Effects of a Preventive and Suppressive Control Scheme on the Development of Thiabendazole‐resistance in Ostertagia SPP

Abstract

Three years after the start of an experiment to assess the merits of thiabendazole (TBZ) treatment of trichostrongylid parasites in weaner sheep, field isolates of Ostertagia spp and Trichostrongylus spp were made from weaner sheep treated under one of three treatment schemes. Treatment frequencies were "nil", "planned" (5 or 6/year) and "regular" (every 3 weeks). In addition an isolate was taken from a group of "tracer" sheep drenched with TBZ every 10 days. Resistance to TBZ was assessed using an in vitro egg hatch assay, pre- and post-treatment faecal egg counts and a controlled anthelmintic efficiency test. Pre- and post-treatment egg counts revealed the presence of TBZ-resistance in field isolates of mixed species. Egg hatch assays indicated a level of resistance for Ostertagia spp which was proportional to the frequency of TBZ treatment. The "planned", "regular" and "tracer" strains of Ostertagia spp had resistance ratios for eggs of 4, 13 and 15 respectively when compared to the "nil" strain. In the anthelmintic efficiency assay treatment with 44 mg kg-1 and 88 mg kg-1 of TBZ removed 82 and 96% respectively of the total Ostertagia burden (adults and larvae) from the "nil" strain and 30 and 75% respectively from the "planned" strain. The same dose rates against the "regular" and "tracer" strains and additional rates of 132 or 176 mg kg-1 against the "tracer" strain failed to reduce the Ostertagia burden significantly. Intestinal Trichostrongylus spp from all isolates were fully susceptible to TBZ at 44 mg kg-1. Levamisole at 7.0 mg kg-1 was highly effective (99% reduction) against the "tracer" strain of Ostertagia.

Survey on anthelmintic resistance to gastrointestinal nematodes in unorganized goat farms of Tamil Nadu

“…The level and type of AR in the gastrointestinal parasites in different farms appeared to be associated with the type and frequency of anthelmintic used and the management practices followed in the farms. The role of management practices and frequent use of anthelmintics in the development of resistance has been well studied (Martin et al 1982;Prichard 1994). Hence, there is an urgent need to educate the farmers about the problems of development of AR and the ways to control it.…”

Anthelmintic resistance: The state of play revisited

“…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.…”

Sheep and goat nematode resistance to anthelmintics: pro and cons among breeding management factors

“…This statement is supported by surveys realised on a regional scale, in New Zealand [59,83]; in Malaysia [33]; in South Africa [95]; in the United Kingdom [53,75]; in Australia [36,72]. The "same" repeated anthelmintic treatment is a major cause, in experimental and oversimplified conditions (three-month-old lambs, synchronous infestation with only one to three gastro-intestinal nematode species...) of positive correlation between intensity of resistance and treatment frequency [5,66,71]. A few authors have questioned the nature of the correlation observed between the number of treatments and resistance development [59,87].…”