Strong Host Specificity Research Articles

The occurrence and pathogenicity of Serratospiculum tendo (Nematoda: Diplotriaenoidea) in birds of prey from southern Italy.

The air sacs of free-ranging birds of prey (n=652) from southern Italy, including 11 species of Accipitriformes and six of Falconiforms, were examined for infections with Serratospiculum tendo (Nematoda: Diplotriaenoidea). Of the 17 species of birds examined, 25 of 31 (80.6%) peregrine falcons (Falco peregrinus) from Calabria Region and a single northern goshawk (Accipiter gentilis) from Campania Region were infected with S. tendo, suggesting a strong host specificity for the peregrine falcon. The northern goshawk and 18 of 25 infected peregrine falcons showed cachexia and all infected birds had bone fractures. At gross examination, air sacculitis and pneumonia were the most common lesions in infected birds. Microscopically, the air-sac walls showed thickening of the smooth muscle cells, resulting in a papillary appearance, along with hyperplasia of the mesothelium and epithelium, and foci of plasma cell infiltration and macrophages associated with several embryonated eggs and adult parasites. Extensive areas of inflammation were found in the lungs, characterized by lymphocytes, macrophages and fibroblasts surrounding embryonated eggs. The northern goshawk also had detachment of the dextral lung with several necrotic foci. In this case, the death of the bird was directly attributed to S. tendo infection. Lesions and pathological changes observed here suggest that S. tendo can cause disease.

A link between host dispersal and parasite diversity in two sympatric cichlids of Lake Tanganyika

SummaryA major goal in ecology is to unravel how species assemblages emerge and how they are structured across the landscape. Host–parasite systems are particularly interesting in this context, as limited host dispersal may promote the differentiation of parasite communities.We examined whether the patterns of species diversity inCichlidogyrus, a genus of monogenean parasitic flatworms with a direct life cycle, are consistent with the hypothesis that parasite diversity is driven by host dispersal. This was carried out by comparing two sympatric cichlid hosts (Tropheus mooriiandSimochromis diagramma) with contrasting dispersal abilities. Genetic connectivity among host populations along the Zambian shoreline of Lake Tanganyika was estimated using microsatellite genotyping.Cichlidogyrusparasites were isolated and identified morphologically to the species level.Simochromis diagramma, a host with a high dispersal capacity, was infected by a low number ofCichlidogyrusspecies, and the parasite assemblages were similar among host populations. In contrast,T. moorii, a host with a low dispersal capacity, was infected by a large number ofCichlidogyrusspecies, and the parasite assemblages differed strongly among host populations. These outcomes were thus as expected from the hypothesis.Because of the strong host specificity of theseCichlidogyrusspecies, a lack of connectivity among host populations might facilitate allopatric speciation of the parasite.

Analysis of the long control region of bovine papillomavirus type 1 associated with sarcoids in equine hosts indicates multiple cross-species transmission events and phylogeographical structure.

Papillomaviruses are a family of slowly evolving DNA viruses and their evolution is commonly linked to that of their host species. However, whilst bovine papillomavirus-1 (BPV-1) primarily causes warts in its natural host, the cow, it can also cause locally aggressive and invasive skin tumours in equids, known as sarcoids, and thus provides a rare contemporary example of cross-species transmission of a papillomavirus. Here, we describe the first phylogenetic analysis of BPV-1 in equine sarcoids to our knowledge, allowing us to explore the evolutionary history of BPV-1 and investigate its cross-species association with equids. A phylogenetic analysis of the BPV-1 transcriptional promoter region (the long control region or LCR) was conducted on 15 bovine and 116 equine samples from four continents. Incorporating previous estimates for evolutionary rates in papillomavirus implied that the genetic diversity in the LCR variants was ancient and predated domestication of both equids and cattle. The phylogeny demonstrated geographical segregation into an ancestral group (African, South American and Australian samples), and a more recently derived, largely European clade. Whilst our data are consistent with BPV-1 originating in cattle, we found evidence of multiple, probably relatively recent, cross-species transmission events into horses. We also demonstrated the high prevalence of one particular sequence variant (variant 20), and suggest this may indicate that this variant shows a fitness advantage in equids. Although strong host specificity remains the norm in papillomaviruses, our results demonstrate that exceptions to this rule exist and can become epidemiologically relevant.

