BackgroundOpportunistic Infections (OIs) and co-infections are the major cause of deaths amongst HIV infected individuals and this mostly depends upon the risk factors, type of exposure and geographic region. The commonest types of infections reported are tuberculosis, chronic diarrhoea, oral candidiasis, herpes simplex virus-2, cytomegalovirus, hepatitis B virus and hepatitis C virus. Due to the scarcity of OIs data available from this region, we had designed a study to determine the frequency of different OIs amongst HIV seropositive patients.MethodsAnalysis of the different spectrum of OIs/Co-infections were carried out with 204 HIV sero-positive patients (142 males and 62 females) who visited the HIV/AIDS Apex Clinic in a tertiary care hospital from March 2006 to March 2009. The CD4+ count was estimated using FACS Calibur, the routine smear test, serology, nested RT-PCR and DNA sequencing were carried out to determine the different OIs.ResultsIn this study, HIV seropositive patients were mostly from middle age group (31-40 yrs) with CD4+ counts in majority of symptomatic AIDS patients below 200 cells/mm3. The common co-infections/opportunistic infections were OC (53.43%), CD (47.05%), HSV-2 (36.76%), TB (35.29%), CMV (26.96%), HBV (15.19%) and HCV (7.35%). Dual infections, like HSV-2 & CMV (15.38%), HSV-2 & TB (14.61%), HSV-2 & oral candidiasis (24.61%) and CMV & oral candidiasis (14.61%) were significant in follow-up patients. Triple infections were also common e.g., TB, CD, OC infection occurring frequently in about 14.21% of the study population. Multiple infections like OC, TB, CD amongst the viral co-infected patients with HSV-2, HCV, CMV and HBV are also reported in this study. The genotyping analysis of the HCV co-infected HIV individuals shows that two belonged to HCV genotype 1 and 8 belonged to genotype 3.ConclusionsA wide spectrum of OIs were observed amongst HIV-infected patients in the HIV/AIDS Apex Clinic. Oral candidiasis, CD, CMV and HSV-2, were the common OIs in those patients. This study aims to provide a clearer picture regarding infections occurring amongst HIV seropositive individuals so that the scientific findings could be translated into sustainable prevention programmes and improved public health policies.Trial registrationNone

The mechanics of shear failure is a key to understanding a wide range of geological processes, from landslides on the surface to faulting in the Earth's interior. It is now a well-established fact that ductile materials yield under a threshold stress condition, forming shear bands of finite length, which eventually influence the paths of their bulk failure. Compression test experiments show mechanically homogeneous isotropic solids undergo shear failure to produce a conjugate set of shear bands or fractures symmetrically oriented to the applied compression direction (Anand & Spitzig, 1980;Bowden & Raha, 1970;Hutchinson & Tvergaard, 1981;Tvergaard et al., 1981). Employing various yield criteria, many workers have provided theoretical solutions to predict the band orientation as a function of material parameters, such as coefficient of internal friction, dilatancy factor, and strain hardening and softening properties (Anand & Spitzig,

Ductile yielding of rocks and similar solids localize shear zones, which often show complex internal structures due to the networking of their secondary shear bands. Combining observations from naturally deformed rocks and numerical modelling, this study addresses the following crucial question: What dictates the internal shear bands to network during the evolution of an initially homogeneous ductile shear zone? Natural shear zones, observed in the Chotonagpur Granite Gneiss Complex of the Precambrian craton of Eastern India, show characteristic patterns of their internal shear band structures, classified broadly into three categories: type I (network of antithetic low-angle Riedel (R) and synthetic P-bands), type II (network of shear-parallel C and P/R bands) and type III (distributed shear domains containing isolated undeformed masses). Considering strain-softening rheology, our two-dimensional viscoplastic models reproduce these three types, allowing us to predict the condition of shear band growth with a specific network pattern as a function of the following parameters: normalized shear zone thickness, bulk shear rate and bulk viscosity. This study suggests that complex anastomosing shear-band structures can evolve under simple shear kinematics in the absence of any pure shear component.

<p>Crustal deformations generally undergo a brittle-ductile transition with depth, producing fault-dominated structures at shallow depths, replaced by ductile shear zones at middle and lower crustal levels. One of the keys to shear zone modelling concerns the choice of rheological approximations that can successfully reproduce the characteristic features of natural ductile shear zones in the models.  With the help of 2D FE (finite element) simulations, this study shows viscoplastic rheology as a suitable rheological approximation to predict the competing growth and orientations of multiple sets of secondary shear bands in a ductile shear zone. The viscoplastic rheology is modelled by combining bulk viscous weakening of the shear zone material and plastic yielding (Drucker-Prager criterion) to replicate strain-softening behaviour, where the instantaneous viscosity decreases nonlinearly with increasing strain. The cohesive strength of the material is also assumed to reduce with progressive plastic strain. This rheological combination allows us to replicate the various shear band networks found in crustal-level ductile shear zones. It also addresses the conditions for fluid flow into ductile shear zones, which leads to metamorphic reactions, mineralisation, etc. We validate our model results with field observations of similar shear band structures from the Eastern Indian Precambrian craton. The present study finally leads us to conclude that a pressure-dependent viscoplastic rheology is an ideal rheological approximation to model ductile shear zones extensively found in this craton.</p>