Epitaxial deposition of silver ultra-fine nano-clusters on defect-free surfaces of HOPG-derived few-layer graphene in a UHV multi-chamber by in situ STM, ex situ XPS, and ab initio calculations.

The growth of three-dimensional ultra-fine spherical nano-particles of silver on few layers of graphene derived from highly oriented pyrolytic graphite in ultra-high vacuum were characterized using in situ scanning tunneling microscopy (STM) in conjunction with X-ray photoelectron spectroscopy. The energetics of the Ag clusters was determined by DFT simulations. The Ag clusters appeared spherical with size distribution averaging approximately 2 nm in diameter. STM revealed the preferred site for the position of the Ag atom in the C-benzene ring of graphene. Of the three sites, the C-C bridge, the C-hexagon hollow, and the direct top of the C atom, Ag prefers to stay on top of the C atom, contrary to expectation of the hexagon-close packing. Ab initio calculations confirm the lowest potential energy between Ag and the graphene structure to be at the exact site determined from STM imaging.

Molecular dynamics simulation studies of structural and mechanical properties of single-walled carbon nanotubes.

Structural and mechanical properties of armchair, zig-zag and chiral single-walled carbon nanotubes are computed by employing Molecular Dynamics simulation technique using Discover code with Compass force field via Materials Studio program developed by the Accelrys. Consistent with the literature, we find that the armchair SWCNT is energetically favored over zig-zag and chiral nanotubes. Predicted structural parameters agree well with experimental observations. Observed radial distribution functions show that the single-walled carbon nanotubes remain crystalline after exposing them to 300 K. The predicted Young's and the Shear moduli were in reasonable agreement with other reports. Our predictions show that the Young's modulus of the tubes increases as the diameter of the tube decreases.

DFT studies of low concentration substitutional doping of transition-metals on single-walled carbon nanotube surface.

Using first principles-density functional theory, a theoretical study of the electronic properties of (5, 5) armchair single-walled carbon nanotube doped with transitions metals (Fe, Co and Ni) is presented. The generalized gradient approximation was used for the exchange-correlation potentials. The energy cut-off of 500 eV was adopted in the study. The main features of electronic band structure and density of states are shown. A systematic comparison of the density of states as well as band structures of pure and doped SWCNT is made. The contribution of the different bands was analyzed from the total and partial density of states curves. These metals are used as catalysts during synthesis of single-walled carbon nanotubes and hence, the choice we have made. Where data is available, the results are compared with previous calculations and with experimental measurements.

Effect of oxygen doping on electrical properties of small radius (2,1) single-walled carbon nanotubes.

We investigated the electrical conductivity of the small radius oxygen-doped (2,1) single-walled carbon nanotubes (SWCNTs) using first-principles density functional theory (DFT). We found that introduction of oxygen does not significantly change the global structure of the SWCNT, and thus the bonding mode of the structure is not remarkably altered. The results show that doping enhances the conductivity of the SWCNT. Oxygen doping increases density of states at the Fermi level, thus the conductivity of the doped SWCNT increases when oxygen is introduced, consistent with experimental observations. These observations were further clarified by comparing band structures of pristine and doped nanotubes.

Evaluation of the cost-effectiveness of pyramidal, modified pyramidal and monoscreen traps for the control of the tsetse fly, Glossina fuscipes fuscipes, in Uganda.

Several trap designs have been used for sampling and control of the tsetse fly, Glossina fuscipes fuscipes, Newstead (Diptera: Glossinidae) based on preferences of individual researchers and program managers with little understanding of the comparative efficiency and cost-effectiveness of trap designs. This study was carried out to evaluate the cost-effectiveness of four commonly used trap designs: monoscreen, modified pyramidal and pyramidal, relative to the standard biconical trap. The study was performed under high tsetse challenge on Buvuma Island, Lake Victoria, Uganda, using a 4 x 4 Latin square design replicated 3 times, so as to separate the trap positions and day effects from the treatment effect. A total of 12 trap positions were tested over 4 days. The monoscreen trap caught significantly higher numbers of G. f. fuscipes (P<0.05) followed by biconical, modified pyramidal and pyramidal traps. Analysis of variance showed that treatment factor was a highly significant source of variation in the data. The index of increase in trap catches relative biconical were 0.60 (pyramidal), 0.68 (modified pyramidal) and 1.25 (monoscreen). The monoscreen trap was cheaper (US$ 2.61) and required less material to construct than pyramidal trap (US$ 3.48), biconical and the modified pyramidal traps (US$ 4.06 each). Based on the number of flies caught per meter of material, the monoscreen trap proved to be the most cost-effective (232 flies/m) followed by the biconical trap (185 flies/m). The modified pyramidal and the pyramidal traps caught 112 and 125 flies/m, respectively.

