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Biomedical subjects

A W Park

Publications and source records attributed to A W Park.

At least 19 recordsLinked to original sources
PubMed2005

Quantitative assessment of the risks of reducing the routine swabbing requirements for the detection of Taylorella equigenitalis.

The transmission of contagious equine metritis (CEM) on stud farms in Britain, Ireland and other European countries is prevented by following the recommendations in the Horserace Betting Levy Board's Code of Practice on CEM. A quantitative risk assessment was undertaken to estimate the likely impact of removing the recommendation, from the 2002 code, to culture endometrial or cervical swabs microaerophilically for the presence of Taylorella equigenitalis, the causative organism. The scientific literature was reviewed for evidence about the anatomical distribution of T. equigenitalis at different times after infection and it was found that, in chronically infected mares, the organism was detectable in the clitoral swabs of nearly 93 per cent, but in the cervical swabs of only 31 per cent. In contrast, in acutely infected mares, the organism was detectable in the clitoral swabs of nearly 69 per cent, but in the cervical swabs of 84 per cent. By using these results, a quantitative risk assessment was undertaken, assessing the likely effects of removing the recommendation that swabs from the cervix of low-risk mares should be cultured for T. equigenitalis. The results were sensitive to the prevalence of the infection, but when it was low, there appeared to be few benefits in continuing to culture cervical swabs routinely. However, such swabs are vital when the disease is suspected.

Algorithms↗
PubMed2004

The effects of strain heterology on the epidemiology of equine influenza in a vaccinated population.

We assess the effects of strain heterology (strains that are immunologically similar but not identical) on equine influenza in a vaccinated population. Using data relating to individual animals, for both homologous and heterologous vaccinees, we estimate distributions for the latent and infectious periods, quantify the risk of becoming infected in terms of the quantity of cross-reactive antibodies to a key surface protein of the virus (haemagglutinin) and estimate the probability of excreting virus (i.e. becoming infectious) given that infection has occurred. The data suggest that the infectious period, the risk of becoming infected (for a given vaccine-induced level of cross-reactive antibodies) and the probability of excreting virus are increased for heterologously vaccinated animals when compared with homologously vaccinated animals. The data are used to parameterize a modified susceptible, exposed, infectious and recovered/resistant (SEIR) model, which shows that these relatively small differences combine to have a large effect at the population level, where populations of heterologous vaccinees face a significantly increased risk of an epidemic occurring.

Animals↗
PubMed2003

Optimising vaccination strategies in equine influenza.

A stochastic model of equine influenza (EI) is constructed to assess the risk of an outbreak in a Thoroughbred population at a typical flat race training yard. The model is parameterised using data from equine challenge experiments conducted by the Animal Health Trust (relating to the latent and infectious period of animals) and also published data on previous epidemics (to estimate the transmission rate for equine influenza). Using 89 ponies, an empirical relationship between pre-challenge antibody and the probability of becoming infectious is established using logistic regression. Changes in antibody level over time are quantified using published and unpublished studies comprising 618 ponies and horses. A plausible Thoroughbred population is examined over the course of a year and the model is used to assess the risk of an outbreak of EI in the yard under the current minimum vaccination policy in the UK. The model is adapted to consider an alternative vaccination programme where the frequency of vaccination in older horses (2-year-olds and upwards) is increased. Model results show that this practical alternative would offer a significant increase in protection. Spread of infection between yards is also considered to ascertain the risk of secondary outbreaks.

Age Factors↗
PubMed1991

The ancient origins of oral pathology.

Belief in a golden age has provided mankind with solace in times of despair and with élan during the expansive periods of history. Dreamers imagine the golden age in the remote past, in paradise lost, free from toil and grief. Optimists put their faith in the future and believe that mankind, Prometheus-like, will master the arts of life through power and knowledge. Thus, the golden age means different things to different men, but the very belief in its existence implies the conviction that perfect health and happiness are birthrights of men. Yet, in reality, complete freedom from disease and from struggle is almost incompatible with the process of living.

Africa↗
PubMed1991

Polyphasic growth-weight response in the guinea pig.

An assessment of the growth rate pattern based on longitudinal weight data of guinea pigs was conducted over the presumptive preweaning and early postweaning period. The study covered the minimum of 44 and maximum of 53 days with means calculated for 3-day intervals involving 13 litters and a total of 40 young. Initial analysis showed males heavier than females at birth and both sexes being inversely proportional to litter size at birth. At the end of the experimental period the males were still heavier than the females but their weight distribution peaked in litter of three while the females were heaviest in the largest litters of five and lightest in the litter of one. Phasic linear regression line analysis revealed 4 litters with a triphasic growth outline and 6 litters with quadrophasic growth outline. Final assessments indicate that the total period of 53 days manifests a quadrophasic growth outline while, in contrast, the period specifically involved with the process of lactation and weaning displays a definite diphasic growth spectrum and is comparable to the tri- or quadrophasic spectrum occurring in the albino rats, rice rats and hamsters.

