PRRS infection causes reproductive problems in sows and stillborn or weak piglets that die soon after birth.
PRRSV infection can cause severe reproductive damage:
In acute PRRS outbreaks, abortions may occur in 1-3% of sows that are between 21 to 109 days of gestation.
After approximately 1 week after onset of acute illness, the second phase of the disease begins. This is a consequence of transplacental transmission of the virus and is characterized by late term reproductive failure. 5-80% of sows may have reproductive failure at any time between 100 and 118 days of gestation. Experimentally it has been found that inoculation of sows at 45 days of gestation does not result in the virus crossing the placenta. After infection at 70 and 85 days of gestation, the virus crosses the placenta in 33% and 80% of cases, respectively.
In addition to reproductive failure, sows and gilts may show:
In the USA, from late 1996, increased disease outbreaks described as severe PRRS, atypical PRRS or "Swine abortion and mortality syndrome (SAMS)" were reported to diagnostic laboratories. The clinical outbreaks are characterized by abortion rate of 10% - 50% within a 4 to 6 week period. Sows and gilts are anorexic and have a fever. The mortality rate of the breeding herd can be up to 5-10% during an outbreak (Haulbur PG et al. 1997) . The same syndrome was described later in Europe (Martelli et al. 2003; Garcia et al. 2004).
Neonatal piglets can display a variety of clinical signs. The most characteristic are dyspnea, tachypnea and death (up to 100% mortality).
Stillborn and weak piglets.
Neonatal piglet infected with PRRSV