Leptospirosis overview and Definition

Leptospirosis is a bacterial disease that affects humans and animals. It is caused by bacteria of the genus Leptospira. In humans, it can cause a wide range of symptoms, some of which may be mistaken for other diseases. Some infected persons, however, may have no symptoms at all. It usually spreads from the urine of the dogs, rats and other rodents.

Without treatment, Leptospirosis can lead to kidney damage, meningitis (inflammation of the membrane around the brain and spinal cord), liver failure, respiratory distress, and even death

Structure of Leptospirosis

Leptospires are thin , coiled , gram negative and aerobic organisms that is it requires the oxygen for its survival. These bacteria are motile, with hooked ends and paired axial flagella enabling them to burrow into the tissue.  The movement is mainly by the spinning of the long axis of the bacterium.

They belongs to the order spirochaetales and the family Leptospiraceae. The organsims are classifies based on the antigenic differences in the lipopolysaccharide envelopes that surround the cell wall. There are two types of the leptospirosis one is pathogenic and other one is non pathogenic. The pathogenic one is called as the Leptospira interrogans and the non pathogenic is called as the Leptospira biflexa.

Animal reservoirs:

The most important  reservoirs are rodents and rats.  Leptospirosis in animals does not easily show the manifested symptoms. The bacterium can reside in the renal tubules of animals of the kidney. This leptospirosis in animals often occurs for months after the initial infection. It can also occurs in the healthy immunized dogs.  The human to human transmission of the disease is very rare and the humans might acquired the disease through the direct exposure with the urine of the animals which are contaminated with the Leptospirosis.


L pomona and L interrogans are seen in cattle and pigs; L grippotyphosa is seen in cattle, sheep, goats, and voles; L ballum and L icterohaemorrhagiae are associated with rats and mice; and L canicola is associated with dogs. Other important serotypes include L autumnalis, L hebdomidis, and L australis. Leptospiral species' and serogroups' host animals vary from region to region. Individual animals may carry several serovars.

Leptospirosis in animals is often subclinical. Leptospires may persist for long periods in the renal tubules of animals by establishing a symbiotic relationship with little or no evidence of disease or pathological changes in the kidney. As a result, animals that serve as reservoirs of host-adapted serovars can shed high concentrations of the organism in their urine without showing clinical evidence of disease.

This leptospiruria in animals often occurs for months after the initial infection. Leptospiruria also has been found to occur in healthy immunized dogs. Leptospiruria in humans is more transient, rarely lasting more than 60 days. Humans and nonadapted animals are incidental hosts. With rare exceptions, man represents a dead end in the chain of infection because person-to-person spread of the disease is rare.



The bacterium releases the endotoxin, hemolysin and lipase increases the toxic nature of the leptospire bacterium. The following manifestations such as vasculitis of capillaries manifested by endothelial edema, necrosis, lymphocytic infiltration.  In the kidenys lepstospires migrate to the interstitium, renal tubules, amd tubular lumen causing the interstitial nephritis and tubular necrosis.

Renal failure occurs due to the renal damage and hypovolemia might occurs due to the dehydration.

Liver involvement is marked by centrilobular necrosis and Kupffer cell proliferation. Jaundice may occur as a result of hepatocellular dysfunction.


Pulmonary involvement is secondary to alveolar and interstitial vascular damage resulting in hemorrhage. This complication is considered to be the major cause of leptospirosis-associated death.

Interstitial myocarditis occurs as the cardiologic features.


Hemorrhage, focal necrosis, and inflammatory infiltration have been documented within the adrenal gland. Although these complications do not appear clinically, some researchers speculate that adrenal insufficiency may mediate, in part, the final vascular collapse associated with fatal leptospirosis. In acute infections the organisms persists in the host immune cells  till the development of opsonizing immunoglobulin in the plasma followed by rapid immune clearance.

Presence of leptospirosis in the eye leads to chronic or recurrent uveitis.


The infection might progress to severe systemic inflammatory syndrome with hemorrhagic features. The disseminated intravascular coagulation may occur with the bleeding.

Alterations in the onset of the mental status leads to the involvement of the cerebral cortex with meningo encephalitis.

Severe and diffuse alveolar hemorrhage with massive hemoptysis can occur in the absence of typical weil disease.

Myocarditis can occur, elevated jugular venous pressure .

Severe and diffuse alveolar hemorrhage with massive hemoptysis can occur in the absence of typical Weil disease.

Cholecystitis and pancreatitis occurs.

Uveitis, iridocyclitis, and chorioretinitis may occur late into illness and may persist for years.


Clinical signs & symptoms

Leptospirosis ranges in severity from no symptoms to a mild illness suggesting a viral infection to a multisystemic syndrome with unique features. It is characterized by sudden onset of the following:


Fever (38-40°C)


Headache, retro-orbital pain, photophobia

Muscle pain localized to the calf and lumbar areas

Conjunctival suffusion

Dry cough

Nausea and vomiting, diarrhea

More severe disease manifests as icteric leptospirosis, also known as Weil disease, with the following features:

Icterus or frank jaundice

Renal failure with oliguria

Hemorrhagic features

Systemic inflammatory syndrome or shock

Differential Diagnosis

Blood cultures:

Blood cultures may be negative if drawn too early or too late. Leptospires may not be detected in the blood until 4 days after the onset of symptoms (7-14 d after exposure). Once the immune system is activated, blood cultures may again become negative. Leptospires may be isolated from the cerebrospinal fluid (CSF) within the first 10 days.


Microscopic agglutination testing:

The agglutination test reveals the antibody and complement reactions.

Chest Xray:

The chest x ray predicts any abnormal area .

Computed tomography:

It uses both the combination of x ray and computer aided device.

It helps to analyse the size, shape and position of any  abnormalities in the vital organs.

MRI scan:

It uses the soft tissue image of the organ. It uses the both the magnet and radiowaves.

Histopathologic findings:

Silver staining and immunofluorescence can identify leptospires in the liver, spleen, kidney, CNS, muscles, and heart. During the acute phase of leptospirosis, histology reveals these organisms without much inflammatory infiltrate


The prognosis is excellent on the appropriate treatment.


Avoid contact with the urine by the rats and other rodents

Wash the hands properly before taking meals

Avoid touching the animals

Prevent the entry of rodents to home.