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Biomedical subjects

D E Jacobs

Publications and source records attributed to D E Jacobs.

At least 37 records · Page 2Linked to original sources
PubMed1999

Characterisation of Ascaris from human and pig hosts by nuclear ribosomal DNA sequences.

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.

Animals↗
PubMed1998

Evaluation of flea control strategies using fipronil on cats in a controlled simulated home environment.

Three groups of six cats were kept in similar carpeted pens in which a self-replicating population of Ctenocephalides felis had been established. One group was left untreated, but the other groups were treated every 28th day with 0.5 ml of a 10 per cent fipronil spot-on formulation, and the cats in one of the treated groups also wore a methoprene collar. No fleas were found on any of the treated cats, either during the first 13 weeks of the study, when heavy flea burdens were developing in the control pen, or over the next 11 weeks when a declining number of fleas was present on the control group.

Animals↗
PubMed1998

The contribution of lead-contaminated house dust and residential soil to children's blood lead levels. A pooled analysis of 12 epidemiologic studies.

In 1992, the U.S. Congress passed the Residential Lead-Based Paint Hazard Reduction Act, which requires the promulgation of health-based dust lead and soil lead standards for residential dwellings to prevent undue lead exposure in children. Unfortunately, the levels of lead in house dust and soil that are associated with elevated blood lead levels among U.S. children remain poorly defined. This pooled analysis was done to estimate the contributions of lead-contaminated house dust and soil to children's blood lead levels. The results of this pooled analysis, the most comprehensive existing epidemiologic analysis of childhood lead exposure, confirm that lead-contaminated house dust is the major source of lead exposure for children. These analyses further demonstrate that a strong relationship between interior dust lead loading and children's blood lead levels persists at dust lead levels considerably below the U.S. Department of Housing and Urban Development's current postabatement standards and the Environmental Protection Agency's guidance levels. Finally, these analyses demonstrate that a child's age, race, mouthing behaviors, and study-site specific factors influence the predicted blood lead level at a given level of exposure. These data can be used to estimate the potential health impact of alternative health-based lead standards for residential sources of lead exposure.

Child, Preschool↗
PubMed1998

Molecular characterization of a Toxocara variant from cats in Kuala Lumpur, Malaysia.

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.

Animals↗
PubMed1997

PCR-based methods for identification of potentially zoonotic ascaridoid parasites of the dog, fox and cat.

Genomic DNA was extracted from ascaridoid nematodes collected from dogs, foxes and cats. A region spanning the second internal transcribed spacer (ITS-2) of the ribosomal DNA of each sample was amplified by PCR. Representative ITS-2 products for each nematode species (Toxocara canis, Toxocara cati and Toxascaris leonina) were sequenced. Restriction sites were identified for use as genetic markers in a PCR-linked RFLP assay. The three species could be differentiated from each other and from other ascaridoids that may be found in human tissues by use of two endonucleases, HinfI and RsaI. Primers were designed to unique regions of the ITS-2 sequences of the three species for use in diagnostic PCR procedures and primer sets evaluated against panels of homologous and heterologous DNA samples. Results suggest that both methods are good candidates for further development for the detection and/or identification of ascaridoid larvae in human tissues.

Animals↗
PubMed1997

Ostertagia nianqingtanggulaensis Kúng & Li, 1965 (Nematoda: Trichostrongyloidea) from sheep and goats at high altitudes in Nepal.

The trichostrongyloid nematode Ostertagia nianqingtanggulaensis Kúng & Li, 1965, previously recorded only from sheep in Tibet, is redescribed and is shown to be a common parasite of both sheep and goats at higher altitudes in the Himalayan foothills of western Nepal. Herbage examination indicated that infective larvae can overwinter on snow covered slopes. Use of tracer animals confirmed that migratory flocks are exposed to infection when grazing on alpine pastures during the summer months. In contrast, nearby non-migratory flocks kept at lower altitudes did not harbour O. nianqingtanggulaensis and tracer animals grazed with these flocks did not become infected with this species.

