Noise-induced synchronization and anti-resonance in excitable systems; Implications for information processing in Parkinson's Disease and Deep Brain Stimulation

We study the statistical physics of a surprising phenomenon arising in large networks of excitable elements in response to noise: while at low noise, solutions remain in the vicinity of the resting state and large-noise solutions show asynchronous activity, the network displays orderly, perfectly synchronized periodic responses at intermediate level of noise. We show that this phenomenon is fundamentally stochastic and collective in nature. Indeed, for noise and coupling within specific ranges, an asymmetry in the transition rates between a resting and an excited regime progressively builds up, leading to an increase in the fraction of excited neurons eventually triggering a chain reaction associated with a macroscopic synchronized excursion and a collective return to rest where this process starts afresh, thus yielding the observed periodic synchronized oscillations. We further uncover a novel anti-resonance phenomenon: noise-induced synchronized oscillations disappear when the system is driven by periodic stimulation with frequency within a specific range. In that anti-resonance regime, the system is optimal for measures of information capacity. This observation provides a new hypothesis accounting for the efficiency of Deep Brain Stimulation therapies in Parkinson's disease, a neurodegenerative disease characterized by an increased synchronization of brain motor circuits. We further discuss the universality of these phenomena in the class of stochastic networks of excitable elements with confining coupling, and illustrate this universality by analyzing various classical models of neuronal networks. Altogether, these results uncover some universal mechanisms supporting a regularizing impact of noise in excitable systems, reveal a novel anti-resonance phenomenon in these systems, and propose a new hypothesis for the efficiency of high-frequency stimulation in Parkinson's disease

Low Sputum Smear Positive Tuberculosis among Pulmonary Tuberculosis Suspects in a Tertiary Hospital in Mwanza, Tanzania

Early diagnosis of tuberculosis (TB) and prompt initiation of treatment are essential for an effective tuberculosis control programme. In many resource limited settings microscopic diagnosis is still the pivotal tool in the diagnosis of pulmonary TB. This study aimed at evaluating laboratory microscopic diagnosis of tuberculosis in a tertiary hospital in Mwanza, Tanzania. This retrospective hospital based study reviewed consecutively from TB registry and patients’ files a total of 5,922 TB suspects who submitted their sputum for examination between January 2007 and May 2010 at Bugando Medical Centre (BMC). Among TB suspects (mean age=36.1±13.6 years) female accounted for 54.1% of the patients. The prevalence of HIV among TB patients was 59.4%. The sputum smear positivity rate among the TB suspects was 6.1%; the rate was higher in HIV positive than in HIV negative patients (9.9 % versus 3.2%, P-value < 0.001). The overall positivity rate for the first smear was 94.2% with an incremental percentage yield of 5.2% and 0.6% for the second and third smears, respectively. The study found that 28.6% of patients who were positive in the first smear did not return for the second smear. The risk factors among smear positive TB patients were co-illness (32.5%), previous history of TB (7.5%) and history of positive TB contact (4.7%). These findings also show that as CD4+ T Cells count increases, the quantity AFB in sputum smear also increase although not statistically significant. The sputum smear positivity rate at Bugando Medical Centre is low and more than a quarter of initial TB suspects who were positive in the first smear were lost to follow up posing a threat of continuous transmission of tuberculosis to the community. The finding of more sputum smear positivity rate among HIV positive than HIV negative patients at BMC requires a prospective study to ascertain whether it is a reality or a coincidence.\u

Human Wildlife Conflicts to communities surrounding Mikumi National Parks in Tanzania: A case of selected villages

Human wildlife interaction is not a new phenomenon, it has existed since the beginning of humankind, it is evidenced by the fact that, many national parks are surrounded by human residents. The interaction between human and wildlife is of different nature depending on the culture of the surrounding human as well as wildlife community. For decade's human wildlife conflicts has been a great conservation challenge due to increased human population, International trade and change of policies. The challenge is more significant in a sense that it negatively affects both human and wildlife sustainability. Therefore a study was conducted to villages surrounding Mikumi national Park to assess reasons for conflicts between human and wildlife and account how communities prevent wild animals to destructs their agriculture products. Three villages were selected for study (Doma, Maharaka and Mkata, all villages surrounds Mikumi National Park Ecosystems. Different methodology includes: - Field observation, Household survey, Field interview, In-depth interview and Ethnography study were used. However descriptive analysis and non parametric test were performed by using SPSS 16 versions and Kruskal-wallis test respectively to compute mean, standard error, percentages and differences of wildlife consumption. Results suggests that, there is a gradual increase of human-wildlife conflicts which lead to loss of people's lives, as well as their livelihoods such as farms and farms product. Statistically results depicted that the average size of the farm affected at Doma, Maharaka and Mkata villages were 3.8 ± 0.1, 2.0 ± 0.1 and 2.2 ± 0.1 acres respectively, while at Mkata village 32 goats, 24 sheep and 76 cattle were reported to be killed by wild carnivores. In other way conflicts may result to poaching activities which may threaten the existence of huge herbivores such as Elephants and Rhinoceros. Apart from that, conflicts may lead to poor performances of tourism industry in the country. Research recommends that more efforts should be taken by the government and other stakeholders to prevent conflicts around all national parks so as to create good and conducive environment for human being life and wildlife in order to allow good performance of tourism industry for economic development of the country

