(Stoneham and Coles 2006 ; Traill 2008 ). In dogs, no reports of anthlemintic
resistance were published until very recently; indeed, two isolates ofA. caninum
resistant to pyrantel have now been identified in Australia (Kopp et al. 2009 ).
In addition, evidence of lack of efficacy has been reported for heartworm preventa-
tives in the USA (McCall 2005 ); thus far, however, such treatment failures are
largely imputed to owner non-compliance.
Despite the palpable need for new classes of antihelmintics to counter the
mounting threat of resistance, the flow of novel molecules reaching the livestock
endoparasiticide market has been disappointingly slow. The recent discovery,
development and launch of a new anthelmintic class for use in sheep, the amino-
acetonitrile derivatives (AADs), have been the only innovation seen since the MLs
were introduced more than 25 years ago (Kaminsky et al. 2008 ). Control strategies
that preserve the efficacy of existing classes of anthelmintics are therefore crucial to
the mitigation of anthelmintic resistance. However, despite the development of a
variety of measures to reduce selection for resistance, the problem continues to
impact on small ruminant production worldwide. A new paradigm under discussion
calls into question the whole-flock approach to anthelmintic treatment. The concept
is based on leaving a proportion of animals untreated to ensure that the worm
population in refugia (residing in untreated infected animals and on pasture)
provides a sufficient susceptible gene pool. This unexposed nematode population
is then available to dilute, and to mate with, any worms that survive treatment (van
Wyk et al. 2006 ). A European initiative (PARAsite SOLutions, also known as
PARASOL) has been established for a sustainable control of nematodes in live-
stock. This project proposes Targeted Selective Treatment (TST) as a strategy to
slow the rate of development of anthelmintic resistance by retaining a susceptible
worm population in refugia: with TST, only clinically affected animals are treated.
Table 3Reported occurrence of anthelmintic resistance in gastro-intestinal nematodes of sheep
and cattle in EU
Countries Species Class References
United
Kingdom
Denmark
Sweden
Netherlands
Germany
France
Italy
Spain
Slovakia
Belgium
Ireland
Greece
Sheep
Cattle
Sheep
Sheep
Cattle
Sheep
Sheep
Cattle
Sheep
Sheep
Sheep
Sheep
Sheep
Cattle
Sheep
SheepBZ, LV, ML
ML
BZ, LV, ML
BZ
ML
BZ, ML
BZ, LV, ML
ML
BZ
LV, ML
BZ, LV, ML
BZ, ML
BZ
ML
BZ, LV
BZBartley et al. ( 2003 ); Sargison et al. ( 2001 , 2005 , 2007 )
Coles et al. ( 1998 ,2001)
Bjørn et al. ( 1991 ); Maingi et al. ( 1997 )
Ho ̈glund et al. ( 2009 )
Demeler et al. ( 2009 )
Borgsteede et al. ( 2007 )
Duwel et al. ( 1987 ); Bauer et al. ( 1988 )
Kleinschmidt et al. ( 2008 ); Demeler et al. ( 2009 )
Palcy et al. ( 2010 )
Traversa et al. (2007a)
Alvarez-Sa ́nchez et al. ( 2006 ); Dı ́ez-Ban ̃os et al. ( 2008 )
Cˇernˇanska ́et al. ( 2006 )
Vercruysse et al. ( 1989 )
Demeler et al. ( 2009 )
O’Brien et al. ( 1994 ); Patten et al. ( 2007 )
Papadopoulos et al. ( 2001 )
BZ: Benzimidazoles; LV: Levamisole; ML: Macrocyclic Lactones
Population Medicine and Control of Epidemics 123