Inactivation of Norovirus Surrogate and Hepatitis A Virus in Suspension and in Dried Mussels Using Thermal Treatment

Introduction:  Norovirus (NoV), as the most serious foodborne virus, is a cause of epidemic gastroenteritis worldwide. Murine norovirus (MNV-1) has emerged as a more suitable model for NoV studies.  Together with NoV, hepatitis A virus (HAV) infection is one of the major causes of foodborne diseases, particularly in developing countries.  These two viruses are regarded as the potential foodborne virus present in dried mussels (Mytilus edulis) commonly manufactured by thermal treatment and followed by drying.

Purpose: This study was conducted to investigate the effectiveness of thermal treatment for the inactivation of MNV-1 and HAV in suspension and dried mussels. 

Methods: Viral suspensions of about 7 log TCID₅₀/ml were exposed to 60, 85, or 100°C of water bath for certain reaction time. Ground dried mussels containing viral suspensions were also exposed to 60, 85, or 100°C of water bath. After reaction, each virus was recovered and calculated as 50% tissue culture infectious dose /ml (log TCID₅₀/ml).

Results: When MNV-1 in suspension was treated with 60°C for 5, 10, and 15 min, the reduction was 3.03, 3.69, and 4.35 log TCID₅₀/ml, respectively. MNV-1 was also reduced to 5.88 log TCID₅₀/ml by of 85°C for 6 min. When HAV in suspension was treated with 60°C for 5, 10, and 15 min, the reduction was 3.61, 4.48, and 5.06 log TCID₅₀/ml, respectively. HAV was greatly reduced to 5.66 log TCID₅₀/ml by 85°C for 10 min. When MNV-1 in dried mussels was treated with 60°C for 5, 10, and 15 min, the reduction was 0.78, 2.00, and 3.35 log TCID₅₀/ml, respectively. When MNV-1 in dried mussels was treated with 85°C for 3, 6, and 10 min, the reduction was 1.95, 2.40, and 3.68 log TCID₅₀/ml, respectively. When HAV in dried mussels was treated with 60°C for 5, 10, and 15 min, the reduction was 1.34, 1.94, and 3.16 log TCID₅₀/ml, respectively. When HAV in dried mussels was treated with 85°C for 3, 6, and 10 min, the reduction was 2.36, 3.43, and 4.38 log TCID₅₀/ml, respectively. Both MNV-1 and HAV in dried mussels were completely inactivated by 85°C for 15 min and over 85°C.

Significance: This study demonstrates that MNV-1 and HAV in dried mussels was greatly reduced up to 3 log TCID₅₀/ml by over 85°C for 10 min.