Diversification of an emerging pathogen in a biodiversity hotspot: Leptospira in endemic small mammals of Madagascar.

Biodiversity hotspots and associated endemism are ideal systems for the study of parasite diversity within host communities. Here, we investigated the ecological and evolutionary forces acting on the diversification of an emerging bacterial pathogen, Leptospira spp., in communities of endemic Malagasy small mammals. We determined the infection rate with pathogenic Leptospira in 20 species of sympatric rodents (subfamily Nesomyinae) and tenrecids (family Tenrecidae) at two eastern humid forest localities. A multilocus genotyping analysis allowed the characterization of bacterial diversity within small mammals and gave insights into their genetic relationships with Leptospira infecting endemic Malagasy bats (family Miniopteridae and Vespertilionidae). We report for the first time the presence of pathogenic Leptospira in Malagasy endemic small mammals, with an overall prevalence of 13%. In addition, these hosts harbour species of Leptospira (L. kirschneri, L. borgpetersenii and L. borgpetersenii group B) which are different from those reported in introduced rats (L. interrogans) on Madagascar. The diversification of Leptospira on Madagascar can be traced millions of years into evolutionary history, resulting in the divergence of endemic lineages and strong host specificity. These observations are discussed in relation to the relative roles of endemic vs. introduced mammal species in the evolution and epidemiology of Leptospira on Madagascar, specifically how biodiversity and biogeographical processes can shape community ecology of an emerging pathogen and lead to its diversification within native animal communities.

Rickettsiaspp. in Seabird Ticks from Western Indian Ocean Islands, 2011–2012

We found a diversity of Rickettsia spp. in seabird ticks from 6 tropical islands. The bacteria showed strong host specificity and sequence similarity with strains in other regions. Seabird ticks may be key reservoirs for pathogenic Rickettsia spp., and bird hosts may have a role in dispersing ticks and tick-associated infectious agents over large distances.

Selection of habitat by a marine amphipod

AbstractMarine algae are known to provide habitats for a wide range of marine organisms. Populations of marine epiphytal invertebrates are generalists and are less adapted to live in only one macroalga species. However, there are some examples of local adaptation and, in particular, amphipods have shown strong host specificity. Amphitholina cuniculus, an amphipod with an alga‐burrowing habit, has been mainly observed in Bifurcaria bifurcata mats on the intertidal rocky shores of the southern region of the Galician coast (NW Spain; 42º11.27′ N, 8º48.25′ W). We designed a laboratory experiment conducted in June 2009 to analyse the association between the amphipod and the macroalga. In particular, we hypothesised that (i) this species would exhibit different behaviour during the day and at night, and (ii) adults of A. cuniculus would prefer B. bifurcata as habitat rather than Fucus vesiculosus or Sargassum muticum. Results supported the hypothesis that adults of A. cuniculus preferred B. bifurcata, although such preferences did not show the day/night variability predicted. This amphipod might be considered a specialist species, at least on rocky intertidal shores along the Galician coast.

Molecular phylogenetic characterization of Collyriclum faba with reference to its three host-specific ecotypes

Collyriclum faba (Bremser in Schmalz, 1831) is a monostome digenetic trematode with unknown life cycle. On its definitive bird host, C. faba occurs in pairs within a subcutaneous cyst, the location of which on the host body is the base for differentiating three ecotypes of C. faba. Here we examined the hypothesis connecting strong host-specificity of the ecotypes with the possible existence of cryptic speciation among C. faba. Analysis of conserved nuclear ribosomal DNA regions rejected the cryptic speciation hypothesis. Analyses of the variable ITS1 and ITS2 regions revealed that, despite some differentiation between the ecotypes, several large-scale indels occur in multiple ecotypes. Individuals from multiple cysts affecting each host individual differed in their ITS1 sequences, suggesting the individuals infecting a single host did not have common parents. Since we were the first to sequence C. faba, we attempted to verify its position in the current taxonomic system (Plagiorchiida: Gorgoderoidea). We found that C. faba segregates with the superfamily Microphalloidea (in order of maximum likelihood phylogeny: Prosthogonimidae, Pleurogenidae and Microphallidae) instead of any species of the superfamily Gorgoderoidea, as proposed in the past. The results necessitate reclassification of the family Collyriclidae as a member of Microphalloidea.

