L. interrogans causes leptospirosis, which occurs as two rec-ognizable clinical syndromes as anicteric leptospirosis and icteric leptospirosis. The incubation period varies from 2 to 30 days, but is usually about 10–14 days.
Approximately, 90% of infections with L. interrogans manifest as a mild anicteric (absence of jaundice) form of the disease. These clinically inapparent infections are diagnosed only by demon-stration of specific leptospira antibodies in the patient serum.
Approximately 10% of the patients develop icteric manifesta-tions of the disease, otherwise known as Weil’s disease. The disease is characterized by the development of jaundice. The disease shows two distinct phases: septicemic and immune (leptospuric). These two phases of illness are continuous and indistinguishable.
First stage is the septicemia or leptospiremia stage. This stage is so called because during this phase, Leptospira organ-isms are usually isolated from the blood, CSF, and most tissues by culture. This stage is characterized by a nonspecific improvement during which the temperature falls down and the patient becomes afebrile and relatively asymptomatic.
Immune or leptospuric stage: The second stage startswith the recurrence of fever. This stage is called immune or leptospuric stage, because circulating antibodies may be detected in serum or leptospira may be isolated from the urine, but not from blood or CSF. This stage occurs as a result of body’s immune response to infection. This stage is character-ized by the diseases affecting specific organs, such as meninges, liver, kidney, and eye.
Aseptic meningitis is the most important clinical mani-festation. Profound jaundice, renal dysfunction, pulmonary dysfunction, hepatic necrosis, and hemorrhagic diastases are other severe manifestations.
Mortality is very high (5–10%) with Weil’s syndrome. It may be as high as 22% in cases of Weil’s syndrome associated with hepatorenal involvement and jaundice, and in older patients.