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<br>[1]. Davey RB, Pound JM, Klavons JA, Lohmeyer KH, Freeman JM, Olafson PU. Analysis of doramectin in the serum of repeatedly treated pastured cattle used to predict the probability of cattle fever ticks (Acari: Ixodidae) feeding to repletion. Exp Appl Acarol. 2012 Apr;56(4):365-74. doi: 10.1007/s10493-012-9525-1.
Abstract
Analysis of doramectin concentration in blood serum of pastured cattle injected repeatedly (12 treatments) at two different dosage rates and 28-day intervals throughout the year was used to predict the probability that cattle fever ticks could successfully feed to repletion during the interval between any two consecutive treatments. Treatment at ~270 μg/kg indicated that serum doramectin concentration dropped below the baseline concentration estimated for tick survival (8 ppb) in 7 of the 12 treatments. However, the longest period between any two treatments during which the doramectin concentration remained below the 8 ppb baseline level for successful tick feeding was 15 days, making it virtually impossible for any ticks to reach ovipositional status prior to a subsequent treatment. At a dosage rate of ~540 μg/kg, the concentration dropped below the baseline tick survival level (8 ppb) only once, following the initial treatment, and the duration during which the concentration remained below the baseline level prior to the subsequent treatment was only 6 days. Thus, at the high dosage rate results indicated, with absolute certainty, that no ticks could successfully feed to repletion between any two consecutive treatments. Based on the data obtained in the study it was concluded that analysis of doramectin concentration in serum of treated animals would be a reliable predictor for assessing the probability that ticks could successfully develop to repletion. More importantly, results demonstrated that the trial policy, instituted by the Cattle Fever Tick Eradication Program, of repeatedly treating cattle with doramectin injections at 25-28 day intervals for eliminating cattle fever ticks would produce little or no risk of any viable ticks developing to repletion and re-infesting the field between treatment applications.
<br>[2]. Wang XJ, Zhang J, Wang JD, Huang SX, Chen YH, Liu CX, Xiang WS. Four new doramectin congeners with acaricidal and insecticidal activity from Streptomyces avermitilis NEAU1069. Chem Biodivers. 2011 Nov;8(11):2117-25. doi: 10.1002/cbdv.201000295.
Abstract
Four new doramectin congeners, 1-4, were isolated from Streptomyces avermitilis NEAU1069. The structures of 1-4 were elucidated on the basis of spectroscopic analysis, including 1D- and 2D-NMR as well as HR-ESI-MS, ESI-MS, UV, and IR, and comparison with literature data. All compounds exhibited noticeable acaricidal and insecticidal activities. Especially compound 2 was found to be the most potent pesticide of the compounds evaluated with the IC(50) values of 10.2, 65.1 and 124.4 μg/ml against adult two-spotted spider mites (Tetranychus urticae Koch), two-spotted spider mite eggs, and Mythimna separata, respectively, which are comparable to those of commercial pesticide milbemycin A(3)/A(4) as positive reference.
<br>[3]. Sarre C, Claerebout E, Vercruysse J, Levecke B, Geldhof P, Pardon B, Alvinerie M, Sutra JF, Geurden T. Doramectin resistance in Haemonchus contortus on an alpaca farm in Belgium. Vet Parasitol. 2012 Apr 30;185(2-4):346-51.
Abstract
Parasitism by gastrointestinal nematodes is a health concern in New World Camelids (NWC) worldwide, and anthelmintic treatment is often needed for parasite control. Although anthelmintic resistance has been reported in ruminants worldwide, data in NWC are only scarce. In the present study, a case of suspected doramectin resistance in alpacas was examined. A field efficacy study was conducted for the evaluation of two different dosages of doramectin using a faecal egg count reduction test. A group of 8 alpacas was treated with a subcutaneous injection of doramectin at 0.2mg/kg bodyweight. Individual faecal samples were collected before treatment and 7 days after treatment. The faecal egg counts indicated a treatment efficacy of only 68%. To determine whether the treatment failure was caused by true anthelmintic resistance or suboptimal dosage in this animal species, a group of 4 alpacas was subsequently treated at 0.3mg/kg bodyweight. Faecal egg counts 7 days post treatment were reduced by only 41%, indicating that the treatment failure was more likely to be caused by the presence of resistant parasites on this farm. Coprocultures of faecal samples collected after treatment indicated the presence of 98.5% Haemonchus contortus and a small percentage of Cooperia oncophora (<1.5%). A controlled efficacy trial in sheep, for which the optimal dosage of doramectin is known, was conducted to ensure that this truly was a case of resistant parasites. Infective larvae collected from the faeces of these alpacas were used to infect eight nematode-free lambs. These lambs were assigned to one of two groups based on faecal egg counts post infection. One group was treated with doramectin injectable at 0.2mg/kg bodyweight, the other group served as a non treated control group. Pharmacokinetics indicated that the doramectin treatment was adequate, yet an efficacy of only 16% was determined on day 7 after treatment. Identification of the larvae after treatment revealed 100% H. contortus. On day 7 after treatment, H. contortus worm counts were only reduced by 8% in the treated lambs. The results of the present study report for the first time a case of doramectin resistance in alpacas, mainly in H. contortus.
<br>[4]. Lobetti R. .Successful resolution of oesophageal spirocercosis in 20 dogs following daily treatment with oral doramectin. Vet J. 2012 Jul;193(1):277-8.
Abstract
The purpose of this study was to evaluate the effect of a daily oral dose of doramectin in dogs with spirocercosis. Twenty naturally infected dogs were treated with 0.5mg/kg doramectin administered orally once daily for 42days. In 13 of the dogs there was resolution of the nodules after 42days. Nodules were eliminated in five of the remaining seven dogs following treatment for an additional 42days. In the remaining two dogs, treatment continued for a further 42days (total 126days), resulting in complete resolution. No adverse events associated with treatment were observed. This study concluded that doramectin at 0.5mg/kg once a day is effective in the elimination of Spirocerca lupi nodules in dogs.
<br>[5]. Wang JB, Pan HX, Tang GL. Production of doramectin by rational engineering of the avermectin biosynthetic pathway. Bioorg Med Chem Lett. 2011 Jun 1;21(11):3320-3.
Abstract
In an attempt to construct a strain that produces doramectin, the loading module of Ave polyketide synthase (PKS) from Streptomyces avermitilis M1 was replaced with a cyclohexanecarboxylic (CHC) unique loading module from phoslactomycin PKS. Additionally, the CHC-CoA biosynthetic gene cassette was introduced into the engineered strain, which provided the precursor for directed biosynthesis of doramectin. The doramectin production ability of the final mutant S. avermitilis TG2002 was increased about six times and the ratio of Dor to Ave was enhanced 300 times more than the original strain.
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