Summary
Pigs (9 [± 1] weeks old) were inoculated with Streptococcus suis type 2, pseudorabies virus (prv), or both. For each pig of groups A, B, and C the inoculum of S suis was 109 colony-forming units. For each pig of groups A, B, and D the inoculum of prv was 5 × 103 tcid50 of either prv strain 4892 (group A, n = 9) or prv isolate B (group B, n = 9). The prv strain 4892 is a highly virulent strain; isolate B causes mild clinical signs of infection in inoculated pigs. Group-C pigs (n = 9) were given S suis alone, and group-D pigs (n = 3) were inoculated only with prv isolate B. Clinical signs of infection and development of lesions were readily seen in pigs of groups A, B, and C. Duration and severity of clinical signs of disease and lesions were reduced m pigs of group C, compared with those of the other 2 groups. Lesions, such as polyarthritis and fibrinous pericarditis, were more abundant and acute in the groups of pigs given mixed challenge exposure, compared with pigs inoculated exclusively with S suis type 2 (group C). The group of pigs inoculated with prv isolate В alone did not manifest clinical signs of disease or lesions. Average daily gain for group-C pigs was higher, compared with that of other groups; the difference was statistically significant at P < 0.02 and P < 0.05 for groups B and D, respectively. Spread of S suis within the tissues of infected pigs was higher in pigs of groups A and B, compared with pigs of group C. Total number of isolations was 8, 15, and 7 for groups A, B, and C, respectively; S suis was isolated from more than 1 tissue specimen from some pigs. The rate of pigs carrying S suis was 4 of 4 in group-A, 7 of 9 in group-B, and 5 of 9 in group-C pigs. It was concluded that clinical disease associated with S suis type 2 was enhanced by concomitant infection with prv and such effect was common to both prv strains tested, the highly virulent strain and the strain with low virulence.
