Comparing PCR tests to diagnose Leishmania infection in dogs

Abstract

There is a need for standardization and simplification of the existing methods for molecular detection of Leishmania infantum in the canine reservoir host. The commercially available OligoC-TesT kit incorporates standardized PCR reagents with rapid oligochromatographic dipstick detection of PCR products and is highly sensitive for use in humans but not yet independently validated for use in dogs. Here we compare the sensitivity of OligoC-TesT with those of nested kinetoplast DNA (kDNA) PCR, nested internal transcribed spacer 1 (ITS-1) PCR, and a PCR-hybridization protocol, using longitudinal naturally infected canine bone marrow samples whose parasite burdens were measured by real-time quantitative PCR (qPCR). The sensitivity of OligoC-TesT for infected dogs was 70% (95% confidence interval [CI], 63 to 78%), similar to that of kDNA PCR (72%; 95% CI, 65 to 80%; P = 0.69) but significantly greater than those of PCR-hybridization (61%; 95% CI, 53 to 69%; P = 0.007) and ITS-1 nested PCR (54%; 95% CI, 45 to 62%; P < 0.001); real-time qPCR had the highest sensitivity (91%; 95% CI, 85 to 95%; P < 0.001). OligoC-TesT sensitivity was greater for polysymptomatic and oligosymptomatic dogs than for asymptomatic dogs (93%, 74%, and 61%, respectively; P = 0.005), a trend also observed for the other qualitative PCR methods tested (P <or= 0.05). Test positivity increased with increasing parasite burdens, as measured by real-time qPCR: OligoC-TesT and kDNA PCR detected 100% and 99% of positive samples when parasite burdens exceeded 74 and 49 parasites/ml, respectively. OligoC-TesT has high sensitivity for detection of canine Leishmania infections; its ease of operation and ease of interpretation are further advantages for veterinary diagnostic laboratories and for large-scale survey work in developing countries.