Low sensitivity of nested PCR using Plasmodium DNA extracted from stained thick blood smears: an epidemiological retrospective study among subjects with low parasitaemia in an endemic area of the Brazilian Amazon region

BACKGROUND: The success of PCR technique depends on many factors, such as high quality DNA pellets obtained from blood samples, good reagents and adequate conditions of amplification. Taking these limitations into account, a retrospective epidemiological study for malaria diagnosis was conducted in a mesoendemic area in the Brazilian Amazon. METHODS: A nested PCR protocol with DNA extracted from two blood storage devices obtained from Giemsa-stained thick blood smears and filter-papers was used for malaria diagnosis. The extracted DNA was used as a template to amplify approximately 100 bp species-specific sequences of the small subunit of the ribosomal RNA (18S SSU rRNA) of Plasmodium sp. The prevalence of single and mixed infections was examined in a cross-sectional survey carried out among 369 miners living in the district of Apiacás, Mato Grosso State. The parasitemia levels detected by microscopic examination were compared to the PCR results. RESULTS: DNA samples isolated from blood on filter-paper allowed the detection and identification of Plasmodium in 165 (44.7%) of the 369 individuals evaluated, while only 62 (16.8%) had positive results using DNA obtained from thick smears, a similar rate observed by microscopic examination. The sensitivities of PCR using DNA from blood smears and filter-papers were 65% and 73.0%, respectively. Low parasite infections (below 20 parasites/µL blood) were not detected when thick blood smears were used as a DNA source. CONCLUSIONS: Although the blood preserved as thick blood smears provides an alternative and useful tool for malaria molecular diagnosis, its relatively poor performance at low level parasitemias impairs the correct determination of malaria prevalence in epidemiological studies. However, the results obtained in the present study confirm that the use of filter-paper to collect blood is useful for field studies

Signatures of large composite Dark Matter states

We investigate the interactions of large composite dark matter (DM) states with the Standard Model (SM) sector. Elastic scattering with SM nuclei can be coherently enhanced by factors as large as A^2, where A is the number of constituents in the composite state (there exist models in which DM states of very large A > 10^8 may be realised). This enhancement, for a given direct detection event rate, weakens the expected signals at colliders by up to 1/A. Moreover, the spatially extended nature of the DM states leads to an additional, characteristic, form factor modifying the momentum dependence of scattering processes, altering the recoil energy spectra in direct detection experiments. In particular, energy recoil spectra with peaks and troughs are possible, and such features could be confirmed with only O(50) events, independently of the assumed halo velocity distribution. Large composite states also generically give rise to low-energy collective excitations potentially relevant to direct detection and indirect detection phenomenology. We compute the form factor for a generic class of such excitations - quantised surface modes - finding that they can lead to coherently-enhanced, but generally sub-dominant, inelastic scattering in direct detection experiments. Finally, we study the modifications to capture rates in astrophysical objects that follow from the elastic form factor, as well as the effects of inelastic interactions between DM states once captured. We argue that inelastic interactions may lead to the DM collapsing to a dense configuration at the centre of the object.Comment: 30 pages, 5 figures, v2; references and minor additional comments adde

Imaging fascicular organization of rat sciatic nerves with fast neural electrical impedance tomography

Imaging compound action potentials (CAPs) in peripheral nerves could help avoid side effects in neuromodulation by selective stimulation of identified fascicles. Existing methods have low resolution, limited imaging depth, or are invasive. Fast neural electrical impedance tomography (EIT) allows fascicular CAP imaging with a resolution of <200 µm, <1 ms using a non-penetrating flexible nerve cuff electrode array. Here, we validate EIT imaging in rat sciatic nerve by comparison to micro-computed tomography (microCT) and histology with fluorescent dextran tracers. With EIT, there are reproducible localized changes in tissue impedance in response to stimulation of individual fascicles (tibial, peroneal and sural). The reconstructed EIT images correspond to microCT scans and histology, with significant separation between the fascicles (p < 0.01). The mean fascicle position is identified with an accuracy of 6% of nerve diameter. This suggests fast neural EIT can reliably image the functional fascicular anatomy of the nerves and so aid selective neuromodulation

Low sensitivity of nested PCR using <it>Plasmodium </it>DNA extracted from stained thick blood smears: an epidemiological retrospective study among subjects with low parasitaemia in an endemic area of the Brazilian Amazon region

Abstract Background The success of PCR technique depends on many factors, such as high quality DNA pellets obtained from blood samples, good reagents and adequate conditions of amplification. Taking these limitations into account, a retrospective epidemiological study for malaria diagnosis was conducted in a mesoendemic area in the Brazilian Amazon. Methods A nested PCR protocol with DNA extracted from two blood storage devices obtained from Giemsa-stained thick blood smears and filter-papers was used for malaria diagnosis. The extracted DNA was used as a template to amplify approximately 100 bp species-specific sequences of the small subunit of the ribosomal RNA (18S SSU rRNA) of Plasmodium sp. The prevalence of single and mixed infections was examined in a cross-sectional survey carried out among 369 miners living in the district of Apiacás, Mato Grosso State. The parasitemia levels detected by microscopic examination were compared to the PCR results. Results DNA samples isolated from blood on filter-paper allowed the detection and identification of Plasmodium in 165 (44.7%) of the 369 individuals evaluated, while only 62 (16.8%) had positive results using DNA obtained from thick smears, a similar rate observed by microscopic examination. The sensitivities of PCR using DNA from blood smears and filter-papers were 65% and 73.0%, respectively. Low parasite infections (below 20 parasites/µL blood) were not detected when thick blood smears were used as a DNA source. Conclusions Although the blood preserved as thick blood smears provides an alternative and useful tool for malaria molecular diagnosis, its relatively poor performance at low level parasitemias impairs the correct determination of malaria prevalence in epidemiological studies. However, the results obtained in the present study confirm that the use of filter-paper to collect blood is useful for field studies.</p

Elastic scattering of F-17 on Pb-208 and F-17 breakup cross section at Coulomb barrier energies

We have studied the elastic scattering of the exotic 17F nuclei from 208Pb at Coulomb barrier energies. For the measurement we used a new detector array with pixel structure and a large solid angle. Optical potential analysis shows that 17F has an imaginary potential much less deep than 19F. Information on the exclusive 17F breakup cross section has been deduced too