La transmission des infections àPneumocystis

Is Pneumocystis pneumonia (PcP) a transmissible fungal disease? Does nosocomial PcP occur? Is there Pneumocystis transmission in the community? These questions, which could not be tackled before the 2000s, may at present be approached using either noninvasive detection methods or experimental transmission models. Represented by a unique entity (P.carinii) for almost one century, the Pneumocystis genus was shown to contain several species, being P.jirovecii the sole species identified in humans hitherto. Molecular methods combined with cross infection experiments revealed strong host specificity that precludes Pneumocystis inter-species transmission. In contrast, respiratory transmission between mammals of a same species is usually highly active, even between immunocompetent hosts. Other transmission ways could also exist. New data show that human being is the unique P.jirovecii reservoir; it would constitute the sole infection source in both hospital and community.

Identifying hosts of families of viruses: a machine learning approach.

Identifying emerging viral pathogens and characterizing their transmission is essential to developing effective public health measures in response to an epidemic. Phylogenetics, though currently the most popular tool used to characterize the likely host of a virus, can be ambiguous when studying species very distant to known species and when there is very little reliable sequence information available in the early stages of the outbreak of disease. Motivated by an existing framework for representing biological sequence information, we learn sparse, tree-structured models, built from decision rules based on subsequences, to predict viral hosts from protein sequence data using popular discriminative machine learning tools. Furthermore, the predictive motifs robustly selected by the learning algorithm are found to show strong host-specificity and occur in highly conserved regions of the viral proteome.

Temporal stability and species specificity in bacteria associated with the bottlenose dolphins respiratory system

We demonstrate that the exhaled breath condensate, or 'blow', from marine mammals can be used to examine respiratory associated microbial communities using non-invasive sampling methods. Blow samples from two species of bottlenose dolphin, Tursiops truncatus and T. aduncus, along with hybrid offspring, were examined using molecular microbial ecology methods. A temporal analysis revealed that microbial community structure of each individual remained distinct from other individuals over a two-month period, indicting strong host specificity. The taxonomic composition of samples, based on pyrosequencing of the V1-V3 regions of the 16S rRNA gene, from 24 healthy individuals was dominated by the Cardiobacteraceae lineage of Gammaproteobacteria, comprising on average 52% of sequences in all samples. Sequences in this taxa were associated with novel clades that contain only sequences from dolphin respiratory tracts. Other genera that likely form part of the core biota include the Saccharospirillaceae (Gammaproteobacteria), Arcobacter (Epsilonproteobacteria), Hydrogenimonaceae (Epsilonproteobacteria), Halotalea (Gammaproteobacteria), Aquimarina (Flavobacteria) and Helococcus (Clostridia). Significant differences between samples from different species were observed only at the species/ strain level, driven by the relative contributions of strains from the most common phylogenetic lineages. Analysis of communities associated with hybrid animals provides tentative evidence for a paternal role in community assembly. Clear overlap was observed with data collected by capture and swabbing of bottlenose dolphins blowholes, indicating this method provides a novel non-invasive alternative to monitoring marine mammal population health.

Nonhost and basal resistance: how to explain specificity?

Nonhost resistance to plant pathogens can be constitutive or induced by microbes. Successful pathogens suppress microbe-induced plant defences by delivering appropriate effectors, which are apparently not sufficiently effective on nonhost plant species, as can be concluded from the strong host specificity of many biotroph plant pathogens. Such effectors act on particular plant targets, such as promoters or motifs in expressed sequences. Despite much progress in the elucidation of the molecular aspects of nonhost resistance to plant pathogens, very little is known about the genes that determine whether effectors can or cannot suppress the basal defence. In hosts they can, in nonhosts they cannot. The targets determining the host status of plants can be identified in inheritance studies. Recent reports have indicated that nonhost resistance is inherited polygenically, and exhibits strong similarity and association with the basal resistance of plants to adapted pathogens.

