Leptospirosis, a spirochetal
infection, causes a wide spectrum of disease ranging from
asymptomatic infection, or
influenza-like symptoms, to severe
jaundice and
renal failure. Humans become infected through skin or mucous membrane contact with infected animal urine or urine-contaminated water or soil. The most common source of human
infection worldwide is rats. However, in the United States, dogs, livestock, wild mammals, and cats are also sources. Once leptospires penetrate mucous membranes or breaks in the skin, they disseminate to all parts of the body. Five to ten percent of those infected will have severe
leptospirosis with
jaundice, known as
Weil's disease. The classical presentation of
leptospirosis is that of a biphasic illness. The initial septicemic phase lasts 4 to 7 days and is characterized most commonly as a mild
influenza-like illness. During the secondary immune phase, leptospires disappear from the blood and cerebrospinal fluid. However, circulating
antibodies cause immune-mediated
meningitis,
uveitis,
rash, and, very rarely,
circulatory collapse associated with
Weil's disease. Pulmonary involvement occurs in 20% to 70% of patients. The more severe pulmonary manifestations are rare. Although attempts should be made to isolate leptospires from the blood or cerebrospinal fluid, the diagnosis is usually established by serologic tests. The effectiveness of antimicrobial
therapy in treating
leptospirosis has been difficult to assess because of the high variability of the disease's
clinical course, although in severe cases,
antibiotic therapy is effective even when treatment is delayed. Prevention is difficult because it is almost impossible to eliminate the large animal reservoir of
infection.