Disease-driven reduction in human mobility influences human-mosquito contacts and dengue transmission dynamics

Heterogeneous exposure to mosquitoes determines an individual’s contribution to vector-borne pathogen transmission. Particularly for dengue virus (DENV), there is a major difficulty in quantifying human-vector contacts due to the unknown coupled effect of key heterogeneities. To test the hypothesis that the reduction of human out-of-home mobility due to dengue illness will significantly influence population-level dynamics and the structure of DENV transmission chains, we extended an existing modeling framework to include social structure, disease-driven mobility reductions, and heterogeneous transmissibility from different infectious groups. Compared to a baseline model, naïve to human pre-symptomatic infectiousness and disease-driven mobility changes, a model including both parameters predicted an increase of 37% in the probability of a DENV outbreak occurring; a model including mobility change alone predicted a 15.5% increase compared to the baseline model. At the individual level, models including mobility change led to a reduction of the importance of out-of-home onward transmission (R, the fraction of secondary cases predicted to be generated by an individual) by symptomatic individuals (up to -62%) at the expense of an increase in the relevance of their home (up to +40%). An individual’s positive contribution to R could be predicted by a GAM including a non-linear interaction between an individual’s biting suitability and the number of mosquitoes in their home (>10 mosquitoes and 0.6 individual attractiveness significantly increased R). We conclude that the complex fabric of social relationships and differential behavioral response to dengue illness cause the fraction of symptomatic DENV infections to concentrate transmission in specific locations, whereas asymptomatic carriers (including individuals in their pre-symptomatic period) move the virus throughout the landscape. Our findings point to the difficulty of focusing vector control interventions reactively on the home of symptomatic individuals, as this approach will fail to contain virus propagation by visitors to their house and asymptomatic carriers.     

Ammoniated Silver Carbonate for the Demonstration of Lysosomes

Hortega's ammoniated silver carbonate method was used to demonstrate lysosomes in the central nervous system and kidney of adult rats. Formol-CaCl₂, (10%:1%) fixed, frozen sections were impregnated for 10 min in Hortega's solution: 30 ml of 10% AgNO₂ and 90 ml of 5% Na₂CO₃, with concentrated NH₄OH added until the precipitate dissolved, then distilled water to make 400 ml. This procedure revealed silver-positive cytoplasmic structures whose form, shape and distribution were similar to that seen by staining adjacent sections for acid phosphatase. A short fixation of 18-24 hr appears to be essential. A useful, nonenzymatic method for the demonstration of lysosomes is thereby available.     

Polyamines and protein kinase I. Induction of ornithine decarboxylase and activation of protein kinase in rat glioma cells

The activities of cAMP-dependent and independent protein kinases were determined after feeding confluent glioma C6-BU-1 cultures. It has been shown that the activity of both enzymes rose considerably after feeding, and that the ratio of ³²P incorporation into histone, in the absence and the presence of cAMP, was maximal 4 hours after feeding. This increase in protein kinase activity was followed by the activation of ornithine decarboxylase and accumulation of putrescine. Spermine, at millimolar concentrations, inhibited protein kinase, apparently by inactivating the catalytic subunit. It is suggested that this inhibition of protein kinase by polyamines is another regulatory mechanism, which controls cellular growth.     

CAMKII Activation Is Not Required for Maintenance of Learning-Induced Enhancement of Neuronal Excitability

Pyramidal neurons in the piriform cortex from olfactory-discrimination trained rats show enhanced intrinsic neuronal excitability that lasts for several days after learning. Such enhanced intrinsic excitability is mediated by long-term reduction in the post-burst after-hyperpolarization (AHP) which is generated by repetitive spike firing. AHP reduction is due to decreased conductance of a calcium-dependent potassium current, the sI_AHP. We have previously shown that learning-induced AHP reduction is maintained by persistent protein kinase C (PKC) and extracellular regulated kinase (ERK) activation. However, the molecular machinery underlying this long-lasting modulation of intrinsic excitability is yet to be fully described. Here we examine whether the CaMKII, which is known to be crucial in learning, memory and synaptic plasticity processes, is instrumental for the maintenance of learning-induced AHP reduction. KN93, that selectively blocks CaMKII autophosphorylation at Thr286, reduced the AHP in neurons from trained and control rat to the same extent. Consequently, the differences in AHP amplitude and neuronal adaptation between neurons from trained rats and controls remained. Accordingly, the level of activated CaMKII was similar in pirifrom cortex samples taken form trained and control rats. Our data show that although CaMKII modulates the amplitude of AHP of pyramidal neurons in the piriform cortex, its activation is not required for maintaining learning-induced enhancement of neuronal excitability.     

The effect of starch and of a heteropolysaccharide fraction from Phaseolus vulgaris on development and fecundity of Callosobruchus chinensis (Coleoptera: Bruchidae)

A heteropolysaccharide fraction was isolated from Phaseolus vulgaris beans in which it comprises at least 1% of the dry weight of the beans. This heteropolysaccharide increases larval mortality and decreases the rate of larval development and the number of eggs deposited by females of Callosobruchus chinensis, when incorporated in artificial beans in which the larvae feed. It is composed of galactose, glucose, xylose, arabinose and traces of rhamnose, as determined after acid hydrolysis. Of these individual sugars, arabinose and xylose affect adult fecundity as well. However, partial enzymic hydrolysis of the heteropolysaccharide fraction by C. chinensis larval midgut contents releases only glucose, galactose and trace amounts of arabinose, and the integral structure of heteropolysaccharide may be necessary for biological activity. the incorporation of the starch granules of Phaseolus vulgaris beans into artificial beans increases larval mortality and decreases the rate of larval development of C. chinensis. It is suggested that the heteropolysaccharide fraction as well as the starch are part of a complex of natural components of Phaseolus vulgaris beans that make these beans resistant to C. chinensis.

