| 1. |
- Andersson, Martin, et al.
(författare)
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Co-Infection with 'Candidatus Neoehrlichia mikurensis' and Borrelia afzelii in Ixodes ricinus Ticks in Southern Sweden.
- 2013
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Ingår i: Vector Borne and Zoonotic Diseases. - : Mary Ann Liebert Inc. - 1557-7759 .- 1530-3667. ; 13:7, s. 438-442
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Tidskriftsartikel (refereegranskat)abstract
- Abstract The tick-borne bacterium 'Candidatus Neoehrlichia mikurensis' has recently been recognized as a human pathogen in Europe and appears to be the second most common pathogenic bacterium in Ixodes ricinus ticks in central Europe, second to Borrelia afzelii. Here, we investigate the prevalence of 'Candidatus N. mikurensis' in host-seeking ticks in southern Sweden and the rate of co-infection with B. afzelii. We developed a real-time qPCR assay targeting the groEL gene of 'Candidatus N. mikurensis' and applied this assay to 949 I. ricinus ticks collected at several locations over 2 years. We found an overall prevalence of 6.0%, which means that Candidatus N. mikurensis is one of the most common tick-transmitted zoonotic agents in this area. Co-infections with both 'Candidatus N. mikurensis' and B. afzelii occurred in 2.1% of the ticks, which is significantly more than expected under random co-occurrence. The infection intensity (number of bacterial cells) of 'Candidatus N. mikurensis' was not affected by co-infection with B. afzelii, and vice versa. We conclude that there is a risk for simultaneous transmission of these 2 tick-borne pathogens. The potential medical consequences of this require further investigation.
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| 2. |
- Andersson, Martin, et al.
(författare)
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Infection dynamics of the tick-borne pathogen 'Candidatus Neoehrlichia mikurensis' and co-infections with Borrelia afzelii in bank voles in Southern Sweden.
- 2014
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Ingår i: Applied and Environmental Microbiology. - 0099-2240. ; 80:5, s. 1645-1649
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Tidskriftsartikel (refereegranskat)abstract
- The tick-borne bacterium 'Candidatus Neoehrlichia mikurensis' has recently been recognized as a human pathogen. Together with Borrelia afzelii, it is one of the most common pathogens found in the tick Ixodes ricinus. Here, we compared the epidemiology of 'Candidatus N. mikurensis' and B. afzelii by longitudinal sampling from May to September in one of their most abundant vertebrate hosts, the bank vole (Myodes glareolus), using real-time PCR for detection and quantification. The prevalence of 'Candidatus N. mikurensis' and B. afzelii was 19% (50/261) and 22% (56/261), respectively. The prevalence of 'Candidatus N. mikurensis' increased significantly during the sampling season. The clearance rate of 'Candidatus N. mikurensis' was significantly higher than that of B. afzelii. We found a high frequency of double infections; 46% of all samples infected with 'Candidatus N. mikurensis' also had a co-infection with B. afzelii. The frequency of co-infections was significantly higher than expected from the prevalence of each pathogen. The high level of co-infections can be caused by interactions between the pathogens or might reflect variation in general susceptibility among voles.
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| 3. |
- Andersson, Martin, et al.
(författare)
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Multiple-Strain Infections of Borrelia afzelii: A Role for Within-Host Interactions in the Maintenance of Antigenic Diversity?
- 2013
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 181:4, s. 545-554
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Tidskriftsartikel (refereegranskat)abstract
- Genetically diverse infections are common but little is known about what effects coinfecting strains have on each other in natural host-parasite systems. To explore the nature and consequences of interactions in the wild, we studied the tick-transmitted bacterium Borrelia afzelii in one of its main reservoir hosts, the bank vole Myodes glareolus. We measured overall infection intensity with quantitative polymerase chain reaction (PCR) and resolved the composition of multiple infections using strain-specific PCR assays targeting the ospC gene (which encodes an immunodominant surface protein). We found seven different strains, as defined by ospC genotype. There was little evidence for interactions affecting infection intensities, but strains were highly aggregated (i.e., there were more multiple infections than expected from random co-occurrence). Moreover, there was a positive correlation between the difference at the amino acid level between two OspC types and their degree of association. Overall, the observed patterns suggest that facilitation is more important than competition in this system and that more diverse infections have an advantage in establishing and/or maintaining infection. We propose that this advantage is one of the factors that favors antigenic diversity.
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| 4. |
- Andersson, Martin, et al.
(författare)
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Wild Rodents and Novel Human Pathogen Candidatus Neoehrlichia mikurensis, Southern Sweden.
- 2011
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Ingår i: Emerging Infectious Diseases. - : Centers for Disease Control and Prevention (CDC). - 1080-6040. ; 17:9, s. 1716-1718
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Tidskriftsartikel (refereegranskat)abstract
- We examined small mammals as hosts for Anaplasmataceae in southern Sweden. Of 771 rodents, 68 (8.8%) were infected by Candidatus Neoehrlichia mikurensis, but no other Anaplasmataceae were found. Candidatus N. mikurensis has recently been found in human patients in Germany, Switzerland, and Sweden, which suggests that this could be an emerging pathogen in Europe.
