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Biomedical subjects

A J Hall

Publications and source records attributed to A J Hall.

At least 127 records · Page 7Linked to original sources
PubMed1994

Hydrothermal and oceanic pH conditions of possible relevance to the origin of life.

Because of the continuous focusing of thermal and chemical energy, ancient submarine hot springs are contenders as sites for the origin of life. But it is generally assumed that these would be of the acid and high-temperature 'black smoker' variety (Corliss et al., 1981). In fact today the greater part of the ocean circulates through off-ridge springs where it issues after modification at temperatures of around 40 degrees C or so but with the potential to reach 200 degrees C. Such offridge or ridge-flank springs remind us that there are other candidate sites for the origin of life. Although there is no firm indication of the pH of these off-ridge springs we have argued that the solutions are likely to be alkaline rather than acid, We test the feasibility of this idea using EQ geochemical water-rock interaction modelling codes (Wolery 1983) and find that for a range of possible initial chemistries of Hadean seawater, the pH of issuing solutions at around 200 degrees C is around one or more units alkaline. Such pH values hold for interaction with both basaltic and komatiitic crust. The robustness of this result suggests to us that alkaline submarine springs of moderate temperature, carrying many hundreds of ppm HS to the ocean basins, are also serious contenders as sites for the origin of life, particularly as Hadean seawater was probably slightly acid, with a dissolved iron concentration approaching 100 ppm. On mixing of these solutions, supersaturation, especially of iron sulphide, would lead to the precipitation of colloidal gels. In our view iron sulphide was the likely substance of, or contributor to, the first vesicle membranes which led to life, as the supply organic molecules would have been limited in the Hadean. Such a membrane would have bid catalytic properties, expansivity, and would have maintained the natural chemiosmotic gradient, a consequence of the acid ocean and the alkaline interior to the vesicles.

Evolution, Planetary↗
PubMed1994

The epidemiology of melioidosis in Ubon Ratchatani, northeast Thailand.

BACKGROUND: Melioidosis, or infection with Pseudomonas pseudomallei is an important cause of morbidity and mortality in South East Asia and Northern Australia. The epidemiology of melioidosis in Ubon Ratchatani, Northeast Thailand was studied over a 5-year period from 1987 to 1991. METHODS: Rates and, when possible, the risks of developing melioidosis were calculated. The numerator was the number of culture-proven cases of melioidosis seen in the 1000-bed referral hospital of the province. The denominators were obtained from the population census, a survey of Health, Welfare and Use of Traditional Medicine, and the North Eastern Meterological Centre, Thailand. RESULTS: The average incidence of human melioidosis was 4.4 (95% confidence interval [CI]: 3.8-5.0) per 100,000. The disease affected all ages with the highest incidence in 40-60 years olds. Melioidosis was 1.4 (95% CI: 0.4-5.3) times more common in males than females. The disease showed a significant seasonal variation in incidence, and a strong linear correlation with rainfall (r = 0.7, 95% CI: 0.5-0.9) Adults exposed to soil and water in their work (most were rice farmers) had an increased risk of melioidosis (in the 40-59 year age group, relative risk = 4.1, 95% CI: 2.4-6.9). Most adult patients had an underlying disease (mainly diabetes mellitus) predisposing them to this infection. CONCLUSION: Melioidosis may result from either acute exposure to the organism in the soil and water, or 're-activation' of an asymptomatic childhood infection (by an unidentified possibly infective seasonal cofactor). The results from this analysis are consistent with both hypotheses. Further epidemiological studies are needed to identify risk factors so that optimal strategies for control of melioidosis may be developed.

Adolescent↗
PubMed1994

A single base pair deletion in the promoter region of the factor IX gene is associated with haemophilia B.

Patients with the haemophilia B Leyden phenotype show a distinct pattern of factor IX expression characterized by a post-pubertal increase in FIX levels and the remission of clinical symptoms in adult life. This phenotype has previously been linked to single base mutations within transcription factor binding sites in a region of approximately 40 bp around the major start point of transcription of the FIX gene. Here we report a novel mutation in this region within the transcription factor C/EBP binding site at +1 to +18. The mutation is a single base pair deletion from a triplet of thymine residues at +6 to +8. We show that the extent to which this mutation disrupts the binding of C/EBP to its binding site is less marked than the disruption caused by the +13 A-->G mutation of FIX Norwich (1). This correlates with age-matched phenotypic data we have available for the patient reported here and that of FIX Norwich.

