The effect of the DNA preparation method on the sensitivity of PCR for the detection of Trypanosoma evansi in rodents and implications for epidemiological surveillance efforts

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Trypanosoma evansi is responsible for the most largely distributed animal trypanosomosis, affecting a wide range of wild and domestic animals. Its surveillance requires the implementation of standardized and reliable diagnostic tools. Although the development of polymerase chain reaction (PCR) tools has greatly improved our diagnostic capacity, factors affecting their sensitivity need to be acknowledged and accounted for in the interpretation of results. The targeted gene and the primer design have already been shown to greatly affect the sensitivity of a PCR, and the best-performing sets of primers have been previously identified. However, the sensitivity of the PCR is also largely influenced by the DNA extraction or sample preparation method. In this paper, we selected 6 DNA extraction or blood sample preparation methods representative of what would be used in a budget-constrained setting: phenol–chloroform, Chelex®, Flexigen (Qiagen®) kit, Genekam® kit and two original protocols using sodium hydroxide. We studied the effects of the preparation method on the detection limit of the subsequent PCR. Our results show that the extraction method strongly affects the PCR sensitivity. The classical phenol–chloroform extraction method allowed for the PCR with the lowest detection limit. Some combinations of extraction method and primer set had detection limits that were not compatible with their use as a reliable diagnostic test, and would severely reduce the performance of a surveillance program. Therefore, we encourage laboratories to carefully select their sample preparation and PCR protocols, depending on the aimed sensitivity, cost, safety, time requirement and objectives.