SEARCH · PubMed Health

Results for “Pathogen”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 469 records · Page 26Linked to original sources

PubMed1989

Characterization of factors determining Rickettsia tsutsugamushi pathogenicity for mice.

Pathogenicity of Rickettsia tsutsugamushi for laboratory mice is known to be influenced by at least three factors: (i) route of inoculation, (ii) antigenic strain, and (iii) natural resistance of the host. By using Karp, Gilliam, and Kato strains of R. tsutsugamushi, we examined the effect of these three pathogenicity factors on the kinetics of infection and the development of immunity in BALB/cDub and C3H/HeDub mice. The appearance of rickettsemia in the pathogenic infections generally preceded infections of reduced pathogenicity by 1 to 2 days in both magnitude and time of onset. Mice infected by the subcutaneous route with normally pathogenic rickettsiae, i.e., Gilliam-infected C3H/HeDub mice and Karp-infected BALB/cDub mice, consistently maintained a detectable rickettsemia over a 1-year period. Rickettsiae were recovered from the spleens of 95% (19 of 20) of these mice 52 weeks postinfection. In contrast, mice with infections of reduced pathogenicity, i.e., BALB/cDub mice infected by intraperitoneal and subcutaneous inoculation with Gilliam, did not have detectable rickettsemia from week 20 through week 52 postinfection except for a single mouse on week 44 postinfection. Rickettsiae were detected in the spleens of only 40% (8 of 20) of these mice after 1 year. In both Gilliam-infected mouse strains, protection against heterologous challenge with Karp or Kato rickettsial strains was incomplete up to 7 days postimmunization. Infections of reduced pathogenicity did not result from an enhanced systemic immune response by the host. The onset of the humoral response was not different for the pathogenic and reduced-pathogenicity infections. Pathogenicity differences seemed to result from the more rapid growth of the rickettsiae in the pathogenic infections.

Animals↗

PubMed2004

[Rapid diagnosis of common pathogenic bacteria infection in newborn infants by 16SrDNA oligonucleotide array].

OBJECTIVE: The rapid identification of pathogenic bacteria is important for earlier effective patient management and antimicrobial therapy, especially for the infant patient, whose immunological system is not fully developed. However conventional microbiogical techniques of bacterial identification, culture and isolation of pathogenic bacteria, identification by biochemistry and serological assay, are time-consuming and require intensive labor. On the basis of special gene sequence, PCR provides simple and rapid way to identify bacteria. But it is difficult to identify all of bacteria species which are suspicious of pathogenic agents. Oligonucleotide arrays provide a powerful tool for parallel detection of target genes. The objective of this study was to test a reverse oligonucleotide assay, which hybridize with the PCR product of 16SrDNA using a pair of universal primers, to rapidly identify common infant pathogenic bacteria. METHODS: By comparison and analysis of the 16SrDNA sequences of common pathogenic bacteria, a region, which has numerous sequence variations and flanked by highly conserved sequences, was found. A pair of universal primers was designed according to its flanking conservative sequence, and a set of probes specially targeting to eight species of infant pathogenic bacteria, including staphylococcus aureus, Pseudomonas aeruginosa, Klebsiella pneumoniae, Streptococcus faecalis, Hemophilus influenzae, Enterobacter cloacae, Escherichia coli, and Acinetobacter baumannii,according to the variable sequences. The probes were fixed on the nylon membrane with positive electricity, and hybridized them with the products of PCR using the universal primers. RESULTS: The universal primers could amplify the target sequence from bacteria including the eight common infant pathogenic bacteria and Staphylococcus epidermidis, Enterobacter aerogenes, Streptococcus pneumoniae,beta-hemolytic streptococcus, Neisseria meningitides, Citrobacter freundii, Bacillus subtilis, and Salmonella infantis,but could not amplify rotavirus and human DNA as control. The results showed that the oligonucleotide array could specially hybridize with the eight bacteria to be examined and could not hybridize with other bacteria. The lowest concentration of DNA (product of PCR) for oligonucleotide array was about 25 ng/ml. The results proved that the probes are highly selective and the oligonucleotide arrays could parallelly detect the eight common infant pathogenic bacteria. The results suggested that the oligonucleotide array system was able to identify the eight common infant pathogenic bacteria from clinical specimens and the results were the same as identified by automated bacterial detection machine. From the further experiments, the oligonucleotide array system could directly diagnose the common infant pathogenic bacteria from the broths of samples culture. CONCLUSIONS: Despite limited number of identifiable bacteria and lack of information on antibiotic susceptibility of bacteria, the reverse oligonucleotide assay system, which contains amplification of the segment of 16rDNA from samples using the universal primers and parallel detection of PCR products using specific probes, is an effective method to rapidly identify the eight common infant pathogenic bacteria.

