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Biomedical subjects

C E Webb

Publications and source records attributed to C E Webb.

18 recordsLinked to original sources
PubMed2005

Mark-release-recapture study to measure dispersal of the mosquito Aedes aegypti in Cairns, Queensland, Australia.

In Queensland, Australia, in response to isolated cases of dengue infection, larval control of the vector Aedes aegypti (L.) (Diptera: Culicidae) is targeted at breeding sites within 200 m of a case and interior spraying with a pyrethroid adulticide is targeted at premises within 100 m. To ascertain whether these limits are appropriate, we conducted a mark-release-recapture study to measure the dispersal of female Ae. aegypti in the city of Cairns where transmission occurs. Female mosquitoes reared from wild collected eggs were differentially marked with fluorescent dust depending on whether they were to be released blood-fed or non-blood-fed, and a total of 1,948 females was released. A total of 132 sticky ovitraps was set at 64 premises within a 200 m radius and collections of trapped adults were made at 5-15 days post-release. Sixty-seven females (3.4%) were recaptured, with the furthest being caught 200 m from the release point, and the mean distance travelled was 78 m. Overall, 23.1% of the recaptures outside the release site were taken beyond 100 m by day 15. Dispersal was comparable for both blood-fed and non-blood-fed releases. There was a significant tendency for dispersal to be in a north-westerly direction, probably because of the presence of numerous containers and heavy shading by trees in this direction and a busy road to the south of the release point that appeared to inhibit dispersal. The results suggest that adulticiding may have to be extended beyond 100 m if more than 8 days have elapsed since female Ae. aegypti could have fed upon a viraemic dengue case. The study also shows that dispersal is not random, and that it may be possible to maximize vector control by taking into account environmental factors that affect the direction of female mosquito flight.

Aedes↗
PubMed1999

Towards management of mosquitoes at Homebush Bay, Sydney, Australia. I. Seasonal activity and relative abundance of adults of Aedes vigilax, Culex sitiens, and other salt-marsh species, 1993-94 through 1997-98.

The mosquitoes associated with 2 saline wetlands at Homebush Bay, Sydney, Australia, were investigated over 5 consecutive seasons. Twenty-one species were collected in adult traps at the 2 sites but the saline wetlands supported larvae of only 4 species: Aedes alternans, Aedes camptorhynchus, Aedes vigilax, and Culex sitiens. Of these, Ae. vigilax and Cx. sitiens were the most common, and their peak abundances generally occurred during February and April, respectively. Both wetlands were influenced by tides and rainfall-runoff, and a lack of regular tidal exchange in the mangroves and inadequate drainage of the saltmarsh provided potential habitat. Populations of Ae. vigilax and Cx. sitiens at the Newington site were greater than those at the Bicentennial Park site, because of more extensive habitat at the former, but were diminished by irregular ground-based applications of temephos during the middle 3 years of the study. Populations at the Bicentennial Park site, not subjected to the larvicide, were typically smaller but more consistently related to influences of tide and rainfall through the 5 seasons. During the final season, populations of both species in both wetlands were enhanced by exceptional tide penetration and rainfall. Helicopter applications of Bacillus thuringiensis israelensis larvicide were employed at both sites and effectively suppressed populations of both pest species. For future management, provision of full tidal exchange and water recirculation to reduce the area of water impounded within the mangroves and retained in depressions on the marshes should significantly suppress the pest populations and relieve reliance on control agents.

Aedes↗
PubMed1995

Impact of alpha-bungarotoxin on transmitter release at the neuromuscular junction of the rat.

The drug, alpha-bungarotoxin (BTX) is believed to be a 'pure' nicotinic antagonist. Hence, use of this drug should avoid the secondary actions associated with other nicotinic antagonists. The hypothesis that the motor nerve terminal responds to the presence of acetylcholine (ACh) by releasing less transmitter was tested by examining the effects of BTX on end-plate potentials (EPPs), miniature end-plate potentials (MEPPs), and quantal release at the rat diaphragm neuromuscular junction. Analysis of EPP and MEPP amplitudes and quantal release demonstrate that BTX significantly increases transmitter release at the onset of tetanic stimulation (50 Hz). Like other nicotinic antagonists, BTX was not able to sustain enhanced quantal release during a brief train of 40 stimuli and resulted in greater decline in EPP amplitude during tetanic stimulation. The data suggests that negative feedback regulation by presynaptic autoreceptors only serves a functional role at the onset of stimulation and that other factors such as transmitter supply or adenosine regulation may serve to dominate transmitter release during maintained tetanic stimulation.

