Cytopathology of pathogenic and nonpathogenic Naegleria species for cultured rat neuroblastoma cells.

The cytopathology for rat neuroblastoma cells (B-103) and the pathogenicity for B6C3F1 mice of four species of Naegleria have been compared. Both live amoebae and cell-free extracts of N. australiensis, N. fowleri, N. gruberi, and N. lovaniensis added to 51Cr-labeled B-103 cells caused release of radiolabel. All four species of Naegleria exhibited surface extensions termed food cups. Only N. fowleri and N. australiensis were pathogenic for mice. Electron microscopic observations of cultures of either N. australiensis or N. lovaniensis with B-103 cells established that the cytopathology involved lysis of the B-103 target cells.     

Dispersion and bias: can we trust geometric means?

Geometric means are frequently used to estimate the intensity of parasite infection within a population. In this article, Tony Fulford uses Schistosoma mansoni field data to illustrate that such estimates are biased and, more importantly, that the degree of bias can vary markedly with host age. Similar problems plague the interpretation of prevalence. The cause can be traced back to age-dependent differences in the dispersion of parasites among hosts.     

Twinning propensity and offspring in utero growth covary in rural African women

In humans and other mammals, some females are more likely to experience twin pregnancies than others, but the reasons behind such individual variation are poorly understood. One hypothesis invokes variation in the dynamics of the insulin-like growth factor (IGF) system, which also regulates foetal growth. Using data from a rural African population living in a highly seasonal environment, we test a novel prediction generated by this hypothesis, that maternal twinning status predicts offspring birthweight. We found that among singleton offspring who experience a favourable in utero environment (born January-June), births before and after twins are, respectively, associated with a 134.07 g and 226.41 g increase in birthweight compared with those born to non-twinning mothers. These results were not mediated by maternal anthropometry. This is consistent with a role for the IGF system in individual variation in twinning propensity, a possibility with implications for understanding mechanisms of life-history variation in humans and other vertebrates.     

Elastohydrodynamics of the Eyelid Wiper

This paper presents an elastohydrodynamic model of the human eyelid wiper. Standard lubrication theory is applied to the fluid layer between the eyelid wiper and ocular surface. The role of the lubrication film is to reduce the shear stresses by preventing solid to solid contact between the eyelid wiper and ocular surface. For the lubrication film to be effective, it is required that the orientation of the eyelid wiper changes between the opening and closing phases of a blink. In order to model this, the hydrodynamic model is coupled with an elastic mattress model for the soft tissue of the eyelid wiper and ocular surface. This leads to a one-dimensional non-linear partial differential equation governing the fluid pressure in the lubrication film. In order to solve the differential equation, a loading condition or constraint equation must be specified. The resulting system is then solved numerically. The model allows predictions of the tear film flux from under the upper eyelid, as well as normal and shear stresses acting on the ocular surface. These factors are important in relation to dry eye syndrome, deformation of the cornea and contact lens design. It is found that the pressure and shear stress under the eyelid act across a length of approximately 0.1 mm which is consistent with clinical observations. It order to achieve a flow of tears from under the upper eyelid during a blink, the model requires that the normal force the eyelid applies to the ocular surface during the closing phase of the blink is significantly higher than during the opening phase of the blink. Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users.     

Iron incorporation and post-malaria anaemia

Background

Iron supplementation is employed to treat post-malarial anaemia in environments where iron deficiency is common. Malaria induces an intense inflammatory reaction that stalls reticulo-endothelial macrophagal iron recycling from haemolysed red blood cells and inhibits oral iron absorption, but the magnitude and duration of these effects are unclear.

Methodology/Principal Findings

We examined the red blood cell incorporation of oral administered stable isotopes of iron and compared incorporation between age matched 18 to 36 months old children with either anaemia post-malaria (n = 37) or presumed iron deficiency anaemia alone (n = 36). All children were supplemented for 30 days with 2 mg/kg elemental iron as liquid iron sulphate and administered ⁵⁷Fe and ⁵⁸Fe on days 1 and 15 of supplementation respectively. ⁵⁷Fe and⁵⁸Fe incorporation were significantly reduced (8% vs. 28%: p<0.001 and 14% vs. 26%: p = 0.045) in the malaria vs. non-malaria groups. There was a significantly greater haemoglobin response in the malaria group at both day 15 (p = 0.001) and 30 (p<0.000) with a regression analysis estimated greater change in haemoglobin of 7.2 g/l (s.e. 2.0) and 10.1 g/l (s.e. 2.5) respectively.

Conclusion/Significance

Post-malaria anaemia is associated with a better haemoglobin recovery despite a significant depressant effect on oral iron incorporation which may indicate that early erythropoetic iron need is met by iron recycling rather than oral iron. Supplemental iron administration is of questionable utility within 2 weeks of clinical malaria in children with mild or moderate anaemia.