Bacterial Infections↗

PubMed2026

Pathogen local adaptation shapes Pierce's disease of grapevines outcomes under field conditions.

Climate change is broadly expected to increase the range of many plant diseases, yet the current status of local thermal adaptation in many pathogens is poorly understood. Xylella fastidiosa (Xf) is a global bacterial plant pathogen that causes Pierce's disease (PD) of grapevines and infects over 700 other host plant species, impacting both agricultural and natural ecosystems. In a common garden experiment with 477 vines in the field, we compared PD outcomes from a local (colder climate in CA) vs non-local (warmer climate in CA) bacterial strain in 13 Mediterranean grapevine varieties over 3 years. Relative to the local strain, there was 77% lower overwinter survival in the non-local strain from a warmer climate, strongly indicating local adaptation in these CA Xf populations. Host genotype also had a significant effect on pathogen winter survival, and grapevine varieties differed in PD susceptibility. Additionally, we assessed in planta evolution of the two pathogen strains over 3 years by whole-genome sequencing 58 field-derived isolates. There were convergent loss-of-function mutations in genes encoding minor Type IV pilin (T4P) proteins, which control twitching motility and other virulence phenotypes, suggesting rapid adaptive evolution. Our results suggest local adaptation to cold temperatures in a bacterial plant pathogen and a possible role for minor Type IV pilins in thermal adaptation. These findings demonstrate the urgent need to incorporate X. fastidiosa evolution and local thermal adaptation into global models of PD spread. Differentiating pathotypes with distinct thermal adaptations will improve disease forecasting and inform quarantine decisions.IMPORTANCEForecasting the movement of plant pathogens is a critical issue under global warming to effectively manage future plant disease outbreaks. Yet, current plant pathogen local thermal adaptation is often unaccounted for, especially in bacterial pathogens. Our study examines local adaptation to temperature in a bacterial plant pathogen, Xylella fastidiosa, that causes disease in grapevines in addition to infecting 700 other plant species. In a large-scale field experiment across 13 grapevine varieties, we demonstrate local adaptation in pathogen winter survival in distinct Xylella fastidiosa strains. Additionally, we found evidence of adaptive evolution in just 3 years, as we observed convergent mutations after resequencing strains that evolved in the field. Our results suggest that X. fastidiosa populations-even within a small geographic area-have distinct adaptations to winter temperatures and may exhibit differential responses to warming winters.

Type IV pili↗

PubMed2006

Pathogen and biological contamination management: the road ahead.

Multiplication of certified pathogen-free stock plants in vitro makes an important contribution to the production of disease-free planting material for vegetatively propagated crops. Meristem culture is extensively used to eliminate pathogens and contaminants from microbially contaminated plants prior to micropropagation. The approach to pathogen and contamination management differs. It is essential to avoid the release of pathogen-contaminated microplants and to ensure this the plant pathogen-testing guidelines and protocols issued by the Food and Agriculture Organisation (FAO) and its regional representative organizations should be followed. Where in vitro methods are used to eliminate pathogens, the progeny plants should be established in vivo under quarantine conditions and tested under FAO guidelines before being used as stock plants for in vitro multiplication. At establishment of microplants in vitro (stage 1), cultures should be culture-indexed for the presence of microbial contaminants. If pathogen-and contaminant-free cultures are established, then the risk is that of managing laboratory contamination by common environmental microorganisms based on Hazard Analysis Critical Control Points (HACCP) principles. International plant health certification organizations are conservative and rely on established pathogen indexing protocols. They are reluctant to accept DNA-based tests and do not accept testing of in vitro cultures. Given that in time both of these restrictions may be relaxed, micropropagators may look forward to availing more of diagnostic service providers using polymerase chain reaction-based multiplex assays for pathogen-indexing and advances in diagnostic kits for environmental microorganisms in support of laboratory contamination management; with the caveat that molecular tests for pathogens may continue to require confirmation by inoculation of indicator plant species.