Age Factors↗
PubMed1990

Dental abrasion pattern in a selected group of Malaysians.

Among 350 inhabitants of two villages, 31 (8.9%) cleaned their teeth using table salt and charcoal applied to their forefinger or a Melastoma brush. As a result, all had distinct forms of abrasion cavity on the labial surfaces of their teeth. All of the above three agents are highly abrasive and injurious to both the hard and soft oral tissues. This dying practice is only popular among a very small number of persons in the older age group, and should be discouraged.

Adult↗
PubMed1989

Growth in the myopathic Syrian hamster (Cricetus auratus).

The objective was to assess the effect of the hereditary myopathic disease (muscular dystrophy) on 4 growth parameters: body-weight, head-body length, skull weight and cranial length in the Syrian hamster over a 4-13 month period. A control colony of 34 males and 32 females was compared to a muscular dystrophy colony consisting of 37 males and 27 females. The monthly means of the 4 growth parameters were computed and full data were used for computations of analysis of variance with regression of each group, sex and growth parameter. Intersex and intergroup comparisons of the same parameters were made using analysis of covariance. In the controls, the male bodies were heavier and longer than the female bodies; males grew over the total period. In dystrophic hamsters, males were heavier than females, but females were longer. In both control and dystrophic hamsters, female skulls were longer and heavier. In all parameters the means of the control colony were greater than those of the dystrophic colony relative to age. The disease factor in the muscular dystrophy colony adversely influenced all 4 growth parameters.

Animals↗
PubMed1987

Variation in the growth of the preweaning Syrian hamster (Cricetus auratus).

An assessment of the growth rate spectrum based on a longitudinal weight study of golden hamsters was undertaken over the preweaning period. The period covered 23 days with data probes at 24-hourly intervals and encompassed 16 litters providing a birth number of 120 young and a weaning survival number of 82. Subsequent analysis directed initially at the pooled or averaged data showed sex differences with males gaining weight faster than females. Further analysis showed the total period to have three definitive break-points and therefore four phases of growth activity. The segmented linear regression line calculations showed that the phasic duration of males in the second and third phases were two days later than the females. Following data-analysis adjustments and taken into account aberrations of the sample, final indications pointed to the preweaning hamster growth spectrum as quadrophasic, exhibiting a stable first phase, a second and third phase terminating earlier in females and a final weaning weight being heavier in males. The growth curves demonstrated a 'U' shaped outline and formed an integral part of hamster preweaning precocity.

Analysis of Variance↗
PubMed1985

Postnatal somatometry of the rat facial skeleton.

Growth of the rat facial skeleton over a 40 day period from birth was examined relative to 8 length and 4 width parameters of animals subject to somatic growth retardation experimentally induced by overtaxing the maternal lactational capacity by means of excessively large cross-fostered litters. Least squares regression lines were calculated for the preweaning period (day 1-20); the postweaning period (day 21-40) and the total period (day 1-40), thereafter being recalculated into segmented regression lines relative to the physiological growth phases. Specific phases of growth activity were noted throughout the 40 days with those in the preweaning period showing a marked consistency concomitant with the maternal lactational ability and subsequent emergence of biological weaning. A consistent phasic growth spectrum with definitive breaks in continuity supports the original postulate (Brody, 1927) that growth curves consist of phases of exponential activity delineated by changes in growth rate. Due to the inclusion of both control and experimental samples, the breakage points of the phases marking the change of growth rate different and were therefore reciprocated by alterations of phasic duration. Phasic growth occurred in the postweaning period with some degree of variance which did not permit an assessment of the causation factors with sufficient validity. The postweaning period of the experimental sample exhibited varying degrees of growth recovery (catch-up) in the majority of the facial parameters. Covariance analysis of the parameters in most instances showed that the parameters, as defined, and the bone units incorporated within them manifested a characteristic growth response in each sample irrespective of the modifying influence of the environmental factors.

Animals↗
PubMed1984

Cranial postnatal growth of the rat relative to environmental variance.

Neurocranial growth during the first 40 days of postnatal development was biometrically investigated relative to the specific parameters of calvarium length and width; basioccipital length and width; basisphenoid length; biparietal width; frontal bone length and cranial vault length. Specimens were obtained from rat litters subject to moderate nutritional suppression by raising the litter numbers above the norm via the cross-fostering technique and causing the overtaxing of the lactational capacity. Alterations in growth rate occurred throughout the pre- and postweaning periods with clearly demarcated phases of growth. Male and female growth in the preweaning period was uniform within each litter type but the phasic growth changes in the experimental litters differed from the control litters with regression line breakage emerging at different points and altering the phasic lengths. The preweaning phasic spectrum in both control and experimental litters was evidently linked to the maternal lactation capacity--relative to quantity and duration. Weaning was insidious in both litter types but occurred earlier in the experimental litters although the continuity of growth was maintained up to the end of the definitive preweaning period (day 20). The definitive postweaning period (day 21-40) showed considerable heterogeneity--unsatisfactory scatter--with differing regression line breakage points and phasic lengths. Analysis based on the total period (day 1-40) brought compensatory adjustments and indicated more acceptable phasic patterns in the postweaning period with confirmation of catch-up growth in the experimental litters. Allometric analysis of the parameters revealed varying rates of growth, line breakage points and differing phasic lengths indicating that each neurocranial parameter and the skeletal unit forming it had an individual characteristic response spectrum mostly attributable to the functional matrix with emphasis on the capsular rather than the periosteal.

