Pathogenesis of Porcine Reproductive and Respiratory Syndrome Virus-induced Increase in Susceptibility to Streptococcus suis Infection

Abstract

Abstract. Eighty 3-week-old crossbred pigs were randomly assigned to six groups (13-14 pigs/group). Group 1 pigs served as uninoculated controls, group 2 pigs were inoculated intranasally (IN) with Streptococcus suis serotype 2, group 3 pigs were inoculated IN with a modified live porcine reproductive and respiratory syndrome virus (PRRSV) vaccine, group 4 pigs were inoculated IN with the same vaccine and with S. suis, group 5 pigs were inoculated IN with VR-2385 (a high-virulence strain of PRRSV), and group 6 pigs were inoculated IN with VR-2385 and S. suis. Pigs exposed to both PRRSV and S. suis were inoculated with PRRSV 7 days prior to S. suis inoculation. The pigs were 26 days old when inoculated with S. suis. Respiratory disease was significantly more severe in groups 5 and 6. Mortality rate was the highest in group 6 (87.5%). This rate was significantly higher than that observed in all other groups except group 4 (37.5%). The mortality rate in group 2, inoculated with S. suis alone, was 14.3%. No pigs from groups 1, 3, or 5 died prior to the scheduled necropsies at 10 and 28 days postinoculation with PRRSV (DPI). To study the effect of PRRSV and/or S. suis on pulmonary clearance by pulmonary intravascular macrophages, six pigs from each group were intravenously infused with 3% copper phthalocyanine tetrasulfonic acid in saline prior to necropsy at 10 DPI. Mean copper levels in the lungs of pigs in groups 2, 5, and 6 were significantly lower than those in control pigs. The mean percentage of lung tissue grossly affected by pneumonia at 10 DPI was 0%, 1%, 0%, 3%, 64%, and 62% for groups 1-6, respectively. Both gross and microscopic interstitial pneumonia lesions were significantly more severe in the VR2385-inoculated groups (5 and 6). PRRSV was isolated from bronchoalveolar lavage fluid collected at necropsy from 100% of the pigs in groups 5 and 6, 71.4% of pigs in group 4, 38.5% of pigs in group 3, and none of the pigs in groups 1 or 2. Streptococcus suis serotype 2 was cultured from the internal tissues of 7.7%, 28.6%, and 78.6% of the pigs in groups 2, 4, and 6, respectively. Streptococcus suis serotype 2 was isolated from whole blood at necropsy from 7.7%, 35.7%, and 78.6% of pigs in groups 2, 4, and 6, respectively. Significantly more pigs in group 6 had S. suis isolated from whole blood and internal tissues. In summary, both high-virulence PRRSV and S. suis decreased copper clearance, and the incidence of isolation of S. suis and PRRSV was higher in dually inoculated pigs. PRRSV-induced suppression of pulmonary intravascular macrophage function may in part explain PRRSV-associated increased susceptibility to S. suis infection.

Application of a pathogen microarray for the analysis of viruses and bacteria in clinical diagnostic samples from pigs

“…Nursery pigs inoculated with PRRSV followed by S. suis develop moderate to severe respiratory disease, mild to severe lameness with associated joint effusion, and have increased mortality. 7,26 The remaining bacteria are considered normal flora or opportunistic; present on surfaces in the upper respiratory tract, oral cavity, epidermis, or present in feces. 19 The last sample evaluated in this study was tonsil, a tissue that is sampled by scraping, swabbing, or removal at the time of postmortem examination.…”

“…Within this group, S. suis is an important swine pathogen and a disease cofactor frequently associated with PRRSV and PCV-2 infections. 7,26 The other bacterial pathogens identified were Enterococcus sp. (4/6 samples), Psychrobacter sp.…”

Functional Definition and Global Regulation of Zur, a Zinc Uptake Regulator in a Streptococcus suis Serotype 2 Strain Causing Streptococcal Toxic Shock Syndrome

“…Streptococcus suis infections are one of the primary and secondary bacterial diseases causing serious economic losses in pig industries worldwide each year (58,64). These pathogens are generally categorized into 35 serotypes on the basis of the difference in their capsular antigens, of which serotype 2 is a prevalent serotype most frequently isolated from diseased piglets and human patients (58).…”

Intracellular Concentrations of Fosfomycin in Alveolar Macrophages from Weaning Piglets

“…They are a common cause of morbidity and mortality. Therefore, they are considered one of the most significant problems in modern intensive swine production systems (Gardner and Hird, 1990;Galina et al, 1994;Done and Paton, 1995;Christensen et al, 1999;Thanawongnuwech et al, 2000;Carr, 2001;Cloutier et al, 2003;Dosen et al, 2007). The intracellular and interstitial fluids are the pulmonary biophase of facultative microorganisms such as Mycoplasma hyopneumoniae, Bordetella bronchisceptica, Salmonella cholerasuis, Pasteurella multocida and Streptococcus spp.…”