Biomarkers↗

PubMed2003

Pathogenic archaea: do they exist?

Archaea are microorganisms that are distinct from bacteria and eukaryotes. They are prevalent in extreme environments, and yet found in most ecosystems. They are a natural component of the microbiota of most, if not all, humans and other animals. Despite their ubiquity and close association with humans, animals and plants, no pathogenic archaea have been identified. Because no archaeal pathogens have yet been identified, there is a general assumption that archaeal pathogens do not exist. This review examines whether this is a good assumption by investigating the potential for archaea to be or become pathogens. This is achieved by addressing: the diversity of archaea versus known pathogens, opportunities for archaea to demonstrate pathogenicity and be detected as pathogens, reports linking archaea with disease, and immune responses to archaea. In addition, molecular and genomic data are examined for the presence of systems utilised in pathogenesis. The view of this report is that, although archaea can presently be described as non-pathogenic, they have the potential to be (discovered as) pathogens. The present optimistic view that there are no archaeal pathogens is tainted by a severe lack of relevant knowledge, which may have important consequences in the future.

Animals↗

PubMed2006

Enhanced identification of viral and atypical bacterial pathogens in lower respiratory tract samples with nucleic acid amplification tests.

The advantages of nucleic acid amplification tests (NAT) over conventional methods for the detection of pathogens in lower respiratory tract samples have not been established. NAT for respiratory pathogens were performed on 439 endotracheal tube (ETT) and bronchoalveolar lavage (BAL) samples. A potential pathogen was detected in 87 samples. Of 22 samples that tested positive by conventional methods, 15 tested positive for the same pathogen by NAT, 1 tested positive for a different pathogen, 2 had co-infections identified only by NAT, and 4 tested negative by NAT. An additional 73 pathogens were detected by NAT in 65 samples including 30 pathogens that were missed by conventional methods (19 adenovirus, 6 respiratory syncytial virus, 3 parainfluenza virus 1-4, 2 influenza A), 41 pathogens not routinely identified by conventional methods in most laboratories (23 rhinovirus, 8 human coronavirus OC43, 5 human metapneumovirus (hMPV), 2 human coronavirus 229E, 2 human coronavirus NL63, 1 Chlamydophila pneumoniae) and 2 pathogens from samples where no respiratory virus testing was requested (1 influenza A, 1 parainfluenza virus). Four of 52 patients who had multiple BAL samples submitted on the same day had negative and positive results by NAT on different samples. NAT improves detection of potential pathogens from ETT and BAL samples.

Adolescent↗

PubMed2001

Inducible defense against pathogens and parasites: optimal choice among multiple options.

Defense against pathogen, parasites and herbivores is often enhanced after their invasion into the host's body. Sometimes different options are adopted depending on the identity and the quantity of the pathogen, exemplified by the switch between Th1 and Th2 systems in mammalian immunity. In this paper, we study the optimal defense of the host when two alternative responses are available, which differ in the effectiveness of suppressing the growth of pathogen (parasite, or herbivore), the damage to the host caused by the defense response, and the magnitude of time delay before the defense response becomes fully effective. The optimal defense is the one that minimizes the sum of the damages caused by the pathogen and the cost due to defense activities. The damage by pathogens increases in proportion to the time integral of the pathogen abundance, and the cost is proportional to the defense activity. We can prove that a single globally optimal combination of defense options always exists and there is no other local optimum. Depending on the parameters, the optimal is to adopt only the early response, only the late response, or both responses. The defense response with a shorter time delay is more heavily used when the pathogen grows fast, the initial pathogen abundance is large, and the difference in time delay is long. We also study the host's optimal choice between constitutive and inducible defenses. In the constitutive defense, the response to pathogen attack works without delay, but it causes the cost even when the pathogen attack does not occur. We discuss mammalian immunity and the plant chemical defense from the model's viewpoint.

Animals↗

PubMed1993

Hazards from pathogenic microorganisms in land-disposed sewage sludge.