Altitude↗
PubMed1997

Comparison of flea control strategies using imidacloprid or lufenuron on cats in a controlled simulated home environment.

OBJECTIVE: To compare the effect of monthly treatments with imidacloprid (an adulticide) or lufenuron (an insect development inhibitor) for protecting cats against Ctenocephalides felis felis in a simulated home environment. ANIMALS: 3 matched groups of 4 cats each. PROCEDURE: A self-propagating flea life cycle continuously exposing cats to 'natural' infestation was established in 3 pens. Small artificial infestations were later superimposed to mimic the effect of a cat roaming outdoors and acquiring extraneous fleas. One pen housed an untreated control group, and the other 2 pens housed cats treated every 28th day with an imidacloprid spot-on formulation or lufenuron suspension, respectively. Flea counts were performed at 14-day intervals for 112 days. RESULTS: Flea numbers increased on control cats around day 42 when mean counts on cats in the imidacloprid and lufenuron groups decreased by 100 and 86.8 percent, respectively. Fleas were not found on any imidacloprid-treated cat, but lufenuron-treated cats were consistently parasitized. CONCLUSIONS: Imidacloprid administered at monthly intervals maintained flea burdens below the limit of detection, whereas clinically important flea populations developed in the lufenuron treatment pen. CLINICAL RELEVANCE: Results from this experimental model suggest that flea populations within a home may be controlled by carefully timed on-host treatments with potent long-acting insecticides such as imidacloprid.

Administration, Cutaneous↗
PubMed1996

A novel approach to flea control on cats, using pyriproxyfen.

Pyriproxyfen is a new insect growth regulator with potent activity against developing stages of the cat flea, Ctenocephalides felis. To determine its duration of action after application as a spot-on topical treatment, 20 cats were allocated to two groups. One group acted as untreated controls, and each cat in the other was given a single dose of 1 mg/kg pyriproxyfen. Each cat was infected with fleas at weekly intervals and caged. Eggs were collected and their viability determined as a measure of the effect of the agent on adult fleas. The effect of the transfer of pyriproxyfen from each cat to its immediate surroundings was monitored by observing the development of fertile flea eggs placed on samples of blanket taken from each cage. Results from untreated control cats showed that the experimental conditions were favourable for the lifecycle of the flea. Flea reproduction on treated cats was inhibited completely for seven weeks and substantially for at least a further two weeks. Blankets used by cats treated up to two weeks previously prevented flea development entirely and substantial control was still achieved up to four weeks after treatment.

Animals↗
PubMed1996

Evaluation of the effect of the fenbendazole sustained-release intraruminal device on the immunity of calves to lungworm.

Each of 10 set-stocked calves was given a fenbendazole sustained-release intraruminal bolus at turnout for the control of parasitic bronchitis while a group of 10 similar calves was left untreated. The respiratory rates of the control calves were not greatly increased during the grazing season, but persistent coughing was evident from early July when they all had patent lungworm infections. Only occasional coughing was reported from the bolus-treated calves except for a transient increase in its frequency in late September. In mid-August, one of the treated calves was passing lungworm larvae and when they were housed six of the 10 had patent infections. In August tracer calves picked up an average of 23.5 lungworms per day from the control paddock but only 2.1 from the paddock grazed by the treated calves. In September the corresponding figures were 7.6 and 19.2 lungworms per day, respectively, from the control and 'treated' paddocks. After housing, the post mortem worm counts after an experimental challenge with Dictyocaulus viviparus larvae were reduced by 99.2 and 98.7 per cent (P < 0.0001), respectively, for the control and bolus-treated calves in comparison with weight-matched parasite-naive calves. Thus, despite a relatively low level of challenge during the grazing season, the treated animals had developed a considerable degree of protective immunity.

