rK39-ICT Is Less Sensitive in Africa as Compared to Asia.

Leishmaniasis is a fatal systemic disease that occurs due to bite of Leishmania donovani carrier sandfly.  In Asia, Africa and Brazil Viseral Leishmaniasis is most prevalent and is caused by Leishmania donovani complex (L.infantum+L.donovani).

An immunochromatographic test, rK39 (an antibody based test) is used to detect the disease. This test is based on dual 39 amino acid repeats of a Sudanese L. donovani-obtained kinesin homologue of rK39, flanked by HASPB sequences.  However this test has less sensitivity in Africa than in Asia. Possible reasons for such variation could be:

  1. Molecular diversity that is continent specific
  2. Variable immunological response due to different IgG anti-Leish patient levels.

Immunoglobulin G or IgG titers were determined for VL patients from India and Sudan. It was found that IgG titers of VL patients from Sudan were less than Indian VL patients. About 46-61 folds higher mean ELISA titers were found for Indian VL patients as compared to Sudanese patients. Higher titers occurred in adults (both sexes) and children less than 16 years old. Possible cause for such lower titers could be Zinc deficiency or either variable antigencity. Malnutrition of zinc, iron and protein are known to trim down immune responses in experimental models.  Extensive research on zinc deficient models has established earlier that reduced B-cell responses and impairment of memory cells occurs. This could explain as why rK39-ICT has lower sensitivity in African areas or a lower titer of IgG.Picture1 Picture2

Since VL is not the only version of disease caused by Leishmania, other types like (post kala-azar dermal leishmaniasis) PKDL could be of curiosity. Assessment of PKDL patient antibody levels might be the future study of the authors. Such efforts could really speed up the process of disease detection in future and save many lives by earlier and easier diagnosis.

Reference:  Significantly Lower Anti-Leishmania IgG Responses in Sudanese versus Indian Visceral Leishmaniasis. Tapan Bhattacharyya, Duncan E. Bowes, Sayda El-Safi, Shyam Sundar, Andrew K. Falconar, Om Prakash Singh, Rajiv Kumar, Osman Ahmed, Marleen Boelaert, Michael A. Miles. (2014) DOI: 10.1371/journal.pntd.0002675

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