Sewage sludge is a complex mixture of organic and inorganic compounds of biological and mineral origin that are precipitated from wastewater and sewage during primary, secondary, and tertiary sewage treatment. Present in these sludges are significant numbers of microorganisms that include viral, bacterial, protozoan, fungal, and helminth pathogens. The treatment of sludge to reduce biochemical oxygen demand, solids content, and odor is not always effective in reducing numbers of pathogens. This becomes a public health concern because the infectious dose for some of these pathogens may be as low as 1 particle (virus) to 50 organisms (Giardia). When sludge is applied to land for agricultural use and landfill compost, these pathogens can survive from days (bacteria) to months (viruses) to years (helminth eggs), depending on environmental conditions. Shallow aquifers can become contaminated with pathogens from sludge and, depending on groundwater flow, these organisms may travel significant distances from the disposal site. Communities that rely on groundwater for domestic use can become exposed to these pathogens, leading to a potential disease outbreak. Currently, methods to determine the risk of disease from pathogens in land-disposed sludge are inadequate because the sensitivity of pathogen detection is poor. The application of recombinant DNA technology (gene probes and polymerase chain reaction) to environmental samples may provide increased sensitivity for detecting specific pathogens in land-disposed sludge and greatly improved risk assessment models for our exposure to these sources of pathogens.

Hazardous Waste↗

PubMed1997

[1996 pathogen incidence and resistance status in peritonitis].

Severe intra-abdominal infection is associated with a high mortality rate. In addition to risk factors in the patients, the causal pathogens and the selection of appropriate therapeutic procedures play an essential part in the course of these conditions. In the majority of intra-abdominal infections mixed aerobic/anaerobic infections, mostly with some involvement of enterobacteria and also of enterococci and staphylococci can be demonstrated. In addition to surgical intervention a calculated antimicrobial initial treatment of intra-abdominal infections with an antibiotic with an adequate effect to combat the pathogen concerned can contribute to improving the patient's prognosis. A calculated antibiotic treatment can only be effectively and reliably carried through if the frequency of the pathogen and the resistance situation are known. Retrospective evaluations of data on the sensitivity and frequency of pathogens from a defined group of subjects allow conclusions on the epidemiological situation in a particular catchment area or in a medical sector and thus make it possible to calculate the appropriate therapy for infections. In 1996 a total of 2,779 bacterial isolates from the intra-abdominal infection sector were examined: 935 Enterobacteriaceae, 83 nonfermenters, 177 Staphylococcus spp., 211 Enterococcus spp., 39 Streptococcus spp., and 1334 different anaerobic bacteria. Fresh clinical isolates were available for all pathogens tested. The most frequent gram-negative pathogen was E. coli (60%) and the most frequent gram-positive pathogen, E. faecalis (44%); the most frequent anaerobic pathogen was B. fragilis (39%). Taurolodine had the lowest resistance rate against gram-negative and anaerobic pathogens. Teicoplanin had the highest activity against gram-positive pathogens.

Anti-Bacterial Agents↗

PubMed2004

Using sediment budgets to investigate the pathogen flux through catchments.

We demonstrate a materials budget approach to identify the main source areas and fluxes of pathogens through a landscape by using the flux of fine sediments as a proxyfor pathogens. Sediment budgets were created for three subcatchment tributaries of the Googong Reservoir in south-eastern New South Wales, Australia. Major inputs, sources, stores, and transport zones were estimated using sediment sampling, dam trap efficiency measures, and radionuclide tracing. Particle size analyses were used to quantify the fine-sediment component of the total sediment flux, from which the pathogen flux was inferred by considering the differences between the mobility and transportation of fine sediments and pathogens. Gullies were identified as important sources of fine sediment, and therefore of pathogens, with the pathogen risk compounded when cattle shelter in them during wet periods. The results also indicate that the degree of landscape modification influences both sediment and pathogen mobilization. Farm dams, swampy meadows and glades along drainage paths lower the flux of fine sediment, and therefore pathogens, in this landscape during low-flow periods. However, high-rainfall and high-flow events are likely to transport most of the fine sediment, and therefore pathogen, flux from the Googong landscape to the reservoir. Materials budgets are a repeatable and comparatively low-cost method for investigating the pathogen flux through a landscape.

