title: Comparison of visceral leishmaniasis diagnostic antigens in African and Asian Leishmania donovani reveals extensive diversity and region-specific polymorphisms.
abstract: BACKGROUND
  Visceral leishmaniasis (VL), caused by infection with Leishmania donovani complex, remains a major public health problem in endemic regions of South Asia, East Africa, and Brazil. If untreated, symptomatic VL is usually fatal. Rapid field diagnosis relies principally on demonstration of anti-Leishmania antibodies in clinically suspect cases. The rK39 immunochromatographic rapid diagnostic test (RDT) is based on rK39, encoded by a fragment of a kinesin-related gene derived from a Brazilian L. chagasi, now recognised as L. infantum, originating from Europe. Despite its reliability in South Asia, the rK39 test is reported to have lower sensitivity in East Africa. A reason for this differential response may reside in the molecular diversity of the rK39 homologous sequences among East African L. donovani strains.
  
  
  RESULTS
  Coding sequences of rK39 homologues from East African L. donovani strains were amplified from genomic DNA, analysed for diversity from the rK39 sequence, and compared to South Asian sequences. East African sequences were revealed to display significant diversity from rK39. Most coding changes in the 5' half of repeats were non-conservative, with multiple substitutions involving charge changes, whereas amino acid substitutions in the 3' half of repeats were conservative. Specific polymorphisms were found between South Asian and East African strains. Diversity of HASPB1 and HASPB2 gene repeat sequences, used to flank sequences of a kinesin homologue in the synthetic antigen rK28 designed to reduce variable RDT performance, was also investigated. Non-canonical combination repeat arrangements were revealed for HASPB1 and HASPB2 gene products in strains producing unpredicted size amplicons.
  
  
  CONCLUSIONS
  We demonstrate that there is extensive kinesin genetic diversity among strains in East Africa and between East Africa and South Asia, with ample scope for influencing performance of rK39 diagnostic assays. We also show the importance of targeted comparative genomics in guiding optimisation of recombinant/synthetic diagnostic antigens.
authors.affiliation: Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom. Tapan.Bhattacharyya@lshtm.ac.uk
authors.forename: Tapan
authors.initials: T
authors.lastname: Bhattacharyya
authors.forename: Marleen
authors.initials: M
authors.lastname: Boelaert
authors.forename: Michael A
authors.initials: MA
authors.lastname: Miles
mesh_terms: D000349:Africa; D000953:Antigens, Protozoan / Q000235:genetics*; D001208:Asia; D003955:Diagnostic Tests, Routine / Q000379:methods; D014644:Genetic Variation; D006801:Humans; D007118:Immunoassay / Q000379:methods; D007893:Leishmania donovani / Q000235:genetics*; D007898:Leishmaniasis, Visceral / Q000469:parasitology*; D008969:Molecular Sequence Data; D058974:Phylogeography; D015800:Protozoan Proteins / Q000235:genetics*; D012680:Sensitivity and Specificity; D017422:Sequence Analysis, DNA
chemical_list: D000953:Antigens, Protozoan; D015800:Protozoan Proteins; C079253:K39 antigen, Leishmania