Experimental airborne transmission of Streptococcus suis capsular type 2 in pigs

Experimental airborne transmission of Streptococcus suis type 2 was studied in specific pathogen free piglets. Forty piglets were allotted to five gro ups of eight 7-week-old animals and housed in three separated units. Negati ve control pigs (group 1) were housed in unit A and infected batches were h oused in units B (group 2) and C (groups 4). In units B and C, non-inoculat ed groups (groups 3 and 5, respectively), 40 cm distant from the respective inoculated group and without any physical contact between them, also took place. Six animals of groups 2 and 4 were inoculated intravenously with 2 x 10(8) colony forming units (cfu) of a mild and a high virulent S. suis str ains, respectively. The remaining animals in these groups and pigs from gro ups 1, 3, 5 received broth medium in the same way. Differences among virule nce of S. suis capsular type 2 were observed in inoculated pigs of groups 2 and 4. Pigs from group 2 became carriers, showing only mild symptoms. By c ontrast, animals from group 4 presented an acute form of the disease. All t he indirect contact pigs in groups 3 and 5 had S. suis in palatine tonsils from day 6 after the infection and they presented clinical manifestations s imilar to those observed in experimentally infected pigs. Two direct contac t animals were also contaminated in the upper respiratory tract but surpris ingly they did not show any symptoms. Airborne transmission of S. suis in e xperimentally pigs was demonstrated in the present study. Indirect infectio ns, as described in this study, are a more realistic way to infect pigs tha n other experimental procedures and may be used to further study the pathog enesis of the infection caused by this important pathogen. (C) 2001 Elsevie r Science B.V. All rights reserved.