D E Jacobs

Royal Veterinary College, Londinium, England, United Kingdom

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Publications (82)152.19 Total impact

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    ABSTRACT: Although on-animal topical treatment with compounds such as imidacloprid has revolutionized the control of the cat flea, Ctenocephalides felis (Bouché) (Siphonaptera: Pulicidae), the development of insecticide resistance is a continuing threat. As part of a highly co-ordinated and unprecedented resistance monitoring programme for C. felis, 1437 flea isolates were collected by veterinary clinics in Australia, Germany, France, the U.K. and 29 states in the U.S.A. from 2002 to 2009. About 65% of the collections were made from June to October each year and 71% of the collections were from cats. Collections of flea eggs were sent to one of five different laboratories, where they were tested with a diagnostic dose of imidacloprid (3 p.p.m.) applied to larval flea-rearing medium. Of the 1437 collections received, 1064 contained adequate numbers of eggs for testing. Of these isolates, untreated eggs failed to hatch in 22.7% and were not considered valid bioassays. Survival rates >5% and development of adult fleas (a threshold for further testing) occurred in only 22 isolates. They were re-tested with the same diagnostic dose and none produced >5% adult emergence. Complete dose-response bioassays were performed on three of the isolates that had triggered a second test and produced slopes, intercepts and LC(50) values similar to those for existing susceptible laboratory strains. Results confirmed sustained susceptibility of C. felis to imidacloprid, despite its widespread use for over a decade.
    Medical and Veterinary Entomology 03/2011; 25(1):1-6. · 2.33 Impact Factor
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    ABSTRACT: ABSTRACTA controlled study was carried out in two replicated trials, each using three groups of domestic cats artificially infested with Ctenocephalides felis. In each trial three cats were treated with fenthion, three were treated with a dichlorvos/fenitrothion formulation, both at the recommended dose rate and the remainder acted as untreated controls. Good knockdown efficacy was evident 24 hours after both treatments. Efficacy values of 85 per cent or more were maintained for at least 15 days with fenthion and for less than eight days with dichlorvos/fenitrothion.
    Journal of Small Animal Practice 06/2008; 34(9):434 - 435. · 0.91 Impact Factor
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    ABSTRACT: Trials were conducted to evaluate the anthelmintic effect of a combination of epsiprantel at a dose rate of 5-5 mg/kg bodyweight and pyrantel pamoate at 5 mg pyrantel base/kg against Toxocara canis in prenatally infected unweaned greyhound pups, Toxascaris leonina, Uncinaria stenocephala, Trichuris vulpis and Dipylidium caninum in naturally infected adolescent greyhounds and Ancylostoma caninum, U stenocephala. Taenia hydatigena and Taenia pisiformis in artificially infected laboratory beagles. The product was well accepted and produced no obvious side effects. Percentage efficacy values based on post mortem worm counts were: T hydatigena 100; T pisiformis 100; D caninum 100; adult T canis 84-0; adult T leonina 96-5; immature T leonina 99-8; U stenocephala 99-0 and 87-7; A caninum 92-7; and T vulpis 43-3.
    Journal of Small Animal Practice 06/2008; 31(2):59 - 63. · 0.91 Impact Factor
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    ABSTRACT: In a series of three replicated and controlled trials, nine dogs artificially infected with Ctenocephalides felis were treated with a systemically active ‘spot-on’ formulation of fenthion, six with a topical spray containing dichlorvos and fenitrothion and six with a surface active ‘spot-on’ preparation containing permethrin, all at recommended dose rates. Good knockdown efficacy was apparent at eight hours with the dichlorvos/fenitrothion combination and at 24 hours with the other formulations. Efficacy values in excess of 95 per cent persisted for at least 22 days in the case of the systemic fenthion preparation and the permethrin product and eight days for the dichlorvos and fenitrothion combination. Twenty-nine days after treatment there was still substantial protection in the fenthion- and permethrin-treated animals, indicated by an 88 and a 77 per cent reduction in flea counts in the two groups, respectively.
