A Comparison Between Manual Count, Flow Cytometry and Quantitative Real-Time Polymerase Chain Reaction as a Means of Determining Babesia rossi Parasitaemia in Naturally Infected Dogs

Purpose Light microscopic manual count is the current gold standard for parasite quantification. The ability to determine parasite density in whole blood is crucial to understanding disease pathogenesis and finding a suitable automated method of Babesia rossi parasite quantification would facilitate higher throughput and provide results that are more objective. This study investigated both peripheral capillary and central venous whole blood to estimate the correlations between light microscopy, flow cytometry and quantitative real-time polymerase chain reaction (qPCR). Methods Peripheral capillary and central venous blood were sampled from 40 naturally B. rossi-infected dogs and 10 healthy control dogs. Samples were analysed by reverse line blot hybridization assay to confirm a mono-B. rossi infection. Capillary blood parasite density was detected using light microscopic manual counting and venous blood parasitaemia detected by manual counts, flow cytometry and qPCR. Results A significant correlation was found between the venous manual counts and flow cytometry (r(s) = 0.465; P < 0.001), as well as qPCR (r(s) = - 0.500; P < 0.001). A significant correlation was also observed between the capillary manual counts compared to venous manual counts (r(s) = 0.793; P < 0.001), flow cytometry (r(s) = 0.399; P = 0.004), and qPCR (r(s) = - 0.526; P < 0.001). Conclusions The study results suggest that qPCR is of value as an alternative to the gold standard manual count for detecting B. rossi parasitaemia in canine whole blood and that flow cytometry may be useful with further refinement of issues such as background fluorescence and the influence of reticulocytes.