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A R Walker

Publications and source records attributed to A R Walker.

At least 19 recordsLinked to original sources
PubMed2006

Validation of the proposed International Society for Heart and Lung Transplantation grading system for primary graft dysfunction after lung transplantation.

BACKGROUND: A scoring system was recently proposed to grade the severity of primary graft dysfunction (PGD), a frequent early complication of lung transplantation. The purposes of this study are to: (1) validate the PGD grading system with respect to patient outcomes; and (2) compare the performance of criteria employing the arterial oxygenation to fraction of inspired oxygen (P/F) ratio to an alternative grading system employing the oxygenation index (OI). METHODS: We retrospectively reviewed the medical records of 402 patients having undergone lung transplantation at our institution from 1992 through 2004. The ISHLT PGD grading system was modified and grades were assigned up to 48 hours post-transplantation as follows: Grade 1 PGD, P/F > 300; Grade 2, P/F 200 to 300; and Grade 3, P/F < 200. A worst score T(0-48) was also assigned, which reflects the highest grade recorded between T0 and T48. RESULTS: The prevalence of severe PGD (P/F Grade 3) declined after transplant, from 25% at T0 to 15% at T48. Grouping patients by P/F grade at T48 demonstrated the clearest differentiation of 90-day death rates (Grade 1, 7%; Grade 2, 12%; Grade 3, 33%) (p = 0.0001). T48 OI grade also differentiates 90-day death rates. There was no difference in longer-term survival between patients with PGD Grades 1 and 2. OI grade at T0 qualitatively improved differential mortality between Grades 1 and 2; however, the differences did not reach statistical significance. Patients with a worst score T(0-48) of Grade 3 PGD did have significantly decreased long-term survival, as well as longer ICU and hospital stay, when compared with Grades 1 and 2 PGD. Significant risk factors for short- and long-term mortality in our multivariate model were P/F Grade 3 [worst score T(0-48) as well as T0 grade], single-lung transplant, use of cardiopulmonary bypass and high pre-operative mean pulmonary artery pressure. CONCLUSIONS: There is an increased risk of short- and long-term mortality and length of hospital stay associated with severe (Grade 3) PGD. The proposed ISHLT grading system can rapidly identify patients with poor outcomes who may benefit from early, aggressive treatment. Refinement of the scoring system may further improve patient risk stratification.

Adolescent↗
PubMed2006

The known distribution and ecological preferences of the tick subgenus Boophilus (Acari: Ixodidae) in Africa and Latin America.

A compilation of the known distribution of Boophilus ticks in Africa and Latin America is presented, together with details on climate preferences. B. annulatus is recorded mainly in the western part of a strip from the equator to parallel 20 degrees N. It associates with woodlands and forests (lowland rain forest and secondary grassland). This species is also present in the Mediterranean region, associated to woodland and open areas. B. decoloratus extends southern to parallel 20 degrees N, in woodland with montane vegetation and Zambezian miombo; some records have been collected in the highveld grassland. B. geigyi is mainly collected in the western range of a stripe extending between parallels 5 degrees N and 18 degrees N, associated with Sudanian woodland, lowland rain forest with secondary grassland and woodland. Confirmed records of microplus in Africa are restricted to Malagasy region and south and eastern Africa, being predominant in the Zambezian miombo, deciduous forest with secondary grassland, and woodland. In Latin America, microplus is abundant in the Mesoamerican corridor to Venezuela and Colombia, and southern in Brazil and Argentina. The tick is mainly associated to the biomes of Chaco and Pampas in Argentina, the North-central moist Andes, the Atlantic forest (southern range) and the moist Meso-American vegetation (northern range). Most collections of B. annulatus and B. geigyi came from areas where winter minimum temperature is above 15 degrees C, maximum temperatures remain between 33 and 36 degrees C and maximum rainfall is recorded between June and September. B. decoloratus and African B. microplus are recorded in sites with low temperatures in May-September. Minimum temperature requirements are similar for both B. decoloratus and African B. microplus, and both are around 4 degrees C less than the value recorded for collections of Latin-American B. microplus. The rainfall pattern observed for decoloratus shows a minimum in May and June. The requirements of total rainfall are highest for B. microplus in Latin America, while records of African B. microplus are concentrated in areas of low rainfall between May and October, and high rainfall between November and March (low rainfall in the same period for B. decoloratus). Statistical analysis revealed the existence of populations (demes) with ecologically different requirements within each tick species. Both B. annulatus and B. decoloratus showed many different demes clearly associated to defined areas. The collections of Latin American B. microplus are very homogeneous according climate preferences and well separated from the African counterpart.