    Journal of Small Animal Practice 04/2008; 35(5):244 - 246. · 0.91 Impact Factor
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    ABSTRACT: A flea larval bioassay was developed by an international team of scientists to monitor the susceptibility of fleas (Ctenocephalides felis) to imidacloprid (Advantage, Bayer HealthCare). The assay was validated using laboratory and field isolates of C. felis. Flea eggs representing different field isolates of C. felis were collected by veterinarians in the United States, United Kingdom, and Germany. Of the 972 flea isolates obtained during the 5-year study, 768 contained sufficient numbers of eggs to conduct the larval bioassay. Greater than 5% survival occurred for only six of the field isolates evaluated. Further evaluation and analysis of these isolates demonstrated that they did not differ significantly in their susceptibility to imidacloprid from the reference strains used to develop the assay. Collections of field flea isolates will continue in an attempt to detect and document any change in the susceptibility of field flea populations to imidacloprid.
    Veterinary therapeutics: research in applied veterinary medicine 02/2006; 7(2):86-98. · 1.69 Impact Factor
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    ABSTRACT: The susceptibility of four laboratory strains of cat fleas, Ctenocephalides felis (Bouche), to imidacloprid was determined by three different laboratories, by using a standardized bioassay protocol. The probit lines generated by the different laboratories were very similar, with LC50 values ranging from 0.32 to 0.81 ppm. Based on these data, a diagnostic dose (DD) of 3 ppm imidacloprid in larval rearing media was provisionally identified for detecting shifts in tolerance, possibly as a consequence of incipient imidacloprid resistance. None of the larvae from the susceptible laboratory strains survived the DD. Eighteen field-collected isolates were evaluated for their susceptibility to imidacloprid and to validate a DD of 3 ppm. Probit lines from 18 field-collected isolates were very similar, with LC50 values ranging from 0.14 to 1.52 ppm. When exposed to the DD, between 3 and 10% of the exposed larvae emerged as adults from only three of the 18 isolates. All other field isolates gave 100% mortality at the DD. Under the criteria established (>5% survivorship at 3 ppm), two isolates would be established on mammalian hosts and more extensive tests conducted to exclude or confirm the presence of resistance. The DD of 3 ppm is robust enough to eliminate most of the susceptible isolates collected until today, yet low enough to identify possible isolates for further testing.
    Journal of Medical Entomology 08/2005; 42(4):631-6. · 1.82 Impact Factor
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    ABSTRACT: The "Imidacloprid Flea Susceptibility Monitoring Team" has aim to develop and validate a bioassay to effectively monitor and document susceptibility of cat flea (Ctenocephalides felis) isolates to imidacloprid. A larval bioassay was developed, standardized and validated and agreed upon by the team as the reference diagnostic test kit as research has shown that the proposed WHO adult test was not reliable. The selected 3 ppm discriminating dose, determined from evaluating year 2000 field isolates, was approximately 2 times the highest LC95 of the control laboratory flea strains. In 2001 and 2002, this standardized bioassay was used to test more than 190 separate egg collections from individual flea isolates from USA, UK and Germany. If survivorship in the 3 ppm assay is confirmed, the LD50 values of this isolate and the laboratory strains will be determined by a dose-response study in the range of 0.005 to 3 ppm imidacloprid. By comparison of these LD50 values it can be estimated whether a shift in susceptibility to imidacloprid has occurred. In either case the flea isolate will be researched extensively. Currently an in-vivo test which will evaluate the on-host efficacy of Advantage is being established. None of the to date tested isolates revealed reduced susceptibility to imidacloprid.
    Parasitology Research 08/2003; 90 Suppl 3:S127-8. · 2.33 Impact Factor
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    ABSTRACT: Strategies for controlling cat fleas, Ctenocephalidesfelisfelis (Bouché), have undergone dramatic changes in the past 5 yr. With the advent of on-animal treatments with residual activity the potential for the development of insecticide resistance increases. A larval bioassay was developed to determine the baseline susceptibility of field-collected strains of cat fleas to imidacloprid. All four laboratory strains tested showed a similar level of susceptibility to imidacloprid. Advantages of this bioassay are that smaller numbers of fleas are required because flea eggs are collected for the test. Insect growth regulators and other novel insecticides can also be evaluated. Using a discriminating dose, the detection of reduced susceptibility in field strains can be determined with as few as 40 eggs.
