Co-infection of the four major Plasmodium species: effects on densities and gametocyte carriage

BACKGROUND: Co-infection of the four major species of human malaria parasite Plasmodium falciparum (Pf), P. vivax (Pv), P. malariae (Pm), and P. ovale sp. (Po) is regularly observed, but there is limited understanding of between-species interactions. In particular, little is known about the effects of multiple Plasmodium species co-infections on gametocyte production. METHODS: We developed molecular assays for detecting asexual and gametocyte stages of Pf, Pv, Pm, and Po. This is the first description of molecular diagnostics for Pm and Po gametocytes. These assays were implemented in a unique epidemiological setting in Papua New Guinea with sympatric transmission of all four Plasmodium species permitting a comprehensive investigation of species interactions. FINDINGS: The observed frequency of Pf-Pv co-infection for asexual parasites (14.7%) was higher than expected from individual prevalence rates (23.8%Pf x 47.4%Pv = 11.3%). The observed frequency of co-infection with Pf and Pv gametocytes (4.6%) was higher than expected from individual prevalence rates (13.1%Pf x 28.2%Pv = 3.7%). The excess risk of co-infection was 1.38 (95% confidence interval (CI): 1.09, 1.67) for all parasites and 1.37 (95% CI: 0.95, 1.79) for gametocytes. This excess co-infection risk was partially attributable to malaria infections clustering in some villages. Pf-Pv-Pm triple infections were four times more frequent than expected by chance alone, which could not be fully explained by infections clustering in highly exposed individuals. The effect of co-infection on parasite density was analyzed by systematic comparison of all pairwise interactions. This revealed a significant 6.57-fold increase of Pm density when co-infected with Pf. Pm gametocytemia also increased with Pf co-infection. CONCLUSIONS: Heterogeneity in exposure to mosquitoes is a key epidemiological driver of Plasmodium co-infection. Among the four co-circulating parasites, Pm benefitted most from co-infection with other species. Beyond this, no general prevailing pattern of suppression or facilitation was identified in pairwise analysis of gametocytemia and parasitemia of the four species. TRIAL REGISTRATION: This trial is registered with ClinicalTrials.gov, Trial ID: NCT02143934

qRT-PCR versus IFA-based quantification of male and female gametocytes in low-density Plasmodium falciparum infections and their relevance for transmission

Accurate quantification of female and male gametocytes and sex ratios in asymptomatic low-density malaria infections are important for assessing their transmission potential. Gametocytes often escape detection even by molecular methods, therefore ultralow gametocyte densities were quantified in large blood volumes.; Female and male gametocytes were quantified in 161 PCR-positive Plasmodium falciparum infections from a cross-sectional survey in Papua New Guinea. Ten-fold concentrated RNA from 800 µL blood was analyzed using female-specific pfs25 and male-specific pfmget or mssp qRT-PCR. Gametocyte sex ratios from qRT-PCR were compared with those from immunofluorescence assays (IFA).; Gametocytes were identified in 58% (93/161) P. falciparum-positive individuals. Mean gametocyte densities were frequently below 1 female and 1 male gametocyte/µL by qRT-PCR. The mean proportion of males was 0.39 (95% confidence interval, 0.33-0.44) by pfs25/pfmget qRT-PCR; this correlated well with IFA results (Pearsons r2 = 0.91; P < .001). A Poisson model fitted to our data predicted 16% P. falciparum-positive individuals that are likely to transmit, assuming at least 1 female and 1 male gametocyte per 2.5 µL mosquito bloodmeal.; Based on model estimates of female and male gametocytes per 2.5 µL blood, P. falciparum-positive individuals detected exclusively by ultrasensitive diagnostics are negligible for human-to-mosquito transmission.Estimating the transmission potential of ultralow-density malaria infections informs interventions. Almost all infections with ≥1 female and male gametocyte per 2.5 µL mosquito bloodmeal, and thus with highest likelihood of contributing to human-to-mosquito transmission, were detectable by standard molecular diagnostics

Late Endosomal Cholesterol Accumulation Leads to Impaired Intra-Endosomal Trafficking

Background Pathological accumulation of cholesterol in late endosomes is observed in lysosomal storage diseases such as Niemann-Pick type C. We here analyzed the effects of cholesterol accumulation in NPC cells, or as phenocopied by the drug U18666A, on late endosomes membrane organization and dynamics. Methodology/Principal Findings Cholesterol accumulation did not lead to an increase in the raft to non-raft membrane ratio as anticipated. Strikingly, we observed a 2–3 fold increase in the size of the compartment. Most importantly, properties and dynamics of late endosomal intralumenal vesicles were altered as revealed by reduced late endosomal vacuolation induced by the mutant pore-forming toxin ASSP, reduced intoxication by the anthrax lethal toxin and inhibition of infection by the Vesicular Stomatitis Virus. Conclusions/Significance These results suggest that back fusion of intralumenal vesicles with the limiting membrane of late endosomes is dramatically perturbed upon cholesterol accumulation

Temperature dependence of the upper critical field of an anisotropic singlet superconductivity in a square lattice tight-binding model in parallel magnetic fields

Upper critical field parallel to the conducting layer is studied in anisotropic type-II superconductors on square lattices. We assume enough separation of the adjacent layers, for which the orbital pair-breaking effect is suppressed for exactly aligned parallel magnetic field. In particular, we examine the temperature dependence of the critical field H_c(T) of the superconductivity including the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO or LOFF) state, in which the Cooper pairs have non-zero center-of-mass momentum q. In the system with the cylindrically symmetric Fermi-surface, it is known that H_c(T) of the d-wave FFLO state exhibits a kink at a low temperature due to a change of the direction of q in contrast to observations in organic superconductors. It is shown that the kink disappears when the Fermi-surface is anisotropic to some extent, since the direction of q is locked in an optimum direction independent of the temperature.Comment: 5 pages, 5 figures, revtex.sty, submitted to J.Phys.Soc.Jp

