New Pathological Lesions Developed in Pigs by a “Non-virulent” Strain of Glaesserella parasuis

Abstract

Glaesserella parasuis is a Gram-negative bacterium that causes Glässer's disease, a common pathology found in young pigs characterized by polyarthritis, polyserositis, and meningitis. The bacterium has 15 known serovars that have been classified by virulence. Serovars 1, 4, 5, and 12 are considered highly virulent and used in most studies. Serovars 3, 6, 7, 9, and 11 are considered avirulent. Recent reports that serovar 7 is an emerging problem in the pig industry indicate that the association of virulence and serovar may not always be reliable. This led us to infect colostrum-deprived piglets with the reference serovar 7 strain (SV7 strain 174) that had been passaged through pigs and characterize the clinical and pathological signs. We observed that SV7 strain 174 caused clinical signs consistent with Glässer's disease in all infected piglets that succumbed to infection for up to day 5 post-infection. Macroscopic and microscopic lesions were consistent with those found in piglets infected with conventional virulent serovars. In addition, we describe novel microscopic lesions associated with Glässer's disease such as endophthalmitis and thymic depletion. Thus, our findings indicate that SV7 strain 174 causes classical signs of Glässer's disease in colostrum-deprived piglets and some caution should be used in employing vaccine strategies based on association between capsular serovar and virulence.

Molecular characterization of Glaesserella parasuis strains isolated from North America, Europe and Asia by serotyping PCR and LS-PCR

“…An important finding in this present study and other recent studies [28][29][30] was that serovar 7 is a significant disease-associated serovar of G. parasuis. In this study, serovar 7 was assigned to 10.9% of all internal samples (ranked 4 th most prevalent serovar) and 15.6% of all systemic isolates (ranked second most prevalent serovar).…”

“…The serovars of utmost clinical significance were identified in samples from internal sites (serovars 4, 5/12, 1, 7, and 13) in this study. These serovars have been previously considered disease-associated [12,13,[22][23][24][25][26][27][28][29][30]. Variable sample sizes limited our ability to discern significant differences in serovar prevalence at the country level.…”

Proof of Concept for Prevention of Natural Colonization by Oral Needle-Free Administration of a Microparticle Vaccine

“…Since our goal was to evaluate the vaccine formulation's ability to prevent natural infection by G. parasuis, we sought to implement an infection model that more closely mimics the natural infection process. Over the last decade we have performed G. parasuis challenge experiments in pigs using the intratracheal route since it delivers a consistent challenge dose to the lungs (6,7,11) and strategically overcomes the direct attack of the humoral and cellular components of the innate immune system present on the upper respiratory tract. To provide a more natural route of infection for vaccine evaluation we developed an intranasal infection model to mimic acquisition of G. parasuis by natural transmission.…”

“…Glaesserella parasuis is a common inhabitant of the porcine upper respiratory tract, its only ecological niche, but may disseminate to distant systemic sites by entering into the bloodstream and produce a severe inflammatory disease in young piglets, known as Glässer's disease (6,7). Glässer's disease can be prevented by the use of whole cell inactivated vaccines (bacterins) administered by the intramuscular route, which induces protective immunity through systemic IgGs capable of detecting and killing G. parasuis by classical complement system activation or opsonophagocytosis (8).…”

“…(E) A second challenge experiment to reproduce the results illustrated in the graphic 2a. Two doses of G. parasuis 174 strain [2×106 (n=5) and 4×10 7 (n=5)] were evaluated in conventional pigs. (F, G) Represent the rectal temperatures of each group infected with the two doses described above.…”