Colonization of suckling pigs by Streptococcus suis with particular reference to pathogenic serotype 2 strains.
Three swine commercial farms with high mortality rates in nursery pigs due to Streptococcus suis serotype 2 were studied. Brain samples from diseased animals were collected for a period of 6 to 10 mo and used to isolate the strain that was responsible for the mortality (virulent strain) in each farm. Tonsil swabs from piglets at 5, 10 and 15 d were taken to assess both total colonization and colonization by the virulent strain. The effect of sow vaccination against S. suis on colonization was evaluated in 1 of the farms. All suspect tonsil isolates were identified biochemically and then tested against serotype 2. The genomic patterns of serotype 2 isolates were compared to that of the virulent strain using Rep-PCR. Results showed that total colonization by S. suis occurred very early in the pigs' life, with most animals being colonized by weaning age. Prevalence of colonization by serotype 2 strains was much lower than total colonization. After comparing serotype 2 isolates with the virulent strains, only 1 tonsillar isolate had the same genomic pattern as the virulent strain and it belonged to a 4-week-old weaned pig. The genomic pattern of the virulent strain was not found in any tonsillar isolate from 15-day-old or younger pigs. Although limited by sample size, sow vaccination against S. suis increased total colonization at the same time significantly decreasing colonization by serotype 2 strains. Even though most pigs are colonized early in age by S. suis, colonization by the virulent strain is of low prevalence and delayed in time. This could constitute a risk factor for developing the disease later in time, because animals would be colonized when maternal immunity is no longer present, allowing the organism to become systemic.
Torremorell
M
M
Department of Clinical and Population Sciences, College of Veterinary Medicine, University of Minnesota, St. Paul 55108, USA.
Calsamiglia
M
M
Pijoan
C
C
D000818:Animals; D000833:Animals, Suckling; D001921:Brain / Q000382:microbiology*; D014066:Palatine Tonsil / Q000382:microbiology; D016133:Polymerase Chain Reaction; D012703:Serotyping; D013290:Streptococcal Infections / Q000382:microbiology / Q000401:mortality / Q000662:veterinary*; D017011:Streptococcus suis / Q000145:classification* / Q000302:isolation & purification / Q000472:pathogenicity*; D013552:Swine; D013553:Swine Diseases; D014611:Vaccination / Q000662:veterinary; D014774:Virulence; D014886:Weaning