A standardised BCR resistance test for all anticoagulant rodenticides

Abstract

This paper presents a reappraisal of the blood clotting response (BCR) tests for anticoagulant rodenticides, and proposes a standardised methodology for identifying and quantifying physiological resistance in populations of rodent species. The standardisation is based on the International Normalised Ratio, which is standardised against a WHO international reference preparation of thromboplastin, and allows comparison of data obtained using different thromboplastin reagents. The methodology is statistically sound, being based on the 50% response, and has been validated against the Norway rat (Rattus norvegicus) and the house mouse (Mus domesticus). Susceptibility baseline data are presented for warfarin, diphacinone, chlorophacinone and coumatetralyl against the Norway rat, and for bromadiolone, difenacoum, difethialone, flocoumafen and brodifacoum against the Norway rat and the house mouse. A 'test dose' of twice the ED 50 can be used for initial identification of resistance, and will provide a similar level of information to previously published methods. Higher multiples of the ED 50 can be used to assess the resistance factor, and to predict the likely impact on field control.

Blood clotting response test for detecting resistance to second generation anticoagulant bromadiolone in house rat (Rattus rattus)

“…In this rat species, PCA of 17% corresponded approximately with an INR of 5 using Diagen rabbit brain thromboplastin reagent (Prescott et al, 2007). In present studies, PCA of 22.3% corresponded with PT and INR of 70.3 sec and 3.8, respectively in male rats and PCA of 27.6% corresponded with PT and INR of 63.6 sec and 3.5, respectively in female rats.…”

“…From the standard curve for PCA vs PT obtained in present studies, the calibration of PT will be poor at still lower plasma concentrations and PCA values (Fig 3,4). Prescott and Buckle (2000) and Prescott et al (2007) also found calibration curve replication to be poor when determined particularly at low dilutions.…”

“…OEEP/EPPO (1995) guidelines propose lethal feeding period test and blood clotting response (BCR) test to detect resistance. Though laboratory feeding tests with anticoagulant bait are the final proof of resistance, but procedures are slow, unhumane and labour intensive (Prescott et al, 2007). The BCR tests have several advantages over feeding tests (Gill et al, 1994).…”

“…These two rodent species typically have resting clotting times that are equivalent to an INR of 1.3, while Bandicota bengalensis have resting clotting times that are equivalent to INR between 2.4 and 3.3 (Hussain, 1998). The BCR test based on the use of the INR and baselines provided by Prescott et al (2007) are suitable for determining the incidence and, in particular, for assessing the level of resistance in populations of wild Norway rats (Endepols et al, 2012).…”

“…They are more quickly performed, are considered to be more humane and are independent of the feeding behaviour of animals. They offer a useful primary tool for routine use for detecting physiological resistance against anticoagulants (Prescott et al, 2007).…”