Ivermectin (IVM) resistance of Cooperia spp. in cattle has
become an increasing and global problem. The early detection of
anthelmintic resistance (AR) is important to propose strategies to slow
down the development of resistance and requires sensitive, reliable,
economic high-throughput and practical tests. The purpose of the present
study was to apply a larval migration inhibition test (LMIT) for
evaluating IVM and MOX efficacy against well-characterized field
isolates of Cooperia spp. infecting cattle in Brazil. Eight
isolates were used for IVM and seven for MOX. The following EC50 values
of IVM were observed for the isolates: Susceptible, 1.16 ηmol; Nova
Alvorada do Sul I, 4.09 ηmol (RF= 3.52); Campo Grande BNA, 3.57 ηmol
(RF= 3.07); Campo Grande TBR, 4.09 ηmol (RF= 3,52); Nova Alvorada do Sul
II, 2.50 ηmol (RF= 2.15); Bandeirantes, 11.35 ηmol (RF= 9.78); Campo
Grande II, 6.03 ηmol (RF= 5.20); and Porto Mortinho, 8,63 ηmol (RF=
7.44). For MOX, the following EC50 values were observed: Susceptible,
0.75 ηmol; Campo Grande BNA, 0.93 ηmol (RF= 1.24); Campo Grande TBR,
0.36 ηmol (RF= 0.48); Nova Alvorada do Sul II, 2.57 ηmol (RF= 3.42);
Bandeirantes, 1.43 ηmol (RF= 1.90); Campo Grande II, 1.08 ηmol (RF=
1.44); and Porto Mortinho, 0.49 ηmol (RF= 0.65). The LMIT used in the
present study can be a useful tool for in vitro evaluation of IVM, but not of MOX. However, such methodology cannot be used in large-scale studies yet. The isolates of Cooperia spp. showed various degrees of resistance to IVM, though remaining susceptible to MOX
Veja a versão online do Articles in Press http://dx.doi.org/10.1016/j.vetpar.2012.08.012
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