Objective—To characterize the genetic diversity of
Haemophilus parasuis field isolates with regard to
serovar, herd of origin, and site of isolation.
Sample population—Isolates of H parasuis obtained
from pigs in 15 North American herds and multi-farm
Procedure—98 H parasuis isolates were genotyped
with the enterobacterial repetitive intergeneic consensus
based-polymerase chain reaction (ERIC-PCR) technique
and serotyped via agar gel precipitation test.
Genomic fingerprints were analyzed and dendrograms
were constructed to identify strains from the same
serovar group, herd of origin, or isolation site and to
evaluate the genetic variability within these categories.
Results—Serovar 4 (39%) and nontypeable (NT) isolates
(27%) were most prevalent. Thirty-four distinct
strains were identified among the 98 isolates, using a
90% similarity cutoff. Strains from serovar 4 and NT
isolates had high genetic diversity (12 and 18 strains,
respectively). One to 3 major clusters of prevalent
strains could be identified in most of the evaluated
herds. Haemophilus parasuis strains isolated from the
upper respiratory tract were either serovar 3 or NT
isolates. Potentially virulent strains (isolated from systemic
sites) were either serovars 1, 2, 4, 5, 12, 13, or
14, or NT isolates.
Conclusions and Clinical Relevance—Although H
parasuis had high genetic diversity overall, only a few
strains caused disease in these herds. The ERIC-PCR
technique was more discriminative than serotyping,
and a broad genetic variety was observed within particular
serovar groups. (Am J Vet Res 2003;