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Leptospirosis is a zoonotic disease of worldwide prevalence. Although wild mammals are the primary natural reservoir of pathogenic strains, domestic animals represent a major source of human infection. Most often, transmission is indirect, by human contact with soil, food, or water contaminated by urine from an infected animal.
The clinical manifestations of leptospirosis are variable, ranging from a mild infection with fever, chills, headache, conjunctivitis, myalgia, and gastrointestinal symptoms to icteric disease with severe kidney and liver involvement.
Leptospira organisms may be found in the blood at the onset of disease and may persist for approximately 1 week. The organisms also may be found in the urine after week one of the disease. They may persist in the urine for 2 to 3 months; however, shedding may be intermittent and the numbers of organisms present may be low. Urine must be cultured immediately because the organisms cannot survive in acidic urine for more than a few hours.
Leptospirosis is accompanied by a brisk antibody response.
Aids in the diagnosis of leptospirosis
Both IgM and IgG classes of antibody are produced in response to any of 16 leptospira serovars that produce infection. IgM antibody is first detectable within 1 to 2 weeks after onset of illness and peaks at 2 to 4 weeks.
Titers of 1:50 are considered borderline and follow-up specimens should be drawn for isolation of live leptospires (ie, culture) and repeat serology.
Titers > or =1:100 represent recent or active infection.
The overall sensitivity of the assay is 100% and the specificity is 97% when compared to CDC reagents.
Serologic results must be correlated with the clinical picture.
Sera drawn too close to onset of symptoms may precede the initial IgM antibody response.
Acute titers may be delayed or substantially decreased by early and intensive antibiotic treatment.
The assay detects antibody to the genus Leptospira but will not determine which serovar is associated with the infection.
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