Ginzburg-Landau-Gor'kov Theory of Magnetic oscillations in a type-II 2-dimensional Superconductor

We investigate de Haas-van Alphen (dHvA) oscillations in the mixed state of a type-II two-dimensional superconductor within a self-consistent Gor'kov perturbation scheme. Assuming that the order parameter forms a vortex lattice we can calculate the expansion coefficients exactly to any order. We have tested the results of the perturbation theory to fourth and eight order against an exact numerical solution of the corresponding Bogoliubov-de Gennes equations. The perturbation theory is found to describe the onset of superconductivity well close to the transition point $H_{c2}$. Contrary to earlier calculations by other authors we do not find that the perturbative scheme predicts any maximum of the dHvA-oscillations below $H_{c2}$. Instead we obtain a substantial damping of the magnetic oscillations in the mixed state as compared to the normal state. We have examined the effect of an oscillatory chemical potential due to particle conservation and the effect of a finite Zeeman splitting. Furthermore we have investigated the recently debated issue of a possibility of a sign change of the fundamental harmonic of the magnetic oscillations. Our theory is compared with experiment and we have found good agreement.Comment: 39 pages, 8 figures. This is a replacement of supr-con/9608004. Several sections changed or added, including a section on the effect of spin and the effect of a conserved number of particles. To be published in Phys. Rev.

Magnetic-Field Variations of the Pair-Breaking Effects of Superconductivity in (TMTSF)2ClO4

We have studied the onset temperature of the superconductivity Tc_onset of the organic superconductor (TMTSF)2ClO4, by precisely controlling the direction of the magnetic field H. We compare the results of two samples with nearly the same onset temperature but with different scattering relaxation time tau. We revealed a complicated interplay of a variety of pair-breaking effects and mechanisms that overcome these pair-breaking effects. In low fields, the linear temperature dependences of the onset curves in the H-T phase diagrams are governed by the orbital pair-breaking effect. The dips in the in-plane field-angle phi dependence of Tc_onset, which were only observed in the long-tau sample, provides definitive evidence that the field-induced dimensional crossover enhances the superconductivity if the field direction is more than about 19-degrees away from the a axis. In the high-field regime for H//a, the upturn of the onset curve for the long-tau sample indicates a new superconducting state that overcomes the Pauli pair-breaking effect but is easily suppressed by impurity scatterings. The Pauli effect is also overcome for H//b' by a realization of another state for which the maximum of Tc_onset(phi) occurs in a direction different from the crystalline axes. The effect on Tc_onset of tilting the applied field out of the conductive plane suggests that the Pauli effect plays a significant role in determining Tc_onset. The most plausible explanation of these results is that (TMTSF)2ClO4 is a singlet superconductor and exhibits Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states in high fields.Comment: 12 pages, 10 figures. To be published in J. Phys. Soc. Jpn. (vol.77, 2008

Superconducting fluctuations at low temperature

The effect of fluctuations on the transport and thermodynamic properties of two-dimensional superconductors in a magnetic field is studied at low temperature. The fluctuation conductivity is calculated in the framework of the perturbation theory with the help of usual diagram technique. It is shown that in the dirty case the Aslamazov-Larkin, Maki-Thomson and Density of States contributions are of the same order. At extremely low temperature, the total fluctuation correction to the normal conductivity is negative in the dirty limit and depends on the external magnetic field logarithmically. In the non-local clean limit, the Aslamazov-Larkin contribution to conductivity is evaluated with the aid of the Helfand-Werthamer theory. The longitudinal and Hall conductivities are found. The fluctuating magnetization is calculated in the one-loop and two-loop approximations.Comment: 12 pages, 4 figures, submitted to Phys. Rev.

Diversity of Raft-Like Domains in Late Endosomes

BACKGROUND: Late endosomes, the last sorting station in the endocytic pathway before lysosomes, are pleiomorphic organelles composed of tubular elements as well as vesicular regions with a characteristic multivesicular appearance, which play a crucial role in intracellular trafficking. Here, we have investigated whether, in addition to these morphologically distinguishable regions, late endosomal membranes are additionally sub-compartmentalized into membrane microdomains. METHODOLOGY/PRINCIPAL FINDINGS: Using sub-organellar fractionation techniques, both with and without detergents, combined with electron microscopy, we found that both the limiting membrane of the organel and the intraluminal vesicles contain raft-type membrane domains. Interestingly, these differentially localized domains vary in protein composition and physico-chemical properties. CONCLUSIONS/SIGNIFICANCE: In addition to the multivesicular organization, we find that late endosomes contain cholesterol rich microdomains both on their limiting membrane and their intraluminal vesicles that differ in composition and properties. Implications of these findings for late endosomal functions are discussed

Structure of the Fulde-Ferrell-Larkin-Ovchinnikov state in two-dimensional superconductors

Nonuniform superconducting state due to strong spin magnetism is studied in two-dimensional type-II superconductors near the second order phase transition line between the normal and the superconducting states. The optimum spatial structure of the orderparameter is examined in systems with cylindrical symmetric Fermi surfaces. It is found that states with two-dimensional structures have lower free energies than the traditional one-dimensional solutions, at low temperatures and high magnetic fields. For s-wave pairing, triangular, square, hexagonal states are favored depending on the temperature, while square states are favored at low temperatures for d-wave pairing. In these states, orderparameters have two-dimensional structures such as square and triangular lattices.Comment: 11 pages (LaTeX, revtex.sty), 3 figures; added reference