Africa↗
PubMed2006

Cloned Theileria parva produces lesser infections in ticks compared to uncloned T. parva despite similar infections in cattle.

Experimental transmissions of cloned Theileria parva in cattle with Rhipicephalus appendiculatus ticks were compared to transmissions with uncloned T. parva during studies on the potential for genetic recombination during syngamy of Theileria to produce antigenic diversity for evasion of bovine immunity. Prevalence and abundance of T. parva infection in adult ticks, which resulted from the feeding of nymphs on the calves, were significantly higher in the uncloned compared to the cloned T. parva. Development of sporoblasts of T. parva in the ticks to produce infective sporozoites was similar. There was no statistically significant difference in the clinical course of infection in cattle between cloned and uncloned T. parva. It was concluded that cloned T. parva has characteristics that reduce its viability during the tick stages of its life cycle.

Animals↗
PubMed2005

Ticks associated with wild mammals in Ghana.

The host ranges of a collection of 21 tick species found on wild mammals in the savanna, forests and coastal zone of Ghana suggested that most species were adapted to feeding mainly on host species within a single mammalian order, i.e. on artiodactyls (bovids/suids), carnivores, rodents or pholidotes (pangolins). Only a few species were dispersed evenly across a range of orders. Seven out of ten of the most common ticks on forest mammals were significantly associated with a particular host species or a group of closely related host species, which could be viewed as their major host or hosts, but they were also recorded much less frequently on a wide range of host species. Two other species were confined to their major hosts. Only one species appeared to be widely dispersed on forest mammals and to lack a particular major host. The majority of tick species therefore occurred on hosts with very distinctive biological, behavioural and ecological characteristics. The study provided no evidence to support the view that host specificity is an artefact of sampling. Finding that the tick species on Ghanaian wild mammals occurred on particular hosts, as well as in distinct habitats, indicated that tick-host associations are important for tick survival and confirmed the importance of climate and vegetation in tick distribution.

Animals↗
PubMed2005

Outcomes of febrile children presumed to be immunocompetent who present with leukopenia or neutropenia to an ambulatory setting.

UNLABELLED: To determine significant medical outcomes in febrile children presenting to an ambulatory setting with neutropenia and/or leukopenia. METHODS: Retrospective medical record review conducted on febrile patients who had a blood culture drawn, with white blood cell counts less than 5,000/mm3 and/or an absolute neutrophil count less than 1000/mm3. Ninety-one patients were identified; 5 with positive blood culture results, 13 with significant non-oncologic disease, and 3 patients with leukemia who had involvement of 2 or more cell lines. CONCLUSIONS: In the majority of patients, clinical judgment, physical findings, and review of all cell lines of the complete blood cell count identified those with significant disease.

Ambulatory Care↗
PubMed2004

Ehrlichia ruminantium seroprevalence in domestic ruminants in Ghana. II. Point prevalence survey.

Serum samples collected on a single occasion from cattle, sheep and goats at sites in all 10 regions of Ghana were tested for antibodies to Ehrlichia (previously Cowdria) ruminantium, the causative agent of heartwater, by polyclonal competitive ELISA (PC-ELISA). The survey revealed the presence of heartwater-exposed ruminants throughout the country, with local seroprevalence up to 100%. Seronegative, and therefore presumably susceptible, animals were also present in all regions, in some areas in numbers high enough to indicate local endemic instability. Overall seroprevalences in cattle, sheep and goats were 61, 51 and 28% respectively, and were generally higher in the northern part of the country and lower in the forest zone. Amongst animals over 1 year old, two thirds of cattle and sheep, and around one third of goats throughout the country had been exposed to E. ruminantium. In the north, seroprevalence in sheep sampled with and without cattle was similar, whereas in the south seroconversion rates in sheep were significantly higher in areas where cattle were present.