Hantavirus Evolution in Relation to Its Rodent and Insectivore Hosts: No Evidence for Codivergence

Hantaviruses are considered one of the best examples of a long-term association between RNA viruses and their hosts. Based on the appearance of strong host specificity, it has been suggested that hantaviruses cospeciated with the rodents and insectivores they infect since these mammals last shared a common ancestor, approximately 100 million years ago. We tested this hypothesis of host-virus codivergence in two ways: 1) we used cophylogenetic reconciliation analysis to assess the fit of the virus tree onto that of the host and 2) we estimated the evolutionary rates and divergence times for the Hantavirus genus using a Bayesian Markov Chain Monte Carlo method and similarly compared these with those of their hosts. Our reconciliation analysis provided no evidence for a history of codivergence between hantaviruses and their hosts. Further, the divergence times for the Hantavirus genus were many orders of magnitude too recent to correspond with the timescale of their hosts' speciation. We therefore propose that apparent similarities between the phylogenies of hantaviruses and their mammalian hosts are the result of a more recent history of preferential host switching and local adaptation. Based on the presence of clade-defining amino acids in all genomic segments, we propose that the patterns of amino acid replacement in these viruses are also compatible with a history of host-specific adaptation.

Tracking Host Sources of Cryptosporidium spp. in Raw Water for Improved Health Risk Assessment

Recent molecular evidence suggests that different species and/or genotypes of Cryptosporidium display strong host specificity, altering our perceptions regarding the zoonotic potential of this parasite. Molecular forensic profiling of the small-subunit rRNA gene from oocysts enumerated on microscope slides by U.S. Environmental Protection Agency method 1623 was used to identify the range and prevalence of Cryptosporidium species and genotypes in the South Nation watershed in Ontario, Canada. Fourteen sites within the watershed were monitored weekly for 10 weeks to assess the occurrence, molecular composition, and host sources of Cryptosporidium parasites impacting water within the region. Cryptosporidium andersoni, Cryptosporidium muskrat genotype II, Cryptosporidium cervine genotype, C. baileyi, C. parvum, Cryptosporidium muskrat genotype I, the Cryptosporidium fox genotype, genotype W1, and genotype W12 were detected in the watershed. The molecular composition of the Cryptosporidium parasites, supported by general land use analysis, indicated that mature cattle were likely the main source of contamination of the watershed. Deer, muskrats, voles, birds, and other wildlife species, in addition to sewage (human or agricultural) may also potentially impact water quality within the study area. Source water protection studies that use land use analysis with molecular genotyping of Cryptosporidium parasites may provide a more robust source-tracking tool to characterize fecal impacts in a watershed. Moreover, the information is vital for assessing environmental and human health risks posed by water contaminated with zoonotic and/or anthroponotic forms of Cryptosporidium.

A yeast clade near Candida kruisii uncovered: nine novel Candida species associated with basidioma-feeding beetles

Yeasts similar to Candida kruisii were isolated repeatedly from the digestive tracts of basidioma-feeding beetles, especially nitidulids inhabiting and feeding on a variety of agarics in the southeastern USA and Barro Colorado Island, Panama. Based on the identical sequences of the D1/D2 domains of the LSU rRNA gene (rDNA) and host beetle information, the isolates were grouped into 19 genotypes which varied from C. kruisii by up to 38 nucleotide differences in the D1/D2 region. Phylogenetic analysis of rDNA sequences and phenotypic traits placed the isolates in C. kruisii and in nine undescribed taxa. The new species and type strains are designated as Candida pallodes (NRRL Y-27653 T), C. tritomae (NRRL Y-27650 T), C. panamensis (NRRL Y-27657 T), C. lycoperdinae (NRRL Y-27658 T), C. atbi (NRRL Y-27651 T), C. barrocoloradensis (NRRL Y-27934 T), C. aglyptinia (NRRL Y-27935 T), C. stri (NRRL Y-48063 T), and C. gatunensis (NRRL Y-48064 T). A phylogeny based on analysis of a combined database of sequences of SSU and LSU rDNA and the ITS region showed that the nine new species formed a novel sister clade to C. kruisii that was strongly supported by bootstrap analysis. Candida pallodes, C. tritomae, C. panamensis, and C. lycoperdinae formed one subclade, while C. atbi, C. barrocoloradensis, C. aglyptinia, C. stri, and C. gatunensis formed a second distinct subclade within the larger clade. Candida pallodes and C. atbi showed a strong host specificity to beetle species in the genus Pallodes ( Coleoptera: Nitidulidae) collected from a variety of agarics. On the other hand, C. panamensis, C. tritomae, and C. lycoperdinae were associated with several unrelated beetles in Erotylidae, Scarabaeidae, Tenebrionidae, and Curculionidae as well as Lycoperdina ferruginea ( Nitidulidae). Candida pallodes, C. tritomae, C. lycoperdinae, and C. atbi have been isolated repeatedly in the USA, while the other five new species have been found only at Barro Colorado Island, Panama.

