HEAT INACTIVATION KINETICS OF TULANE VIRUS AND AICHI VIRUS

Human noroviruses (HNoVs) and Aichi virus (AiV) causes significant number of gastrointestinal diseases worldwide. Tulane virus (TV), a cultivable HNoV surrogate, is used to determine control measures against HNoV. The objectives of this study were to determine the heat inactivation kinetics of TV and AiV in cell-culture media and TV in spinach using the first-order and Weibull models. TV and AiV in cell-culture media at ~7 log PFU/ml in 2-ml glass vials were heated at 50-58°C [degree Celsius] up to 10 min in a circulating water-bath. Surviving infectious viruses were enumerated by standard plaque assays using confluent host cells in 6-well plates. The Weibull model showed T_d=1 [thermal decimal reduction time] values of 2.53±0.08, 1.99±0.10, 0.57±0.64 and 0.22±0.25 min, respectively at the same temperatures with z-value of 6.99°C for cell culture media in 2-ml glass vials. D-values for TV in spinach in vacuum bags were 7.94±0.09, 4.09±0.04 and 1.43±0.07min and a z-value 10.74±0.01°C by the first-order model and 4.89±0.02, 3.21±0.45 and 0.25±0.38 min for the Weibull model at 50, 54 and 58°C, respectively. TV may not be as suitable a surrogate as MNV-1 (with D_50°C of 36.28 min in cell-culture media and 14.57 min in spinach in 2-ml vials) for HNoV heat inactivation studies in cell culture media in 2-ml glass vials or spinach in vacuum bags owing to its lower D and z-values. D-values for AiV in 2-ml glass vials at 50, 54, and 58°C from the first-order model were 47.62±1.2, 7.14±1.13 and 2.12±0.04 min, respectively, with a z-value of 5.92°C, while the Weibull model showed T_d=1 values of 34.53±0.03, 2.59±0.05 and 0.91±0.06 min for the same temperatures, respectively. Thus, both TV and AiV have lower heat resistance than hepatitis A virus (D_56°C of 8.4 min in buffer in 2-ml glass vials and 8.43 min in spinach in vacuum bags). This study helped in understanding the heat-inactivation kinetics of AiV and TV that provide data for use in thermal processing to ensure food safety.