Objective—To determine whether streptococcal
pneumonia is caused by strains of Streptococcus
zooepidemicus similar to those obtained from the
tonsils of healthy horses.
Sample Population—5 tonsils from healthy horses,
8 tracheal washes and 6 lung specimens from
foals with pneumonia, and 5 nasopharyngeal swab
specimens from donkeys with acute bronchopneumonia.
Procedure—Variable M-like protectively immunogenic
SzP proteins of 5 isolates of S zooepidemicus from
each tonsil and clinical specimen were compared,
using immunoblots. The SzP gene of 13 isolates representative
of various SzP immunoblot phenotypes
from 1 healthy horse and 9 horses and donkeys with
pneumonia were sequenced and compared. Cell-associated
hyaluronic acid concentration and resistance to
phagocytosis of some isolates were measured.
Results—Tonsils of each healthy horse were colonized
by several SzP phenotypes similar to those of
foals or donkeys with pneumonia. In contrast, multiple
isolates from animals with pneumonia had the
same SzP phenotype, indicating infection by a single
strain or clone. Analysis of the SzP sequence confirmed
that differences in immunoblot phenotype
were associated with sequence differences and that
several SzP genotypes were in healthy horses and
animals with pneumonia. Isolates with high concentrations
of cell-associated hyaluronic acid were more
resistant to phagocytosis.
Conclusions and Clinical Relevance—An SzP-specific
immunoblot is a useful, sensitive measure of
diversity among strains of S zooepidemicus. Single
strains with SzP phenotypes similar to those found in
tonsils of healthy horses cause pneumonia. Because
of the diversity of SzP phenotype and genotype
among isolates from animals with pneumonia, SzP
phenotype is not an important determinant of invasiveness
or epizootic capabilities. (Am J Vet Res 2000;61:162–166)
Objective—To determine whether repetitive
sequence-based polymerase chain reaction (rep-PCR)
could be used to differentiate Streptococcus equi isolates,
to examine S equi isolates from throughout the
world, and to determine whether a horse had > 1 subtype
of S equi during an outbreak of disease.
Sample Population—An initial group of 32
S equi isolates, 63 S equi isolates from various geographic
areas, and 17 S equi isolates obtained during
outbreaks of disease.
Procedure—An aliquot of S equi genomic DNA was
amplified, using enterobacterial repetitive intergenic
consensus primers. Gel electrophoresis was performed
on 1.5% agarose gels, and a computed-assisted
program was used to compare rep-PCR results.
Results—Use of these primers to analyze 100 ng of
S equi genomic DNA resulted in patterns of 6 to 14
bands. The 32 initial isolates were separated into 7 rep-
PCR subtypes. There were 30 rep-PCR subtypes found
among 29 S equi isolates obtained from Minnesota,
Michigan, Canada, and Australia and 34 S equi isolates
obtained from Kentucky and other sources.
Furthermore, the same clone was identified in several
horses during an outbreak of disease. Infected horses
on the same farm all had a single clone of S equi.
Conclusion and Clinical Relevance—Analysis of
these results suggests that rep-PCR is useful for
delineating S equi into rep-PCR subtypes. Results
revealed that isolates with the same geographic
source or similar date of collection did not always
have the same rep-PCR subtype. A single clone of
S equi usually predominated during an outbreak of
disease. (Am J Vet Res 2000;61:699–705)
Objective—To develop polymerase chain reaction-restriction
fragment length polymorphism (PCR-RFLP)
analysis for molecular typing of strains of
Streptococcus zooepidemicus and to use the new
typing method to analyze a collection of isolates from
the respiratory tract of Thoroughbreds.
Sample Population—10 strains of S zooepidemicus,
65 isolates from the respiratory tract of 9 yearlings
following long distance transportation, and 89 isolates
from tracheal aspirates of 20 foals with pneumonia.
Procedure—Phenotypic variations in the SzP protein
were detected by western immunoblot analysis.
