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Biomedical subjects

D M Tompkins

Publications and source records attributed to D M Tompkins.

14 recordsLinked to original sources
PubMed2002

Stochasticity accelerates nematode egg development.

Day-degrees models of nematode development assume that temperature stochasticity has no effect on the development rate of infective stages as long as the mean temperature is held constant. This assumption was tested in this study. Unembryonated Heterakis gallinarum eggs were subjected to nocturnal and diurnal daily temperature cycles at 12 and 17 C. respectively, and embryonation was compared with eggs subjected to similar stochastic daily cycles, in which random normal variations in the temperature were added to the 2 temperatures. The prediction that there is no effect of stochasticity was refuted. Embryonation of eggs subjected to variable daily cycles occurred significantly earlier than that of eggs subjected to deterministic daily cycles, suggesting that stochastic variation in temperature accelerated embryonation even though mean temperatures were the same. These findings show that the development time of H. gallnarum eggs is decreased by stochastic variation in temperature, which may have important implications for the effects of climate change on parasite availability.

Animals↗
PubMed2001

Patterns of parasite aggregation in the wild European rabbit (Oryctolagus cuniculus).

Understanding the factors controlling the distribution of parasites within their host population is fundamental to the wider understanding of parasite epidemiology and ecology. To explore changes in parasite aggregation, Taylor's power law was used to examine the distributions of five gut helminths of the wild rabbit. Aggregation was found to be a dynamic process that varied with year, season, host sex, age class, and myxomatosis. Yearly and seasonal changes are thought, in the main, to be the result of variations in weather conditions acting upon infectious stages (or intermediate hosts). Evidence in support of this was the comparatively low degree of fluctuation in the aggregation of the pinworm, Passalurus ambiguus, as the infectious stage of this parasite is likely to be less susceptible to environmental variation. Host age had a marked effect on the level of aggregation of all parasites, but this effect varied between parasite species. P. ambiguus, Trichostrongylus retortaeformis and Cittotaenia denticulata aggregation were lower in adult than juvenile rabbits whilst Graphidium strigosum and Mosgovoyia pectinata aggregation tended to increase with age. Host immunity is thought to be responsible for these differences. Differences in aggregation for different parasites were also seen when the rabbit population was split into males and females. Myxomatosis had a marked effect on helminth distribution with substantially less aggregation in rabbits showing clinical signs of the disease.

Age Factors↗
PubMed2001

Strategies for nematode transmission: selective migration of Trichostrongylus tenuis infective larvae.

Successful transmission of macroparasites is dependent on exposure of susceptible hosts to free-living infective stages. When these hosts are herbivores that feed mostly on a single food plant then natural selection should favour those infective larvae that selectively ascend this main food plant. Red grouse feed predominantly on heather, Calluna vulgaris, so we predict that the infective larvae (L3) of the caecal nematode Trichostrongylus tenuis selectively locate and ascend heather plants. To determine whether the presence of heather influences the horizontal dispersal of T. tenuis L3 across soil, the movement of L3 across trays of soil with and without heather was investigated in the laboratory. More T. tenuis L3 were recovered from soil when heather was present, implying that larval migration may be influenced by chemical cues produced by heather plants. This was investigated in a second experiment, in which the horizontal dispersal of T. tenuis larvae was examined in the presence of heather and grass vegetation. This trial was repeated with larvae of a second species, Haemonchus contortus, a nematode whose hosts feed on a wide range of grass and shrub species. Significantly more larvae of both nematode species were recovered in the region of the heather than the grass or controls. This implies that T. tenuis and H. contortus L3 exhibit selective migration towards heather, perhaps reflecting a general response to plant cues which may be stronger for heather than for grass.

Animals↗
PubMed2001

Differential impact of a shared nematode parasite on two gamebird hosts: implications for apparent competition.

If the deleterious effects of non-specific parasites are greater on vulnerable host species than on reservoir host species then exclusion of the vulnerable host through apparent competition is more likely. Evidence suggests that such a mechanism occurs in interactions between the ring-necked pheasant (Phasianus colchicus), the grey partridge (Perdix perdix), and their shared caecal nematode Heterakis gallinarum. Modelling of the system predicts that the reduced parasite impact on the pheasant compared to the partridge results in the force of infection transmitted from pheasants to partridges being sufficient to cause partridge exclusion. Since the parasite impacts are currently estimated from correlational work, controlled infections were conducted to experimentally compare the impact of H. gallinarum on the two hosts and verify cause and effect. While challenged partridges showed reduced mass gain, decreased food consumption, and impaired caecal activity, in comparison to controls, the only detectable effect of parasite challenge on the pheasant was impaired caecal activity. The impact of H. gallinarum on challenged partridges conforms with previous correlational data, supporting the prediction that parasite-mediated apparent competition with the ring-necked pheasant may result in grey partridge exclusion. However, the observed decrease in the caecal activity of challenged pheasants could imply that H. gallinarum may also have an impact on the fecundity and survival of pheasants in the wild, particularly if food is limiting. If this is the case, the associated decrease in the force of infection to which the partridge is exposed may be sufficient to change the model prediction from partridge exclusion to pheasant and partridge coexistence.