    Journal of Medical Entomology 08/2002; 39(4):671-4. · 1.82 Impact Factor
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    ABSTRACT: To investigate the persistence of flea larvicidal activity in the immediate environment of cats treated with imidacloprid, eggs of the cat flea Ctenocephalides felis felis Bouché (Siphonaptera: Pulicidae), from untreated donor cats, were incubated on samples of fleece blanket taken from the floor of cages used by treated or untreated cats for a total of 10 or 20 6-h periods over 2-4 weeks, respectively. Sufficient imidacloprid accumulated during these periods to reduce the emergence of adult fleas by 94.7-97.6% when the blankets were tested after 18 weeks' storage at room temperature. A typical laundry procedure (washing with detergent at 50 degrees C and low temperature tumble drying) removed this biological activity. Unwashed control blankets did not support the flea life-cycle as effectively as washed blankets or a sand substrate.
    Medical and Veterinary Entomology 10/2001; 15(3):342-5. · 2.33 Impact Factor
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    ABSTRACT: Species-specific identification of ascaridoid nematodes at any developmental stage is a prerequisite for detailed investigation of the life cycles, systematics and epidemiology of this important group, and is also crucial for the diagnosis of associated infections. The morphological identification of some species and/or their larval stages can, however, present considerable difficulty. Recently, PCR-based methods, using genetic markers in the internal transcribed spacers (ITS) of ribosomal DNA, have been shown to provide reliable alternatives to more traditional methods for the specific identification of nematodes. This article provides an account of recent research on the development of PCR-based methods (utilizing ITS sequences) for the specific identification of ascaridoid nematodes of zoonotic potential, for the diagnosis of infections, and for the analysis of genetic variation within and among individual nematodes and their populations. Prospects for using these diagnostic and analytical tools to investigate epidemiological and population genetic questions relating to ascaridoid parasites are also discussed.
    Journal of Helminthology 07/2001; 75(2):101-8. · 1.30 Impact Factor
  • Lynda M. Gibbons, Dennis E. Jacobs, Rehana A. Sani
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    ABSTRACT: Toxocara malaysiensis n. sp. from the small intestine of the domestic cat (Felis catus L.) in Malaysia is described and illustrated. This ascaridoid nematode was previously assumed to be Toxocara canis, which it superficially resembles, or designated Toxocara sp. cf. canis. The new species differs from T. canis in the shape of the cervical alae in cross section, spicule length, and the lip structure. It is also distinct from other species assigned to Toxocara.
    Journal of Parasitology 07/2001; 87(3):660-5. · 1.26 Impact Factor
  • The Veterinary record 07/2001; 148(22):695-6. · 1.63 Impact Factor
  • M J Hutchinson, D E Jacobs, N Mencke
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    ABSTRACT: As the ferret, Mustela putorius furo L. (Carnivora: Mustelidae), is becoming increasingly popular as a pet animal and as it is susceptible to the cat-flea, Ctenocephalides felis felis Bouché (Siphonaptera: Pulicidae), an experimental model was established for evaluating insecticidal treatments on this host. A high establishment rate (76.7-91.8%) was recorded when 60 unfed adult C. felis were placed on ferrets. This provided an adequate infestation for chemotherapeutic evaluation without causing undue discomfort to the host. Twelve ferrets were allocated to two groups matched for sex and individual ability to sustain a flea population. One group was treated topically with an imidacloprid spot-on formulation at a dose rate of 10 mg/kg body-weight on Day 0. All ferrets were infested with C. felis on Days -1, 7, 14, 21 and 28, and flea counts were performed 8 and 24 h post-treatment and one day after each subsequent infestation. Fleas were removed at all but the 8 h count (when they were returned to their host). Flea burdens were reduced by 95.3% (P < 0.001) within 8 h of treatment and 100% efficacy was recorded at 24 h. At 1, 2, 3 and 4 weeks post-treatment, protection against re-infestation was 92.9% (P < 0.001), 55.7% (P < 0.02), 18.3% (NS) and 7.4% (NS), respectively. Thus, at this dose rate, imidacloprid gave excellent efficacy against a resident C. felis population and provided a high level of residual activity for at least one week after treatment.
