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Review Article
Equine piroplasmosis: An updated review
Y. Tamzali
Equine Internal Medicine, Université de Toulouse, INP, ENVT, France.
Corresponding author email: y.tamzali@envt.fr
Keywords:horse; piroplasmosis;Theleria equi;Babesia caballi; imidocarb propionate
Summary
Equine piroplasmosis (EP) is a tick-borne protozoal disease. The
causative agents areBabesia caballiandTheileria equi.
Horses infected withT. equiremain carriers for life. Iatrogenic
means can also be factors for transmission. Typical clinical
signs of acute EP can include fever, anorexia, anaemia,
icterus, congested mucous membranes, tachypnoea and
tachycardia, sweating, and limb and supraorbital oedema. In
severe cases, haemoglobinuria and bilirubinuria are present
as well as a variety of atypical presentations due to organ
damage and dysfunction. Because clinical pathology is not
specific of EP, accurate diagnosis requires specific diagnostic
tests. The value and the pertinence of blood smears,
polymerase chain reaction and serological tests are
presented. Imidocarb propionate is considered as the drug of
choice against EP. However, treatment strategies differ greatly
between endemic and nonendemic regions. In endemic
regions the goal is to reduce clinical disease because
premunition plays an important role in the protection of horses,
while in nonendemic regions the goal of treatment is to
eliminate the risk of transmission with sterilising treatment
protocols. As there is no effective vaccine available to date,
prevention relies mainly on drug therapy, restriction in the
movement of infected horses, and control of tick vectors.
Introduction
Equine piroplasmosis (EP) is a tick-borne protozoal disease that
can be transmitted by ticks to equids. Horses, donkeys and
mules are susceptible to infection, although clinical disease
is rare in donkeys, mules and zebras. There are 2 distinctive
EP causative agents,Babesia caballiandTheileria (Babesia)
equi. It has been proposed thatBabesia equibe reclassified
asTheileria equi(Mehlhorn and Schein 1998). Because both
BabesiaandTheileriaare piroplasms the termequine
piroplasmosiswill be used for this review. Typical EP infections
are characterised by acute haemolytic disease of varying
severity. However, many horses become subclinically infected
with low level parasitaemia and inapparent disease. The
peculiarity ofT. equiinfection compared toB. caballiinfection
is that infected horses remain carriers for life, and serve as
reservoirs for transmission to naïve horses (Schein 1988; DeWaal
1992; Rothschild and Knowles 2007; USDA-APHIS 2010a).
The worldwide prevalence of EP is consistent with
worldwide distribution of competent tick vectors. EP is
endemic in tropical, subtropical and some temperate regions
and has been reported to occur in Southern Europe, Middle
East, Asia and almost all of Latin America (OIE 2013). For
example, a survey conducted in 2002 in the south of France
showed that the seroprevalence was 67% forT. equiand 23%
forB. caballiwhich is consistent with most surveys establishing
T. equias the more frequently encountered EP agent (Mealeyet al. 2011). In these endemic regions most horses are exposed
to EP within the first year of life with case fatality rates of 5–10%
in naïve horses depending on the parasite, the transmission
dose, the health of the horse, and the treatment while this
rate can exceed 50% when infected horses are imported into
regions where populations of naïve horses and vectors are
present (Maurer 1962; Rothschild and Knowles 2007). Equine
piroplasmosis is a disease reportable to the World Organization
for Animal Health (WHO) but depends on the willingness of
governmental bodies to report adequately the EP information
to WHO. There are then some obvious discrepancies between
the published literature and the official countries status
(Heuchertet al. 1999; Sevincet al. 2008; Morettiet al. 2010;
Mujicaaet al. 2011; OIE 2013). In continental Europe, where
most neighbouring countries have no geographical barriers
and horse movements are free, there is a trend for EP to move
towards northern countries from endemic to nonendemic
countries as reported in Belgium, Germany, Switzerland (Boch
1985; Mantranet al. 2004; Sigget al. 2010) and more recently
in The Netherlands (Butleret al. 2012).
Transmission
BecauseB. caballiandT. equiare transmitted by many of
the same tick vectors they frequently coinfect equids. Both
parasites can be transmitted by more than 15 species of the
generaDermacentor,HyalommaandRhipicephalus, while
Rhipicephalus (Boophilus) microplus, which is a tick more
specific to cattle can also transmitT. equito horses (Rothschild
and Knowles 2007). The reservoir of parasites differs greatly
between the 2 types of EP agents. ForB. caballi,ticks serve
as a reservoir because the organism persists in the ticks
through several generations, with transstadial and transovarial
transmission. ForT. equihorses are the primary reservoir
becauseT. equiis transmitted transstadially so that the parasite
is not transmitted to further tick generations; in addition horses
are generally carriers for life if not submitted to sterilising
treatments, which are not implemented in endemic regions
(Uetiet al. 2005). Transovarial transmission ofT. equihas been
reported but the role of this transmission route in natural
transmission is still unclear (Ikadaiet al. 2007). Iatrogenic means
can also be factors of EP transmission in case of blood
contaminated needles and syringes reuse (Gerstenberget al.
1999), or blood transfusion from EP carriers’ donors. This route
represents a major cause of transmission when introducing an
inapparent carrier to a nonendemic region with or without
competent tick vectors.
Summary of life cycles
Babesia caballi
Like mostBabesiaspecies, theB. caballilife cycle targets only
erythrocytes. Infected ticks infect the host while feeding and
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590EQUINE VETERINARY EDUCATION
Equine vet. Educ.(2013)25(11) 590-598
doi: 10.1111/eve.12070
© 2013 EVJ Ltd