Animals↗
PubMed1996

Evaluation of flea control programmes for cats using fenthion and lufenuron.

Four groups of six cats were kept in carpeted pens similarly infected with Ctenocephalides felis. One group was left untreated, but the other groups were treated every 28th day with either an insecticide (fenthion at 30 mg); or an inhibitor of insect development (lufenuron at 133 or 266 mg) or with both. A sudden upsurge in the numbers of fleas occurred on the control cats after 50 days. At this time, the three control strategies had reduced the counts by 91.3, 72.5 and 98.6 per cent, respectively. Thereafter, welfare considerations demanded the limitation of the flea burden on the control cats, but conditions were shown to be favourable for flea development throughout the study. The mean numbers of fleas on the treated groups after six months were 1.2, 11.0 and 0.4 respectively. After this, in addition to the fleas acquired in the pen, the cats were each infected weekly with five fleas to mimic roaming animals introducing extraneous fleas into the home. This produced no obvious effect on the counts and the mean values three months later were 0.5, 11.0 and 0.2, respectively. None of the strategies eradicated the flea population but they all reduced the numbers considerably and worked equally well whether or not small numbers of new fleas were introduced into the system. Significantly lower flea counts were maintained in the early and later stages of the study by the strategies including the insecticide.

Administration, Topical↗
PubMed1996

Strongylus asini (Nematoda, Strongyloidea): genetic relationships with other Strongylus species determined by ribosomal DNA.

Genomic DNA was isolated from adult Strongylus asini collected from zebra. The second ribosomal transcribed spacer (ITS-2) was amplified and sequenced using polymerase chain reaction (PCR) based techniques. The DNA sequence was compared with previously published data for 3 related Strongylus species. A PCR-linked restriction fragment length polymorphism method allowed the 4 species to be differentiated unequivocally. The ITS-2 sequence of S. asini was found to be more similar to those of S. edentatus (87.1%) and S. equinus (95.3%) than to that of S vulgaris (73.9%). This result confirms that S. Asini and S vulgaris represent separate species and supports the retention of the 4 species within 1 genus.

Animals↗
PubMed1996

Effect of sub-lethal doses of albendazole on the fecundity of Dictyocaulus viviparus.

During an evaluation of the efficacy of prolonged low-dose albendazole therapy on nematode infections in calves, it was observed that a dose-rate of 2 mg kg-1 given daily for 10 days was highly effective at expelling Dictyocaulus viviparus, but smaller doses suppressed the faecal output of larvae without killing the lungworms. A more detailed study with four experimentally infected calves given 1 mg kg-1 day-1 for 10 days showed that faecal output of larvae ceased after six to eight days but resumed four to six days after the withdrawal of the drug. The albendazole-induced sterility was therefore reversible. A subsidiary study showed that the strain of parasite used was fully susceptible to albendazole.

Albendazole↗
PubMed1995

Influence of chemoprophylaxis on protective immunity to nematodes in cattle: a two-year study comparing four control strategies.

A two-year study was conducted in three sequential phases. Initially, four matched groups of nine calves grazing similar pastures were subjected to different chemoprophylactic control programmes while a fifth group acted as unprotected controls. After being housed in the autumn, three calves from each group and two parasite-naive controls were challenged experimentally with Ostertagia ostertagi, Cooperia oncophora and Dictyocaulus viviparus. Post mortem worm counts revealed gradations of protective immunity, with the field controls showing the highest level and the naive controls the lowest. In the second grazing season the remaining animals from each group were grazed together with parasitenaive controls on two fields. No further prophylactic treatments were given. One of the naive controls developed severe parasitic bronchitis but the signs in the other groups were milder and transient. It is concluded that the calves protected by chemoprophylaxis in their first grazing season developed marked resistance to gastrointestinal and pulmonary nematodes, but that their level of immunity was influenced by the effectiveness of the prophylactic strategy used.

Animals↗