    Medical and Veterinary Entomology 06/2001; 15(2):212-4. · 2.33 Impact Factor
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    D E Jacobs, M J Hutchinson, W G Ryan
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    ABSTRACT: Control strategies were evaluated over a 6-month period in a home simulation model comprising a series of similar carpeted pens, housing matched groups of six cats, in which the life-cycle of the flea Ctenocephalides felis felis Bouche (Siphonaptera: Pulicidae) had been established. Additional adult fleas were placed on the cats at intervals to mimic acquisition of extraneous fleas from outside the home. Treatment strategies included a single subcutaneous deposition of injectable lufenuron supported by initial treatments with a short-acting insecticidal spray, or monthly topical applications of imidacloprid or fipronil. An untreated control group indicated that conditions were suitable for flea replication and development. Controls had to be combed on 18 occasions to remove excessive flea burdens and two developed allergic reactions. Lufenuron cats were combed once and required two insecticidal treatments in the first month to achieve control. Even so, small flea burdens were constantly present thereafter. Imidacloprid and fipronil treatments appeared to give virtually complete control throughout. Single fleas were found on imidacloprid cats on two occasions, whereas none were recovered from fipronil cats at any time after the first treatment. Tracer cats were used to monitor re-infestation rates at the end of the trial period. Small numbers of host-seeking fleas were demonstrated in all treatment pens, indicating that total eradication had not been accomplished. It is concluded that the home environment simulation model incorporating tracer animals could provide a powerful tool for studying flea population dynamics under controlled conditions but improved techniques are needed for quantifying other off-host life-cycle stages.
    Medical and Veterinary Entomology 04/2001; 15(1):73-7. · 2.33 Impact Factor
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    ABSTRACT: The nuclear ribosomal DNA (rDNA) region spanning the first (ITS-1) and second (ITS-2) internal transcribed spacers was sequenced for 15 taxa of ascaridoid nematodes. The length of the ITS-1 and ITS-2 sequences in the 15 taxa ranged from 392-500 bp and 240 348 bp, respectively. While nucleotide variation of 0-2.9% in the ITS-1 and/or ITS-2 sequences was detected within taxa where multiple samples were sequenced, significantly higher level of nucleotide difference (9.4-66.6%) was detected between the taxa, except for Ascaris suum and A. lumbricoides whose taxonomic status remains uncertain. These interspecific differences were linked with the considerable size differences (0-108 bp) in the rDNA spacers. Phenograms based on the genetic differences among the 15 taxa showed some concordance with previous classification schemes derived from morphological data.
    Parasitology Research 10/2000; 86(9):738-44. · 2.33 Impact Factor
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    ABSTRACT: The hypothesis that dermally applied imidacloprid may transfer from treated cats, Felis catus L., to their immediate environment in quantities sufficient to have a significant effect on developing immature cat fleas, Ctenocephalides felis (Bouché), was tested in a controlled experiment. Flea eggs harvested from untreated donor cats were incubated on replicated samples from blankets used by treated or untreated cats under standardized conditions. As compared with controls, the percentage of adult flea emergence on blankets used by treated animals was reduced by 100% in the 1st wk after treatment and by 84, 60, and 74% in subsequent weeks (P < 0.001).
    Journal of Medical Entomology 04/2000; 37(2):228-30. · 1.82 Impact Factor
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    ABSTRACT: The sequences of the nuclear ribosomal DNA region spanning the first internal transcribed spacer, the 5.8S rRNA gene and the second internal transcribed spacer were determined for Ascaris samples from pigs and humans from different geographical regions. The sequences of the 5.8S gene and the second internal transcribed spacer were the same for all samples examined, whereas all Ascaris samples from humans had six (1.3%) nucleotide differences in the first internal transcribed spacer compared with those from pigs. These differences provided some support for the existence of separate species of Ascaris or population variation within this genus. Using a nucleotide difference within a site for the restriction enzyme HaeIII, a PCR-linked restriction fragment length polymorphism method was established which allowed the delineation of the Ascaris samples from pigs and humans used herein. Exploiting the sequence differences in the first internal transcribed spacer, a PCR-based single-strand conformation polymorphism method was established for future analysis of the genetic structure of pig and human Ascaris populations in sympatric and allopatric zones.