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Résumé Ce travail cherche à préciser pourquoi les graines de haricot (Phaseolus vulgaris) ne sont pas attaquées par la Buche chinoise (Callosobruchus chinensis), espèce cependant très polyphage.Les graines de haricot renferment 1% d'un hétéropolysaccharide, qui s'est révélé accroître la mortalité et ralentir le développement des larves de cette Bruche, mais qui aussi réduit la fécondité des femelles adultes. Ces observations ont été faites à partir d'élevages sur des milieux artificiels normalement favorables, présentés sous forme de haricots, par un moulage approprié.Une hydrolyse acide de cet hétéropolysaccharide libère du galactose, du glucose, du xylose, de l'arabinose et des traces de rhamnose. Ces sucres simples sont testés: l'arabinose et le rhamnose influencent le développement des larves, tandis que le galactose, le xylose et à nouveau l'arabinose, ont un effet sur la fécondité des femelles (réduction de la fécondité à 40% de la normale avec 1% d'arabinose).Toutefois l'hydrolyse enzymatique de cette fraction hétéropolysaccharidique, par le contenu stomacal de larves de C. chinensis reste partielle et libère seulement du glucose, du galactose et des traces d'arabinose. II est possible que la structure intégrale de l'hétéropolysaccharide soit nécessaire à son activité biologique.Un autre facteur défavorable à C. chinensis pourrait être la nature même des grains d'amidon de Phaseolus. Cet amidon incorporé à l'aliment artificiel accroît en effet la mortalité larvaire et ralentit la vitesse de développement. Cet effet défavorable pourrait être dû à la non digestibilité des grains d'amidon entiers.Il est suggéré que la fraction hétéropolysaccharide et l'amidon de Phaseolus sont deux des facteurs présents dans la graine de haricot qui lui confèrent sa résistance naturelle à la Bruche chinoise.

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Supported in part by the Research and Development Authority of the Hebrew University of Jerusalem.     

Structural changes of vegetation and its association with microclimate in a successional gradient of low thorn forest in northeastern Mexico

Understanding how microclimate and vegetation are associated during secondary succession is of primary importance for plant conservation in the face of the increasing land cover modification. However, these patterns are still unstudied for many plant communities. This study aimed to evaluate the structure (species richness, Shannon's diversity index, Simpson´s dominance index, abundance of each species, average height of species, species cover (%), species composition, and indicator values) of a low thorn forest fragment and to analyze its relation with microclimate along a successional gradient. Four stages of succession were delimited by the analysis of Landsat images, in the state of Tamaulipas, northeast Mexico. Statistical models incorporated species richness, diversity indices, abundance, height, and cover, as variables for searching differences between stages, or to evaluate microclimate associations. A total of 70 species, 54 genera, and 27 families were determined. Height of tree layer was the most important variable for discrimination of the successional stages. Conserved areas differed floristically from other stages, associated mainly with the lowest values of wind speed originated by tree layer characteristics. A significant association between species and microclimate was found, being wind speed and relative humidity the most important variables. Some species, due to their high importance values and their patterns of association with microclimate, may be considered as key taxa for low thorn forest, which is a threatened semitropical community in northeast Mexico. Conserved and late successional areas account for climatic regulation of this plant community, and the importance of these forest patches may be considered when establishing biodiversity protection areas.

     

Domestic Animal Hosts Strongly Influence Human-Feeding Rates of the Chagas Disease Vector Triatoma infestans in Argentina

Background

The host species composition in a household and their relative availability affect the host-feeding choices of blood-sucking insects and parasite transmission risks. We investigated four hypotheses regarding factors that affect blood-feeding rates, proportion of human-fed bugs (human blood index), and daily human-feeding rates of Triatoma infestans, the main vector of Chagas disease.

Methods

A cross-sectional survey collected triatomines in human sleeping quarters (domiciles) of 49 of 270 rural houses in northwestern Argentina. We developed an improved way of estimating the human-feeding rate of domestic T. infestans populations. We fitted generalized linear mixed-effects models to a global model with six explanatory variables (chicken blood index, dog blood index, bug stage, numbers of human residents, bug abundance, and maximum temperature during the night preceding bug catch) and three response variables (daily blood-feeding rate, human blood index, and daily human-feeding rate). Coefficients were estimated via multimodel inference with model averaging.

Findings

Median blood-feeding intervals per late-stage bug were 4.1 days, with large variations among households. The main bloodmeal sources were humans (68%), chickens (22%), and dogs (9%). Blood-feeding rates decreased with increases in the chicken blood index. Both the human blood index and daily human-feeding rate decreased substantially with increasing proportions of chicken- or dog-fed bugs, or the presence of chickens indoors. Improved calculations estimated the mean daily human-feeding rate per late-stage bug at 0.231 (95% confidence interval, 0.157–0.305).

Conclusions and Significance

Based on the changing availability of chickens in domiciles during spring-summer and the much larger infectivity of dogs compared with humans, we infer that the net effects of chickens in the presence of transmission-competent hosts may be more adequately described by zoopotentiation than by zooprophylaxis. Domestic animals in domiciles profoundly affect the host-feeding choices, human-vector contact rates and parasite transmission predicted by a model based on these estimates.