Age Factors↗
PubMed2004

Incidence and prevalence of tick-borne haemoparasites in domestic ruminants in Ghana.

Giemsa-stained thin blood smears prepared monthly from cattle, sheep and goats in the Greater Accra region of Ghana between May 1994 and December 1996 were examined for presence of tick-borne haemoparasites. The majority of animals were less than 2 months old at the start of the survey. Monthly and cumulative incidences are presented of Anaplasma sp., Babesia bigemina, Borrelia sp., Eperythrozoon sp., Theileria mutans and Theileria velifera in cattle, Anaplasma sp., Borrelia sp., and Theileria sp. in sheep, and Anaplasma sp. in goats. T. mutans was the commonest parasite in cattle, with 100% incidence in calves by 10 months of age, and Anaplasma was commonest in small ruminants. The relative prevalence of these haemoparasites in blood smears from cattle, sheep and goats sampled on a single occasion at sites in all 10 regions of Ghana was found to be similar, though actual infection rates were lower. Packed cell volume (PCV) measurements from the sampled animals are also presented; no seasonal trends were evident in the PCV of the cattle, sheep and goats sampled monthly. In animals sampled on a single occasion, mean PCV was significantly higher in cattle and sheep without detectable haemoparasite infection, and in cattle was lowest in animals positive for both Babesia and Anaplasma, while there was no difference in mean PCV levels between parasitised and non-parasitised goats.

Anaplasmosis↗
PubMed2004

Ehrlichia ruminantium seroprevalence in domestic ruminants in Ghana; I. Longitudinal survey in the Greater Accra Region.

Serum samples collected monthly over a 34-month period from cattle, sheep and goats in the Greater Accra Region of Ghana were tested for antibodies to Ehrlichia (previously Cowdria) ruminantium, the causative agent of heartwater, by polyclonal competitive ELISA (PC-ELISA). Maternal antibodies, detected in about half of animals followed from under 1 month old, declined to negative levels within 2-4 months. Amblyomma variegatum tick vectors were present on livestock in rural areas throughout the year, and first seroconversion occurred at any age, although the majority of calves seroconverted between 1 and 10 months old, sheep by 11 months, and goats by 7 months. All the cattle in the study became seropositive by 20 months of age, except one animal which subsequently died of heartwater. Following seroconversion, 25% of bovine sera tested negative in the PC-ELISA. Just over half the sheep in the survey seroconverted before or during the study period; following seroconversion, less than 3% of ovine sera became PC-ELISA negative. About a quarter of the goats seroconverted, and 34% of their post-seroconversion sera tested negative in the PC-ELISA. Overall, the serology indicated that virtually all cattle on the survey farms were exposed to E. ruminantium without suffering disease, but that a substantial proportion of sheep and goats escaped exposure and thus formed a susceptible population. E. ruminantium was detected in brains of 14, 36 and 4% of cattle, sheep and goats submitted for post mortem at the Accra Veterinary Laboratory, indicating that sheep were most at risk from heartwater disease.

Animals↗
PubMed2004

An updated list of the ticks of Ghana and an assessment of the distribution of the ticks of Ghanaian wild mammals in different vegetation zones.

Twenty one species of ticks belonging to five genera of the family Ixodidae (Order Acari, sub-order Ixodida) - Amblyomma, Haemaphysalis, Hyalomma, Ixodes and Rhipicephalus (including the sub-genus Rhipicephalus (Boophilus)) - were collected from 1260 mammals, representing 29 species, 14 families and 6 orders, in four vegetation zones in Ghana during the period 1971-1978. Four other species were collected from humans in 1977. In all, eight species appeared to be new records for Ghana: Amblyomma tholloni Neumann; Dermacentor circumguttatus Neumann; Haemaphysalis houyi Nuttall & Warburton; Ixodes loveridgei Arthur; Ixodes oldi Nuttall; Ixodes vanidicus Schultze; Rhipicephalus complanatus Neumann; Rhipicephalus cuspidatus Neumann. The updated list of tick species in Ghana given here includes 41 species of ixodid ticks and four species of argasid ticks. Most species have been found in neighbouring regions of West Africa but 56 of the 121 different combinations of ixodid tick species and host species found in the collection described here have not apparently been reported before. The new combinations recorded here bring the total number of different combinations of ixodid tick species and mammalian host species now reported in Ghana to 151. The tick species found on wild mammals in Ghana mostly differed from those reported from domestic stock by other authors. The data showed that different tick species occurred in different vegetation zones and that most species displayed a pronounced preference for certain groups of related host species. Some tick species were found in the savanna feeding mainly on large bovids and/or suids; others were found in forests feeding mainly on small bovids, large rodents or small carnivores.