    International Journal for Parasitology 04/1999; 29(3):469-78. · 3.40 Impact Factor
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    ABSTRACT: The sequences of the nuclear ribosomal DNA region spanning the first internaltranscribed spacer, the 5.8S rRNA gene and the second internal transcribed spacer weredetermined for Ascaris samples from pigs and humans from different geographicalregions. The sequences of the 5.8S gene and the second internal transcribed spacer were the samefor all samples examined, whereas all Ascaris samples from humans had six (1.3%)nucleotide differences in the first internal transcribed spacer compared with those from pigs.These differences provided some support for the existence of separate species of Ascarisor population variation within this genus. Using a nucleotide difference within a site for therestriction enzyme HaeIII, a PCR-linked restriction fragment length polymorphismmethod was established which allowed the delineation of the Ascaris samples from pigsand humans used herein. Exploiting the sequence differences in the first internal transcribedspacer, a PCR-based single-strand conformation polymorphism method was established for futureanalysis of the genetic structure of pig and human Ascaris populations in sympatric andallopatric zones. © 1999 Australian Society for Parasitology. Published by Elsevier Science Ltd.All rights reserved.Ascaris; Internal transcribed spacer; Ribosomal DNA; Polymerasechain reaction; Restriction fragment length polymorphism; Single-strand conformationpolymorphism
    International Journal for Parasitology 03/1999; 29(3):469-478. · 3.40 Impact Factor
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    ABSTRACT: The sequences of the nuclear ribosomal DNA region spanning the first internaltranscribed spacer, the 5.8S rRNA gene and the second internal transcribed spacer weredetermined for Ascaris samples from pigs and humans from different geographicalregions. The sequences of the 5.8S gene and the second internal transcribed spacer were the samefor all samples examined, whereas all Ascaris samples from humans had six (1.3%)nucleotide differences in the first internal transcribed spacer compared with those from pigs.These differences provided some support for the existence of separate species of Ascarisor population variation within this genus. Using a nucleotide difference within a site for therestriction enzyme HaeIII, a PCR-linked restriction fragment length polymorphismmethod was established which allowed the delineation of the Ascaris samples from pigsand humans used herein. Exploiting the sequence differences in the first internal transcribedspacer, a PCR-based single-strand conformation polymorphism method was established for futureanalysis of the genetic structure of pig and human Ascaris populations in sympatric andallopatric zones. © 1999 Australian Society for Parasitology. Published by Elsevier Science Ltd.All rights reserved.Ascaris; Internal transcribed spacer; Ribosomal DNA; Polymerasechain reaction; Restriction fragment length polymorphism; Single-strand conformationpolymorphism
    International Journal for Parasitology 03/1999; · 3.40 Impact Factor
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    ABSTRACT: The ascaridoid nematode of cats from Kuala Lumpur, Malaysia, previously identified morphologically as Toxocara canis, was characterized using a molecular approach. The nuclear ribosomal DNA (rDNA) region spanning the first internal transcribed spacer (ITS-1), the 5.8S gene and the second internal transcribed spacer (ITS-2) was amplified and sequenced. The sequences for the parasite from Malaysian cats were compared with those for T. canis and T. cati. The sequence data showed that this taxon was genetically more similar to T. cati than to T. canis in the ITS-1, 5.8S and ITS-2. Differences in the ITS-1 and ITS-2 sequences between the taxa (9.4-26.1%) were markedly higher than variation between samples within T. canis and T. cati (0-2.9%). The sequence data demonstrate that the parasite from Malaysian cats is neither T. canis nor T. cati and indicate that it is a distinct species. Based on these data, PCR-linked restriction fragment length polymorphism (RFLP) and single-strand conformation polymorphism (SSCP) methods were employed for the unequivocal differentiation of the Toxocara variant from T. canis and T. cati. These methods should provide valuable tools for studying the life-cycle, transmission pattern(s) and zoonotic potential of this parasite.
    Parasitology 09/1998; 117 ( Pt 2):155-64. · 2.35 Impact Factor