Animals↗
PubMed2000

The role of oxygen availability in the embryonation of Heterakis gallinarum eggs.

The importance of oxygen availability in the embryonation of the infective egg stages of the gastrointestinal nematode parasite Heterakis gallinarum was studied in the laboratory. Unembryonated H. gallinarum eggs were kept under either aerobic conditions by gassing with oxygen, or anaerobic conditions by gassing with the inert gas nitrogen, under a range of constant temperatures. Oxygenated eggs embryonated at a rate influenced by temperature. Conversely, eggs treated with nitrogen showed no embryonation although when these eggs were transferred from nitrogen to oxygen gas after 60 days of treatment, embryonation occurred. This demonstrated that oxygen is an essential requirement for H. gallinarum egg development, although undeveloped eggs remain viable, even after 60 days in low oxygen conditions. The effects of climate on the biology of free-living stages studied under constant laboratory conditions cannot be applied directly to the field where climatic factors exhibit daily cycles. The effect of fluctuating temperature on development was investigated by including an additional temperature group in which H. gallinarum eggs were kept under daily temperature cycles between 12 and 22 degrees C. Cycles caused eggs to develop significantly earlier than those in the constant mean cycle temperature, 17 degrees C, but significantly slower than those in constant 22 degrees C suggesting that daily temperature cycles had an accelerating effect on H. gallinarum egg embryonation but did not accelerate to the higher temperature. These results suggest that daily fluctuations in temperature influence development of the free-living stages and so development cannot be accurately predicted on the basis of constant temperature culture.

Animals↗
PubMed1999

Regulation of nematode fecundity in the ring-necked pheasant (Phasianus colchicus): not just density dependence.

Patterns of nematode fecundity were investigated for infections of the caecal worm Heterakis gallinarum in the ring-necked pheasant (Phasianus colchicus). Worm length was a good predictor of parasite fecundity. After controlling for worm length no other factors, including parasite intensity, were related to worm fecundity. Density dependence in worm size was detected in natural infections at parasite intensities above a threshold of 96 worms (worm size decreased with increasing parasite intensity). However, below this threshold, worm size actually decreased with decreasing parasite intensity (inverse density dependence). The interaction between density dependence and inverse density dependence in regulating the development and subsequent fecundity of H. gallinarum worms in ring-necked pheasants was demonstrated in an infection experiment. Density dependence was observed in the stunted growth of worms in heavily infected hosts, relative to worms in lightly infected hosts. Inverse density dependence in worm size was the common pattern across hosts by the end of the experiment, when parasite intensities were below the density dependence threshold. This is the first study to document both density dependence and inverse density dependence in parasite fecundity in the same host-helminth system.

Animals↗
PubMed1995

Comparative effects of mites and lice on the reproductive success of rock doves (Columba livia).

We report experimental data comparing the effects of Mesostigmatid mites and Ischnoceran lice on the reproductive performance of a single group of captive rock doves (Columba livia). Several components of host reproductive success were compared for the two groups, including number of eggs laid, hatching success, nestling growth rates, fledging success, post-fledging body mass and survival. Adult body mass and survival were also compared. There was a dramatic difference in the effects of the mites and lice. The former drove host reproductive success to zero, mainly by agitating adults and causing them to incubate eggs less faithfully. Nestling growth rates and post-fledging survival were also significantly reduced by mites. Lice showed no effect on reproductive success whatsoever, even though the feather damage they cause is known to have energetic consequences (Booth, Clayton & Block, 1993). Neither parasite had a significant effect on adult birds. Although Ischnocera are found on most species of birds, our results for lice constitute the first experimental test of the impact of Ischnocera on avian reproductive success (preliminary report by Clayton & Tompkins, 1994). We discuss reasons for the different effects of mites and lice, including the relationship of horizontal (mites) and vertical (lice) transmission to the evolution of virulence.

Animals↗
PubMed1994

Ectoparasite virulence is linked to mode of transmission.

