Investigation of Bartonella acquisition and transmission in Xenopsylla ramesis fleas (Siphonaptera: Pulicidae)

Bartonella are emerging and re-emerging pathogens affecting humans and a wide variety of animals including rodents. Horizontal transmission of Bartonella species by different hematophagous vectors is well acknowledged but vertical transmission (from mother to offspring) is questionable and was never explored in fleas. The aim of this study was to investigate whether the rodent flea, Xenopsylla ramesis, can acquire native Bartonella from wild rodents and transmit it transovarially. For this aim, Bartonella-free laboratory-reared X. ramesis fleas were placed on six naturally Bartonella-infected rodents and six species-matched Bartonella-negative rodents (three Meriones crassus jirds, two Gerbillus nanus gerbils and one Gerbillus dasyurus gerbil) for 7 days, 12-14h per day. The fleas that were placed on the Bartonella-positive rodents acquired four different Bartonella genotypes. Eggs and larvae laid and developed, respectively, by fleas from both rodent groups were collected daily for 7 days and molecularly screened for Bartonella. All eggs and larvae from both groups were found to be negative for Bartonella DNA. Interestingly, two of five gut voids regurgitated by Bartonella-positive fleas contained Bartonella DNA. The naturally infected rodents remained persistently infected with Bartonella for at least 89 days suggesting their capability to serve as competent reservoirs for Bartonella species. The findings in this study indicate that X. ramesis fleas can acquire several Bartonella strains from wild rodents but cannot transmit Bartonella transovarially.     

Density-dependent host selection in ectoparasites: An application of isodar theory to fleas parasitizing rodents

Parasites should make the same decisions that every animal makes regarding fitness reward. They can maximize reproductive success by selection of those habitats that guarantee the greatest fitness output. We consider the host population as a habitat of a parasite population. Consequently, hosts (=habitats) that differ quantitatively or qualitatively will support different numbers of parasites. The nature of habitat selection can be detected by isodars, lines along which habitat selection yields equivalent fitness reward. We applied this approach to study host selection of five fleas, each infesting two desert rodents. Xenopsylla conformis, Xenopsylla ramesis, Nosopsyllus iranus theodori and Stenoponia tripectinata medialis parasitize Gerbillus dasyurus and Meriones crassus. Synosternus cleopatrae pyramidis parasitizes Gerbillus andersoni allenbyi and Gerbillus pyramidum. Three fleas ( X. conformis, X. ramesis and S. c. pyramidis) were able to perceive quantitative (amount of the resource; e.g. organic matter in the nest for flea larvae) and/or qualitative (pattern of resource acquisition; e.g. host defensiveness) differences between hosts. Two other fleas did not perceive between-host differences. X. conformis was a density-dependent host selector that showed sharp selectivity at low density. X. ramesis and S. c. pyramidis were density-independent host selectors with a direct correspondence of density with habitat quality. N. i. theodori and S. t. medialis were non-selectors with no relationship at all between density and host quality. The results of the application of the isodar theory suggest that ectoparasites, like other animals, behave as if they are able to make choices and decisions that favour environments in which their reproductive benefit is maximized.     

Comments on relationships between native seed preferences of shrub-steppe granivores and seed nutritional characteristics

Summary Kelrick et al. (1986) argued that seed preferences of desert granivores are strongly influenced by soluble carbohydrate contents of native seed species. They assumed that bitterbrush (Purshia tridentata) seeds are eaten in their entirety by rodents, but in fact these granivores eat only embryos of bitterbrush seeds. Embryos have a much lower percentage of soluble carbohydrate than whole bitterbrush seeds, and the correlation between preference and soluble carbohydrate content of seeds for six native species becomes non-significant when embryo values are substituted for whole-seed values.     

Connecting mitochondria and innate immunity

Viral infection results in the activation of multiple signaling pathways, but how these pathways are coordinated remains a mystery. Two studies, one published in this issue of Cell (Seth et al., 2005) and the other in Molecular Cell (Xu et al., 2005), identify a new intracellular signaling protein that is required for activating type I interferon expression in response to viral infection. In addition,Seth et al. (2005) show that the function of this protein, which they call MAVS, requires that it be localized to the mitochondria. This observation establishes an unexpected link between innate immunity and an organelle with evolutionary origins in aerobic bacteria.     

Lymphocyte choriomeningitis virus plays hide-and-seek with type 1 interferon

In this issue, Macal et?al. (2012); Walsh et?al. (2012), and Wang et?al. (2012) examine how adaptive immune responses to acute and chronic lymphocyte choriomeningitis virus infection are regulated by type 1 interferon produced early during infection by different cell types upon activation by intracellular nucleic acid sensors.     

