Leptospira interrogans: Characteristics and Disease

• Leptospira interrogans is a cylindrical, tightly coiled, corkscrew-shaped spirochete.
• It has a thin axial filament and curved ends.
• This organism is an obligate aerobe.
• It exhibits motility due to two long periplasmic flagella.
• These flagella extend the length of the bacteria and are anchored at opposite ends.
• Leptospira interrogans is sensitive to drying and many disinfectants.
• Many serovariants exist, characterized by polysaccharide differences in the lipopolysaccharide component of the outer membrane.

Epidemiology and Transmission

• Leptospirosis is a zoonotic disease, primarily transmitted to humans through water or food contaminated with animal urine.
• Entry into the human body can occur via small skin abrasions or the conjunctiva.

Clinical Manifestations

• Leptospira interrogans causes leptospirosis, known as infectious jaundice, marsh fever, Weil disease, and swineherd’s disease.
• The disease occurs in two phases, acute septic and immune.

First Phase

• Fever occurs one to two weeks after infection and spirochetes appear in the blood.
• The fever decreases after about one week.

Second Phase

• Spirochetes reappear, invading the liver, kidneys, and CNS, in cases of biphasic disease.
• This invasion results in jaundice, hemorrhage, tissue necrosis, and aseptic meningitis.
• The second stage lasts for three or more weeks and involves a rise in circulating IgM antibodies.
• Protective immunity develops following the disease.
• Biphasic disease has a mortality rate of up to 10%.

Laboratory Diagnosis

• Leptospira are thin and at the limit of the resolving power of a light microscope, so they cannot be seen by conventional light microscopy.
• Darkfield microscopy can be used but is relatively insensitive and capable of yielding non-specific findings.
• Neither Gram stain nor silver stain is available for detecting Leptospira.
• Visual demonstration of spirochetes in urine, blood, or CSF can be done.
• Diagnosis is usually based on serological tests, such as the microscopic agglutination test, but this does not indicate an active infection.
• The organism can be cultured in a specialized medium from clinical specimens, but this is not commonly done.
• The incidence of leptospirosis is very low in developed countries, though the disease occurs worldwide.
• Less than 100 cases of clinically significant Leptospira interrogans infections are reported annually in the United States.

Treatment

• Penicillin G is the treatment of choice.

Prevention

• Avoiding contact with contaminated environments is the primary prevention method.
• Doxycycline is effective in preventing disease in exposed persons.