Base Composition↗
PubMed1994

Comparison of mortality between villages with and without Primary Health Care workers in Upper River Division, The Gambia.

Health services utilization was analysed in a rural area of the The Gambia. In general, health workers were consulted frequently. However, verbal autopsies showed that children who died had rarely consulted health workers, particularly if they came from villages where such workers were not posted. Traditional healers were consulted frequently, independently of the presence of a village health worker. The relationship between cause specific mortality and the utilization of health services is discussed. Childhood mortality was similar in villages with or without a primary health care worker at the time of the study.

Cause of Death↗
PubMed1993

The influence of age on the development of the hepatitis B carrier state.

The relation between the age at infection with hepatitis B virus (HBV) and the development of the carrier state is examined by using data from a number of published and unpublished surveys. A remarkably consistent relation was found. Infants infected perinatally (within the first 6 months of life) were found to have a high probability of becoming carriers (0.885; 95% C.L. 0.84-0.93). Over the infant and early childhood age classes there was found to be a sharp decrease in the proportion of infections which lead to the carrier state. By adulthood (over 15 years) the probability of developing the carrier status was found to be about 0.1. A model was fitted to the data by using maximum likelihood, which provides a good empirical description of the observed data and can be used to predict the expected probability of developing the carrier state given the age at infection. It is postulated that, as a result of this rapid decline in the probability of becoming a carrier during early childhood, a mass childhood immunization campaign, which will tend to postpone the average age at infection in the unvaccinated community, will have a disproportionately large impact on the rate of generation of new carriers.

Adolescent↗
PubMed1993

Efficacy of hepatitis B vaccine in the Gambian expanded programme on immunisation.

Because of the high prevalence of hepatitis B virus (HBV) infection in The Gambia, HBV vaccination has been incorporated into the national expanded programme on immunisation. We have assessed the efficacy of the vaccine against HBV infection and chronic carriage by examining 720 3-4-year-old children who had received the vaccine in infancy and 816 who had not received it. The vaccine was 84% (95% CI 78-89%) effective against infection and 94% (84-98%) effective against chronic carriage. Vaccinated infants of mothers positive for hepatitis B surface and e antigens were at greater risk of breakthrough infection and chronic carriage than infants of uninfected mothers. The high vaccine efficacy against the HBV carrier state, the main risk factor for the development of chronic liver disease and liver cancer, offers hope that the prevalence of these diseases may be reduced in the future.

Carrier State↗
PubMed1993

The pattern of infant and childhood mortality in Upper River Division, The Gambia.

A system has been established to document births and deaths in children in a large, rural, West African population, using community reporters. Causes of death in children under the age of 5 years were investigated using post-mortem questionnaires completed by field assistants. There was a marked seasonal incidence of all major causes of death with peak rates in the rainy season. Acute lower respiratory infections (ALRI) were the most frequent cause of death in children under 5 years of age. Other major causes of death were malaria, acute gastro-enteritis and chronic diarrhoea with malnutrition. Mortality from all the major causes of death decreased with increasing village size. Our findings have implications for interventions against childhood mortality.

Acute Disease↗
PubMed1993

Risk factors for mortality from acute lower respiratory tract infections in young Gambian children.