Using PCR-RFLP analysis, genotypes were obtained
with primer sets from the SzP gene, followed by
restriction endonuclease digestion of the amplicons.
Results—Unique genotypic patterns were obtained
with a primer set designed from both ends of the
structural gene and the restriction endonuclease Dde
I. Forty-five isolates from the lymphoid tissue within
the pharyngeal recess (ie, pharyngeal tonsil) of yearlings
included 10 SzP genotypes and SzP phenotypes.
Isolates from the trachea of each yearling were of a
single genotype that was also present among isolates
from the pharyngeal tonsil of the same horses.
Isolates from tracheal aspirates of foals belonged to
Conclusion and Clinical Relevance—Analysis of the
SzP gene by use of PCR-RFLP was effective for molecular
typing of strains of S zooepidemicus in the study of
respiratory tract disease in horses. Results of PCR-RFLP
analysis indicate that a single strain of S zooepidemicus
can migrate from the pharyngeal tonsil to the trachea at
a high rate in horses undergoing long distance transportation.
(Am J Vet Res 2002;63:1298–1301)
Objective—To determine concentrations of IgA and
IgG subclasses in serum, colostrum, milk, and nasal
wash samples of adult horses and foals.
Animals—Seven 2-year-old Welsh ponies, 27 adult
mixed-breed horses, and 5 Quarter Horse mares and
Procedure—Serum was obtained from ponies and
adult horses. Colostrum and milk were obtained from
mares and serum and nasal wash samples from their
foals immediately after parturition and on days 1, 7,
14, 28, 42, and 63. Nasal wash samples were also
obtained from 23 adult horses. Concentrations of
immunoglobulins were determined by use of inhibition
ELISA. To determine transfer of maternal isotypes
to foals, concentrations in colostrum and milk were
compared with those in foal serum. Serum half-lives
of isotypes in foals were also determined.
Results—IgGb was the most abundant isotype in
serum and colostrum from adult horses, whereas IgA
was the predominant isotype in milk. The major isotype
in nasal secretions of adult horses and foals ≥ 28
days old was IgA, but IgGa and IgGb were the major
isotypes in nasal secretions of foals ≤ 14 days old.
Serum half lives of IgGa, IgGb, IgG(T), and IgA in foals
were 17.6, 32, 21, and 3.4 days, respectively.
Conclusions and Clinical Relevance—The early
immunoglobulin repertoire of neonatal foals comprised
IgGa, IgG(T), and IgA; endogenous synthesis of
IgGb could not be detected until 63 days after birth.
The restricted repertoire of immunoglobulins in foals
may influence humoral immune responses to vaccination.
(Am J Vet Res 2000;61:1099–1105)
Objective—To develop a method for typing
Streptococcus equi on the basis of the DNA
sequence of the genes that produce an M-like protein
and to compare isolates among the United States,
Japan, and other countries.
Sample Population—S equi strains CF32, Hidaka/95/2,
and NCTC9682 as well as 82 other isolates from the
United States, Japan, and other countries obtained during
1975 to 2001.
Procedure—DNA sequences of the structural genes
( SeM and SzPSe) that produce M-like proteins were
determined for 3 representative strains to find a variable
region. Variability in this region of SeM was then
determined for the other isolates. Amino acid
sequences were deduced and analyzed phylogenetically
by use of the neighbor-joining method.
Results—Sequence diversity was detected in the
N-terminal region of SeM but not in SzPSe of the 3
representative strains. Base substitutions in the
variable region of SeM varied in a nonsynonymous
manner, resulting in variation in the amino acid
sequence. Eighty-five isolates were categorized as
32 types of SeM on the basis of differences in the
deduced amino acid sequences.
Conclusions and Clinical Relevance—This study
documented a region in the N-terminal portion of
SeM that varies in a nonsynonymous manner. This
information should be useful in molecular epidemiologic
studies of S equi. (Am J Vet Res 2005;