S. Pesch, V. F. Ohlinger. IPVS. 2000
The PRRSV infection within an infected herd depends on the number of immune animals and the presence and number of naive animals that are susceptible to infection. Field virus can spread from infected animals within the herd as well as from animals that are introduced into the herd. Usually suckling piglets loose their maternal antibodies to PRRSV about 3 weeks after birth. Those animals are highly susceptible to PRRSV infections via
• suckling piglets that were born viremic,
• that were infected from sows or
• that were infected in continuous weaning systems.
Thus the highest amount of field virus can be detected in piglets after weaning.