Influence of climatic factors on Ixodes ricinus nymph abundance and phenology over a long-term monthly observation in Switzerland (2000-2014).

BACKGROUND: One of the major public health challenges in the field of communicable diseases consists of being able to predict where and when a population is at risk of being infected by a pathogen. In the case of vector-borne diseases, such predictions often require strong ecological knowledge of the vector life-cycle and the environmental conditions promoting or preventing its establishment and maintenance. In this study, we analyse how climatic factors influence the abundance and phenology of the Lyme borreliosis vector Ixodes ricinus in a Swiss temperate forest, based on a long-term monthly observation over a period of 15 years (2000 and 2014). RESULTS: Our results show that questing nymph density significantly decreased during the study period in the sampling area. Although the analyses of climatic variables point out the relative importance of air temperature, relative humidity and saturation deficit on nymph questing activity, the global trends followed by these variables over the study period failed to fully explain the observed decline. However, nymph phenology was additionally explained by the presence of climatic thresholds that limit the questing behaviours of ticks. Most notably, we found that the presumed upper threshold of air saturation deficit, which strongly limits the increase of questing nymph density and is typically reached in the middle of spring, was reached significantly earlier and earlier over years. CONCLUSIONS: In addition to phenology per se, the use of climatic thresholds may help to predict the presence and abundance of questing ticks in Lyme borreliosis endemic areas. Tick sensitivity to temperature or saturation deficit thresholds also suggests that extreme climatic events more than global trends may affect tick population dynamics. These two points may be of high importance in epidemiological short-term as well as long-term predictions. However, the highly unexplained variability in nymph density underlines the need for further studies that include other factors such as tick host abundance or tick microhabitats, two potentially influent factors that were not assessed in the present study.

Congenital syphilis in Switzerland: gone, forgotten, on the return.

INTRODUCTION: Acquired syphilis has re-emerged in many Western European countries. In contrast to international guidelines, screening for syphilis in pregnancy is not generally recommended in Switzerland. There has been an increase in the incidence of laboratory syphilis notifications in recent years, regardless of gender and age. METHODS: We conducted a retrospective study, evaluating the total numbers of pregnant women with positive syphilis serology (Treponema pallidum Particle Agglutination assay, TPPA) from 2000 to 2009, and evaluated the clinical management and outcome of their offspring. In addition, we sought to determine cases of infectious syphilis (primary, secondary, and early latent syphilis) reported to the Swiss Federal Office of Public Health in women of childbearing age, which has previously been shown to precede changes in the incidence of congenital syphilis within a population. RESULTS: Out of 13,833 women who gave birth at our institution, positive syphilis serology was found in 9 pregnant women during the 10 years studied. A total of 6 pregnant women were diagnosed having syphilis infection during pregnancy. Regarding their offspring, 8 of the 9 newborns were tested serologically. One neonate experienced congenital syphilis because the adequately treated mother developed re-infection after treatment. Within the Swiss population, infectious syphilis cases in women of childbearing age increased substantially from 2006 to 2009. CONCLUSIONS: The epidemiologic data suggest that congenital syphilis could become a medical problem in Switzerland due to the rise of infectious syphilis cases in women of childbearing age that have been shown to be followed by changes in the congenital syphilis incidence. The persistence of congenital syphilis in Switzerland along with this rise of infectious syphilis in women of childbearing age suggests a potential for improvement of prenatal care and syphilis control programmes.

Identification of host bloodmeal source and Borrelia burgdorferi sensu lato in field-collected Ixodes ricinus ticks in Chaumont (Switzerland).

To evaluate the importance of vertebrate species as tick hosts and as reservoir hosts in two endemic areas for Lyme borreliosis in Switzerland, we applied molecular methods for the analysis of bloodmeal source and Borrelia infection in questing Ixodes ricinus L. ticks. In total, 1326 questing ticks were simultaneously analyzed for Borrelia and for blood meal remnants by using reverse line blot. An overall infection prevalence of 19.0% was recorded for Borrelia sp., with similar rates in both sites. Using a newly developed method for the analysis ofbloodmeal targeting the 12S rDNA mitochondrial gene, identification of host DNA from field-collected ticks was possible in 43.6% of cases. Success of host identification at the genus and species level reached 72%. In one site, host identification success reached its maximum in spring (93% in May), decreasing in summer (20% in July) and rising in autumn (73% in October). In the other site, identification rate in ticks remained low from April to July and increased in autumn reaching 68% in October and November. The most prevalent identified host DNA was artiodactyls in both sites. Red squirrel DNA was significantly more frequently detected in ticks collected in one site, whereas insectivore DNA was more frequent in ticks in the other site. DNA from more than one vertebrate host was detected in 19.5% of nymphs and 18.9% of adults. Host DNA was identified in 48.4% of the Borrelia infected ticks. Although DNA from all Borrelia species was found in at least some ticks with DNA from mammals and some ticks with DNA from birds, our results confirm a general association of B. afzelii and B. burgdorferi sensu stricto with rodents, and B. valaisiana and B. garinii with birds.

A comparison of two DNA extraction approaches in the detection of Borrelia burgdorferi sensu lato from live Ixodes ricinus ticks by PCR and reverse line blotting.