Intracellular impedance measurements reveal non-ohmic properties of the extracellular medium around neurons

The electrical properties of extracellular space around neurons are important to understand the genesis of extracellular potentials, as well as for localizing neuronal activity from extracellular recordings. However, the exact nature of these extracellular properties is still uncertain. We introduce a method to measure the impedance of the tissue, and which preserves the intact cell-medium interface, using whole-cell patch-clamp recordings in vivo and in vitro. We find that neural tissue has marked non-ohmic and frequency-filtering properties, which are not consistent with a resistive (ohmic) medium, as often assumed. In contrast, using traditional metal electrodes provides very different results, more consistent with a resistive medium. The amplitude and phase profiles of the measured impedance are consistent with the contribution of ionic diffusion. We also show that the impact of such frequency-filtering properties is possibly important on the genesis of local field potentials, as well as on the cable properties of neurons. The present results show non-ohmic properties of the extracellular medium around neurons, and suggest that source estimation methods, as well as the cable properties of neurons, which all assume ohmic extracellular medium, may need to be re-evaluated.Comment: 32 pages, 9 figure

Evaluation of a village-informant driven demographic surveillance system in Karonga, Northern Malawi

This paper describes and evaluates the first demographic surveillance system (DSS) in Malawi, covering a rural population of 30,000. Unlike others, the Karonga DSS relies on trained village informants using formatted registers for the primary notification of vital events and migrations. Seven project enumerators subsequently collect detailed data on events notified by the village informants, using stringent identification procedures for households and individuals. Internal movements are traced systematically to augment event registration and data quality. Continuous evaluation of data collection is built into the methods. A re-census conducted after 2 years indicated that the routine system had registered 97% of 1,588 births, 99% of 521 deaths and 92% of 13,168 movements.demographic surveillance system, evaluation, INDEPTH network, Karonga, Malawi, methods, migration, village informant, vital registration

Microscale Inhomogeneity of Brain Tissue Distorts Electrical Signal Propagation

Interpretations of local field potentials (LFPs) are typically shaped on an assumption that the brain is a homogenous conductive milieu. However, microscale inhomogeneities including cell bodies, dendritic structures, axonal fiber bundles and blood vessels are unequivocally present and have different conductivities and permittivities than brain extracellular fluid. To determine the extent to which these obstructions affect electrical signal propagation on a microscale, we delivered electrical stimuli intracellularly to individual cells while simultaneously recording the extracellular potentials at different locations in a rat brain slice. As compared with relatively unobstructed paths, signals were attenuated across frequencies when fiber bundles were in between the stimulated cell and the extracellular electrode. Across group of cell bodies, signals were attenuated at low frequencies, but facilitated at high frequencies. These results show that LFPs do not reflect a democratic representation of neuronal contributions, as certain neurons may contribute to the LFP more than others based on the local extracellular environment surrounding them

Comparison of the estimated incidence of acute leptospirosis in the Kilimanjaro Region of Tanzania between 2007-08 and 2012-14

Background: The sole report of annual leptospirosis incidence in continental Africa of 75–102 cases per 100,000 population is from a study performed in August 2007 through September 2008 in the Kilimanjaro Region of Tanzania. To evaluate the stability of this estimate over time, we estimated the incidence of acute leptospirosis in Kilimanjaro Region, northern Tanzania for the time period 2012–2014. Methodology and Principal Findings: Leptospirosis cases were identified among febrile patients at two sentinel hospitals in the Kilimanjaro Region. Leptospirosis was diagnosed by serum microscopic agglutination testing using a panel of 20 Leptospira serovars belonging to 17 separate serogroups. Serum was taken at enrolment and patients were asked to return 4–6 weeks later to provide convalescent serum. Confirmed cases required a 4-fold rise in titre and probable cases required a single titre of ≥800. Findings from a healthcare utilisation survey were used to estimate multipliers to adjust for cases not seen at sentinel hospitals. We identified 19 (1.7%) confirmed or probable cases among 1,115 patients who presented with a febrile illness. Of cases, the predominant reactive serogroups were Australis 8 (42.1%), Sejroe 3 (15.8%), Grippotyphosa 2 (10.5%), Icterohaemorrhagiae 2 (10.5%), Pyrogenes 2 (10.5%), Djasiman 1 (5.3%), Tarassovi 1 (5.3%). We estimated that the annual incidence of leptospirosis was 11–18 cases per 100,000 population. This was a significantly lower incidence than 2007–08 (p&lt;0.001). Conclusions: We estimated a much lower incidence of acute leptospirosis than previously, with a notable absence of cases due to the previously predominant serogroup Mini. Our findings indicate a dynamic epidemiology of leptospirosis in this area and highlight the value of multi-year surveillance to understand leptospirosis epidemiology

