Inferring associations among parasitic gamasid mites from census data

Within a community, the abundance of any given species depends in large part on a network of direct and indirect, positive and negative interactions with other species, including shared enemies. In communities where experimental manipulations are often impossible (e.g., parasite communities), census data can be used to evaluate the strength or frequency of positive and negative associations among species. In ectoparasite communities, competitive associations can arise because of limited space or food, but facilitative associations can also exist if one species suppresses host immune defenses. In addition, positive associations among parasites could arise merely due to shared preferences for the same host, without any interaction going on. We used census data from 28 regional surveys of gamasid mites parasitic on small mammals throughout the Palaearctic, to assess how the abundance of individual mite species is influenced by the abundance and diversity of other mite species on the same host. After controlling for several confounding variables, the abundance of individual mite species was generally positively correlated with the combined abundances of all other mite species in the community. This trend was confirmed by meta-analysis of the results obtained for separate mite species. In contrast, there were generally no consistent relationships between the abundance of individual mite species and either the species richness or taxonomic diversity of the community in which they occur. These patterns were independent of mite feeding mode. Our results indicate either that synergistic facilitative interactions among mites increase the host’s susceptibility to further attacks (e.g., via immunosuppression) and lead to different species all having increased abundance on the same host, or that certain characteristics make some host species preferred habitats for many parasite species. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Integrating mental health into primary care in Sverdlovsk

Introduction Mental disorders occur as frequently in Russia as elsewhere, but the common mental disorders, especially depression, have gone largely unrecognised and undiagnosed by policlinic staff and area doctors.Methods This paper describes the impact and sustainability of a multi-component programme to facilitate the integration of mental health into primary care, by situation appraisal, policy dialogue, development of educational materials, provision of a training programme and the publication of standards and good practice guidelines to improve the primary care of mental disorders in the Sverdlovsk region of the Russian Federation.Results The multi-component programme has resulted in sustainable training about common mental disorders, not only of family doctors but also of other cadres and levels of professionals, and it has been well integrated with Sverdlovsk's overall programme of health sector reforms.Conclusion It is possible to facilitate the sustainable integration of mental health into primary care within the Russian context. While careful adaptation will be needed, the approach adopted here may also hold useful lessons for policy makers seeking to integrate mental health within primary care in other contexts and settings.     

Identifying the neural circuitry of alcohol craving and relapse vulnerability

With no further intervention, relapse rates in detoxified alcoholics are high and usually exceed 80% of all detoxified patients. It has been suggested that stress and exposure to priming doses of alcohol and to alcohol-associated stimuli (cues) contribute to the relapse risk after detoxification. This article focuses on neuronal correlates of cue responses in detoxified alcoholics. Current brain imaging studies indicate that dysfunction of dopaminergic, glutamatergic and opioidergic neurotransmission in the brain reward system (ventral striatum including the nucleus accumbens) can be associated with alcohol craving and functional brain activation in neuronal systems that process attentional relevant stimuli, reward expectancy and experience. Increased functional brain activation elicited by such alcohol-associated cues predicted an increased relapse risk, whereas high brain activity elicited by affectively positive stimuli may represent a protective factor and was correlated with a decreased prospective relapse risk. These findings are discussed with respect to psychotherapeutic and pharmacological treatment options.     

Co-occurrence of ectoparasites on rodent hosts: null model analyses of data from three continents

We studied patterns of species co-occurrence in communities of ectoparasitic arthropods (ixodid ticks, mesostigmate mites and fleas) harboured by rodent hosts from South Africa ( Rhabdomys pumilio ), South America ( Scapteromys aquaticus and Oxymycterus rufus ) and west Siberia ( Apodemus agrarius , Microtus gregalis , Microtus oeconomus and Myodes rutilus ) using null models. We compared frequencies of co-occurrences of parasite species or higher taxa across host individuals with those expected by chance. When non-randomness of parasite co-occurrences was detected, positive but not negative co-occurrences of parasite species or higher taxa prevailed (except for a single sample of mesostigmate mites from O. rufus ). Frequency of detection of non-randomness of parasite co-occurrences differed among parasite taxa, being higher in fleas and lower in mites and ticks. This frequency differed also among host species independent of parasite taxon, being highest in Microtus species and lowest in O. rufus and S. aquaticus . We concluded that the pattern of species co-occurrence in ectoparasite communities on rodent hosts is predominantly positive, depends on life history of parasites and may be affected to a great extent by life history of a host.     

Similarity in ectoparasite faunas of Palaearctic rodents as a function of host phylogenetic, geographic or environmental distances: Which matters the most?