Animals↗
PubMed2004

Some puzzling situations in the onset, occurrence and future of coronary heart disease in developed and developing populations, particularly such in sub-Saharan Africa.

Coronary heart disease (CHD) was rare in developed populations until the early 1900s; this prevailed even among the small segments who were prosperous and who, in measure, had most of the currently recognised risk factors. However, in the 1930s, with improved circumstances from general rises in socio-economic state, there were major increases in the occurrence and mortality rate from the disease, the latter reaching a third of the total mortality in some countries, as in the United Kingdom (UK). Puzzlingly, the inter-population diversity of the increases in CHD has been such that there are as much as five fold differences in CHD mortality rates, as, for example, between Poland and Spain. Within recent years, with appropriate treatments, the mortality rate has halved in some countries, again, as in the UK. However, the incidence rate of the disease has diminished little or hardly at all. Risk factors include a familial component and, nutritionally, over-eating, a high fat intake, relatively low intakes of plant foods, especially of vegetables and fruit and, non-nutritionally, smoking, excessive alcohol consumption and a low level of everyday physical activity. On the one hand, known risk factors, broadly, are considered to be capable of explaining only about half of the variation in the occurrence of the disease. Even at present, known risk factors far from fully explain the epidemiological differences in mortality rates. Yet, on the other hand, there is abundant evidence that in population groups, among whom risk factors are low or have been reduced, CHD incidence and mortality rates are lower. Notwithstanding this knowledge, broadly, there is very little interest in the general public in taking avoiding measures. As to the situation in developing populations, in sub-Saharan Africa, in urban Africans, as in Johannesburg, South Africa, despite considerable westernisation of life style and with rises in risk factors, CHD remains of very low occurrence, the situation thereby resembling, historically, its relatively slow emergence in developed populations. In most eastern countries, mortality rates remain relatively low, as in Russia and Japan. However, in major contrast, in India, rates have risen considerably in urban dwellers. Indeed, in Indian immigrants, as in those in the UK, their rate actually exceeds that in the country's white population. In brief, much remains to be explained in the epidemiology of the disease.

Africa South of the Sahara↗
PubMed2001

Tick-Theileria interactions in response to immune activation of the vector.

Watt, D. M., Walker, A. R., Lamza, K. A., and Ambrose, N. C. 2001. Tick-Theileria interactions in response to immune activation of the vector. Experimental Parasitology 97, 89-94. Immune mechanisms towards the haemoprotozoan parasite Theileria parva were investigated in their tick vector, Rhipicephalus appendiculatus. The exoskeletons of adult ticks were initially pierced with bacteria-coated, saline-coated, or sterile dry glass needles. Haemolymph was extracted from the ticks at 6, 24, 48, and 72 h postinjection and applied to bacterial plates to measure the growth inhibition effects. The inhibition zones were larger with all the injected groups compared to uninjected controls. The largest inhibition zones were seen 24 h after injection with bacteria-coated needles. An experiment was carried out to investigate whether antibacterial immune responses were relevant to the parasite/tick relationship and, if so, which parasite form was most vulnerable. R. appendiculatus nymphs were infected with T. parva by feeding on an infected calf and were then injected with needles on days 7, 13, 15, and 17 throughout their moult in an attempt to induce tick immune responses at the same time as different lifecycle forms of T. parva would be present. Salivary glands from the moulted adult ticks in the control and different treatment groups were dissected out and examined for the presence of T. parva sporoblasts. No difference in infection levels was seen in any of the treatment groups compared with the controls, suggesting that immune responses in R. appendiculatus, induced by bacterial injection, do not affect T. parva infections. The fecundity of injected ticks was compared with that of uninjected controls to ensure that the injection procedure itself was not detrimental to the ticks. Injected females had higher engorgement masses than controls but reduced levels of egg hatching.