We tested two approaches to extract Borrelia DNA from live Ixodes ricinus ticks before polymerase chain reaction (PCR) and reverse line blotting (RLB): DNA extraction of one half of the tick after incubation in BSK medium and DNA extraction of the other half of the tick directly, using ammonium hydroxide. Among 2079 ticks, 31.2% (n=649) were found to be Borrelia-infected by PCR-RLB test using at least one of the DNA extraction methods. Five hundred four ticks (24.2%) were found infected after incubation in BSK and 481 (23.1%) after direct DNA extraction from the tick. The difference was not significant. However, these prevalences were significantly lower when only one method was applied (23.1% and 24.2%) compared to the prevalence obtained by the use of both methods (31.2%). In 313 infected ticks discordant results were obtained, i.e., one half of the tick was found to be infected whereas the other half was uninfected. Among these ticks, B. garinii and B. burgdorferi sensu stricto (ss) were significantly more frequently identified in the half tick incubated in BSK. No significant differences were observed for B. burgdorferi ss, B. valaisiana, and for undetermined Borrelia species.

Molecular identification of bloodmeal source in Ixodes ricinus ticks using 12S rDNA as a genetic marker.

We developed an efficient molecular method for the identification of the bloodmeal sources in the tick Ixodes ricinus (L.), the European vector of the agents of Lyme borreliosis and tick-borne encephalitis. An approximately 145-bp orthologous fragment of the vertebrate mitochondrial 12S rDNA was used as a molecular marker to discriminate host vertebrate species. The method consists of a single run polymerase chain reaction amplification of the 12S rDNA molecular marker by using nondegenerate primers followed by a reverse line blot hybridization assay by using specific oligonucleotide probes. The palette of probes allowed us to distinguish major groups of host vertebrates (e.g., mammals, small rodents, artiodactyls, birds, lizards) and to identify the bloodmeal sources at the genus or species level. External primers were designed and used to sequence the 12S rDNA molecular marker of a broad range of known or potential host vertebrate species (n = 60), including mammal (n = 28), bird (n = 31), and reptile (n = 1) species. The use of this technique coupled with known methods for identification of tick-borne pathogens (e.g., Borrelia burgdorferi sensu lato) allowed us to determine the source of infective bloodmeal and to identify reservoir species. The present method was successfully used to identify the source of bloodmeals in all feeding I. ricinus ticks and in half of questing field-collected I. ricinus ticks. Moreover, the bloodmeal source was identified in 65% of ticks infected with B. burgdorferi sensu lato. Further development of this technique may be envisaged for the detection of other vector-borne pathogens and their reservoir hosts.

Phenology of Ixodes ricinus and infection with Borrelia burgdorferi sensu lato along a north- and south-facing altitudinal gradient on Chaumont Mountain, Switzerland.

Questing Ixodes ricinus L. ticks were collected monthly from 2003 to 2005 on the north- and south-facing slopes of Chaumont Mountain in Neuchâtel, Switzerland, at altitudes varying from 620 to 1,070 m. On the south-facing slope, questing tick density was higher than on the north-facing slope, and it decreased with altitude. Density tended to increase with altitude on the north-facing slope. Saturation deficit values higher than 10 mmHg and lasting for >2 mo were often recorded on the south-facing slope, explaining seasonal patterns of questing tick activity. The overall prevalence of Borrelia burgdorferi sensu lato was 22.4%, and prevalence differed according to exposure and among years. No difference was noticed between nymphs and adults. Four Borrelia species were identified. Mixed infections were detected in 52 ticks, B. garinii and B. valaisiana (n = 21) and B. afzelii and B. burgdorferi s.s. (n = 20) were the most frequent associations observed. The density of infected ticks varied from 3.6 to 78.7 infected nymphs per 100 m2 and from 0.6 to 16.9 infected adults per 100 m2, both slopes combined. The study on the south-facing slope was a follow-up of a previous study carried out at the same location during 1999-2001. Comparison of climatic data between the two periods showed a marked increase in saturation deficit. Substantial differences in density and phenology of ticks also were observed. At high elevations, ticks were significantly more abundant during the current study. This can be explained by rising temperatures recorded during summer at altitude, reaching values similar to those registered in the first study beneath. At the lowest altitude, adults were significantly less abundant, probably due to long-lasting high saturation deficits that impaired nymphal survival. The density of Borrelia-infected ticks was higher than in the previous study.

Ixodes ricinus density and infection prevalence of Borrelia burgdorferi sensu lato along a North-facing altitudinal gradient in the Rhône Valley (Switzerland).

Questing Ixodes ricinus ticks were sampled monthly along a north-facing altitudinal gradient in the canton of Valais, Switzerland, from March 2004 to February 2005. Tick density and infection with Borrelia burgdorferi sensu lato were monitored. Ticks were collected by flagging vegetation at three different altitudes (750 m, 880 m, and 1020 m above sea level). Ticks were examined for Borrelia by polymerase chain reaction (PCR) followed by reverse line blot. At the three altitudes, questing tick activity was not observed under 10 degrees C and was reduced when saturation deficit was higher than 5 mm Hg, most questing tick activity was occurred between 2 mm Hg and 7 mm Hg. Tick density and peak tick density were highest at 1020 m. High saturation deficits at the lowest altitudes appear to impair the tick population. The prevalence of B. burgdorferi infection in nymphs and adults decreased with altitude. The prevalence of infection was higher in adult ticks (47%) than in nymphs (29%). Four B. burgdorferi sensu lato genospecies were detected: B. afzelii (40%), B. garinii (22%), B. valaisiana (12%) and B. burgdorferi sensu stricto (6%). Mixed infections were detected in 13% of infected ticks.