Relationship between resistance factors and treatment efficacy when bromadiolone was used against anticoagulant-resistant Norway rats (Rattus norvegicusBerk.) in Wales

Abstract

We investigated the relationship between the severity and incidence of resistance among Norway rats (Rattus norvegicus) on a farm in Wales and the subsequent outcome of a practical rodent control operation. Bromadiolone resistance factors were estimated for rats trapped on the farm using the blood clotting response test, and were found to be 2 to 3 for male rats and approximately 6 for females. The incidence of resistance in the rat population was high. Infestation size was estimated by census baiting and tracking, and was found to be substantial, with a maximum of 6.5 kg of bait being eaten on a single night. A proprietary rodenticide (Deadline TM ), containing 0.005% bromadiolone, was used to control the infestation. The duration of baiting was 35 days and, according to the two methods of assessment used, treatment success was in the region of 87 and 93%. No evidence was observed of a significant impact of resistance on the rat control operation, and the remaining rats of this very heavy infestation would probably have been controlled if baiting had continued for longer.

Susceptibility to the anticoagulants bromadiolone and coumatetralyl in wild Norway rats (Rattus norvegicus) from the UK and Germany

“…To overcome the latter in human haematology, all thromboplastin reagents are calibrated against a WHO standard reference material (Denson 1998). BCRtests for anticoagulant rodenticides were recently adapted to accommodate such standardisation, not available when earlier BCR-tests were developed; and baselines for most anticoagulants were reassessed (RRAC 2003;Prescott et al 2007). Investigations presented in this paper are the first proof of this new method and derived baselines to compare strains of wild Norway rat, and to investigate the degree of resistance in wild populations.…”

“…Surprisingly, only on one out of five farms in the resistance area of Wales could a considerable incidence and degree of resistance be confirmed. More details about the study on that farm are reported elsewhere (Buckle et al 2007). The low level of resistance on four out of five farms allows us to conclude that the situation has apparently not worsened in Wales, even though anticoagulants have been used there for decades after first resistance was reported.…”

“…The incidence of rats not responding to multiples of the CD strain ED 50 for bromadiolone was very low on four out of five farms in Wales (Table III). Details of the testing conducted at the single farm (site 1) where a higher incidence was determined are reported elsewhere (Buckle et al 2007). …”

“…The INR thus provides a common scale of measurement for all methods. The International Normalised Ratio has been adopted in the RRAC standardised BCR test protocol (RRAC 2003;Prescott et al 2007), to standardise between the commercially available test kits for measuring clotting time. All BCR-tests were conducted according to this test protocol.…”

“…As a result of this work a new BCR test protocol, which relies on a WHO standard was developed in conjunction with baselines for most anticoagulants (RRAC 2003;Prescott et al 2007). We employed this test protocol to compare the susceptibility to the anticoagulants coumatetralyl and bromadiolone of strains of wild Norway rat and the Hampshire resistant strain, and in rats trapped on farms in Wales, UK and Westphalia, Germany.…”