Different host species harbour parasite faunas that are anywhere from very similar to very different in species composition. A priori, the similarity in the parasite faunas of any two host species should decrease with increases in either the phylogenetic distance, the distinctness of the environments occupied or the geographical distance between these hosts. We tested these predictions using extensive data on the faunas of fleas (Insecta: Siphonaptera) and gamasid mites (Acari: Parasitiformes) parasitic on rodents across the Palaearctic. For each pair of host species, we computed the similarity in parasite faunas based on both species composition as well as the phylogenetic and/or taxonomic distinctness of parasite species. Phylogenetic distances between hosts were based on patristic distances through a rodent phylogeny, geographic distances were computed from geographic range data, and environmental dissimilarity was measured from the average climatic and vegetation scores of each host range. Using multiple regressions on distance matrices to assess the separate explanatory power of each of the three dependent variables, environmental dissimilarity between the ranges of host species emerged as the best predictor of dissimilarity between parasite faunas, especially for fleas; in the case of mites, phylogenetic distance between host species was also important. A closer look at the data indicates that the flea and mite faunas of two hosts inhabiting different environments are always different, whilst hosts living in similar environments can have either very similar or dissimilar parasite faunas. Additional tests showed that dissimilarity in flea or mite faunas between host geographic ranges was best explained by dissimilarity in vegetation, followed by dissimilarity in climatic conditions. Thus, external environmental factors may play greater roles than commonly thought in the evolution of host-parasite associations.     

Do Fleas Affect Energy Expenditure of Their Free-Living Hosts?

Background

Parasites can cause energetically costly behavioural and immunological responses which potentially can reduce host fitness. However, although most laboratory studies indicate that the metabolic rate of the host increases with parasite infestation, this has never been shown in free-living host populations. In fact, studies thus far have shown no effect of parasitism on field metabolic rate (FMR).

Methodology and Results

We tested the effect of parasites on the energy expenditure of a host by measuring FMR using doubly-labelled water in free-living Baluchistan gerbils (Gerbillus nanus) infested by naturally occurring fleas during winter, spring and summer. We showed for the first time that FMR of free-living G. nanus was significantly and positively correlated with parasite load in spring when parasite load was highest; this relationship approached significance in summer when parasite load was lowest but was insignificant in winter. Among seasons, winter FMRs were highest and summer FMRs were lowest in G. nanus.

Discussion

The lack of parasite effect on FMR in winter could be related to the fact that FMR rates were highest among seasons. In this season, thermoregulatory costs are high which may indicate that less energy could be allocated to defend against parasites or to compensate for other costly activities. The question about the cost of parasitism in nature is now one of the major themes in ecological physiology. Our study supports the hypothesis that parasites can elevate FMR of their hosts, at least under certain conditions. However, the effect is complex and factors such as season and parasite load are involved.     

Arachidonoyl amino acids and arachidonoyl peptides: Synthesis and properties

N-Arachidonoyl (AA) derivatives of amino acids (glycine, phenylalanine, proline, valine, γ-aminobutyric acid (GABA), dihydroxyphenylalanine, tyrosine, tryptophan, and alanine) and peptides (Semax, MEHFPGP, and PGP) were synthesized in order to study the biological properties of acylamino acids. The mass spectra of all the compounds at atmospheric pressure electrospray ionization display the most intense peaks of protonated molecular ions; the detection limits for these compounds are 10 fmol per sample. AA-Gly showed the highest inhibitory activity toward fatty acid amide hydrolase from rat brain (IC₅₀ 6.5 μM) among all the acylamino acids studied. AA-Phe, AA-Tyr, and AA-GABA exhibited a weak but detectable inhibitory effect (IC₅₀ 55, 60, and 50 μM, respectively). The acylated amino acids themselves, except for AA-Glu, were stable to the hydrolysis by this enzyme. All the arachidonoylamino acids inhibited cabbage phospholipase D to various degrees; AA-GABA and AA-Phe proved to be the most active (IC₅₀ 20 and 27 μM, respectively). Attempts to detect the biosynthesis of AA-Tyr in homogenates of rat liver and nerve tissue in vitro were unsuccessful; however, AA-dopamine and AA-Phe, the products of its metabolism, were found. The highest contents of these metabolites were detected in liver homogenate and in the brain homogenate, respectively. Acylamino acids exert no cytotoxic effect toward the glioma C6 cells. It was shown that N-acylation of Semax with arachidonic acid results in enhancement of its hydrolytic stability and increases its affinity for the sites of specific binding in rat cerebellum membranes.     

Temporal dynamics of a T-cell mediated immune response in desert rodents

Immunocompetence, the general capacity of an individual host to mount an immune response against pathogens, is commonly assessed by the response to a challenge of the immune system by injection of phytohaemagglutinin (PHA). The response to PHA is commonly considered a reliable estimate of the T-cell mediated immune response. We investigated the temporal pattern of the PHA response in 10 rodent species from the Negev desert, Israel. We hypothesized that the temporal dynamics of the PHA response would differ among species with different natural patterns of flea parasitism. We injected PHA subcutaneously in the footpad of each rodent and measured its PHA response 6, 24 and 48 h after injection. Rodent species showed two types of PHA response. One type was rapid and characteristic of rodents that had either species-poor flea assemblages, or that are rarely attacked by fleas. This response peaked approximately 6 h after PHA injection. The second type of response was delayed and was typical of rodents that have either species-rich flea assemblages or high abundance and prevalence of fleas or both. Their response to PHA peaked 24 h after injection. Furthermore, rodents that responded promptly had a lower maximum response than rodents with a delayed response. Our results suggest the occurrence of a trade-off between intensity and latency of the PHA response and, therefore, the necessity to account for the relationship between maximum PHA response and time after injection when making interspecific comparisons of immunocompetence.