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ners in sample collection and management of equine
premises was a critical component of the overall
outbreak response.Lessons learned from recent VS outbreaks include
the following:
fi Planning and preparedness for large-scale
VSV outbreaks needs to occur at all levels from
the individual horse owner, the practitioner,
the event manager, the laboratories, extension
agents, to state and federal animal health
ofcials.
fi Education and outreach materials containing
the most accurate information and updated
response protocols is needed for horse owners
and private practitioners.
fi Specic planning and response protocols are
needed for equine shows and events.
fi Responsiveness to calls and timely quarantine
releases are key to owner compliance with mit-
igation strategies.
fi The equine industry needs timely and regular
updates on the VS outbreak situation and the
currently affected areas to facilitate equine
movement.
fi Interstate and international movement re-
quirements during a VS outbreak are highly
variable and can be confusing to follow. Con-
tinued standardization and negotiation of
movement requirements based on known sci-
entic principles of the disease is needed.
fi Private practitioners are our most valuable re-
source in the future management of VS.
6. Equine Piroplasmosis and Equine Infectious
Anemia
Although the natural transmission of the causative
agents of equine piroplasmosis (EP) and equine in-
fectious anemia (EIA) in the United States are not
even remotely related, the ongoing problem with
iatrogenic transmission of these two diseases ties
them closely together. Before examining the ongo-
ing iatrogenic transmission issue of both diseases,
there was a single large-scale outbreak of EP due to
natural tick-borne transmission in the United
States, which warrants discussion and eventually
led to the ndings of the iatrogenic transmission
problem in a specic population of horses. In October 2009, Theileria (Babesia) equi
infection
was conrmed in a herd of Quarter Horses that were
used as working cow horses on a large ranch in
south Texas. Of the 360 horses present on the
ranch at the time, 292 horses were ultimately con-
rmed to be infected with T. equi
on the premises.
Nearly 2500 horses were tested for EP as part of the
traceback and epidemiological investigation with a
total of 413 T. equi-positive horses eventually dis-
closed in direct connection with the outbreak.
6
Active natural transmission of T. equi
to horses on
the index ranch was conrmed to have been occur-
ring via Amblyomma cajennense
andDermacentor variabilis
ticks, with
Amblyomma cajennense iden-
tied as the primary tick species involved. Epide-
miological investigation and testing of the horses
sold from the premises indicated that T. equi
infec-
tion had likely been present in horses on the ranch
since prior to 1990 and that frequent movement of
horses in the 1980s and prior between the ranch in
south Texas and premises in South America that
were owned by the ranch was the likely source of the
outbreak. Although traces were located and tested EP-posi-
tive in 16 different United States states, there was
no tick-borne transmission of T. equi
from the EP-
positive traces to other horses in any location out-
side of south Texas. Given that Amblyomma
cajennense ticks are not known to have become es-
tablished outside of south Texas and were deter-
mined to be the primary vector involved on the index
ranch, it seems likely that this may be the reason for
the absence of natural transmission in other loca-
tions even in cases where EP-positive horses had
been maintained in pastures with no reported tick
control for up to 20 years since having left the index
ranch. It was determined from this outbreak that
specic high-risk factors were needed on a premises
for infected horses to efciently transmit T. equi
to
other horses via the tick-borne route in a pasture
situation. These factors included the presence of
multiple T. equi-
infected horses, heavy infestation
by competent tick species, possibly the maintenance
of competent vectors year round, and long periods of
time in these high-risk conditions. In initial response to disclosure of the T. equi-
infected herd in Texas, many states implemented
movement-testing requirements for horses originat-
ing in Texas. In addition, given previous isolated
ndings of T. equiinfection with spread by iatro-
genic transmission in Quarter Horse racehorses
with ties to unsanctioned racing in Florida in 2008
7
and Missouri/Kansas in 2009, 8New Mexico began
requiring EP testing of Quarter Horse racehorses
entering racetracks. New Mexico began nding a
small number of T. equi-infected horses in this pop-
ulation right away and racetracks in other states
subsequently began requiring EP testing to enter
sanctioned racetracks. Since November 2009, more than 292,000 domes-
tic U.S. horses have been tested for EP through this
active surveillance and movement testing. To date,
262 EP-positive horses (252 Theileria equi-positive,
10 Babesia caballi
-positive) have been identied
through this surveillance. These positive horses
are unrelated to the 2009 Texas ranch outbreak.
Of the 262 positive horses identied through active
surveillance, 213 were Quarter Horse racehorses, 13
were Thoroughbred racehorses, one was a Quarter
Horse roping horse, three were identied during an
illegal importation investigation, and 32 were
horses previously imported to the United States be-
fore August 2005 under the complement xation
test.
9 The epidemiology investigations conducted
AAEP PROCEEDINGS fiVol. 62fi2016 345
IN-DEPTH: INFECTIOUS DISEASE OUTBREAK MANAGEMENT

Link
https://pubs.aaep.org/0A4370h/62ndAnnCon2016/html/index.html?page=369