Animals↗
PubMed1984

Tooth mineralisation relative to somatic growth retardation in the rat.

The morphology and sequence of mineral deposition on the crowns of rat molar teeth have been investigated by means of contact radiography relative to their postnatal development following a period of somatic retardation induced by nutritional suppression. Differences in deposition appeared 3 days after birth in the first molar crown and continued until day 7. Second molar differences manifested between day 4 and 5 reaching a comparable level by day 10. Third molar mineralisation appeared identical in both control and experimental specimens indicating that they were not sensitive to the influence of direct maternal control since lactation at the time of mineralisation was being superceded by general food sources. The slowing of molar crown growth is not regarded as a mineral deficit but basically related to the organic matrix and protein and energy deficiency.

Aging↗
PubMed1983

Postnatal skull growth of the rat relative to environmental variance.

Rat growth during the first 40 days of postnatal development was examined relative to cranial length, facial height and bizygomatic width of animals subject to nutritional suppression induced by increased litter size during the preweaning period. The postulate (Brody, 1927) that growth curves consist of phases of exponential activity delineated by alterations in the growth rate thus inducing breaks in the continuity was confirmed in the skull. The preweaning and postweaning periods showed three clearly demarcated phases of growth within each period. Breakage points of the phases--alteration in growth rate--differed between the control and experimental litters thus changing the length of the specific phases. Within the preweaning period of both types of litter the phasic characteristics appeared directly linked to the maternal capacity--quantitatively and in duration, while the latter part of the preweaning period and the postweaning period remained within the province of external or non-maternal food supplies. The postweaning of the experimental animals exhibited catch-up growth phenomena in all parameters with a slight variation relative to catch-up growth phenomena in all parameters with a slight variation relative to the sexes. In general terms, analysis of the total period of investigation indicated that growth within the preweaning period was more active although sexual dimorphism was not significant. In addition, relative growth (allometric) analysis of the three parameters showed varying growth rates, breakage points and hence phasic lengths indicating that irrespective of environmental factors that each parameter and the bone units incorporated in it manifested a response as a whole which was characteristic of the parameter.

Animals↗
PubMed1982

Growth variability in the rat.

Growth of rats during the first 40 days of postnatal life was investigated in relation to the parameters of head-body length, weight and cranial length on the basis of standard growing litters of 6 young and experimental litters of 12-14 young--the latter exhibiting a range of differences attributable to nutritional suppression. A characteristic triphasic growth spectrum manifested in all the parameters of both sexes and litter type within the preweaning period (day 1-20) of development. In the postweaning period (day 21-40) three phases of growth were also detected during analysis. Growth was shown to be at its greatest potential during the preweaning period but did not exhibit any sexual dimorphism in either type of litter. Differences in growth potential existed between the standard litter and the experimental litter but these did not detract from the overall triphasic pattern apart from slight alterations in the individual phasic length. Analysis of the postweaning period of development showed that growth was considerably slower compared to the preweaning period with sexual dimorphism appearing in the parameters. In addition, relative growth (allometric) analysis of the three parameters indicated that the growth rates differed throughout the whole of the developmental period (day 1-40) irrespective of the conditions imposed on the litter types indicating that each parameter possessed an individual growth response.

Animals↗
PubMed1981

Responses of tooth eruption and alveolar bone subject to somatic growth retardation in the rat.

The morphogenesis and regression of the osteodental fissure formed by alveolar bone in the maxillary and mandibular regions has been investigated in relation to eruption of the dentition during and following a period of somatic retardation stemming from nutritional suppression. Fissural formation occurred above the first and second molars of the maxilla and mandible, morphologically within normal limits but retarded by two days. During eruption a sequence of cuspal perforations of the alveolar bone took place behind the edge of the alveolar crest which later disintegrated as the bulk of the crown moved upwards. The appearance of the specific cusps of the experimental animals was two days behind that of the controls. Eruption through the oral mucosa was fairly rapid and the deficit noted in the bone emergence phase was reduced to one day. As in control animals, fissural formation did not occur over the third molars which were totally encapsulated by bone. Eruption of third molars in experimental animals was similar to control observations- no difference in timing and the removal of the encapsulating bone being achieved by the rapid enlarging of a wedge-shaped area at the mesio-occlusal aspect. Observation of eruption through alveolar bone is regarded as a more accurate assessment of changes in the early phases.

Alveolar Process↗