Biology subjects

Voordouw, M. J.

Publications and source records attributed to Voordouw, M. J..

6 recordsLinked to original sources

bioRxiv2021

Beech tree masting explains the inter-annual variation in the fall and spring peaks of Ixodes ricinus ticks with different time lags

BackgroundThe tick Ixodes ricinus is an important vector of tick-borne diseases including Lyme borreliosis. In continental Europe, the nymphal stage of I. ricinus often has a bimodal phenology with a large spring/early summer peak and a smaller fall peak. While there is consensus about the origin of the spring nymphal peak, there are two alternative hypotheses for the fall nymphal peak, direct development versus delayed diapause. These two hypotheses make different predictions about the time lags of the correlations between the spring peak, the fall peak, and seed production (masting) by deciduous trees. MethodsTo determine which hypothesis is most important for explaining the fall peak, we used data from a long-term surveillance study (15 years) on the density of I. ricinus nymphal ticks at 4 different elevation sites in an area of Switzerland that is endemic for Lyme borreliosis, and long-term data on the mast of the European beech tree from the literature. ResultsI. ricinus nymphs had a bimodal phenology at the three lower elevation sites, but a unimodal phenology at the top elevation site. At the lower elevation sites, the density of nymphs (DON) in the fall was strongly correlated with the DON in the spring of the following year. The inter-annual variation in the densities of I. ricinus nymphs in the fall and spring were best explained by a 1-year versus a 2-year time lag with the beech tree masting index. Fall nymphs had higher fat content and are younger than spring nymphs. All of these observations are consistent with the direct development hypothesis for the fall peak of I. ricinus nymphs at our study site. Our study provides new insight into the complex bimodal phenology of this important disease vector. ConclusionsPublic health officials in Europe should be aware that following a strong mast year, the DON will increase 1 year later in the fall and 2 years later in the spring and summer. Population ecology studies of I. ricinus should consider that the spring and fall peak in the same calendar year represent different generations of ticks.

ecology↗

bioRxiv2021

Borrelia infection in rodent host has dramatic effects on the microbiome of ticks

BackgroundVector-borne diseases remain major causes of human morbidity and mortality. It is increasingly recognized that the community of microbes inhabiting arthropods can strongly affect their vector competence, but the role of the tick microbiome in Borrelia transmission - the cause of Lyme disease - remains unclear. ResultsHere, we use a large-scale experiment to clarify the reciprocal interactions between Borrelia afzelii and the microbiome of Ixodes ricinus, its primary vector. In contrast to other reports, we find that depletion of the bacterial microbiome in larval ticks has no effect on their subsequent acquisition of B. afzelii during blood feeding on infected mice. Rather, exposure to B. afzelii-infected hosts drives pervasive changes to the tick microbiome, decreasing overall bacterial abundance, shifting bacterial community composition, and increasing bacterial diversity. These effects appear to be independent of the acquisition of B. afzelii by ticks, suggesting they are mediated by physiological or immunological aspects of B. afzelii infection in the rodent host. ConclusionsManipulation of the microbiome of I. ricinus larvae had no effect on their ability to acquire B. afzelii. In contrast, B. afzelii infection in the mouse had dramatic effects on the composition of the gut microbiome in I. ricinus nymphs. Our study demonstrates that vector-borne infections in the vertebrate host shape the microbiome of the arthropod vector.

microbiology↗

bioRxiv2020

Borrelia afzelii does not suppress the development of anti-tick immunity in bank voles

Vector-borne pathogens manipulate their vertebrate hosts to enhance their transmission to arthropod vectors. The ability of vertebrate hosts to develop acquired immunity against arthropod vectors represents an existential threat for both the vector and the pathogen. The purpose of the study was to test whether the tick-borne spirochete bacterium Borrelia afzelii could suppress the development of acquired immunity to its tick vector Ixodes ricinus in the bank vole Myodes glareolus, which is an important host for both the tick and the pathogen. We created a group of B. afzelii-infected bank voles and an uninfected control group by exposing lab-reared animals to infected or uninfected ticks. At 1, 2, and 3 months post-infection, all bank voles were infested with larval I. ricinus ticks. The bank voles developed a strong antibody response against tick salivary gland extract proteins. This anti-tick immunity had negative effects on tick fitness traits including engorged larval weight, unfed nymphal weight, larva-to-nymph molting time and larva-to-nymph molting success. Infection with B. afzelii did not suppress the development of acquired immunity against I. ricinus ticks. The development of anti-tick immunity was strongly correlated with a dramatic temporal decline in both the bacterial abundance in the host ear tissues and the host-tick transmission success of B. afzelii. Our study suggests that the development of anti-tick immunity in bank voles has important consequences for the density of infected ticks and the risk of Lyme borreliosis. ImportanceMany pathogens enhance their persistence and transmission by suppressing the immune system of their host. We used an experimental infection approach to test whether the Lyme disease pathogen, Borrelia afzelii, could suppress the development of acquired immunity against its tick vector (Ixodes ricinus) in the bank vole (Myodes glareolus), but found no evidence for this phenomenon. Uninfected and B. afzelii-infected bank voles both developed a strong IgG antibody response against tick salivary gland extract following repeated infestations with I. ricinus ticks. The development of anti-tick immunity was negatively correlated with the abundance of B. afzelii in ear tissue biopsies and with host-to-tick transmission to I. ricinus ticks. Our study suggests that anti-tick immunity in the bank vole reduces the prevalence of this important tick-borne pathogen.

