COUNTERMEASURES TO PREVENT THE PORCINE RESPIRATORY DISEASE COMPLEX (PRDC)
Location: Virus and Prion Research Unit
Title: Studies of Pathogenesis, Transmission, and Heterologous Protection of Four Isolates of Haemophilus parasuis in a Highly Susceptible Swine Population
Submitted to: American Association of Swine Veterinarians Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: September 1, 2009
Publication Date: March 6, 2010
Citation: Brockmeier, S., Loving, C.L., Register, K.B., Nicholson, T.L., Bayles, D.O., Phillips, G.J. 2010. Studies of pathogenesis, transmission, and heterologous protection of four isolates of Haemophilus parasuis in a highly susceptible swine population [abstract]. 2010 American Association of Swine Veterinarians Annual Meeting. p. 127-129.
Pigs from an experimental herd that is free from known swine pathogens were used in a study with several Haemophilus parasuis isolates in an effort to identify isolates of varying virulence to sequence in order to determine virulence factors for this pathogen. Each of 4 groups of 5 pigs each varying in age from 36 to 68 days were inoculated with a different isolate of H. parasuis intranasally (SW114, 12939, MN-H, and 29755), with a fifth group of 5 pigs serving as sham inoculated controls. Three of the 4 isolates caused systemic disease, with pigs showing signs of disease (lameness, depression, neurologic signs) from 1 to 5 days post infection. All 5 pigs from the 12939 and 4/5 pigs from the 29755 and MN-H groups had to be euthanized or died peracutely. H. parasuis was isolated from systemic sites (pleura, peritoneum, joint, and/or meninges ) from 12/13 of these pigs. One pig each from the 29755 and the MN-H group and all the SW114 pigs remained healthy with no clinical signs of disease; however, H. parasuis was isolated from nasal swabs from these pigs indicating they were colonized. One control pig each was placed into the room with the lone survivor from the 29755 and the MN-H groups to determine whether transmission would occur. The contact pig placed in with the MN-H pig became ill 5 days later, was euthanized and had lesions of full blown polyserositis. The contact pig placed with the 29755 pig became lame 7 days later, was euthanized and H. parasuis was isolated from the joint. The 2 survivors from the initial 29755 and MN-H challenge remained healthy. The 5 surviving SW114 pigs and the surviving 29755 and MN-H pigs were then rechallenged with the 12939 isolate to determine if they would be protected from a heterologous virulent strain. The 3 surviving control pigs were also challenged with 12939. All three control pigs developed systemic disease similar to the initial challenge, but all pigs previously challenged with SW114, 29755, and MN-H remained healthy. Thus, pigs within susceptible groups can remain healthy and serve as reservoirs for transmission, and heterologous protection using avirulent isolates is possible. Draft genome sequences have now been obtained from 3 of these isolates of H. parasuis. Preliminary comparisons suggest considerable variation in the gene complement of distinct strains. Bioinformatics approaches are being used to discover genes that are conserved among strains as well as those that are unique. These results will provide a basis for testing the role of potential virulence genes in swine infection studies and may also allow development of detection assays that discriminate between strains of high and low virulence.