Two modes of ligand recognition by TLRs

Toll-like receptors (TLRs) are membrane-bound sensors that detect and respond to microbial infection. Two studies in Cell, one in this issue, reveal how TLRs recognize their ligands. Kim et al. (2007) recently reported the structure of TLR4 bound to the accessory protein MD-2 and its antagonist, the drug eritoran. In this issue, Jin et al. (2007) describe the crystal structure of a complex between TLR1, TLR2, and a lipopeptide ligand.     

Rewind to recover: dedifferentiation after cardiac injury

In adult mammals, cardiomyocytes are known to reactivate an embryonic gene-expression program after injury. In this issue of Cell Stem Cell, Kubin et al. (2011) show that oncostatin M regulates this dedifferentiation which, while beneficial for recovery from acute injury, if persistent results in heart failure in both rodents and humans.     

Phylogenetic place of guinea pigs: no support of the rodent-polyphyly hypothesis from maximum-likelihood analyses of multiple protein sequences

Graur et al.'s (1991) hypothesis that the guinea pig-like rodents have an evolutionary origin within mammals that is separate from that of other rodents (the rodent-polyphyly hypothesis) was reexamined by the maximum-likelihood method for protein phylogeny, as well as by the maximum-parsimony and neighbor-joining methods. The overall evidence does not support Graur et al.'s hypothesis, which radically contradicts the traditional view of rodent monophyly. This work demonstrates that we must be careful in choosing a proper method for phylogenetic inference and that an argument based on a small data set (with respect to the length of the sequence and especially the number of species) may be unstable.      

The powerstroke and camshaft of the RIG-I antiviral RNA detection machine

The innate immune sensor RIG-I responds to infection by binding to viral double-stranded RNA (dsRNA). In this issue of Cell, Kowalinski et?al. (2011) and Luo et?al. (2011) reveal the structure of RIG-I, and in combination with functional analyses, they show how RIG-I recognizes viral RNA to initiate signaling and a type I interferon response.     

Keeping 'trk' of antidepressant actions

Despite growing evidence that increased brain-derived neurotrophic factor (BDNF) and hippocampal adult neurogenesis are necessary for the behavioral actions of antidepressants in rodents, the cellular mechanisms involved in these effects are still unknown. Li et al. in this issue of Neuron demonstrate that the presence of TrkB, the high-affinity receptor for BDNF, in hippocampal neural progenitor cells is required for the neurogenic and behavioral actions of antidepressant treatments.     

Viperin turns coat in cytomegalovirus infection

Cytomegalovirus infection is associated with cytoskeletal alterations and cell swelling (cytomegaly), which have been attributed to the viral mitochondria-localized inhibitor of apoptosis (vMIA) protein. In a recent issue of Science, Seo et?al. (2011) showed that the antiviral host protein viperin is co-opted to function with vMIA for facilitating infection.     

Inflammation in 3D

Our view of the response to infection is limited by current methodologies, which provide minimal spatial information on the systemic inflammatory response. In this issue, Attia et?al. (2012) describe a cutting-edge approach to image the inflammatory response to infection, which includes identification of host proteins in three dimensions.     

荒漠生态系统鼠类对土壤和植被的扰动效应

干扰形成的斑块对荒漠生态系统时空异质性的维系和发展具有重要意义。鼠类作为生物干扰的重要代表,是荒漠生态系统斑块形成的主要来源,它们已从生理、形态、行为进化出一系列特点适应了荒漠生态系统的严酷环境,同时其挖掘、采食行为也深刻影响着荒漠生态系统的环境。本文主要从鼠类活动对土壤(包括土壤发生过程、土壤斑块的形成、土壤理化性质)和植物群落(包括物种多样性、生产力、植物种子)的扰动效应做了归纳总结,旨在阐明鼠类在荒漠生态系统中的作用。     

Wheel-Running Activity Patterns of Five Species of Desert Rodents

In contrast to the extensive laboratory data on activity patterns in rodent species inhabiting temperate zones, much less is known about the activity patterns of desert rodents. In order to address this issue, we measured wheel-running activity patterns in males and females of five species of wild-trapped desert rodents (Dipodillus dasyurus, Gerbillus andersoni, Gerbillus pyramidum, Meriones shawi, and Acomys cahirinus) in long 'summer-like' and short, 'winter-like' day lengths. The specific goals of the present study were to characterize activity patterns in several desert rodent species in the laboratory and to determine if activity patterns are expressed in a seasonal or sexually dimorphic manner. Specifically, wheel-running was measured for 11 weeks in long days followed by 11 weeks in short days to test for photoperiodic entrainment as well as responsiveness to changes in the light-dark cycle. All animals exhibited rhythmic patterns of wheel-running with consistent onsets and offsets that had well-defined relations with the light-dark cycle. All individuals of G. andersoni showed nocturnal activity patterns. Most individuals of G. pyramidum had nocturnal activity patterns, but some individuals showed a short bout of activity at the beginning of the light period. Most individuals of D. dasyurus and M. shawi showed bimodal (i.e., nocturnal and diurnal) activity patterns, although some showed markedly nocturnal activity patterns. There was no sexual dimorphism in wheel running activity rhythms in any of the species examined. As expected, decreases in day length resulted in an overall increase in the duration of activity in all species. Collectively, these data provide an initial characterization of activity patterns within desert rodents in a controlled laboratory setting.     

