Assessing the performance of remotely-sensed flooding indicators and their potential contribution to early warning for leptospirosis in Cambodia

Remote sensing can contribute to early warning for diseases with environmental drivers, such as flooding for leptospirosis. In this study we assessed whether and which remotely-sensed flooding indicator could be used in Cambodia to study any disease for which flooding has already been identified as an important driver, using leptospirosis as a case study. The performance of six potential flooding indicators was assessed by ground truthing. The Modified Normalized Difference Water Index (MNDWI) was used to estimate the Risk Ratio (RR) of being infected by leptospirosis when exposed to floods it detected, in particular during the rainy season. Chi-square tests were also calculated. Another variable—the time elapsed since the first flooding of the year—was created using MNDWI values and was also included as explanatory variable in a generalized linear model (GLM) and in a boosted regression tree model (BRT) of leptospirosis infections, along with other explanatory variables. Interestingly, MNDWI thresholds for both detecting water and predicting the risk of leptospirosis seroconversion were independently evaluated at -0.3. Value of MNDWI greater than -0.3 was significantly related to leptospirosis infection (RR = 1.61 [1.10–1.52]; χ2 = 5.64, p-value = 0.02, especially during the rainy season (RR = 2.03 [1.25–3.28]; χ2 = 8.15, p-value = 0.004). Time since the first flooding of the year was a significant risk factor in our GLM model (p-value = 0.042). These results suggest that MNDWI may be useful as a risk indicator in an early warning remote sensing tool for flood-driven diseases like leptospirosis in South East Asia

Long-Lasting Immune Protection and Other Epidemiological Findings after Chikungunya Emergence in a Cambodian Rural Community, April 2012.

The East/Central/South African genotype of Chikungunya virus with the E1-A226V mutation emerged in 2011 in Cambodia and spread in 2012. An outbreak of 190 cases was documented in Trapeang Roka, a rural village. We surveyed 425 village residents within 3-4 weeks after the outbreak, and determined the sensitivity and specificity of case definitions and factors associated with infection by CHIKV. Self-reported clinical presentation consisted mostly of fever, rash and arthralgia. The presence of all three clinical signs or symptoms was identified as the most sensitive (67%) and specific (84%) self-reported diagnostic clinical indicator compared to biological confirmation by MAC-ELISA or RT-PCR used as a reference. Having an indoor occupation was associated with lower odds of infection compared with people who remained at home (adjOR 0.32, 95%CI 0.12-0.82). In contrast with findings from outbreaks in other settings, persons aged above 40 years were less at risk of CHIKV infection, likely reflecting immune protection acquired when Chikungunya circulated in Cambodia before the Khmer Rouge regime in 1975. In view of the very particular history of Cambodia, our epidemiological data from Trapeang Roka are the first to support the persistence of CHIKV antibodies over a period of 40 years

Topological features in the ferromagnetic Weyl semimetal CeAlSi: Role of domain walls

In the ferromagnetic (FM) Weyl semimetal CeAlSi both space-inversion and time-reversal symmetries are broken. Our quantum oscillation (QO) data indicate that the FM ordering modifies the Fermi surface topology and also leads to an unusual drop in the QO amplitude. In the FM phase, we find a pressure-induced suppression of the anomalous and the loop Hall effects. This cannot be explained based on the electronic band structure or magnetic structure, both of which are nearly pressure independent. Instead, we show that a simplified model describing the scattering of Weyl fermions off FM domain walls can potentially explain the observed topological features. Our study highlights the importance of domain walls for understanding transport in FM Weyl semimetals

Impaired Antibody-Independent Immune Response of B Cells in Patients With Acute Dengue Infection

Dengue is a mosquito-borne viral disease caused by dengue virus (DENV). The disease is endemic to more than 100 countries with 390 million dengue infections per year. Humoral immune responses during primary and secondary DENV infections are well-investigated. However, the impact of DENV infection on B cell subsets and their antibody-independent functions are not well-documented. Through this study, we aimed to define the distribution of B cell subsets in the acute phase of DENV infection and characterize the effect of DENV infection on B cell functions such as differentiation into memory and plasma cells and cytokine production. In our cohort of Cambodian children, we observed decreased percentages of CD24(hi)CD38(hi) B cells and CD27(-) naive B cells within the CD19 population and increased percentages of CD27(+)CD38(hi)CD138(+) plasma cells as early as 4 days post appearance of fever in patients with severe dengue compared to patients with mild disease. Lower percentages of CD19(+)CD24(hi)CD38(hi) B cells in DENV-infected patients were associated with decreased concentrations of soluble CD40L in patient plasma and decreased platelet counts in these patients. In addition, CD19(+)CD24(hi)CD38(hi) and CD19(+)CD27(-) B cells from DENV-infected patients did not produce IL-10 or TNF-alpha upon stimulation in vitro, suggesting their contribution to an altered immune response during DENV infection. In addition, CD19(+)CD27(-) naive B cells isolated from dengue patients were refractory to TLR/anti-IgM stimulation in vitro, which correlated to the increased expression of inhibitory Fc gamma receptors (Fc gamma R) CD32 and LILRB1 on CD19(+)CD27(-) naive B cells from DENV-infected patients. Collectively, our results indicate that a defective B cell response in dengue patients may contribute to the pathogenesis of dengue during the early phase of infection

Topology and Magnetism in Quantum Materials

In this thesis, we study various electron systems with nontrivial topological characters emerging in real space, in reciprocal space, or driven by electron-electron interactions, from which a variety of extraordinary properties in thermodynamics, transport, and optics are uncovered. We begin with systems hosting real-space skyrmion spin texture known to induce an emergent magnetic field for conduction electrons in metallic magnets, resulting in observable anomalies in transport phenomena such as Hall effect and Nernst effect. We examine how the topological charge density of skyrmions can be tuned by the Zeeman field coupled to the spin texture, which in turn tunes the emergent magnetic field. Conduction electrons sensing such a tuneable emergent magnetic field are shown to exhibit anomalous quantum oscillations in physical quantities in addition to the conventional quantum oscillations from Landau quantization due to an orbital magnetic field. We then turn to study the impact of skyrmions on the optical Hall conductivity of the conduction electrons, from which a high-frequency resonant feature is found. A sum rule is discovered, which relates properties of the Hall resonance to the density of skyrmions in the system. The second part of the thesis is inspired by a remarkable oxide ferromagnet SrRuO$_3$ where both momentum-space and real-space topology have been reported. Earlier works suggested the presence of topological Weyl nodes in the band structure, while Hall-effect experiments on its thin films detected anomalies reminiscent of the Hall-effect signature of skyrmions. In fact, there is a debate on the skyrmion origin versus the momentum space Berry curvature origin of these anomalies. Intriguingly, similar anomalies are observed in magneto-optical Kerr effect in thin films. We provide theoretical evidence suggesting a common origin from magnetic domains for the observed anomalies: (1) Kerr anomalies arise from magnetic domains and an unusual non-monotonic relation between Kerr angle and magnetization, whereas (2) Hall anomalies may be linked to highly skew domain-wall scatterings, occurring when there are Weyl nodes near the Fermi level. Finally, we study a bilayer Haldane model where Hubbard interactions can drive a topologically trivial band insulator into a strongly correlated topological phase. A slave-rotor mean-field approach is used to study its phase diagram and its properties, including its edge electron spectral function.Ph.D