microbiology↗

bioRxiv2019

Competition among Gardnerella subgroups from the human vaginal microbiome

Gardnerella spp. are hallmarks of bacterial vaginosis, a clinically significant dysbiosis of the vaginal microbiome. Gardnerella has four subgroups (A, B, C and D) based on cpn60 sequences. Multiple subgroups are often detected in individual women, and interactions between these subgroups are expected to influence their population dynamics and associated signs and symptoms of bacterial vaginosis. In the present study, contact-independent and contact-dependent interactions between the four Gardnerella subgroups were investigated in vitro. The cell free supernatants of mono- and co-cultures had no effect on growth rates of the Gardnerella subgroups suggesting that there are no contact-independent interactions (and no contest competition). For contact-dependent interactions, mixed communities of 2, 3 or 4 subgroups were created and the initial (0 h) and final population sizes (48 h) were quantified using subgroup-specific PCR. Compared to the null hypothesis of additive interactions, most (69.3%) of the mixed communities exhibited competition (p < 0.0001). Competition reduced the growth rates of subgroups A, B and C. In contrast, the growth rate of subgroup D increased in the presence of the other subgroups (p < 0.0001). All subgroups were able to form biofilm alone and in mixed communities. Our study suggests that there is scramble competition among Gardnerella subgroups, which likely contributes to the observed distributions of Gardnerella spp. in vaginal microbiomes and the formation of the multispecies biofilms characteristic of bacterial vaginosis.

microbiology↗

bioRxiv2019

Maternal antibodies provide strain-specific protection against infection with the Lyme disease pathogen in a wild rodent

The vertebrate immune system can produce antibodies that protect the host against pathogens. Females can transmit antibodies to their offspring, which provide short-term protection against infection. The tick-borne bacterium Borrelia afzelii causes Lyme disease in Europe and consists of multiple strains that cycle between the tick vector (Ixodes ricinus) and vertebrate hosts such as the bank vole (Myodes glareolus). We used a controlled experiment to show that infected female bank voles transmit protective antibodies to their offspring that are specific for the strain of B. afzelii. To test the specificity of protection, the offspring were challenged with either the same strain to which the mothers had been exposed or a different strain. The maternal antibodies protected the offspring against the same strain, but not against the different strain. The offspring from the uninfected control mothers were equally susceptible to both strains. Our study shows that maternal antibodies provide strong but highly strain-specific protection against B. afzelii in an important rodent reservoir host. The transmission of maternal antibodies may have important consequences for the epidemiology of multiple-strain pathogens in nature.\n\nAuthor SummaryMany pathogens that cause infectious disease consist of multiple strains. In vertebrate hosts, the immune system can generate antibodies that are highly specific for different pathogen strains. Mothers can transmit these antibodies to their offspring and thereby protect them from infectious disease. To date, few studies have investigated whether this transgenerational transfer of protective antibodies is important for pathogens that cycle in wild animal populations. The tick-borne spirochete bacterium Borrelia afzelii causes Lyme disease in Europe and cycles between Ixodes ticks and wild rodent hosts, such as the bank vole (Myodes glareolus). The purpose of our study was to test whether female bank voles infected with B. afzelii transmit antibodies to their offspring that protect them from an infected tick bite. Our study found that infected mothers do transmit antibodies, but the offspring were only protected against the strain of B. afzelii to which their mothers had been exposed and not to a different strain (i.e. protection was highly strain-specific). The broader implications of our study is that the transfer of protective antibodies between generations in the vertebrate host population could be important for organizing the community of pathogen strains that circulate in nature.

immunology↗

bioRxiv2018

Whole body transcriptomes and new insights into the biology of the tick Ixodes ricinus

BackgroundIxodes ricinus is the most important vector of tick-borne-diseases in Europe. A better knowledge of its genome and transcriptome is important for developing control strategies. Previous transcriptomic studies of I. ricinus have focused on gene expression during the blood meal in specific tissues. To obtain a broader picture of changes in gene expression during the blood meal, our study analysed the transcriptome at the level of the whole body for both nymphal and adult ticks. I. ricinus ticks from a highly inbred colony at the University of Neuchatel were used. We also analysed previously published RNAseq studies to compare the genetic variation between three wild strains and three lab strains, including the strain from Neuchatel.\n\nResultsRNA was extracted from whole tick bodies and the cDNA was sequenced, producing 162,872,698 paired-end reads. Our reference transcriptome contained 179,682 contigs, of which 31% were annotated using Trinotate. Gene expression was compared between ticks that differed with respect to stage (nymph, adult), sex (female, male), and feeding status (unfed, partially fed). We found that blood feeding in nymphs and female adult ticks increased the expression of cuticle-associated genes. Using a set of 5,422 single nucleotide polymorphisms to calculate the heterozygosity, we found that the wild tick populations of I. ricinus had much higher levels of heterozygosity than the three lab populations.\n\nConclusionUsing high throughput strand-oriented sequencing for whole ticks in different stages and feeding conditions, we obtained a de novo assembly that significantly increased the genomic resources available for I. ricinus. Our study illustrates the importance of analysing the transcriptome at the level of the whole body to gain additional insights into how gene expression changes over the life cycle of an organism. Our comparison of several RNAseq datasets shows the power of transcriptomic data to accurately characterize genetic polymorphism and for comparing different populations or sources of sequencing material.

genomics↗