Analysis of the Environmental Persistence of Tulane Virus, a Novel Cultivable Surrogate for Human Norovirus

Introduction: Human noroviruses (HuNoV) are the most common cause of acute viral gastroenteritis and the leading cause of foodborne disease. Their environmental persistence is an important feature that influences their transmissibility by foodborne routes.  Because HuNoV cannot be cultured in vitro, cultivatable surrogate viruses are often used to predict their behavior, although such predictions are not always accurate. Tulane virus (TV), which has features more similar to HuNoV than do other surrogates, is a promising alternative.  

Purpose: To evaluate the environmental persistence of TV using infectivity assay and reverse transcription-qPCR (RT-qPCR), as appropriate.  

Methods: TV was inoculated onto stainless steel coupons that were held at room temperature for up to 42 days. Virus inoculum was periodically recovered by elution, followed by RNA extraction (with and without prior RNase treatment to serve as proxy for infectivity) and RT-qPCR (for quantification of genome copy number). Parallel infectivity assays were done using the 50% Tissue Culture Infectious Dose (TCID₅₀) method. 

Results: By RT-qPCR, there was approximately a 2-log reduction in the concentration of TV over 42 days on stainless steel. There was no statistically significant difference in virus titer when comparing RNase-treated to non-treated samples.  A similar 2-log reduction in virus titer over 42 days was observed for TV using the TCID₅₀assay.  No statistically significant differences between RT-qPCR and infectivity assay results were observed.  

Significance: Similar to previous studies with HuNoV on surfaces, TV showed a high degree of environmental persistence.  The lack of statistically significant differences when comparing persistence by RT-qPCR and infectivity assay is unique, as persistence is almost always greater when measured by RT-qPCR. TV is a promising surrogate for HuNoV in environmental persistence studies.