Animals↗
PubMed2001

Inverse relationship between microsatellite instability and K-ras and p53 gene alterations in colon cancer.

Some studies have shown an inverse relationship between microsatellite instability in colon cancer and mutations in p53 and K-ras, whereas others have not. We therefore evaluated these features in a population-based sample of 496 individuals with colon cancer. Microsatellite instability was determined by a panel of 10 tetranucleotide repeats, the Bethesda consensus panel of mono- and dinucleotide repeats, and coding mononucleotide repeats in transforming growth factor-beta receptor type II, hMSH3, BAX, hMSH6, and insulin-like growth factor receptor type II. Mutations in codons 12 and 13 in K-ras were evaluated by sequencing. p53 overexpression (as detected by immunohistochemistry) was used as an indicator of p53 mutation; this was evaluated in 275 of the tumors. K-ras mutations were present in 33.2% of tumors, p53 overexpression in 51.5%, and microsatellite instability (as determined by the Bethesda consensus panel) in 12.5%. K-ras mutations were significantly less common in unstable tumors than stable tumors (11.8% versus 36.9%, P: < 0.001). p53 overexpression was significantly less common in unstable tumors than stable tumors (20.0% versus 55.7%, P: < 0.001). These inverse relationships between microsatellite instability and ras gene mutations and p53 overexpression were shown to be independent of tumor site in logistic regression analyses. All other measures of instability also showed statistically significant inverse relationships independent of tumor site with alterations in ras and p53, and instability results determined by the panel of 10 tetranucleotide repeats were highly significantly related to those determined by the Bethesda consensus panel. Coding mononucleotide repeat mutations were significantly more common in unstable tumors than stable tumors (85.7% versus 1.0%, P: < 0.001). We conclude that there is an inverse relationship between microsatellite instability and mutations in p53 and K-ras, and that the molecular profile of colon cancers with microsatellite instability is characterized by relatively infrequent mutations in K-ras and p53 and relatively frequent mutations in coding mononucleotide repeats.

Adult↗
PubMed2001

A novel plastid-targeted J-domain protein in Arabidopsis thaliana.

Arabidopsis cDNAs encoding ATJ11, the smallest known J-domain protein, have been isolated and characterized. The precursor protein of 161 amino acid residues was synthesized in vitro and imported by isolated pea chloroplasts where it was localized to the stroma and cleaved to a mature protein of 125 amino acid residues. The mature protein consists of an 80 amino acid J-domain, and N- and C-terminal extensions of 24 and 21 amino acid residues, respectively, which show no similarity to regions in other DnaJ-related proteins. ATJ11 produced in Escherichia coli stimulated the weak ATPase activity of E. coli DnaK, but was unable to stimulate refolding of firefly luciferase by DnaK, and inhibited refolding by DnaK, DnaJ and GrpE. ATJ11 is encoded by a single-copy gene on chromosome 4, and is expressed in all plant organs examined. A paralogue of ATJ11, showing 72% identity, is encoded in a 4.5 Mb duplication of chromosome 4 on chromosome 2. These proteins represent a novel class of J-domain proteins.

Adenosine Triphosphatases↗
PubMed2001

World pandemic of obesity: the situation in Southern African populations.