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| 5. |
- Barclay, Victoria C, et al.
(författare)
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CD4(+)T cells do not mediate within-host competition between genetically diverse malaria parasites
- 2008
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Ingår i: Royal Society of London. Proceedings B. Biological Sciences. - : The Royal Society. - 1471-2954. ; 275:1639, s. 1171-1179
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Tidskriftsartikel (refereegranskat)abstract
- Ecological interactions between microparasite populations in the same host are an important source of selection on pathogen traits such as virulence and drug resistance. In the rodent malaria model Plasmodium chabaudi in laboratory mice, parasites that are more virulent can competitively suppress less virulent parasites in mixed infections. There is evidence that some of this suppression is due to immune-mediated apparent competition, where an immune response elicited by one parasite population suppress the population density of another. This raises the question whether enhanced immunity following vaccination would intensify competitive interactions, thus strengthening selection for virulence in Plasmodium populations. Using the P. chabaudi model, we studied mixed infections of virulent and avirulent genotypes in CD4(+)T cell-depleted mice. Enhanced efficacy of CD4(+)T cell-dependent responses is the aim of several candidate malaria vaccines. We hypothesized that if immune-mediated interactions were involved in competition, removal of the CD4(+)T cells would alleviate competitive suppression of the avirulent parasite. Instead, we found no alleviation of competition in the acute phase, and significant enhancement of competitive suppression after parasite densities had peaked. Thus, the host immune response may actually be alleviating other forms of competition, such as that over red blood cells. Our results suggest that the CD4(+)-dependent immune response, and mechanisms that act to enhance it such as vaccination, may not have the undesirable affect of exacerbating within-host competition and hence the strength of this source of selection for virulence.
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| 6. |
- Carlsson, Fredric, et al.
(författare)
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The germ theory revisited : A noncentric view on infection outcome
- 2024
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - 0027-8424. ; 121:17
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Tidskriftsartikel (refereegranskat)abstract
- The germ theory states that pathogenic microorganisms are responsible for causing infectious diseases. The theory is inherently microbe-centric and does not account for variability in disease severity among individuals and asymptomatic carriership—two phenomena indicating an important role for host variability in infection outcome. The basic tenet of the germ theory was recently challenged, and a radically host-centric paradigm referred to as the “full-blown host theory” was proposed. According to this view, the pathogen is reduced to a passive environmental trigger, and the development of disease is instead due to pre-existing immunodeficiencies of the host. Here, we consider the factors that determine disease severity using established knowledge concerning evolutionary biology, microbial pathogenesis, and host–pathogen interactions. We note that the available data support a noncentric view that recognizes key roles for both the causative microbe and the host in dictating infection outcome.
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| 7. |
- Clough, Dagmar, et al.
(författare)
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Contrasting patterns of structural host specificity of two species of Heligmosomoides nematodes in sympatric rodents.
- 2014
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Ingår i: Parasitology Reseach. - : Springer Science and Business Media LLC. - 1432-1955 .- 0932-0113. ; 113:12, s. 4633-4639
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Tidskriftsartikel (refereegranskat)abstract
- Host specificity is a fundamental property of parasites. Whereas most studies focus on measures of specificity on host range, only few studies have considered quantitative aspects such as infection intensity or prevalence. The relative importance of these quantitative aspects is still unclear, mainly because of methodological constraints, yet central to a precise assessment of host specificity. Here, we assessed simultaneously two quantitative measures of host specificity of Heligmosomoides glareoli and Heligmosomoides polygyrus polygyrus infections in sympatric rodent hosts. We used standard morphological techniques as well as real-time quantitative PCR and sequencing of the rDNA ITS2 fragment to analyse parasite infection via faecal sample remains. Although both parasite species are thought to be strictly species-specific, we found morphologically and molecularly validated co- and cross-infections. We also detected contrasting patterns within and between host species with regard to specificity for prevalence and intensity of infection. H. glareoli intensities were twofold higher in bank voles than in yellow-necked mice, but prevalence did not differ significantly between species (33 vs. 18 %). We found the opposite pattern in H. polygyrus infections with similar intensity levels between host species but significantly higher prevalence in mouse hosts (56 vs. 10 %). Detection rates were higher with molecular tools than morphological methods. Our results emphasize the necessity to consider quantitative aspects of specificity for a full view of a parasites' capacity to replicate and transmit in hosts and present a worked example of how modern molecular tools help to advance our understanding of selective forces in host-parasite ecology and evolution.
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| 8. |
- Clough, Dagmar, et al.
