Microbial Nitrogen Limitation Increases Decomposition

With anthropogenic nutrient inputs to ecosystems increasing globally, there are long-standing, fundamental questions about the role of nutrients in the decomposition of organic matter. We tested the effects of exogenous nitrogen and phosphorus inputs on litter decomposition across a broad suite of litter and soil types. In one experiment, C mineralization was compared across a wide array of plants individually added to a single soil, while in the second, C mineralization from a single substrate was compared across 50 soils. Counter to basic stoichiometric decomposition theory, low N availability can increase litter decomposition as microbes use labile substrates to acquire N from recalcitrant organic matter. This “microbial nitrogen mining” is consistently suppressed by high soil N supply or substrate N concentrations. There is no evidence for phosphorus mining as P fertilization increases short- and long-term mineralization. These results suggest that basic stoichiometric decomposition theory needs to be revised and ecosystem models restructured accordingly in order to predict ecosystem carbon storage responses to anthropogenic changes in nutrient availability

Decreasing household contribution to TB transmission with age: a retrospective geographic analysis of young people in a South African township

BACKGROUND: Tuberculosis (TB) transmission rates are exceptionally high in endemic TB settings. Adolescence represents a period of increasing TB infection and disease but little is known as to where adolescents acquire TB infection. We explored the relationship between residential exposure to adult TB cases and infection in children and adolescents in a South African community with high burdens of TB and HIV. METHODS: TB infection data were obtained from community, school-based tuberculin skin test (TST) surveys performed in 2006, 2007 and 2009. A subset of 2007 participants received a repeat TST in 2009, among which incident TB infections were identified. Using residential address, all adult TB cases notified by the community clinic between 1996 and 2009 were cross-referenced with childhood and adolescent TST results. Demographic and clinic data including HIV status were abstracted for TB cases. Multivariate logistic regression models examined the association of adult TB exposure with childhood and adolescent prevalent and incident TB infection. RESULTS: Of 1,100 children and adolescents included in the prevalent TB infection analysis, 480 (44%) were TST positive and 651 (59%) were exposed to an adult TB case on their residential plot. Prevalent TB infection in children aged 5-9 and 10-14 years was positively associated with residential exposure to an adult TB case (odds ratio [OR]:2.0; 95% confidence interval [CI]: 1.1-3.6 and OR:1.5; 95% CI: 1.0-2.3 respectively), but no association was found in adolescents [greater than or equal to]15years (OR:1.4; 95% CI: 0.9-2.0). HIV status of adult TB cases was not associated with TB infection (p=0.62). Of 67 previously TST negative children, 16 (24%) converted to a positive TST in 2009. These incident infections were not associated with residential exposure to an adult TB case (OR: 1.9; 95% CI: 0.5-7.3). CONCLUSIONS: TB infection among young children was strongly associated with residential exposure to an adult TB case, but prevalent and incident TB infection in adolescents was not associated with residential exposure. The HIV-status of adult TB cases was not a risk factor for transmission. The high rates of TB infection and disease among adolescents underscore the importance of identifying where infection occurs in this age group

Childhood tuberculosis infection and disease: A spatial and temporal transmission analysis in a South African township

Background. Tuberculosis (TB) remains a leading cause of South African mortality and morbidity. While adult TB arises from both recent and prior infection, childhood TB results from recent infection and reflects ongoing transmission occurring despite current TB control strategies. Setting. A South African community with high rates of TB and HIV disease. Outcomes. A Geographic Information System was used to spatially and temporally define the relationships between TB exposure, infection and disease in children <15 years of age, with exposure to adult HIV-positive and HIV-negative TB disease on residential plots between 1997 and 2007. Results. During the study period the annual adult TB notification rate increased from 629 to 2106/100,000 and <15yrs TB notification rate ranged between 664/100,000 and 1044/100,000. The mean exposure to adult TB for uninfected children, TB-infected, TB cases was 5.1%, 5.4% and 33% per annum and the mean number of adult smear-positive cases per exposed child was 1.0, 1.6 and 1.9 respectively. Acquisition of TB infection was not associated with HIV status of adult exposure TB case and 36% of child TB cases were diagnosed prior to the temporally closest adult case on their plot. Conclusions. Childhood infection and disease were quantitatively linked to infectious adult TB prevalence in an immediate social network. Childhood infection should be monitored in high burden settings as a marker of ongoing TB transmission. Improved knowledge of township childhood and adult social networks may also facilitate targeted active case finding, which may provide an adjunct to presently failing TB control strategies

Remote sensing of HIV care programmes using centrally collected laboratory results: Can we monitor ART programme effectiveness?

Aims. We describe a monitoring system at population level of patients on antiretroviral therapy (ART) using centrally collected laboratory data. We demonstrate an analogous process of remote sensing using a large set of laboratory results and illustrate the tremendous density of information stored. We moved from an individual to a community view of ART rollout, similar to remote sensing used in the earth and biological sciences when the spatial scale of the investigation is too large to be performed at ground level. Methods. This was a retrospective cohort study of patients from January 2004 to June 2011. A total of 188 759 individual laboratory results representing 26 445 patients were analysed for average CD4 and viral load by year. Results. The data showed an increasing state of health of the population and allowed for hypothesis generation when the trends did not follow expected paths. Conclusion. In this analysis we moved away from individual-centred data to population-level data in order to assess ART programme performance. Routine patient-monitoring data had great utility in assessment of population health. These methods are useful in monitoring and evaluation and effectiveness studies as they are easy to collect, reliable (not requiring much human matching or interventions) and scalable from a single clinic to an entire population. The larger the sample size, the more reliable the results, as confounders (such as incorrectly identified transfers out, lost-to-follow-up patients and transfers in) would be removed

Estimating age-mixing patterns relevant for the transmission of airborne infections.

INTRODUCTION: Age-mixing patterns can have substantial effects on infectious disease dynamics and intervention effects. Data on close contacts (people spoken to and/or touched) are often used to estimate age-mixing. These are not the only relevant contacts for airborne infections such as tuberculosis, where transmission can occur between anybody 'sharing air' indoors. Directly collecting data on age-mixing patterns between casual contacts (shared indoor space, but not 'close') is difficult however. We demonstrate a method for indirectly estimating age-mixing patterns between casual indoor contacts from social contact data. METHODS: We estimated age-mixing patterns between close, casual, and all contacts using data from a social contact survey in South Africa. The age distribution of casual contacts in different types of location was estimated from the reported time spent in the location type by respondents in each age group. RESULTS: Patterns of age-mixing calculated from contact numbers were similar between close and all contacts, however patterns of age-mixing calculated from contact time were more age-assortative in all contacts than in close contacts. There was also more variation by age group in total numbers of casual and all contacts, than in total numbers of close contacts. Estimates were robust to sensitivity analyses. CONCLUSIONS: Patterns of age-mixing can be estimated for all contacts using data that can be easily collected as part of social contact surveys or time-use surveys, and may differ from patterns between close contacts

The effect of systemic cocaine on spinal nociceptive reflex activity in the rat

In the anesthetized rat, cocaine (25 mg/kg i.p.), enhanced the frequency potentiation of nociceptively evoked polysynaptic discharges but did not affect the polysynaptic reflex discharge to single nociceptive stimuli or the habituation of this reflex to repetitive pinch stimuli. The non-nociceptive, short-latency reflex discharge was suppressed for 10-15 min after cocaine administration. The neurogenic extravasation response to antidromic cutaneous C-fiber stimulation was unaffected by cocaine. These findings suggest that systemic cocaine, in doses analgesic for the rat, does not suppress spinal nociceptive reflexes.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27430/1/0000468.pd