Theory suggests that the evolution of parasite virulence is linked to the dynamics of parasite transmission. All else being equal, parasites transmitted vertically from parents to offspring should be less virulent than parasites capable of horizontal transmission to unrelated hosts. This is because the fitness of vertically transmitted parasites is tightly linked to the reproductive success of the host, whereas the fitness of horizontally transmitted parasites is relatively independent of host reproduction. The virulence-transmission relation has seldom been tested because of difficulties inherent in comparing virulences of different parasite-host systems. We compared the virulence of lice and mites infesting a single group of captive rock doves (Columba livia). Lice, which were vertically transmitted, had no detectable effect on host fitness, whereas horizontally transmitted mites drove host reproductive success to zero. These results, in conjunction with a survey of the literature, support the hypothesis that ectoparasite virulence is linked to the mode of transmission.

Animals↗
PubMed1993

Improving survival: infection control and burns.

In the past, survival of the thermally injured patient was greatly hindered by invasive infection that originated in the burn wound. Current treatment modalities, including early excision of the burn wound and prompt wound closure, administration of systemic antibiotics and topical antimicrobial agents, and mechanical isolation, have improved survival. However, infection and the sequelae of infection continue to be the leading causes of morbidity and mortality for the thermally injured patient. In addition, the burn patient remains highly susceptible to other infectious processes. A thorough understanding of infection control and burns are essential to the successful treatment of burn injuries.

Anti-Infective Agents↗
PubMed1988

Significant reductions in mortality for children with burn injuries through the use of prompt eschar excision.

During the past 19 years, mortality due to burn injuries has markedly declined for children at the Boston Unit of the Shriners Burns Institute (SBI), dropping from an average of 9% of SBI admissions during 1968-1970 to an average of 1% during 1981-1986. Detailed statistical analysis using logistic regression was necessary for determining whether this decline in mortality was explained by changes in patient characteristics, such as age or burn size, which are known to strongly influence the outcome of burn injuries. This dramatic decline in mortality during the past 19 years was not the result of change in the age of the patients or their burn sizes; rather, it may be attributed to improvements in burn care. Results of this statistical analysis indicated that, for burn injury patients whose ages ranged from 11 days to 19 years, age had no demonstrable effect on survival from a burn injury. Children survived burn injuries at least as well if not better than the young adult (20-29 years of age). Also, infants (less than 1 year old) survived as well as other children (2-19 years old). Dramatic improvement in survival occurred in patients with burns covering more than 50% of the body surface area. Since 1979, mortality has been essentially eliminated for patients with burn sizes less than 70% of the total body surface area (of 296 patients with burns covering 15-69% of the total body surface area, only two patients died). During the period 1979-1986, 29 of 37 patients (78%) survived an 80% or greater total body surface area thermal injury.

Administration, Topical↗
PubMedDate not supplied

Burn-induced cosmetic disfigurement: can it be measured reliably?

Cosmetic disfigurement was measured reliably by averaging the ratings of four or more viewers of color slide photographs of severely burned children and young adults. Raters were clinical and nonclinical staff at a burn hospital. Reliability for four-person rating of overall cosmetic disfigurement (unclothed) was .94; for overall disfigurement (clothed) it was .86; for irregularity, thickness, and discoloration it was .78, .79, and .72, respectively. Profession, sex, and years of contact with burned patients did not influence inter-rater agreement. Any randomly selected panel of four raters produced reliable average ratings. The effect of impaired skin texture on overall ratings of cosmetic disfigurement (both clothed and unclothed) was three to five times as important as the effect of impaired color. Despite its subjectivity, cosmetic disfigurement can be measured reliably. This report describes a formal procedure for such measurement and discusses ways of using that procedure to improve patient care.

Adolescent↗
PubMedDate not supplied

Sleep disorders in children after burn injury.

Eighty-two children and adolescents between the ages of 30 months and 20 years (mean, 11.8 years) who were admitted to one of two pediatric burn units with a mean initial burn injury of 43.8% total body surface area and a mean age at time of injury of 4.2 years were studied 1 year or more after burn injury (mean, 7.3 years). Subjects were found to have profound at-home sleep disorders, which were manifested as nightmares in 30 subjects (37%), bed-wetting in 20 (24%), and sleep-walking in 6 (18%). Dream content related to normal childhood topics in 45 patients (55%), burn injury in 6 (7%), and burn treatment in 5 (6%). No relationship exists between age at time of burn, length of time after burn injury, cause of burn injury, family history of nightmares, or patient history of bed-wetting and the incidence of nightmares. Daytime naps were reported in 50 subjects (63%), although 46 (mean age, 11.7 years) were well beyond the normal age for napping.

Adolescent↗