field workers, farmers.
- Global distribution: Worldwide, the highest burden of the disease has a reported from urban slums of Brazil, India, and Thailand.
- Phases of Infections:
- The acute or bacteremic/septicemic phase
- Immune phase: Aseptic meningitis
First Phase: Acute or bacteremic/septicemic phase
- Entry via mucous membranes of the eyes, nose, or mouth or through skin abrasion
- Vascular damage: Spirochetes can be found in the walls of capillaries, medium, and large-sized vessels. The exact mechanism of vascular damage is not clear.
- Penetration and invasion of tissues are due to active motility and release of hyaluronidase.
- Invade bloodstream and hematogenous spread multiple sites of the body:
- producing fever,
- dysfunction of the liver (jaundice),
- kidneys (uremia),
- lungs (hemorrhage)
- central nervous system (aseptic meningitis)
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.
Incubation period: 5-14 days
Two distinct clinical syndromes:
- Mild anicteric febrile illness: 90% of patients. Biphasic in nature; septicemic phase followed by immune phase.
- Weil’s disease (hepato-renal-hemorrhagic syndrome)
- a severe form of the leptospirosis infection (icteric) which occurs in approximately 10% of patients
- jaundice and significant liver damage
- kidney and/or vascular dysfunction
- lethal pulmonary hemorrhages
- Typical biphasic course may not be present.
- death is up to 10% of cases
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.
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.