Trichostrongylus colubrifortnis and Ostertagia circumcincta resistant to levamisole, morantel tartrate and thiabendazole:occurrence of field strains

Anthelmintic resistance: The state of play revisited

“…One of the important limitations of FECRT is that test results may not estimate anthelmintic efficacy accurately because nematode egg output does not always correlate well with actual worm numbers, and the test only measures effects on egg production by mature worms. A good correlation has been found between faecal egg counts and worm counts for H. contortus, but not for T. colubriformis (Sangster et al, 1979) or T. circumcincta (Martin et al, 1985). Egg counts for Nematodirus spp.…”

“…Egg counts are logarithmically transformed to stabilize variances and expressed as geometric means for the groups (Sangster et al, 1979;Martin et al, 1982). Dash et al (1988) argued that the arithmetic mean may be more appropriate in FECRTs because the geometric mean underestimates total egg output and transformation of data may vary between laboratories, thus, making comparisons difficult.…”

Multiple anthelmintic resistance in a field strain ofHaemonchus Contortus in goats

“…Ovine strains of Ostertagia and Trichostron~lus showing multiple resistance to anthelmintics were first reported in Australia (Sangster et al, 1979). In a recent report from South Africa, Haemonchus contortus has been reported to have developed resistance to a number of anthelmintics, including ivermectin (Van Wyk and Malan, 1988).…”

Benzimidazole resistance in cyathostomin populations on horse farms in western Anatolia, Turkey

“…This imidazothiazole compound has a similar mode of action as pyrantel (Martin 1997), and it is known from Oesophagostomum spp. in pigs (Bjørn et al 1990) and trichostrongyle species in small ruminants (Sangster et al 1979) that resistance to levamisole can also result in resistance to pyrantel or its related compound morantel. Thus a side-resistance to pyrantel might have been selected by levamisole on farm D. However, unequivocal evidence of resistance is missing because pyrantel is known per se to have a slightly lower efficacy against cyathostomins than BZ or macrocyclic lactones (Kaplan 2002).…”