Objective—To determine the incidence of bovine
papillomavirus (BPV) type 1 or 2 in sarcoids and other
samples of cutaneous tissues collected from horses
in the western United States.
Animals—55 horses with sarcoids and 12 horses
Procedure—Tissue samples (tumor and normal skin
from horses with sarcoids and normal skin, papillomas,
and nonsarcoid cutaneous neoplasms from
horses without sarcoids) were collected. Tissue samples
were analyzed for BPV-1 or -2 DNA, using a polymerase
chain reaction (PCR) and restriction fragment
length polymorphism. The PCR products from 7 sarcoid-
affected horses were sequenced to evaluate percentage
homology with expected sequences for BPV-1 or -2.
Results—Most (94/96, 98%) sarcoids contained BPV
DNA. Sixty-two percent of the tumors examined had
restriction enzyme patterns consistent with BPV-2.
Thirty-one of 49 (63%) samples of normal skin
obtained from horses with sarcoids contained BPV
DNA. All samples subsequently sequenced had
100% homology with the expected sequences for the
specific viral type. All tissues from healthy horses,
nonsarcoid neoplasms, and papillomas were negative
for BPV DNA.
Conclusions and Clinical Relevance—Bovine papillomaviral
DNA was detected in essentially all sarcoids
examined. There appears to be regional variation in
the prevalence of viral types in these tumors. The fact
that we detected viral DNA in normal skin samples
from horses with sarcoids suggests the possibility of
a latent viral phase. Viral latency may be 1 explanation
for the high rate of recurrence following surgical excision
of sarcoids. (Am J Vet Res 2001;62:741–744)
Objective—To determine expression of a transforming
gene (E5) of bovine papillomavirus in sarcoids,
other tumors, and normal skin samples collected
from horses with and without sarcoids.
Sample Population—23 sarcoids and 6 samples of
normal skin obtained from 16 horses with sarcoids, 2
samples of normal skin and 2 papillomas obtained
from horses without sarcoids, and 1 papilloma
obtained from a cow.
Procedure—Protein was extracted from tissue samples
collected from horses and incubated with
agarose beads covalently coupled to Staphylococcus
aureus protein A and an anti-E5 polyclonal antibody.
Following incubation, proteins were eluted from the
beads and electrophoresed on a 14% polyacrylamide
gel and transferred to a polyvinylidene difluoride
membrane. The E5 protein was detected by use of
western blot analysis, using a chemiluminescence
Results—All 23 sarcoids had positive results for
expression of E5 protein. Quantity of viral protein
appeared to vary among sarcoids. All other tissues
examined had negative results for E5 protein. Highest
expression for E5 protein was observed in biologically
aggressive fibroblastic variants of sarcoids, compared
with expression in quiescent tumors.
Conclusions and Clinical Relevance—This study
documented that activation and expression of the E5
gene is evident in sarcoids obtained from horses.
These data support the conclusion that infection with
bovine papillomavirus is important in the initiation or
progression of sarcoids in horses. Treatment strategies
designed to increase immune recognition of
virally infected cells are warranted. (Am J Vet Res