Occurrence of Norovirus genogroup II in leafy greens in the region of Marrakech using a molecular method

Leafy greens are important vectors for enteric viruses, including human noroviruses (HuNoV), which are a leading cause of foodborne disease. These viruses can contaminate the agricultural environment through untreated wastewater or direct contamination. While studies on HuNoV in vegetables have been conducted, few have focused on Morocco. This study aimed to detect HuNoV in leafy greens collected in the region of Marrakech region over a fifteen-week period (March-June 2023). For this purpose, 112 samples (coriander, lettuce and parsley) were collected and analysed using the ISO 15216-2:2019 method with minor modifications, after validation. The method involved eluting viruses using an alkaline buffer, concentrating them through polyethylene glycol precipitation, and detecting viral RNA via real-time RT-PCR. The applied method yielded variable recovery rates among the tested matrices, with coriander showing the highest recovery (1.5%), followed by lettuce (1.2%) and parsley (0.6%), confirming a significant matrix-dependent variation in HuNoV recovery (ANOVA, P < 0.001). This method enabled the assessment of leafy green contamination, which was found to be 0.89% (1/112). This study underscores the need to enhance detection methods to better assess the risks associated to noroviruses in leafy greens, with implications for human health.