Author: Marie Hartley, Staff Writer, 2010.

What causes leptospirosis?

Leptospirosis is caused by corkscrew-shaped bacteria belonging to the genus Leptospira. Leptospirosis is a zoonosis (an infectious disease which can be transmitted from animals to humans). Wild and domestic animals such as rodents, dogs, cattle, pigs, and horses are the reservoirs of the disease. Rats are the most common source of the disease worldwide. Leptospires may live for months to years within the kidneys of animals and are excreted in the urine where they can live, outside the body, for several weeks.

Infection is usually transmitted by direct contact with the urine of an infected animal or by contact with a urine-contaminated environment (such as swimming or immersion in contaminated freshwater, or contact with contaminated food or soil). Human-to-human transmission is rare.

The organism gains entry to humans through skin abrasions or the mucous membranes of the nose, mouth, and eyes. The organism then enters the bloodstream, multiplies, and spreads to all organs, particularly the liver and kidneys. In humans, leptospires rarely persist in the kidneys for longer than 60 days. However they can persist in the eyes for much longer.

Where is leptospirosis found?

Leptospirosis is found worldwide, but is more common in tropical countries. The true international incidence of leptospirosis is not known because it is generally under-diagnosed and under-reported. An estimated 100-200 cases are identified annually in the United States.

Risk factors for leptospirosis include:

Clinical features of leptospirosis

The clinical presentation varies from a mild ‘flu-like illness to a severe illness with multi-organ failure. Some infected persons may have no symptoms at all. Leptospirosis may occur in two phases separated by a period of apparent recovery. If a second phase occurs, it is more severe and may result in kidney or liver failure, or meningitis. This phase is also called Weil disease. Approximately 5-10% of patients develop this severe form.

Skin manifestations include:


Case-fatality rates in different parts of the world have been reported to range from less than 5% to 30%. However, these figures are not very reliable as the overall occurrence of the disease is unknown. Elderly people and people with impaired immunity are at the highest risk of death.


Because leptospirosis mimics many other diseases, a plausible history of exposure to infected animals or a contaminated environment is important. Various laboratory tests can be used to confirm infection:


Severe cases are usually treated with intravenous benzylpenicillin. Supportive therapy such as renal dialysis and mechanical ventilation may also be required. Less severe cases are treated with oral antibiotics such as doxycycline or amoxicillin. Third-generation cephalosporins and quinolone antibiotics may also be effective.

A Jarisch-Herxheimer reaction may occur after the start of antibiotic therapy. This is a clinical deterioration due to the release of toxins when large numbers of organisms are killed by antibiotics.


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