Factors Controlling the Activity of Bacteriophage UZ1 against Enterobacter aerogenes Strain BE1 under Simulated Intestinal Conditions

AbstractTo study specific bacteriophage‐bacteria interactions under intestinal conditions, a previously developed in vitro model system was used, combining a common pathogenic bacterium Enterobacter aerogenes BE1 and a for this bacterium specific bacteriophage, phage UZ1. As many environmental factors may influence the phage‐bacterium interaction, the model was used in this study to investigate the effect of inoculum size, presence of oxygen, and physiological hindrance. When monocultures of E. aerogenes BE1/gfp with increasing inoculum size were infected with phage UZ1, complete host lysis was observed up to an inoculum size of 7 log [CFU/mL]. However, at 8 log [CFU/mL], growth was observed and phage resistant E. aerogenes BE1/gfp cells were isolated. Under simulated intestinal conditions, infection with phage UZ1 resulted in a significant decrease, up to 3 log, of E. aerogenes BE1/gfp compared to the non‐phage treated control. However, no complete removal of the bacterial host could be achieved after 18 h. At high inoculum size, resistant bacteria were also isolated. However, growth curve analysis showed a reduced fitness of the phage UZ1‐resistant bacteria, limiting their intestinal proliferation. Another factor responsible for differences in the bacteriolytic efficiency was the presence of oxygen. Under anaerobic conditions, the latent period increased from 20 min to more then 3 h and the burst size decreased from 70 to less than 24, compared to aerobic conditions. In conclusion, the major factors responsible for different bacteriolytic efficacy were resistance to phage infection by mutation and limited oxygen availability. Although no complete removal of the pathogen was obtained under anaerobic conditions, the strong host specificity of the phage, the decrease in bacterial concentrations and the reduced fitness of phage‐resistant bacteria indicate the possibility for prophylactic use of the phage to reduce the risk of E. aerogenes BE1 infections.

Pyricularia setariae: a potential bioherbicide agent for control of green foxtail (Setaria viridis)

One hundred and thirty-three fungal isolates, pathogenic to green foxtail, were evaluated for weed control potential under controlled conditions. To determine weed control efficacy, these pathogens were applied as spore or mycelial suspensions at approximately 105propagules ml−1to green foxtail at the three-leaf stage. One week after inoculation, most isolates caused only minor injury to the plants, but 15 isolates caused 50 to 100% disease. Among the most efficacious isolates, only those ofPyricularia setariaeexhibited strong host specificity to the target weed, revealing no significant pathogenicity on 28 other plant species tested, including many important crops such as wheat, barley, and oat. On green foxtail leaves, conidia of this fungus germinated readily at 14, 20, and 26 C, but the process of germination and appressorial formation was more rapid at the higher temperatures. The fungus applied at the concentration of 105spores ml−1reduced weed fresh weight by 34% 7 d after the treatment when compared with controls, whereas a concentration of 107spores ml−1reduced fresh weight by 87%. This efficacy was comparable with that of the herbicide sethoxydim. When applied to the weed at the one- to four-leaf stages, the fungus reduced green foxtail fresh weight by more than 80%. Efficacy was slightly lower on plants at the five-leaf stage or older. On the green foxtail biotype resistant to the herbicide sethoxydim,P. setariaecaused 80% fresh weight reduction compared with untreated controls, as opposed to 17% achieved with the herbicide. At 20 C, the fungus required a minimum of 6-h dew period to initiate infection, but a 10-h dew period was needed to cause severe damage to green foxtail.