A case-control study has been undertaken in a rural area of The Gambia to evaluate risk factors for death from acute lower respiratory tract infections (ALRI) in young children. On the basis of a post-mortem interview 129 children aged < 2 years were thought to have died from ALRI. These cases were each matched according to age, sex, ethnic group, time and place of death with a child who had died from a cause other than an ALRI and with two live control children. Cases and controls were well matched. Comparison of cases and live controls suggested that exposure to smoke during cooking, parental smoking and exclusive, prolonged breastfeeding were associated with an increased risk of death from ALRI whilst sharing a bed with siblings, use of antenatal and welfare clinics and immunization were associated with a reduced risk of death from ALRI. No associations were found between mortality from ALRI and maternal education and literacy, socioeconomic status or with the age of the mother. Comparison of children who died from causes other than ALRI with the live controls showed a similar pattern of associations and no significant differences were found in any of the risk factors studied between children whose deaths were attributed to ALRI and those whose death was attributed to another cause. Association of death with exposure to smoke during cooking was the strongest risk factor identified. This risk might be altered by reducing smoke exposure during cooking.

Acute Disease↗
PubMed1993

Hepatitis in travellers: epidemiology and prevention.

Viral hepatitis is one of the commonest illnesses to afflict travellers. Hepatitis A is the commonest infection. It is particularly common in travellers from low incidence countries such as those of northern Europe, in those travelling to the high incidence countries of the developing world and in those staying abroad for long periods. Hepatitis B is less common and particularly affects those who engage in sexual activity abroad or who are exposed occupationally. Other forms of viral hepatitis appear rare although epidemiological data is sparse. Hepatitis A, B and yellow fever can be prevented through vaccination of the appropriate groups of travellers.

Adolescent↗
PubMed1993

Magnetic resonance imaging in cervical spine trauma.

The ability of magnetic resonance imaging (MRI) to diagnose locked facets was examined in a series of six patients with traumatic cervical spine fractures. Plain films, computed tomography, and magnetic resonance scanning were done immediately following injury. Cord edema, contusions, and acute disc herniation were well visualized on magnetic resonance images. Magnetic resonance proved to be equally effective in diagnosing unilateral and bilateral locked facets, and demonstrated the disruption of the posterior longitudinal ligament (PLL) with clarity. The magnetic resonance diagnostic criteria of locked facets, herniation of intervertebral discs, and rupture of the posterior longitudinal ligament are described. Besides permitting direct visualization of the spinal cord, MRI may have a role in the diagnosis and management of acute bony injury to the cervical spine.

Adult↗
PubMed1993

The aetiology of ocular toxoplasmosis in Melbourne.

The biological mothers of 23 patients presenting with acute chorioretinal toxoplasmosis had sera screened for the presence of antibodies to Toxoplasma gondii. Twenty-two of the mothers (96%) had positive serology and one (4%) had negative serology. This is consistent with the hypothesis that most cases of ocular toxoplasmosis are congenital in origin, but indicates that some cases are due to acquired toxoplasmosis.

Adolescent↗
PubMed1993

Glucoprivation induces anestrus and lipoprivation may induce hibernation in Syrian hamsters.

Previous results supported the notion that estrous cycles in Syrian hamsters are responsive to the general availability of metabolic fuels, rather than to either fatty acid or glucose availability per se. To test this idea, we monitored estrous cycles in hamsters that were fed ad libitum and treated with a range of doses of 2-deoxy-D-glucose (2-DG), an inhibitor of glucose utilization. Hamsters treated with 2-DG at doses ranging from 750-1,250 mg/kg showed normal estrous cycles, but higher doses (1,750 or 2,000 mg/kg) induced anestrus. While it is clear from these data that estrous cycles are affected by glucoprivation, it is not clear whether they are responsive to decreased fatty acid availability. Groups of hamsters were fed ad libitum and treated with a range of doses of methyl palmoxirate (MP), an inhibitor of fatty acid utilization. Some of the hamsters that received the highest doses became torpid and thus were not tested for lordosis. None of the euthermic, MP-treated hamsters became anestrous. Other experiments examined the role of glucose availability in fasted hamsters. Hamsters with a high body fat content were protected from fasting-induced anestrus. In contrast, fat food-deprived hamsters treated with low doses of 2-DG (750 mg/kg) became anestrous. Thus fatty acids mobilized from adipose tissue did not prevent fasting-induced anestrus when glucose utilization was blocked. One interpretation is that during fasting fatty acid utilization spares glucose for other tissues involved in the control of estrous cycles.(ABSTRACT TRUNCATED AT 250 WORDS)

Anestrus↗