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mainly on drug therapy, restriction in the movement of
infected horses, and control of tick vectors.
Restricting the movement of infected horses
Currently, the countries that restrict the movement of
serologically positive horses are the USA, Canada, Australia,
Japan, Mexico and Brazil (Rothschild and Knowles 2007).
For example in the USA, a horse that isB. caballipositive is
quarantined and may be allowed to enter after treatment
and subsequently tested negative while a horse that tests
positive forT. equiis denied entrance. If a horse already
resident in the USA is found positive forT. equi,it is quarantined,
exported or subjected to euthanasia. Currently, most of these
T. equipositive horses join the ongoing research projects.
If a resident horse is tested positive forB. caballiit is
simply quarantined, treated and retested for clearance. All
these procedures are monitored by the federal authorities
(USDA-APHIS 2010a,b).
In Europe, the WHO information shows that the
approaches of government agencies vary considerably and
very few countries have border controls except some insular
countries that are in addition naturally protected. As there
are no administrative borders between most of the European
countries the introduction of inapparent carriers from endemic
to nonendemic countries remains difficult to control within
Europe in the absence of strict controls.
Tick-vectors control
The control of infected ticks is a difficult or impossible
undertaking, especially if neighbouring countries are
EP-endemic. Quarantine of horses imported from these regions
(or having travelled in these regions) with administration of
pyrethroids is common sense and may help to minimise the risk
of introducing infected ticks to EP-free regions (USDA-APHIS
2010a).
At major world equestrian competitions, the risk of
spreading EP is prevented by biosecurity measures associating
a strict segregation policy to acaricide treatment for all EP
seropositive horses: natural tick barriers, designated grazing
and exercising areas treated with tick retardant agents,
separate stabling and frequent inspection of horses upon
re-entry into the stables, treatment of all horses with an equine
de-wormer that effectively kills attached ticks prior to entry
but also with an acaricide prior to entry and during stay for
EP-positive horses. In addition, EP-positive horses are shipped
directly from their federally mandated quarantine centre
to special stables within the competition site and are also
required to leave the country directly from these stables.
Conclusion
In Europe, there is a trend for EP to move towards northern
countries from endemic to nonendemic countries. However,
there is a dramatic difference in EP management between
endemic and nonendemic regions. So-called EP-free countries
such as North American countries desire to remain
nonendemic and apply very strict control measures and
sterilising treatments. In endemic countries, premunition
strategies are aimed at reducing clinical signs in case of
overt clinical EP by reducing the level of parasitaemia but
maintaining low-level infection for maintenance of protective
immunity. There is then a need for development of efficient
T. equiclearing methods (both treatment and diagnostic test)and protection. Ongoing research aimed at understanding
immunity may help also the development of future efficient
immunisation strategies.
Author’s declaration of interests
No conflicts of interest have been declared.
Acknowledgements
The author acknowledges Dr Robert H. Mealey, Associate
Professor of Equine Immunology at Washington State University
and Professor Philippe Jacquiet, Professor of Parasitology at
Toulouse Veterinary School, for their help and advices during
the preparation of this review article.
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