Development and optimization of a TaqMan assay for Nosema bombycis, causative agent of pébrine disease in Bombyx mori silkworm, based on the β-tubulin gene

"Pe ' brine" is a devastating disease of Bombyx mori silkworms that is highly contagious and can completely destroy an entire crop of silkworms and is thus a serious threat for the viability and profitability of sericulture. The disease is most commonly attributed to microsporidians of the genus Nosema, which are obligate intracellular parasites that are transmitted through spores. Nosema infections in silkworms are diagnosed primarily through light microscopy, which is labour intensive and less reliable, sensitive, and specific than PCR-based techniques. Here, we present the development and optimization of a new TaqMan based assay targeting the beta-tubulin gene in the pe ' brine disease causing agent Nosema bombycis in silkworms. The assay displayed excellent quantification linearity over multiple orders of magnitude of target amounts and a limit of detection (LOD) of 6.9 x 102 copies of target per reaction. The method is highly specific to N. bombycis with no cross-reactivity to other Nosema species commonly infecting wild silkworms. This specificity was due to three nucleotides in the probe-binding region unique to N. bombycis. The assay demonstrated a high reliability with a Coefficient of variation (CV)