Minimal infective dose of rotavirus.

We studied the minimal infective dose of the gastroenteritis virus, rotavirus. Increasingly lower doses [10(4), 10(3), 10(1), 1, 10(-2) plaque forming units (PFU)] of the OSU strain of porcine rotavirus were administered to highly susceptible (colostrum deprived, cesarean derived) newborn miniature swine piglets. In vitro studies showed that virus infectivity was inactivated in piglet gastric juice, both by low pH and by pH- and concentration-dependent factor(s). These factors remain unidentified, but to prevent intragastric viral inactivation, sodium bicarbonate was administered prior to oral virus inoculation of piglets with virulent (non-tissue culture passaged) virus. The lowest dose of virus to induce clinical illness or to demonstrate viral replication by recovery of significantly more infectious virus than was administered, or both, was 1 PFU. These results should help establish standards for virus contamination of water and recommendations for evaluating disinfection procedures for rotaviruses.