Metacommunity and phylogenetic structure determine wildlife and zoonotic infectious disease patterns in time and space

The potential for disease transmission at the interface of wildlife, domestic animals and humans has become a major concern for public health and conservation biology. Research in this subject is commonly conducted at local scales while the regional context is neglected. We argue that prevalence of infection at local and regional levels is influenced by three mechanisms occurring at the landscape level in a metacommunity context. First, (1) dispersal, colonization, and extinction of pathogens, reservoir or vector hosts, and nonreservoir hosts, may be due to stochastic and niche‐based processes, thus determining distribution of all species, and then their potential interactions, across local communities (metacommunity structure). Second, (2) anthropogenic processes may drive environmental filtering of hosts, nonhosts, and pathogens. Finally, (3) phylogenetic diversity relative to reservoir or vector host(s), within and between local communities may facilitate pathogen persistence and circulation. Using a metacommunity approach, public heath scientists may better evaluate the factors that predispose certain times and places for the origin and emergence of infectious diseases. The multidisciplinary approach we describe fits within a comprehensive One Health and Ecohealth framework addressing zoonotic infectious disease outbreaks and their relationship to their hosts, other animals, humans, and the environment.     

Interaction of pathogenic mycobacteria with the host immune system

Pathogenic mycobacteria, in particular Mycobacterium tuberculosis, the causative agent of tuberculosis, have the remarkable capacity to circumvent destruction within one of the most hostile cell types of a vertebrate host: the macrophage. The ability of pathogenic mycobacteria to survive inside macrophages has been known for more than 30 years; yet, only recently have advances in molecular genetics, biochemistry, immunology, as well as global analysis of gene expression, started to unravel the strategies utilized by these pathogens for intracellular persistence. In addition, the definition of key molecules that are important for intracellular survival opens the possibility to develop new drugs to combat mycobacterial diseases.     

Interactions of pathogenic mycobacteria with host macrophages

Tuberculosis, caused by the bacterium Mycobacterium tuberculosis, is one of the most deadly infectious diseases across the globe. The success of M. tuberculosis is related to its capacity to survive and replicate in macrophages, cells of the host innate immune system that are designed to detect and eliminate pathogens [1,2]. In this review, we will focus on the mechanisms used by the innate system of the host to detect and eliminate mycobacteria and the strategies used by M. tuberculosis to overcome host responses to establish a successful infection.     

Development of a new host vector system in mycobacteria

The hybrid plasmid pYT72/pYT92 constructed from an Escherichia coli plasmid pACYC177 and mycobacterial plasmid pMSC262 isolated from Mycobacterium scroflaceum strain W262 transformed both E. coli and BCG. Phage-sensitive mutants S-10 and S-20 isolated from BCG Tokyo strain showed higher frequency of transformation than the wild-type strain. Frequency of transformation was dependent on age of the culture and the electroporation condition used. Several deletion mutants were generated from pYT72/92 to determine the minimum region for the replication in the mycobacteria. A 2.3-kb fragment of pMSC262 was found to contain an essential region. Using this fragment and pACYC177, a small shuttle vector pYT937 containing two drug-resistance markers, kanamycin- and ampicillin-resistance, was constructed. pYT937 contains AatII, BamHI, BbvII, GsuI, HincII, PstI, ScaI and XbaI cloning sites.     

Species co-occurrences in ectoparasite infracommunities: Accounting for confounding factors associated with space,time, and host community composition

1. We explored patterns of co-occurrence of ectoparasite species on individual hosts from Central Europe (Slovakia) and South America (Argentina) within and between higher taxa while controlling for confounding factors associated with variation between host individuals and host species, as well as spatial and temporal variation. We used a recently developed statistical approach, the hierarchical modelling of species communities. 2. Although the probability of pairwise associations of the majority of species in both regions did not differ from random, all significant species associations in Slovakia were positive, whereas the only three significant species associations in Argentina were negative. On average, associations between ectoparasite species belonging to different higher taxa were positive in Slovakia and negative in Argentina. 3. At the host species level, both positive and negative associations between species were detected in all higher taxa. This was also true for ectoparasite co-occurrences in the same site, habitat, or year; although the number of co-occurring species pairs with high posterior probability was much greater in Slovakia than in Argentina. 4. We conclude that consideration of species co-occurrences across the entire multi-host assemblage and control for confounding spatial and temporal factors provided important insights into parasite community structure.     

Hijacking the host: survival of pathogenic mycobacteria inside macrophages

Mycobacteria are among the most persistent pathogens known today: one-third of the global population is latently infected with Mycobacterium tuberculosis, an organism that is responsible for approximately 2.5 million deaths each year. One key to the pathogenic potential of the mycobacteria lies in their capacity to resist destruction by macrophages. Although it has long been recognized that mycobacteria achieve such resistance by interfering with phagosome--lysosome fusion, recent work has shed some more light on the molecular basis of this highly efficient survival strategy.     

A canonical model for production and distribution of root mass in space and time

A mathematical model is presented for the production and distribution of plant root mass in a substrate in space and time. This model is intended to be used for the interpretation of data on root density profiles. It is assumed that a pulse of root apices appears at the surface of the substrate at zero time, emerging from seeds or stems, and that these apices migrate downwards in the substrate, leaving trails of root mass as they go, giving birth to daughter apices, and dying by terminal differentiation. The model has at least 3 parameters, representing, respectively, initial root generating capacity of root axes at zero time, net rate of root apex reproduction (or extinction), and rate of downwards migration of root apices. Two versions of the model are explored, a nondiffusive version and a diffusive version in which there is an additional parameter representing diffusivity of root apices. It is shown that both versions of this theoretical mechanistic model predict that the profile of root density with depth tends to a steady-state exponential form, parameterised by a density of root mass at zero depth and a logarithmic rate of change of root mass with respect to depth. This form has previously appeared in the literature as an empirical model. Data analyses are performed, using this model, on a set of data in which cultures of plants were subjected to treatment with auxin or by genetic manipulation, and the effects of the various treatments on the parameters of the model are described. Interpretations of the experimental results are proposed in the light of the theoretical results derived in this paper.     