Capacity of community-based organisations to disseminate sleeping sickness information.

OBJECTIVE: To assess the capacity of established community based organisations (CBOs) to disseminate information on sleeping sickness control. DESIGN: Participatory interview process administered to randomly selected CBOs in a tsetse and trypanosomosis endemic area. SETTING: Busia district, Western, Kenya. RESULTS: Community based organisations especially women groups and farmer field schools that are internally initiated have the potential to contribute greatly to sustainable sleeping sickness dissemination strategies. The study indicated a mean reach of between 400-600 persons per day, but with a range of up to 1000 persons per day. CONCLUSION: Internally initiated women groups may be the best options for targeting health education programmes with the aim of ensuring sustained community participation.

Human African trypanosomiasis and human immunodeficiency virus co-infection in Western Kenya.

OBJECTIVE: To determine possible interaction between infections of Trypanosoma brucei rhodesiense sleeping sickness and HIV/AIDS in Western Kenya. DESIGN: Random selection and testing for HIV infections of serum samples from HAT patients using an indirect single phase enzyme linked immunosorbent assay (EAI-Immunocomb II, oragenics). SETTING: National Sleeping Sickness Referral Hospital-Alupe. RESULTS: Four (16%) of the HAT serum samples (n = 25) were found to be seropositive for HIV type 1 and 2 infections, while an additional four (16%) were sero-positive to HIV type 2 infections alone. In contrast, the patients from the local STD clinic showed that 52% (n = 53) were seropositive for both HIV type 1 and 2 infections. No patient from the STD clinic was seropositive for HIV type 2 alone. Calculated Yates Chi square value of 17.31 (P > 0.001) indicated a significant increase in HIV type 2 antibodies in T. brucei rhodesiense sleeping sickness patients. RESULTS: Sixteen percent of the HAT serum samples (n = 25) were found to be seropositive for HIV type 1 and 2 infections, while an additional 16% were sero-positive to HIV type 2 infections alone. In contrast, the patients from the local STD clinic showed that 52% (n = 53) were seropositive for both HIV type 1 and 2 infections. No patient from the STD clinic was seropositive for HIV type 2 alone. Calculated Yates Chi square value of 17.31 (P < 0.001) indicated a significant increase in HIV type 2 antibodies in T. brucei rhodesiense sleeping sickness patients. CONCLUSION: T. brucei rhodesiense sleeping sickness is an immuno-suppressive disease whose patients have shown a higher affinity to HIV type 2 infections more common in central and western Africa. Such patients when treated, appear to recover from HAT but later succumb to full-blown AIDS. It is recommended that CD4+ T cell numbers and CD4/CD8 T cell ratios be assessed toinvestigate response to treatment in HIV positive HAT patients.

Association of trypanosomosis risk with dairy cattle production in western Kenya.

Dairy cattle reared in western Kenya are exposed to medium to high levels of trypanosomosis risk. The social background, farm characteristics and dairy cattle productivity of 90 and 30 randomly selected farmers from medium- and high-risk trypanosomosis areas, respectively, were compared. All the 120 farmers were visited between July and August 2002. Data analysis was performed using descriptive statistics and analysis of variance. The results showed that increased trypanosomosis risk represented by an increase in disease prevalence in cattle of 1% to 20% decreased the density of dairy cattle by 53% and increased the calving interval from 14 to 25 months. The increased risk was also associated with a significant increase in cattle mortalities and in a lactation period of 257 to 300 days. It was concluded that removal of the trypanosomosis constraint on dairy production would lead to expansion of dairying since the domestic demand for dairy products is expected to increase.