Historical Perspective on Pneumocystis carinii Infection

Pneumocystis is a genus of parasitic fungi infecting lung tissues in a wide range of mammal species, displaying a strong host specificity and patterns of co-speciation with their hosts. However, a recent study on Asiatic murids challenged these patterns reporting several Pneumocystis lineages/species shared by different host species or even genera in the Rattini and Murini tribes. Here we screened lung samples of 27 species of African rodents from five families for the presence of Pneumocystis DNA. Using reconstructed multi-locus phylogenies of both hosts and parasites, we tested the hypothesis of their co-evolution. We found that Pneumocystis is widespread in African rodents, detected in all but seven screened host species, with species-level prevalence ranging from 5.9 to 100%. Several host species carry pairs of highly divergent Pneumocystis lineages/species. The retrieved co-phylogenetic signal was highly significant (p = .0017). We found multiple co-speciations, sorting events and two host-shift events, which occurred between Murinae and Deomyinae hosts. Comparison of genetic distances suggests higher substitution rates for Pneumocystis relative to the rodent hosts on neutral loci and slower rates on selected ones. We discuss life-history traits and population dynamics factors which could explain the observed results.

Pneumocystis

AbstractPneumocystis organisms can cause pneumonia in mammals that lack a strong immune defense. The genus Pneumocystis contains many different organisms that can be distinguished by DNA sequence analysis. These different organisms are different species of yeast-like fungi that are most closely related to the ascomycete, Schizosaccharomyces pombe. Each species of Pneumocystis appears to be specific for the mammal in which it is found. The species that infects humans is Pneumocystis jiroveci. P. jiroveci has not been found in any other mammal and the species of Pneumocystis found in other mammals have not been seen in humans. Genetic variation among P. jiroveci samples is common, suggesting that there are many strains. Strain analysis shows that adults can be infected by more than one strain, and suggests that pneumonia can be the result of infection occurring proximal to the time of disease, rather than to reactivation of dormant organisms acquired in early childhood. Nevertheless, long-term colonisation may be occurring. A large fraction of normal children and animals show evidence of infection. A Pneumocystis species that grows in rats has been shown to possess a complex genetic system for surface antigen variation, a strategy employed by other microbes that dwell in immunocompetent hosts. These findings, together with strong host specificity, suggest that Pneumocystis species may be obligate parasites. The source of infection is not clear. Pneumocystis DNA is detectable in the air, but is scarce except in environments occupied by individuals with Pneumocystis pneumonia. In a few cases, there is direct evidence of person to person transmission. In general, however, patients and their contacts have been found to have different strains of P. jiroveci.

Factors related to diversity of decomposer fungi in tropical forests

Recent studies suggest that host-preferences are common among certain groups of tropical fungal decomposers but rare in others, and sometimes occur where we least expect them. Host preferences among microfungi and ascomycetes that decompose leaf litter are common but usually involve differences in relative frequencies more than presence/absence, so their diversity may be loosely correlated with species richness of host trees. Strong host-specificity appears to be rare among wood decomposer fungi, whereas characteristics of their substrata and habitat are very important for this group. Anthropogenic disturbance predisposed a tropical forest to subsequent hurricane damage, and the resulting direct and indirect effects on host diversity and habitat heterogeneity were reflected in the decomposer fungal community more than sixty years after the original disturbance. While species richness of dictyostelid slime molds and functional diversity of their bacterial prey increased with disturbance, the more diverse microfungi and ascomycetes were apparently negatively affected by disturbance.

Food consumption, life history and determinants of host range in the bruchid beetle Specularius impressithorax (Coleoptera: Bruchidae)

The bruchid beetle Apecularius impressithorax, a multivoltine species, feeds on seeds of Erythrina abyssinica (Leguminosae) affecting them in storage. Larval development was indicated by weight loss of infested seeds and five larval instars were detected. Breaking through the emergence disk demands much energy, and was registered by a large weight loss of the beetle. Despite a strong host specificity, the chemistry of S. impressithorax resembled that of other bruchid beetles. During larval development zinc and copper were extracted strongly from food, and accumulated, whereas all other divalent metals (Ca, Mg, Fe, Mn) were mostly excreted. The development time from egg to emergence is reduced with increasing ambient temperature in the range from 20 to 30°C. At 4°C no development occurs, so that seed storage at this temperature is very favourable. Ovipositing beetles have an olfactory preference for seeds of E. abyssinica as host, but after a long delay accept seeds of other species in the absence of the host seed. Larval development terminated after the first instar in seeds of non-host species of the co-occurring miombo woodland trees Acacia erioloba and Brachystegia spiciformis and the pulses Cajanus cajan, Phaseolus vulgaris and Vigna unguiculata, thus S. impressithorax will not affect other stored seeds of forest trees.