Animals↗

PubMed2003

Pathogen frequency in an age-structured population of Plantago lanceolata.

Life-history traits can play important roles in determining the course of ecological species interactions. We explored the consequences of host age on a host-pathogen interaction by quantifying pathogen frequency in an age-structured host population. Our project was motivated by an interest in whether the demographic structure of a host population has consequences for species interactions. In 2 successive years, we planted large cohorts of the perennial herb Plantago lanceolata in its natural environment and observed infection by Fusarium moniliforme, a non-lethal floral fungal pathogen, over 3 years. We documented substantial variation of pathogen frequency across years and between cohorts. Logistic regression revealed that pathogen frequency increased with the number of inflorescences produced and with evidence of prior pathogen presence, whereas it decreased with increasing plant longevity. In addition, interannual variation and an age-year interaction contributed to the observed pathogen frequencies. There was a significant positive effect of age on pathogen frequency overall, but this was not consistent over all ages. Pathogen frequency was higher in 2-year-old plants than in 1-year-olds, suggesting that age-structure can influence the host-pathogen interaction. This pattern did not continue into 3-year-old plants. A possible explanation for this is that selective mortality allows only generally robust plants, and consequently the most resistant plants, to survive to the oldest ages.

Ecology↗

PubMed2006

Antepartum vaginal bleeding, fetal exposure to oral pathogens, and risk for preterm birth at <35 weeks of gestation.

OBJECTIVE: The purpose of this study was to determine the risks for fetal exposure to oral pathogens and the relationship between vaginal bleeding and fetal exposure in preterm birth risk. STUDY DESIGN: An analysis of prospectively collected data for the longitudinal Oral Conditions and Pregnancy Study was conducted. Maternal factors that potentially were associated with fetal exposure to oral pathogens (defined as detection of umbilical cord serum Immunoglobulin M to 1 of 5 oral pathogens) were examined, and the role of vaginal bleeding and fetal exposure to oral pathogens in preterm birth risk was explored. Preterm birth was defined as delivery at <35 weeks of gestation. An adjusted relative risk (95% CI) for fetal exposure was calculated. Adjusted hazard ratios (95% CI) were calculated for preterm birth among women whose data were stratified by the presence/absence of bleeding and/or fetal exposure to oral pathogens. RESULTS: There were complete data for 661 women; 230 women (34.8%) with and 431 women (65.2%) without fetal exposure to oral pathogens. In multivariable analysis, first- or second-trimester bleeding and white race were associated significantly with fetal exposure to oral pathogens (adjusted relative risk, 1.8 [95% CI, 1.3-2.5] and 1.3 [95% CI, 1.1-1.7], respectively). The adjusted hazard ratio for preterm birth among women with first- or second-trimester bleeding and fetal exposure to oral pathogens was 6.4 (95% CI: 2.6-16.0). CONCLUSION: Vaginal bleeding is associated with fetal exposure to oral pathogens, which increases preterm birth risk. Whether bleeding is the cause of or result of fetal exposure to oral pathogens remains to be determined.

Adult↗

PubMed2005

Epidemiology and disease-control under gene-for-gene plant-pathogen interaction.

An introduction of disease-resistant variety of a crop plant often leads to the development of a virulent race in pathogen species that restores the pathogenicity to the resistant crop. This often makes disease control of crop plants extremely difficult. In this paper, we theoretically explore the optimal 'multiline' control, which makes use of several different resistant varieties, that minimizes the expected degree of crop damages caused by epidemic outbreaks of the pathogen. We examine both single-locus and two-locus gene-for-gene (GFG) systems for the compatibility relationship between host genotypes and pathogen genotypes, in which host haplotype has either susceptible or resistant allele in each resistance locus, and the pathogen haplotype has either avirulent or virulent allele in the corresponding virulence locus. We then study the optimal planting strategy of host resistant genotypes based on standard epidemiological dynamics with pathogen spore stages. The most striking result of our single-locus GFG model is that there exists an intermediate optimum mixing ratio for the susceptible and resistant crops that maximizes the final yield, in spite of the fact that the susceptible crop has no use to fight against either avirulent or virulent race of the pathogen. The intermediate mixture is optimum except when the initial pathogen spore population in the season consists exclusively of the virulent race. The optimal proportion of resistant crops is approximately 1/R(0), where R(0) is the basic reproductive ratio of pathogen--the rest (the vast majority if R(0) is large) of crops should be the susceptible genotype. By mixing susceptible and resistant crops, we can force the pathogen races to compete with each other for their available hosts. This competition between avirulent and virulent races prevents the fatal outbreak of the virulent race (the super-race) that can infect all the host genotypes. In the two-locus GFG control, there again exists the optimal mixing ratio for the fraction of universally susceptible genotype and the total fraction of various resistant genotypes, with the ratio close to 1/R(0).