Risk factors for human brucellosis in northern Tanzania

Little is known about the epidemiology of human brucellosis in sub-Saharan Africa. This hampers prevention and control efforts at the individual and population levels. To evaluate risk factors for brucellosis in northern Tanzania, we conducted a study of patients presenting with fever to two hospitals in Moshi, Tanzania. Serum taken at enrollment and at 4–6 week follow-up was tested by Brucella microagglutination test. Among participants with a clinically compatible illness, confirmed brucellosis cases were defined as having a ≥ 4-fold rise in agglutination titer between paired sera or a blood culture positive for Brucella spp., and probable brucellosis cases were defined as having a single reciprocal titer ≥ 160. Controls had reciprocal titers &lt; 20 in paired sera. We collected demographic and clinical information and administered a risk factor questionnaire. Of 562 participants in the analysis, 50 (8.9%) had confirmed or probable brucellosis. Multivariable analysis showed that risk factors for brucellosis included assisting goat or sheep births (Odds ratio [OR] 5.9, 95% confidence interval [CI] 1.4, 24.6) and having contact with cattle (OR 1.2, 95% CI 1.0, 1.4). Consuming boiled or pasteurized dairy products was protective against brucellosis (OR 0.12, 95% CI 0.02, 0.93). No participants received a clinical diagnosis of brucellosis from their healthcare providers. The under-recognition of brucellosis by healthcare workers could be addressed with clinician education and better access to brucellosis diagnostic tests. Interventions focused on protecting livestock keepers, especially those who assist goat or sheep births, are needed

Factors Associated with Change in Sexual Transmission Risk Behavior over 3 Years among HIV-Infected Patients in Tanzania.

The reduction of HIV transmission risk behaviors among those infected with HIV remains a major global health priority. Psychosocial characteristics have proven to be important correlates of sexual transmission risk behaviors in high-income countries, but little attention has focused on the influence of psychosocial and psychological factors on sexual transmission risk behaviors in African cohorts. The CHAT Study enrolled a representative sample of 499 HIV-infected patients in established HIV care and 267 newly diagnosed HIV-infected individuals from the Kilimanjaro Region of Tanzania. Participants completed in-person interviews every 6 months for 3 years. Using logistic random effects models to account for repeated observations, we assessed sociodemographic, physical health, and psychosocial predictors of self-reported unprotected sexual intercourse. Among established patients, the proportion reporting any recent unprotected sex was stable, ranging between 6-13% over 3 years. Among newly diagnosed patients, the proportion reporting any unprotected sex dropped from 43% at baseline to 11-21% at 6-36 months. In multivariable models, higher odds of reported unprotected sex was associated with female gender, younger age, being married, better physical health, and greater post-traumatic stress symptoms. In addition, within-individual changes in post-traumatic stress over time coincided with increases in unprotected sex. Changes in post-traumatic stress symptomatology were associated with changes in sexual transmission risk behaviors in this sample of HIV-infected adults in Tanzania, suggesting the importance of investing in appropriate mental health screening and intervention services for HIV-infected patients, both to improve mental health and to support secondary prevention efforts

Risk factors for human acute leptospirosis in northern Tanzania

Introduction: Leptospirosis is a major cause of febrile illness in Africa but little is known about risk factors for human infection. We conducted a cross-sectional study to investigate risk factors for acute leptospirosis and Leptospira seropositivity among patients with fever attending referral hospitals in northern Tanzania. Methods: We enrolled patients with fever from two referral hospitals in Moshi, Tanzania, 2012–2014, and performed Leptospira microscopic agglutination testing on acute and convalescent serum. Cases of acute leptospirosis were participants with a four-fold rise in antibody titers, or a single reciprocal titer ≥800. Seropositive participants required a single titer ≥100, and controls had titers &#60;100 in both acute and convalescent samples. We administered a questionnaire to assess risk behaviors over the preceding 30 days. We created cumulative scales of exposure to livestock urine, rodents, and surface water, and calculated odds ratios (OR) for individual behaviors and for cumulative exposure variables. Results: We identified 24 acute cases, 252 seropositive participants, and 592 controls. Rice farming (OR 14.6), cleaning cattle waste (OR 4.3), feeding cattle (OR 3.9), farm work (OR 3.3), and an increasing cattle urine exposure score (OR 1.2 per point) were associated with acute leptospirosis. Conclusions: In our population, exposure to cattle and rice farming were risk factors for acute leptospirosis. Although further data is needed, these results suggest that cattle may be an important source of human leptospirosis. Further investigation is needed to explore the potential for control of livestock Leptospira infection to reduce human disease