Concentration, Extraction, and Detection of Enteric Viruses in Raspberries and Blackberries

Introduction: Norovirus (NoV) and hepatitis A virus (HAV) are recognized as leading causes of foodborne illnesses. Recently, these enteric viruses have been implicated in viral gastrointestinal illness associated with soft fruit. Advancements in research have led to the development of rapid and sensitive methods for the extraction and detection of NoV and HAV in soft fruit.

Purpose: The objective of this research was to develop a sensitive and specific method for the concentration, extraction, and detection of enteric viruses in raspberries and blackberries.

Methods: An ultracentrifugation protocol, with the inclusion of murine norovirus (MNV) as an extraction control, was used to concentrate HAV and MNV in fresh and frozen raspberries and blackberries. The berries were spiked with 22, 2.2, and 0.2 PFU/g of HAV and were spiked at 100 PFU/g of MNV. A QiaShredder and the QiaAMP Viral RNA kit were used for RNA extraction followed by RT-qPCR detection.

Results: HAV was detected in fresh and frozen raspberries and blackberries at 22, 2.2, 0.2 PFU/g. The average extraction efficiency of MNV was 50% with minimal to no inhibition. Inhibition was determined by comparing the IAC Ct value of the RT-qPCR negative control and the IAC Ct value of the sample where minimal inhibition is three Ct values or fewer.

Significance: A fast and reliable method for the extraction and detection of enteric viruses in foodborne associated outbreaks is an integral part of outbreak investigation. Overcoming the acidity, pectin, and polyphenols of soft fruit, particularly in raspberries and blackberries, has led to the development of a viable method for detection of HAV at low levels.