Thermal Inactivation of Hepatitis A Virus, Noroviruses, and Simian Rotavirus in Cows' Milk

Consumption of raw or unpasteurized milk is a risk for the consumers because indirect contaminations such as fecal-cross-contamination could occur and determine the presence of enteric viruses. In this study, milk was treated with several temperature and time combinations chosen by performing a preliminary experiment to evaluate the intervals needed to inactivate Hepatitis A virus (HAV) HM175 strain, noroviruses genogroups I and II (GI and GII), and simian rotavirus SA11 at different temperatures. Results were obtained by measuring the genome copies and infectious units by real-time PCR and plaque assays respectively. At 85 °C, one minute and two minutes were needed to achieve 6.6 log₁₀ ± 0.2 and 8 log₁₀ ± 0 reductions of genome copies of HAV respectively. Similar genome copies reduction was also observed for noroviruses (GI and GII) and simian rotavirus. At higher temperatures, 90 s (s) at 90 °C and 60 s at 95 °C were needed to achieve 8 log₁₀ ± 0 reductions of the genome copies of all studied viruses. Significant higher sensitivity of the infectious units of both HAV and simian rotavirus to heat treatment of milk than their genome copies was observed. At boiling point of milk (100.5 °C), 40 s were needed to achieve 8 log₁₀ ± 0 reductions of genome copies of all the studied viruses, while 10 s were needed to achieve 6 log₁₀ ± 0 reductions of the infectious units of HAV and simian rotavirus. Significant higher reduction of infectious units than genome copies was observed confirming that genome copies reduction does not correspond to infectious virus.