The heat sensitivity of hepatitis A virus determined by a simple tissue culture method

A method for estimating residual infectious hepatitis A virus (HAV) after heat treatment of suspensions of the virus was devised. It made use of a readily maintained cell line (FRhK-4) in which the rate of release of HAV antigen into the tissue culture medium was directly proportional to the size of the inoculum. Loss of viral infectivity after heating could be estimated by inoculating heat-treated HAV suspensions into cell monolayers and measuring antigen released from the cultures during 5 weeks of incubation. An inoculum of 10(5) tissue culture infecting doses of HAV suspension in phosphate-buffered saline retained 1.0% of its infectivity after treatment for 2 min, and 0.01% after treatment for 4 min at 65 degrees C. The virus was fully inactivated within 4 min at 70 degrees C, 30 sec at 75 degrees C, 5 sec at 80 degrees C, and virtually instantaneously at 85 degrees C. When HAV was suspended in milk and subjected to statutory pasteurisation conditions, 0.1% of its infectivity remained after 30 min at 62.8 degrees C and 1.0% after 15 sec at 71.6 degrees C. The implications of these results for the heat treatment of food, water, and milk are discussed. It appears that recommended heat processes for milk and shellfish may not be adequate to inactivate HAV.