(författare)
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Effects of protein malnutrition on tolerance to helminth infection
- 2016
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Ingår i: Biology letters. - : The Royal Society. - 1744-9561 .- 1744-957X. ; 12:6
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Tidskriftsartikel (refereegranskat)abstract
- Infection tolerance is the ability of a host to limit the health effects of a given parasite load. A few recent studies have demonstrated genetic variation for tolerance, but little is known about how environmental factors affect tolerance. Here, we used the intestinal nematode Heligmosomoides polygyrus in laboratory mice to test for effects of protein malnutrition on tolerance. We performed an experiment where two different mouse strains (CBA and BALB/c) were fed either adequate-protein food or low-protein food, and trickle-infected with different doses of H. polygyrus larvae during four weeks. We found that protein malnutrition decreases tolerance measured as intestinal barrier function, but only in one of the strains (BALB/c); that is, there was a host genotype-by-environment interaction for tolerance. We conclude that nutritional status can affect tolerance and that sensitivity of tolerance to malnutrition may differ between host genotypes.
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| 9. |
- Drews, Anna, et al.
(författare)
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Expression and phylogenetic analyses reveal paralogous lineages of putatively classical and non-classical MHC-I genes in three sparrow species (Passer)
- 2017
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Ingår i: BMC Evolutionary Biology. - : Springer Science and Business Media LLC. - 1471-2148. ; 17:1
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Tidskriftsartikel (refereegranskat)abstract
- Background: The Major Histocompatibility Complex (MHC) plays a central role in immunity and has been given considerable attention by evolutionary ecologists due to its associations with fitness-related traits. Songbirds have unusually high numbers of MHC class I (MHC-I) genes, but it is not known whether all are expressed and equally important for immune function. Classical MHC-I genes are highly expressed, polymorphic and present peptides to T-cells whereas non-classical MHC-I genes have lower expression, are more monomorphic and do not present peptides to T-cells. To get a better understanding of the highly duplicated MHC genes in songbirds, we studied gene expression in a phylogenetic framework in three species of sparrows (house sparrow, tree sparrow and Spanish sparrow), using high-throughput sequencing. We hypothesize that sparrows could have classical and non-classical genes, as previously indicated though never tested using gene expression. Results: The phylogenetic analyses reveal two distinct types of MHC-I alleles among the three sparrow species, one with high and one with low level of polymorphism, thus resembling classical and non-classical genes, respectively. All individuals had both types of alleles, but there was copy number variation both within and among the sparrow species. However, the number of highly polymorphic alleles that were expressed did not vary between species, suggesting that the structural genomic variation is counterbalanced by conserved gene expression. Overall, 50% of the MHC-I alleles were expressed in sparrows. Expression of the highly polymorphic alleles was very variable, whereas the alleles with low polymorphism had uniformly low expression. Interestingly, within an individual only one or two alleles from the polymorphic genes were highly expressed, indicating that only a single copy of these is highly expressed. Conclusions: Taken together, the phylogenetic reconstruction and the analyses of expression suggest that sparrows have both classical and non-classical MHC-I genes, and that the evolutionary origin of these genes predate the split of the three investigated sparrow species 7 million years ago. Because only the classical MHC-I genes are involved in antigen presentation, the function of different MHC-I genes should be considered in future ecological and evolutionary studies of MHC-I in sparrows and other songbirds.
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| 10. |
- Eriksson, Britas Klemens, et al.
(författare)
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Declines in predatory fish promote bloom-forming macroalgae.
- 2009
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Ingår i: Ecological Applications. - 1051-0761 .- 1939-5582. ; 19:8, s. 1975-1988
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Tidskriftsartikel (refereegranskat)abstract
- In the Baltic Sea, increased dominance of ephemeral and bloom-forming algae is presently attributed to increased nutrient loads. Simultaneously, coastal predatory fish are in strong decline. Using field data from nine areas covering a 700-km coastline, we examined whether formation of macroalgal blooms could be linked to the composition of the fish community. We then tested whether predator or nutrient availability could explain the field patterns in two small-scale field experiments, by comparing joint effects on algal net production from nutrient enrichment with agricultural fertilizer and exclusion of larger predatory fish with cages. We also manipulated the presence of invertebrate grazers. The abundance of piscivorous fish had a strong negative correlation with the large-scale distribution of bloom-forming macroalgae. Areas with depleted top-predator communities displayed massive increases in their prey, small-bodied fish, and high covers of ephemeral algae. Combining the results from the two experiments showed that excluding larger piscivorous fish: (1) increased the abundance of small-bodied predatory fish; (2) changed the size distribution of the dominating grazers, decreasing the smaller gastropod scrapers; and (3) increased the net production of ephemeral macroalgae. Effects of removing top predators and nutrient enrichment were similar and additive, together increasing the abundance of ephemeral algae many times. Predator effects depended on invertebrate grazers; in the absence of invertebrates there were no significant effects of predator exclusion on algal production. Our results provide strong support for regional declines of larger predatory fish in the Baltic Sea promoting algal production by decreasing invertebrate grazer control. This highlights the importance of trophic interactions for ecosystem responses to eutrophication. The view emerges that to achieve management goals for water quality we need to consider the interplay between top-down and bottom-up processes in future ecosystem management of marine resources.
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