Arch Virol (2007) 152: 1009–1017
Printed in the Netherlands
Diversity and evolution of a newly emerged North American Type 1
porcine arterivirus: analysis of isolates collected between 1999 and 2004
, P. Schneider
, W. P. Zhang
, K. S. Faaberg
, E. A. Nelson
, and R. R. R. Rowland
Center for Infectious Disease Research and Vaccinology, Department of Veterinary Science,
South Dakota State University, Brookings, SD, U.S.A.
Department of Diagnostic Medicine and Pathobiology, Kansas State University, Manhattan, KS, U.S.A.
Department of Veterinary and Biomedical Sciences, University of Minnesota, Saint Paul, MN, U.S.A.
Received September 27, 2006; accepted January 3, 2007; published online February 26, 2007
# Springer-Verlag 2007
European-like Type 1 porcine reproductive and re-
spiratory syndrome virus (PRRSV) isolates, known
as North American (NA) Type 1 PRRSV, appeared
in United States (U.S.) swine herds in 1999. Their
diversity and evolution were studied over a ﬁve-
year period by constructing phylogenetic trees using
nsp2 and ORF5 sequences of 20 NA Type 1 isolates,
including the only known isolate from Hawaii. All
but two of the isolates possessed the same 51-nt de-
letion in nsp2, suggesting a clonal origin. Parsimony
and distance analysis showed that viruses could be
placed into two distinct sub-clades, which were sim-
ilar for both nsp2 and ORF5. An incongruity be-
tween the two trees identiﬁed one isolate, 04-41, as
the product of recombination. Recombination anal-
ysis using SimPlot identiﬁed a break point located
downstream of the nsp2=3 junction. Results from
this study suggest that NA Type 1 PRRSV in the U.S.
is a well-established and rapidly evolving group.
However, the forces driving genetic diversity and
separation are complex and remain to be elucidated.
Porcine reproductive and respiratory syndrome vi-
rus (PRRSV) is a member of the family Arteriviridae
[for review see 16]. Genetic comparisons of vi-
ruses from Europe and North America show that
PRRSV can be divided into Types 1 and 2 ge-
notypes, which share only about 60% nucleotide
identity [1, 10]. Historically, Types 1 and 2 viruses
have been restricted to the European and North
American continents, respectively. Since 1999,
Type 1 isolates have become widely reported in
North America [2, 3, 12, 14], and we have desig-
nated these viruses as North American (NA) Type 1
PRRSV. Their rapid and widespread appearance in
the U.S. could be the result of recent and frequent
introductions from European countries. Alternatively,
NA Type 1 viruses could be the result of a more tem-
porally distant introduction by a single virus. They
have become successfully established in U.S. swine
production systems, which are currently dominated
Author’s address: Raymond R. R. Rowland, Department
of Diagnostic Medicine and Pathobiology, 1800 Denison
Ave., Kansas State University, Manhattan, KS 66506, U.S.A.