Crops, Agricultural↗

PubMed2005

The expanding role of microarrays in the investigation of macrophage responses to pathogens.

In the last few years, microarray technology has emerged as the method of choice for large-scale gene expression studies. It provides an efficient and rapid method to investigate the entire transcriptome of a cell. No research field has benefited more from microarray technology than the study of the exquisite interplay between pathogens and hosts. Numerous microarray studies have now been published in this field, which have provided insights into the mechanisms of host defence and the tactics employed by pathogens to circumvent these protection strategies. These studies have led to a more comprehensive understanding of the host immune response and identified new avenues of research for potential control strategies against pathogens. In the past, research has concentrated on human and mouse microarrays to investigate host-pathogen interactions, regardless of the host species. This trend is changing with the ever-expanding sequence resources now available for many pathogen and host species, including livestock animals. The use of species-specific microarrays has furthered our understanding of host-pathogen interactions for particular organisms and aided in the annotation of unknown genes. Macrophages play a central role in the host's innate and adaptive immune responses to pathogens. These cells are in the first line of defence and interact with a wide range of pathogens; many of which have evolved strategies to circumvent the macrophage defence mechanisms and survive within these cells. In this report, we review the wealth of studies using microarray technology to investigate the response of macrophages to pathogens. These studies illustrate how microarray technology has expanded our understanding of the dialogue between macrophage and pathogen and provide examples of the benefits and pitfalls of using this technique. Furthermore, we discuss the resources available to use microarray analysis to study the immune response of a non-human, non-rodent species, the cow.

Animals↗

PubMed2004

Pathogen survival in the external environment and the evolution of virulence.

Recent studies have provided evolutionary explanations for much of the variation in mortality among human infectious diseases. One gap in this knowledge concerns respiratory tract pathogens transmitted from person to person by direct contact or through environmental contamination. The sit-and-wait hypothesis predicts that virulence should be positively correlated with durability in the external environment because high durability reduces the dependence of transmission on host mobility. Reviewing the epidemiological and medical literature, we confirm this prediction for respiratory tract pathogens of humans. Our results clearly distinguish a high-virulence high-survival group of variola (smallpox) virus, Mycobacterium tuberculosis, Cornynebacterium diphtheriae, Bordetella pertussis, Streptococcus pneumoniae, and influenza virus (where all pathogens have a mean percent mortality > or = 0.01% and mean survival time >10 days) from a low-virulence low-survival group containing ten other pathogens. The correlation between virulence and durability explains three to four times of magnitude of difference in mean percent mortality and mean survival time, using both across-species and phylogenetically controlled analyses. Our findings bear on several areas of active research and public health policy: (1) many pathogens used in the biological control of insects are potential sit-and-wait pathogens as they combine three attributes that are advantageous for pest control: high virulence, long durability after application, and host specificity; (2) emerging pathogens such as the 'hospital superbug' methicillin-resistant Staphylococcus aureus (MRSA) and potential bioweapons pathogens such as smallpox virus and anthrax that are particularly dangerous can be discerned by quantifying their durability; (3) hospital settings and the AIDS pandemic may provide footholds for emerging sit-and-wait pathogens; and (4) studies on food-borne and insect pathogens point to future research considering the potential evolutionary trade-offs and genetic linkages between virulence and durability.

Animals↗

PubMed2003

Overland flow transport of pathogens from agricultural land receiving faecal wastes.