Among sub-Saharan Africans in general, a generation or so ago, there was very little gain in weight, or in blood pressure, with age. Even at present, in most populations, especially in the indigent masses, obesity prevalence remains very low, at 1-5%. However, in South Africa and some neighbouring countries, Botswana, Namibia and Zimbabwe, with rise in socio-economic status, urbanization, and diminishing physical activity, the proportion affected has increased. Rises, as noted in Cape Town, have been only slight in men, to 8%; but in women much more so, to 34%, ie to a level similar to that of African-American women. Dietarily, energy intake has increased slightly, that from fat from 15-20% to 25-30%. However, there have been falls in dietary fibre intake, to 20-25 g and 15-20 g daily, in rural and urban areas, respectively. Evidence suggests that the health disadvantage of obesity in African women is less than that in white women, and would seem to have little influence on their proneness to hypertension, coronary heart disease and breast cancer. Traditionally, and even currently, sociologically, the disorder carries little opprobrium. As to the future, the prevalence in women may well increase still further. Regarding treatment, unfortunately among African women desirous of losing weight, sustained reducing measures are near impossible; moreover, pharmacological treatment is too costly to implement.

Africa South of the Sahara↗
PubMed2001

Risk factors in habitats of the tick Ixodes ricinus influencing human exposure to Ehrlichia phagocytophila bacteria.

Ixodes ricinus L. (Acari: Ixodida) were sampled during 1996-99 in southern Scotland, on vegetation using cloth drags, on humans by removal from clothing and on roe deer (Capreolus capreolus L.) by searching legs of culled deer. Developmental microclimate was recorded by automatic recorders and questing microclimate by portable instruments during tick collections. Ticks and deer were examined for infection with Ehrlichia phagocytophila bacteria (Rickettsiales) using microscopy and polymerase chain reaction. This pathogen causes tick-borne fever of sheep in Europe and human granulocytic ehrlichiosis in North America, but in Europe human clinical ehrlichiosis due to E. phagocytophila has not been recorded despite serological evidence of exposure. Among three types of habitat, coniferous woodland was most infested with questing ticks (560 ticks/km of drag; mean numbers collected on long trousers: 24.3 larvae, 13.5 nymphs and 0.8 adult ticks/km walked), deciduous woodland had slightly lower infestation (426 ticks/km drag) and upland sheep pasture had much lower infestation (220 ticks/km drag). Of the three main vegetation types, bracken was least infested (360 ticks/km drag), ericas most (430 ticks/km drag) and grassland had intermediate infestation density (413 ticks/km drag). Questing and developmental microclimates were poor predictors of exposure within these habitats, except lower infestation of pastures was attributed to greater illumination there. Collectors who walked a total of 300 km through all habitats (taking 360 h in all seasons), wearing cotton trousers hanging outside rubber boots, were bitten by only four nymphs and 11 larvae of I. ricinus (but no adult ticks). There was a negative correlation between densities of deer and ticks collected, although presence of deer remains a major indicator of exposure. The proportion of infected ticks was fairly uniform at four sites studied. Overall prevalence of E. phagocytophila in I. ricinus was 3.3% in nymphs (40/1203) but only approximately 1.5% in adults of both sexes (although males do not bite). It was estimated that nymphs of I. ricinus gave 4.4% probability of one infected bite/person/year (for occupational exposure during this research) due to presence in all seasons and habitats, their human biting rate of 0.011 nymphs/h or 0.013 nymphs/km and widespread infection with E. phagocytophila. The frequency distribution of intensity of infection in ticks was approximately normal (mean 98 morulae/nymph infected), thus there is a high risk of receiving a high dose from any one infected tick bite.

Animals↗
PubMed2001

With increasing ageing in Western populations, what are the prospects for lowering the incidence of coronary heart disease?

Coronary heart disease (CHD), rare in the early 1900s, in the 1970s was responsible for almost a third of deaths in Western populations. Although its mortality rate has fallen in the last 20 years, considerably in certain populations, it remains the leading cause of death, and there is little evidence of any fall in its incidence rate. The primary risk factors, which include pattern of diet, smoking practice, and level of physical activity, are well known, but explain only approximately 50% of variation in its occurrence. Despite the numerous health improvement recommendations made, alterations in diet have been relatively slight. Although smoking practice has halved in some populations, its prevalence is now rising in the young. The extent of physical activity is low, compared with that in the past, and may even be decreasing in the young. With the general ageing of populations, the near absence of strong encouragement from the state, and individuals' general failure to reduce risk factors significantly, the chances of decreases in the incidence of CHD appear remote.

Coronary Disease↗