Useful for
Helps in the diagnosis of leptospirosis.
Method name
Enzyme-Linked Immunoassay Spot (Immunodot)
Report name
Leptospira, IgM, S
Type of sample: Serum
Sample required
- Container / Tube:
- Preferred: serum gel
- Acceptable: red top
- Sample volume: 0.3 ml
- Collection Instructions: Serum should be collected according to standard practices. Acute and convalescent specimens obtained to determine seroconversion should be collected 2 or more weeks apart.
Minimum sample volume: 0.1 ml
Clinical information
Leptospirosis is a zoonotic disease with worldwide prevalence, although most infections occur in hot, tropical climates. Wild mammals, typically rodents, are the main natural reservoir for pathogenic Leptospira strains, however domestic animals (eg dogs) also represent a major source of human infection. Leptospira are gram-negative spirochetes with at least 20 different species in the genus. Of these, at least 9 species are considered pathogens, including the most common agent of leptospirosis, Leptospira interrogans.
Transmission occurs through indirect human contact (eg, through mucous membranes or scraped skin) with water, food, or soil contaminated with animal urine containing Leptospira spirochetes. After infection, the incubation period can vary from 3 to 30 days, depending on the inoculum dose and the immune status of the individual.
The clinical manifestations of leptospirosis can range from mild flu-like illness (eg, headache, malaise, fever, arthralgia, fatigue) to fulminant disease with severe liver and kidney involvement. This last manifestation was previously known as Weil’s disease. Leptospira organisms can be found in the blood at the onset of the disease and can persist for about 1 week. Later, spirochetes can be found in the urine and can persist for 2 to 3 months; however, the spread may be intermittent and the number of organisms present may be below.
While Leptospira can be grown in culture, this is a demanding organism and requires immediate transport to the laboratory. Furthermore, detectable growth requires a long incubation (1-6 weeks), which limits the usefulness of the culture for acute diagnosis. For this reason, serological detection of antibodies to Leptospira remains the method of choice for rapid diagnosis. IgM class antibodies against this spirochete are detectable on day 6 of the disease and remain detectable for 2 to 3 months after the onset of symptoms.
Reference values: Negative
Interpretation
Positive:
IgM antibodies against Leptospira species were detected, suggesting recent infection. The presence of antibodies alone cannot be used to definitively diagnose an acute infection, as antibodies from previous exposure or infection may remain detectable for an extended period of time.
Limit:
The result should be interpreted with caution. Additional testing of a second convalescent specimen is recommended. If the sample remains at the limit of reactivity, a second serological method should be considered if leptospirosis infection is still suspected.
Negative:
IgM antibodies against Leptospira were not detected. Since antibodies may not be present or may be present at undetectable levels during early illness, it is recommended to repeat the test of a convalescent specimen collected in 2 to 3 weeks.