title: Design, development and evaluation of rK28-based point-of-care tests for improving rapid diagnosis of visceral leishmaniasis.
abstract: BACKGROUND
  Visceral leishmaniasis (VL) is diagnosed by microscopic confirmation of the parasite in bone marrow, spleen or lymph node aspirates. These procedures are unsuitable for rapid diagnosis of VL in field settings. The development of rK39-based rapid diagnostic tests (RDT) revolutionized diagnosis of VL by offering high sensitivity and specificity in detecting disease in the Indian subcontinent; however, these tests have been less reliable in the African subcontinent (sensitivity range of 75-85%, specificity of 70-92%). We have addressed limitations of the rK39 with a new synthetic polyprotein, rK28, followed by development and evaluation of two new rK28-based RDT prototype platforms.
  
  
  RESULTS
  Evaluation of 62 VL-confirmed sera from Sudan provided sensitivities of 96.8% and 93.6% (95% CI = K28: 88.83-99.61%; K39: 84.30-98.21%) and specificities of 96.2% and 92.4% (95% CI = K28: 90.53-98.95%; K39: 85.54-96.65%) for rK28 and rK39, respectively. Of greater interest was the observation that individual VL sera with low rK39 reactivity often had much higher rK28 reactivity. This characteristic of the fusion protein was exploited in the development of rK28 rapid tests, which may prove to be crucial in detecting VL among patients with low rK39 antibody levels. Evaluation of two prototype lateral flow-based rK28 rapid tests on 53 VL patients in Sudan and 73 VL patients in Bangladesh provided promisingly high sensitivities (95.9% [95% CI = 88.46-99.1 in Sudan and 98.1% [95% CI = 89.93-99.95%] in Bangladesh) compared to the rK39 RDT (sensitivities of 86.3% [95% CI = 76.25-93.23%] in Sudan and 88.7% [95% CI = 76.97-95.73%] in Bangladesh).
  
  
  CONCLUSIONS
  Our study compares the diagnostic accuracy of rK39 and rK28 in detecting active VL cases and our findings indicate that rK28 polyprotein has great potential as a serodiagnostic tool. A new rK28-based RDT will prove to be a valuable asset in simplifying VL disease confirmation at the point-of-care.
authors.affiliation: Infectious Disease Research Institute, Seattle, Washington, United States of America.
authors.forename: Sowmya
authors.initials: S
authors.lastname: Pattabhi
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Whittle
authors.forename: Raodoh
authors.initials: R
authors.lastname: Mohamath
authors.forename: Sayda
authors.initials: S
authors.lastname: El-Safi
authors.forename: Garner G
authors.initials: GG
authors.lastname: Moulton
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Guderian
authors.forename: Danny
authors.initials: D
authors.lastname: Colombara
authors.forename: Asem O
authors.initials: AO
authors.lastname: Abdoon
authors.forename: Maowia M
authors.initials: MM
authors.lastname: Mukhtar
authors.forename: Dinesh
authors.initials: D
authors.lastname: Mondal
authors.forename: Javan
authors.initials: J
authors.lastname: Esfandiari
authors.forename: Shailendra
authors.initials: S
authors.lastname: Kumar
authors.forename: Peter
authors.initials: P
authors.lastname: Chun
authors.forename: Steven G
authors.initials: SG
authors.lastname: Reed
authors.forename: Ajay
authors.initials: A
authors.lastname: Bhatia
mesh_terms: D000328:Adult; D000913:Antibodies, Protozoan / Q000097:blood; D000953:Antigens, Protozoan; D002648:Child; D005260:Female; D006801:Humans; D007118:Immunoassay / Q000379:methods; D007898:Leishmaniasis, Visceral / Q000175:diagnosis*; D008297:Male; D010274:Parasitology / Q000379:methods*; D019095:Point-of-Care Systems; D011994:Recombinant Proteins; D012680:Sensitivity and Specificity; D013397:Sudan
chemical_list: D000913:Antibodies, Protozoan; D000953:Antigens, Protozoan; D011994:Recombinant Proteins