Action Potentials↗
PubMed1983

Variables affecting creatinine clearance prediction.

Patient data were analyzed retrospectively to evaluate the relationship between several body-weight variables and creatinine production and clearance. Data from 722 creatinine clearance determinations in 627 patients older than 12 years were analyzed. Weight variables were actual body weight (ABW), lean body weight (LBW), ideal body weight (IBW), and lean body mass (LBM). Weight-independent and weight-dependent clearance prediction methods were evaluated. Actual creatinine clearance values were compared with these predictions. Use of LBW and IBW produced equivalent estimates of creatinine clearance that were closer to measured values than those obtained with ABW. The use of LBW or IBW was not appropriate in patients less than 60 inches tall nor in morbidly obese patients. Weight-dependent clearance estimation was superior to weight-independent predictions in morbidly obese patients. A new LBM-based clearance estimation formula was derived; it may be useful for patients less than 60 inches tall. The use of LBM, particularly in patients less than 60 inches tall, should be investigated further.

Adult↗
PubMed1982

A multicenter evaluation of variables affecting the predictability of creatinine clearance.

Data from 722 urine collections (627 patients) from 14 medical facilities were used to compare measured creatinine clearance values with clearance estimates calculated using three "urine-free' mathematical formulas. The influence of two patient weight variables (actual weight, lean body weight) and the level of renal function on clearance prediction was assessed. In addition, site parameters (region, facility), time parameters (month, day, day of the week), and patient parameters (age, sex, height, weight, diagnoses) were evaluated for their statistical influence on the relationship between measured clearance and estimates calculated with one of the methods. Strong, statistically significant correlations were observed between clearance values estimated with each prediction method and measured clearances. Although statistical differences were noticed between mean values predicted with each method, these differences were clinically insignificant. Use of lean body weight for calculation of creatinine excretion produced clearance estimates that were significantly lower than those obtained with actual weight and substantially closer to measured clearance values. Among patient variables, age and two specific diagnoses (congestive heart failure and pregnancy), were statistically associated with variability in the relationship between measured and predicted clearance. Interregional and interfacility differences in the measured-predicted clearance relationship, variability associated with the day of the week of collection, and tendency of the urine-free formulas to over-predict clearance support potential inaccuracy of measured clearance determination. The results suggest that inaccuracies in clearance determination, rather than inadequacies of urine-free prediction methods, account for the majority of the observed variability in the relationship.

Age Factors↗
PubMedDate not supplied

Multicenter evaluation of six methods for predicting warfarin maintenance-dose requirements from initial response.

Warfarin maintenance-dose requirements predicted by six mathematical methods based on initial response to therapy were compared with patients' actual dose requirements in a multicenter trial. Data were collected for patients who had received an initial regimen of warfarin sodium 10 mg orally every 24 hours for three days and for whom a prothrombin time (PT) had been determined 16-20 hours after the third dose. Patients' individual dose requirements and PT values were recorded during one to three follow-up visits after discharge from one of seven medical centers. Prothrombin ratios (patient PT divided by control PT) calculated on day 4 were used for maintenance-dose prediction by five methods; a sixth method was based on the cumulative warfarin dose-PT response curve up to a PT value of 20 seconds. For 54 men and 30 women who qualified for the study, 197 maintenance-dose-PT response measurements were recorded; 95 in the first four weeks of therapy, 76 during weeks 5-12, and 26 at 6-12 months after initial treatment. Prothrombin ratios were within the therapeutic range (PT 1.5-2.5 times the control value) in 154 observations, and the mean actual warfarin sodium maintenance dose associated with therapeutic response was 7.6 mg/day. For patients with therapeutic prothrombin ratios, dose predictions by the five methods using prothrombin ratios (PRs) correlated significantly with actual dose requirements. The formula that predicted doses numerically closest to the actual dose is as follows: Dose = 11.17 - 21.08 (log PR). Only 45 observations were obtained for the sixth prediction method, and the correlation between actual and predicted doses was not significant. Initial warfarin maintenance-dose requirements can be predicted effectively based on one PT determination after administration of three daily 10-mg doses.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