New pathways of protective and pathological host defense to mycobacteria

Recent studies have uncovered new mechanisms by which the human immune system attempts to control infection and how pathogens elude these mechanisms. Mycobacterial infections are prime examples of chronic battle fields between host and pathogens. The study of tuberculosis and related mycobacterial infectious diseases such as leprosy have greatly aided in deciphering mechanisms of immune mediated protection and pathology in humans. Here we review recent insights into the role of newly discovered T cell subsets including Th17, Tregs and nonclassically restricted T cells in adaptive immunity to mycobacteria. The role of newly discovered innate immune mechanisms in tuberculosis and leprosy along with recent results from 'unbiased' genome-wide and functional genetic approaches, are deciphering critical host pathways in human infectious disease.     

Variability in space and time: contrasting fruit distribution patterns in the deceptive orchid Orchis militaris

• In angiosperms, a decrease in fruit production towards the apex of individual inflorescences is usually observed. Orchids are thought to be primarily pollination‐limited species, and non‐uniform pollination could cause this decrease pattern in several species. Fruit production was investigated in relation to flower position and floral display size in Orchis militaris (Orchidaceae), a deceptive species.
• Over 2 years, eight populations of O. militaris were studied and fruit position along the inflorescence was recorded. Generalised linear models were performed to examine the effect of population, year, flower position and floral display size on fruit production.
• The dominant pattern was characterised by a higher fruit set in the middle part of the inflorescence (parabolic pattern). A non‐directional pattern of fruit production was also detected in some populations. Within a given population, patterns were generally consistent among years. In one of the two study years and in one of the eight populations specifically, the proximal‐to‐distal decrease in fruit production was dramatic in plants with a large floral display but weak or absent in small displays.
• Our study demonstrates the intraspecific diversity of fruit distribution patterns in O. militaris. Non‐uniform pollination along the inflorescence is likely to be responsible for the parabolic pattern, while irregular visitation could explain the non‐directional pattern of fruit production. Pattern variation among years and between populations could arise from spatiotemporal variation in pollinator assemblages. Resource competition effects could explain the interaction effect between display size and flower position.

     

Accommodating space, time and randomness in network simulation

Interest in the possibility of dynamically simulating complex cellular processes has escalated markedly in recent years. This interest has been fuelled by three factors: the generally accepted value in understanding living processes as integrated systems; the dramatic increase in computational capability; and the availability of new or improved technology for making the quantitative measurements that are needed to drive and validate cellular simulations. Between the extremes of atom-scale and organism-scale simulation is a vast middle-ground requiring simulation strategies that are capable of dealing with a range of spatial, temporal and molecular abundance scales that are crucial for a comprehensive understanding of integrative cell biology. Although at an early stage, methodological improvements and the development of computational platforms provide some hope that simulations will emerge that can bridge the gap between network models and the true operation of the cell as a complex machine.     

Cellular and molecular mechanisms of internalization of mycobacteria by host cells

Mycobacteria are intracellular pathogens capable of invading mononuclear phagocytes, mucosal epithelial cells (including M cells) and Schwann cells. To enter cells, mycobacteria have been shown to interact with several molecules on macrophage and epithelial cell surfaces. This suggests adaptation to the host environment. In this review we address the strategies used by pathogenic mycobacteria to gain access to the intracellular environment.     

Elephants in space and time

Autocorrelation in animal movements can be both a serious nuisance to analysis and a source of valuable information about the scale and patterns of animal behavior, depending on the question and the techniques employed. In this paper we present an approach to analyzing the patterns of autocorrelation in animal movements that provides a detailed picture of seasonal variability in the scale and patterns of movement. We used a combination of moving window Mantel correlograms, surface correlation and crosscorrelation analysis to investigate the scales and patterns of autocorrelation in the movements of three herds of elephants in northern Botswana. Patterns of autocorrelation of elephant movements were long‐range, temporally complicated, seasonally variable, and closely linked with the onset of rainfall events. Specifically, for the three elephant herds monitored there was often significant autocorrelation among locations up to lags of 30 days or more. During many seasonal periods there was no indication of decreasing autocorrelation with increasing time between locations. Over the course of the year, herds showed highly variable and complex patterns of autocorrelation, ranging from random use of temporary home ranges, periodic use of focal areas, and directional migration. Even though the patterns of autocorrelation were variable in time and quite complex, there were highly significant correlations among the autocorrelation patterns of the different herds, indicating that they exhibited similar patterns of movement through the year. These major patterns of autocorrelation seem to be related to patterns of rainfall. The strength of correlation in movement patterns of the different herds decreased markedly at the cessation of major rain events. Also, there was a strong crosscorrelation between strength of autocorrelation of movement and rainfall, peaking at time lags of between three and four weeks. Overall, these approaches provide a powerful way to explore the scales and patterns of autocorrelation of animal movements, and to explicitly link those patterns to temporally variable environmental attributes, such as rainfall or vegetation phenology.