Characterisation of Theileria parva isolates from Kiambu district, Kenya.

Four Theileria parva isolates from Muguga area of Kiambu district, Kenya, were used to establish schizont-infected cell lines. Their protein antigens were then separated by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS page). The isolates were subsequently subjected to protein analysis and characterisation by the western immunoblotting technique. Probing for the polymorphic immunodominant molecule (PIM) was done using monoclonal antibody no. 4. SDS page detected up to 20 protein antigens of molecular mass 35,000-180,000 Da. The western blot analysis revealed a greater heterogeneity in the molecular mass (M(r)) of PIM than previously thought. The M(r) of PIM varied between 80 and 90 kDa. The isolates further revealed different densities of surface epitopes with variable reaction to the monoclonal antibody. The implications of these findings to the epidemiology of east coast fever and immunisation programmes are discussed.

Detection of Trypanosoma brucei rhodesiense in animals from sleeping sickness foci in East Africa using the serum resistance associated (SRA) gene.

The human serum resistance associated (SRA) gene has been found exclusively in Trypanosoma brucei rhodesiense, allowing the unequivocal detection of this pathogen in reservoir hosts and the tsetse vector without recourse to laborious strain characterisation procedures. We investigated the presence of the SRA gene in 264 T. brucei ssp. isolates from humans, domestic animals and Glossina pallidipes from foci of human trypanosomiasis in Kenya and Uganda. The SRA gene was present in all isolates that were resistant to human serum, and absent from all serum sensitive isolates tested. Further, the gene was present in all isolates that had previously been shown to be identical to human infective trypanosomes by isoenzyme characterisation. The SRA gene was detected in isolates from cattle, sheep, pigs, dog, reedbuck, hyena and G. pallidipes from sleeping sickness foci, but was not found in Trypanosoma evansi or in Trypanosoma brucei gambiense isolates. The present study indicates that the SRA gene may be invaluable in detecting and differentiating T. brucei rhodesiense from other T. brucei ssp. in reservoir hosts and tsetse.

Paediatric Sleeping Sickness in Kenya : A Case Report

Sleeping sickness is often considered a disease of adults rather than children due to their reduced exposure to the vector. Presumptive diagnosis of sleeping sickness was however difficult since the clinical signs observed were non-specific. This makes clinical diagnosis difficult. Often the disease in children masquerades as a pulmonary infection that is undetectable on x-ray or auscultation. A male child aged two years and eight months was diagnosed with the disease in western Kenya. The patient presented with severe respiratory distress; hepatosplenomegay and neurological symptoms. The disease transmission was associated with the socio-cultural habit of placing children under bushes whilst farming. The implications of delayed diagnosis on response to treatment are discussed

Occurrence, clinical manifestation and the epidemiological implications of naturally occurring canine trypanosomosis in western Kenya.

Domestic dogs were screened for Trypanosoma brucei infection using the haematocrit centrifugation technique as part of routine active surveillance exercises in the Busia and Teso districts of Kenya. The purpose was to assess the role of dogs as sentinels for the occurrence of human sleeping sickness. Out of 200 dogs screened, five were found to be infected at the various test sites. These five succumbed to the disease within four weeks, and exhibited a distinct and pronounced corneal opacity before death. Blood from two naturally infected dogs were tested for the presence of the serum resistance associated (SRA) gene and one tested positive, confirming it as human infective (T. brucei rhodesiense) prevalence (0.5%). It is considered that the occurrence of this clinical sign could be used as an early warning prediction of future outbreaks. This type of prediction could form an integral part of an indigenous technical knowledge set in areas lying at the edges of the tsetse (Glossina) belts where T. brucei is the main trypanosome species that affects dogs. The occurrence of corneal opacity in dogs could indicate a rise in the levels of T. brucei a proportion of which could be human infective T. b. rhodesiense circulating in the population early enough before disease outbreak occurs. It is thought that during sleeping sickness epidemics the domestic dog will be the first casualty rapidly succumbing to disease long before it is noticed in man. Prompt prediction of disease outbreaks would thus enable early interventions that would reduce the morbidity, mortality and the general economic losses associated with sleeping sickness to be instituted.