fore the index case was identied, and practitioners
should be alert to clinical signs of EP in their
patients.
8. Research Updates
Emergence of infection and disease caused byB.
equiin U.S. horses has led to enhanced research
efforts in several areas. These areas are diagnostic
test validation, particularly PCR, sequencing and
annotation of parasite genomes, testing of chemo-
therapeutics to determine efcacy in removing
transmission risk from infected horses, testing cer-
tain types of ticks for their capacity to transmit
among equids, and determining the efciency of in
utero (transplacental) transmission.
Diagnostic Testing and Genomic Sequencing Research
One theory for the emergence ofB. equiinfection in
horses in the United States is that the use of the
CFT to screen imported horses from 1970 to 2005
allowed the entry of chronically infected horses.
The cELISA was developed and validated based on a
need to have a sensitive test for detection of infection
in chronic carriers of EP pathogens. The cELISA
became the ofcial test method used by the United
States for importation purposes in 2005. Valida-
tion of the PCR test (nested and real-time) in eld
situations is underway. It is important to note
that, because the CFT detects immunoglobulin M
(IgM) antibody, it remains an important tool for the
detection of acute infection.
Sequencing and annotation of theB. equigenome
has recently been completed, and it should allow for
more accurate taxonomic classication and aid in
determination of strain differences for susceptibility
of the parasite to chemotherapeutic agents.
Treatment
A number of chemotherapeutics have been tested for
removing transmission risk from infected horses.
Much of the research concerning ID has focused on
the treatment of acute parasitemia and clinical dis-
ease. There remains controversy concerning the ef-
cacy of ID in its ability to completely remove (clear)
infection and transmission risk from equids. Part
of the controversy is likely because of the previous
use of the CFT to dene clearance of infection.
Because of the lack of sensitivity of the CFT, nega-
tive test results after ID treatment, in some cases,
may have been caused by failure of this test to detect
persisting infection. Second, it has been suggested
that various doses and treatment regimens with ID
may have led to ID-resistant strains of bothB. equi
andB. caballi. The assessment of ID resistance
among EP pathogens is an important current goal of
chemotherapeutic research. High-dose ID removed
transmission risk from twoB. caballiinfected
horses.
8 However, the strain ofB. caballiused in
this study likely had never been exposed to ID and
represented a single strain. Literature also sug-
gests that there may be strain variability (B. caballiandB. equi) in susceptibility to ID. Whether strain
variability in susceptibility to ID is the result of
inaccurate diagnostics, selection of genetic resis-
tance to ID because of inappropriate treatment pro-
tocols, or parasite genetics is not known. The
recent completion of theB. equigenome may help
clarify these questions. The current urgent need
for research related to treatment includes the fol-
lowing questions. (1) Is ID treatment capable of
broadly removing transmission risk of infected
equids? (2) Are there parasite-strain differences in
ID susceptibility to clearance? (3) What do post-
treatment serum antibody and PCR testing of blood
samples predict concerning transmission risk?
A dose-dependant toxicity has been reported with
the treatment of horses with imidocarb.
6
Tick-Competency Research
A critical aspect of testing ticks for transmission
competency is delineating a given tick’s ability to
transovarially transmit to the next generation of
ticks. An ecologically important difference be-
tweenB. caballiandB. equiis that, to date, onlyB.
caballiis known to be transovarially transmitted.
However, as additional ticks capable of transmitting
B. equiare discovered,
11 it is important to determine
if these ticks transovarially transmitB. equi. Ticks
capable of transovarial transmission represent an
additional parasite reservoir and signicantly com-
plicate control measures.
Research Related to in Utero Transmission ofB. equi
In addition to tick and iatrogenic transmission, a
number of reports indicate thatB. equican be trans-
mitted in utero (transplacentally or by vertical
transmission). However, neither the mechanism
nor efciency of this route of transmission is known.
Current research efforts are directed at dening the
efciency of this route of transmission and testing
for markers in the infected mare, which predict her
risk for in utero transmission ofB. equi.
References and Footnotes
1. Mehlorn H, Schein E. Redescription ofBabesia equiLave-
ran, 1901 asTheileria equiMehlorn, Schein 1998.Parasitol
Res1998;84:467– 475.
2. Allsopp MT, Cavalier-Smith T, DeWaal DT, et al. Phylog-
eny and evolution of the piroplasms.Parasitology1994;108:
147–152.
3. Rothschild CM, Knowles DP. Equine piroplasmosis. In:
Sellon DC, Long MT, eds.Equine infectious diseases. St.
Louis, MO: Saunders Elsevier, 2007;465– 473.
4. USDA:APHIS:VS. APHIS factsheet equine piroplasmosis.
Available online at http://www.aphis.usda.gov/publications/
animal_health/content/printable_version/fs_equine_piro.
pdf. Accessed on May 4, 2010.
5. Gerstenberg C, Allen WR, Phipps LP. Mechanical transmis-
sion ofBabesia equiinfection in a British herd of horses, in
Proceedings. 8th International Conference of Equine Infec-
tious Diseases 1998;217–222.
6. Donnellan CMB, Marais HJ. Equine piroplasmosis. In:
Mair TS, Hutchinson RE, eds.Infectious diseases of the horse.
Equine Veterinary Journal Ltd., Ely, Cambridgeshire 2009;
333–339.
6 2010Vol. 56AAEP PROCEEDINGS
IN-DEPTH: EQUINE PIROPLASMOSIS
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