Neutralizing activity in the gastrointestinal contents of piglets vaccinated with a live or formaldehyde-inactivated porcine enterovirus.

Neutralizing activity against porcine enterovirus strain T80 was demonstrated in the gastrointestinal contents of piglets given live T80 virus orally or parenterally, but little or no neutralizing activity was detected in the gastrointestinal contents of piglets given formaldehyde-inactivated virus by either route. The gastrointestinal neutralizing response was first detected 14 days after oral dosing, coincidentally with a fall in the titre and distribution of virus. The neutralizing response was highest at 23 days, and dropped markedly by 36 days, whereas no response was detected until 36 days in piglets which received live virus by the intramuscular route. Virus generally appeared earlier, was more widely distributed, and reached higher titres in the gastrointestinal tract of piglets which received live virus orally than in those which received the same preparation by the intramuscular route. The highest serum neutralizing response occurred in the piglets given live virus orally. The serum response in the piglets which received live virus intramuscularly appeared earlier and was biphasic. The serum response in the piglets receiving formaldehyde-inactivated virus appeared as early as the response to live virus given by the same route, but remained relatively low throughout the period of observation.