Serodiagnosis of Leishmaniasis

Abstract

Leishmaniasis is a spectrum of diseases ranging in severity from cutaneous (CL), post-kala-azar dermal (PKDL), and diffuse cutaneous (DCL) to mucocutaneous (MCL) and visceral (VL) infections that are endemic in 86 tropical and subtropical countries around the world, accounting for 75,000 deaths per year. Different forms of leishmaniases are generally caused by different distinct species of Leishmania having a digenetic life cycle alternating between an aflagellated amastigote form replicative within the macrophages of the host and a flagellated promastigote form that multiplies within the gut of the sandfly. VL, MCL, PKDL, DCL, and CL forms of the disease can be arranged on a priority basis in accordance with the humoral immune responses of host. Generally, the cell-mediated immunity, particularly the delayed-type hypersensitivity to leishmanial antigens, is associated with CL, MCL, PKDL, and cured VL cases. The serodiagnosis of leishmaniasis appears to be an alternative to parasite detection in biopsy samples either by the staining of amastigotes or by culturing the amastigotes, which transform to a promastigote form and replicate. A battery of immunological procedures have been developed or adapted to demonstrate either humoral or cell-mediated immune responses against Leishmania for diagnosis and epidemiological survey. The sensitivity and specificity of such diagnostic methods depend on the type, source, and purity of antigen employed, as some of the leishmanial antigens have common cross-reactive epitopes shared with other microorganisms, particularly Trypanosoma, Mycobacteria, Plasmodia, and Schistosoma. Serodiagnostic techniques for the detection of antileishmanial antibodies have been employed with about 72 to 100, 23 to 90, 83, and 33 to 100% success in VL, CL, MCL, and PKDL patients, respectively. The Leishmanin skin test (LST) is useful to detect MCL and CL, with about 100 and 84% success, respectively. In PKDL, the gradual fall of antileishmanial antibody titer to some extent and the rise of delayed hypersensitivity to the parasite antigen are the characteristic features associated with the chronicity of the disease. The use of whole promastigote as the source of antigens in the direct agglutination test (DAT) and immunofluorescent test (IFAT) gave cross-reactions with the sera of leprosy, tuberculosis, and African trypanosomiasis patients. Again, the use of cell-free extracts of promastigotes generally gave false positive results with the sera of normal human and Chagas' disease, leprosy, tuberculosis, and malaria patients in enzyme-linked immunosorbent assay (ELISA), dot ELISA, immunodiffusion, immunoelectrophoresis, and counter-current Immunoelectrophoresis tests. Leishmanial proteinase, gp63, is not species specific, but appears to be Leishmania specific, so it can be used to detect a case of leishmaniasis. Acid phosphatase and the dp72-kDa protein of L. donovani cross-reacts with the sera of leprosy patients. Active VL cases are confirmed by the positive results obtained for antileishmanial antibody detection and negative for LST. The titers of antibodies against excreted factor (EF) or lipophosphoglycan (LPG) or lipophosphopolysaccharide (LPPS) of Leishmania were found to be insignificant for serodiagnostic purposes. Use of ConA-positive glycoproteins released or secreted by promastigotes of L. donovani showed 100% positive reactions with VL in immunoelectrophoresis. An LPS-like antigen of L. major promastigotes could detect 90% of confirmed CL cases with radioimmunoassay. Detection of leishmanial antigens circulating in immune complexes is considered an indication of active leishmanial infection.

Key Words::

• leishmaniasis
• serodiagnosis of leishmaniasis
• visceral leishmaniasis
• kala-azar
• cutaneous leishmaniasis
• mucocutaneous leishmaniasis
• post-kala-azar dermal leishmaniasis
• diffuse cutaneous leishmaniasis
• direct agglutination test
• indirect fluorescence antibody test
• gel diffusion test
• counter-current immunoelectrophoresis
• immunoelectrophoresis
• enzyme-linked immunosorbent assay
• dot ELISA
• radioimmunoassay
• monoclonal antibodies
• circulating antigen
• leishmanin skin test
• Leishmania.