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Diagnosis of active visceral leishmaniasis
Visceral leishmaniasis (kala azar) is a disseminated intracellular protozoal infection that targets primarily the reticuloendothelial system (liver, spleen, bone marrow) and is caused by Leishmania donovani, Leishmania chagasi, or Leishmania infantum (Leishmania donovani complex).
Transmission is by the bite of sandflies. Clinical symptoms include fever, weight loss, and splenomegaly; pancytopenia and hypergammaglobulinemia are often present. Most (90%) new cases each year arise in rural areas of India, Nepal, Bangladesh, Sudan, and Brazil but the disease has a worldwide distribution, including the Middle East.
Definitive diagnosis has required the microscopic documentation of characteristic intracellular amastigotes in stained smears from culture of aspirates of tissue (spleen, lymph node) or bone marrow. The detection of serum antibodies to the recombinant K39 antigen of Leishmania donovani is an alternative noninvasive sensitive (95%-100%) method for the diagnosis of active, visceral leishmaniasis.
A positive result is consistent with a diagnosis of active visceral leishmaniasis.
This test indicates only the presence of antibodies and should not be used as the sole criteria for diagnosis.
False-positive results may occur in patients with malaria or in the presence of rheumatoid factor.
Specimens containing glycerol or other viscous materials may interfere with the test.
Patients co-infected with HIV and Leishmania may fail to produce antibodies.
Manufacturer's reported sensitivity and specificity (for endemic areas) are > or =90% and 93% to 100% respectively (InBios Kalazar Detect Rapid Test product insert). Validation studies in the Mayo Clinic Division of Clinical Microbiology provided a sensitivity of 94% (panel of 16 known positives) and specificity of 100% (panel of 50 normal blood donors plus 16 positives for other parasitic infections).
1. Carvalho SF, Lemos EM, Corey R, Dietze R: Performance of recombinant K39 antigen in the diagnosis of Brazilian visceral leishmaniasis. Am J Trop Med Hyg 2003;68:321-324
2. Sundar S, Sahu M, Mehta H, et al: Noninvasive management of Indian visceral leishmaniasis: clinical application of diagnosis of K39 antigen strip testing at a kala-azar referral unit. Clin Infect Dis 2002;25:581-586