Considerable investment has been made in recent years in improvements to the microbiological quality of urban wastewater discharges to surface waters, particularly in coastal towns, with the aim of reducing the exposure of bathers and surfers to gastrointestinal pathogens. As this source of pollution has come under greater control, attention has started to focus on diffuse catchment sources of faecal contamination which have been shown to be dominant during high river flows associated with storm events. This association with storm events suggests that rapidly responding hydrological pathways such as overland flow are likely to be important. The aim of this paper is to establish the current state of knowledge of pathogen transport processes in overland flow. In addition, the paper will attempt to convey the way that soil erosion science may aid our understanding of this environmental problem. The scale and nature of faecal waste applications to land in the UK is briefly reviewed, with data presented on both livestock slurry and manure, and human sewage sludge. Particular emphasis is placed on factors influencing the likelihood of pathogens making their way from infected livestock and humans to the soil surface, and therefore the chances of them being available for transport by overland flow. The literature relating to pathogen transport in overland flow is reviewed. Existing pathogen transport models treat pathogens as particles and link pathogen transport models to pathogen die-off kinetics. Such models do not attempt to describe the interactions that may occur between pathogens and soil and waste particles. Although conceptual models describing the possible states in which pathogen transport may occur have been proposed, an understanding of the factors controlling the partitioning of the microorganisms between the different states is only just beginning to emerge. The apparent poor performance of overland flow mitigation measures such as grass buffer strips in controlling the movement of faecal indicators highlights the need for a better understanding the dynamics of microbial transport so that better management approaches may be developed. Examples of on-going research into overland flow transport processes are briefly described and gaps in knowledge identified.

Animals↗

PubMed2000

From protozoa to mammalian cells: a new paradigm in the life cycle of intracellular bacterial pathogens.

It is becoming apparent that several intracellular bacterial pathogens of humans can also survive within protozoa. This interaction with protozoa may protect these pathogens from harsh conditions in the extracellular environment and enhance their infectivity in mammals. This relationship has been clearly established in the case of the interaction between Legionella pneumophila and its protozoan hosts. In addition, the adaptation of bacterial pathogens to the intracellular life within the primitive eukaryotic protozoa may have provided them with the means to infect the more evolved mammalian cells. This is evident from the existence of several similarities, at both the phenotypic and the molecular levels, between the infection of mammalian and protozoan cells by L. pneumophila. Thus, protozoa appear to play a central role in the transition of bacteria from the environment to mammals. In essence, protozoa may be viewed as a 'biological gym', within which intracellular bacterial pathogens train for their encounters with the more evolved mammalian cells. Thus, intracellular bacterial pathogens have benefited from the structural and biochemical conservation of cellular processes in eukaryotes. The interaction of intracellular bacterial pathogens and protozoa highlights this conservation and may constitute a simplified model for the study of these pathogens and the evolution of cellular processes in eukaryotes. Furthermore, in addition to being environmental reservoirs for known intracellular pathogens of humans and animals, protozoa may be sources of emerging pathogenic bacteria. It is thus critical to re-examine the relationship between bacteria and protozoa to further our understanding of current human bacterial pathogenesis and, possibly, to predict the appearance of emerging pathogens.

Amoeba↗

PubMed2004

Pathogen spillover in disease epidemics.

In field experiments manipulating generalist pathogens and host community composition, the presence of a highly susceptible reservoir species drove disease dynamics in multiple nonreservoir species, sometimes decreasing their abundance through apparent competition. The dynamics of generalist pathogens in multispecies host communities remain a major frontier for disease ecology. Of particular interest are how host community structure controls pathogen transmission and how disease spread feeds back to influence the host community. Pathogen spillover occurs when epidemics in a host population are driven not by transmission within that population but by transmission from a reservoir population. Here we review examples of spillover in pathogens infecting humans, domesticated animals, and crops, noting that most empirical evidence for spillover results from nonmanipulative, observational studies. We then present results from two field experiments utilizing an experimentally tractable model system of annual wild grasses and a generalist virus, the barley yellow dwarf virus. In these experiments, the presence of a highly susceptible reservoir species, Avena fatua (wild oats), greatly increased pathogen prevalence in several other species. This result demonstrates pathogen spillover and illustrates the crucial role of host community structure in controlling the dynamics of generalist pathogens. Further, pathogen spillover from A. fatua decreased the abundance of two other host species through pathogen-mediated apparent competition. Thus, our results provide experimental support for theoretical predictions of strong feedbacks between host community structure and generalist disease dynamics.

Animals↗