Evidence for the Colonization of Lactic Acid Bacteria in the Gastrointestinal Tract of Suckling Mink

Lactic acid bacteria are considered indigenous members of the gastrointestinal microflora in a number of animal species (Savage 1977a). Some intestinal strains of lactobacilli and streptococci are aWe to adhere to stratified squamous epithelium of some animals (Tannock et al. 1987), in the non-secreting part of the stomach of piglets (Barrow et al. 1980, Fuller et al. 1978) and rodents (Tannock et al. 1982), and in the crop of poultry (Fuller 1978). The presence of lactic acid bacteria in the digestive tract is believed to be of beneficial value to the host animal (Fuller 1989). The production of organic acids in the stomach or the crop helps maintaining a low pH which may be important for inhibiting the colonization of potentially pathogenic bacteria, particularly in the newborn animal (Barrow et al 1980, Fuller 1977, Fuller 1978). The adhesion of lactobacilli to squamous epithelium is host specific: strains capable of adhering to the epithelium of piglets are usually not able to adhere in rodents or poultry and vice versa (Fuller 1978, Lin & Savage 1984, Tannock et al 1982). Adhesion of lactic acid bacterial strains to other epithelia than stratified squamous epithelium has been reported. Thus, the attachment of lactobacilli to cells from the secreting epithelium of the murine stomach (Kotarski & Savage 1979), to intestinal cells of humans (Goldin & Gorbach 1987), and to columnar epithelial cells of piglets and calves (Mäyrä-Mäkinen et al 1983) has been demonstrated using in vitro methods. In another study the in vivo attachment of Enterococcus faecium to duodenal epithelium of gnotobi-otic chickens was demonstrated (Fuller et al 1981). Recent research indicated that in adult mink lactic acid bacteria are not indigenous members of the intestinal flora, and they do not attach to epithelium in any part of the gastrointestinal tract (Federsen & Jørgensen 1992). The present paper presents evidence that Gram positive cocci may colonize the gut of suckling mink kits and attach to the gut mucosa.     

Neospora caninum Infection in a Litter of Labrador Retriever Dogs in Denmark

Neospora caninum is a recently recognized cyst-forming coccidian parasite associated with severe encephalomyelitis and myositis in dogs of different breeds and ages (Bjerkås et al 1984, Bjerkås & Presthus 1988, Dubey et al. 1988), but has for many years been misdiagnosed as Toxoplasma gondii. In some dogs, the main clinical sign has been attributed to polyradiculoneuritis (Dubey et al. 1988, Cuddon et al. 1992). Furthermore, ulcerative dermatitis (Dubey et al. 1988) and megaoesophagus have been reported (Wolf et al. 1991). The life cycle of the parasite and mode of infection have not been clarified, but transplacental infection seems so far to be the natural route of transmission between intermediate hosts (Dubey & Lindsay 1989). It has been speculated that the disease in young and adult dogs might be due to reactivation of a persistent infection because corticosteroid therapy can activate a latent N. caninum infection (Dubey & Lindsay 1993).     

Old antibiotics target TB with a new trick

Autophagy is now recognized as a cellular defense mechanism that can restrict the growth of Mycobacterium tuberculosis (Mtb). In this issue of Cell Host & Microbe, Kim et?al. (2012) demonstrate that antibiotics routinely used to treat Mtb infection elicit a host autophagy response critical for bacterial clearance.     

Baby in the bathwater: Should we abandon the use of body temperature thresholds to quantify expression of torpor?

Boyles et al. (this issue) argue against the use of body temperature (T_b) thresholds to quantify the expression of torpor in endotherms and our purpose is to provide a counterpoint argument. We contend that T_b thresholds provide valuable information about ecological factors influencing the evolution of thermoregulation. We also point out shortcomings of the so-called heterothermy index proposed as an alternative. However, to be clear, we do agree with Boyles et al. (this issue) that the use of torpor thresholds can limit some aspects of the study of thermoregulation and applaud the more widespread incorporation of theoretical underpinnings proposed by Boyles et al. (this issue) and others.     

Autophagy takes its TOLL on innate immunity

Toll-like receptors (TLRs) activate a complimentary set of defense responses that protect cells during microbial infection. In the recent issue of Immunity, Xu et al. (2007) elucidate a molecular pathway that connects TLR4-mediated innate immune signaling to autophagy, a process of cytoplasmic sequestration and subsequent recycling or degradation.