The phenology and population dynamics of Culicoides spp. in different ecosystems in the Netherlands

The Netherlands has enjoyed a relatively free state of vector-borne diseases of economic importance for more than one century. Emerging infectious diseases may change this situation, threatening the health of humans, domestic livestock and wildlife. In order to be prepared for the potential outbreak of vector-borne diseases, a study was undertaken to investigate the distribution and seasonal dynamics of candidate vectors of infectious diseases with emphasis on bluetongue vectors (Culicoides spp.). The study focused primarily on the relationship between characteristic ecosystems suitable for bluetongue vectors and climate, as well as on the phenology and population dynamics of these vectors. Twelve locations were selected, distributed over four distinct habitats: a wetland area, three riverine systems, four peat land areas and four livestock farms. Culicoides populations were sampled continuously using CO2-baited counterflow traps from July 2005 until August 2006, with an interruption from November 2005 to March 2006. All vectors were identified to species level. Meteorological and environmental data were collected at each location. Culicoides species were found in all four different habitat types studied. Wetland areas and peat bogs were rich in Culicoides spp. The taxonomic groups Culicoides obsoletus (Meigen) and Culicoides pulicaris (Linnaeus) were strongly associated with farms. Eighty-eight percent of all Culicoides consisted of the taxon C. obsoletus/Culicoides scoticus. On the livestock farms, 3% of Culicoides existed of the alleged bluetongue vector Culicoides dewulfi Goetghebuer. Culicoides impunctatus Goetghebuer was strongly associated with wetland and peat bog. Many Culicoides species were found until late in the phenological season and their activity was strongly associated with climate throughout the year. High annual variations in population dynamics were observed within the same study areas, which were probably caused by annual variations in environmental conditions. The study demonstrates that candidate vectors of bluetongue virus are present in natural and livestock-farm habitats in the Netherlands, distributed widely across the country. Under favourable climatic conditions, following virus introduction, bluetongue can spread among livestock (cattle, sheep and goats), depending on the nature of the viral serotype. The question now arises whether the virus can survive the winter conditions in north-western Europe and whether measures can be taken that effectively halt further spread of the disease

Estimates of public health risks through import of Aedes albopictus via Dracaena's in the Netherlands : Investigation in the establlishment of Aedes albopictus : final report

Between September 2005 and October 2007 studies were done in six horticultural companies in the Netherlands to assess the presence of the exotic Aedes albopictus and to determine whether the species had become established. Adult mosquitoes were sampled with liberty plus carbon dioxide traps. The presence of eggs and larvae was studied by ovitraps and inspection of water collections. It is concluded that the current study did not demonstrate the establishment of Aedes albopictus in or around the companies that were studied. At the same time, over a period of 118 collection weeks the tigermosquito was found on 76 of the 118 weeks, suggesting a very regular introduction of the species from abroad. The frequent introductions are a cause for concern, as theoretically Aedes albopictus can survive in the Netherlands under current climate condition

Culicoides species associated with sheep in The Netherlands and the effect of a permethrin insecticide

Culicoides spp. act as vectors for a number of viral diseases of animals including bluetongue in sheep. The aims of this study were to determine: (1) which Culicoides spp. are associated with sheep in The Netherlands; (2) the time of the day when they are most active; and (3) the effect of treatment of animals with a permethrin insecticide. Two pairs of sheep were each housed within mosquito tents of either one or two layers of netting and all trapped Culicoides spp. were identified microscopically. For the permethrin insecticide study, one of two pairs of sheep was treated with 3.6% permethrin and all animals were housed in tents of similar design. Of the 6210 midges captured, 54.1% were identified as C. chiopterus and 42.7% as C. obsoletus. C imicola was not identified. The average insect feeding rate was 35-40% and midge activity was greatest around sunset. Permethrin treatment reduced the number of midges captured by 50% and also resulted in a decrease in the percentage of midges that had fed. The findings provide useful information on the behaviour and distribution of Culicoides spp. that will facilitate the development of appropriate control strategies to minimise the risk of insect-vector borne virus diseases such as bluetongue. (C) 2010 Elsevier Ltd. All rights reserved

The low-temperature induced viable-but-nonculturable state affects the virulence of Ralstonia solanacearum biovar 2

van Overbeek. L. S.. Bergervoet. J. H. W.. Jacobs, F. H. H.. and van Elsas. J. D. 2004. The low-ternperature-induced viable-but-nonculturable state 2. Phytopathology affects the virulence of Ralstonia solanacearum biovar 94:463-469. The physiology and virulence of Ralstonia solanacerum biovar 2 strain 1609. kept in water at 4 and 20degreesC, were studied. At 20degreesC. total cell and plate count (colony forming units: CFU) numbers were similar, between log 5.03 and log 5.55 CFU,and log 5.03 and log 5.51 cells per ml. at days 0 and 132. respectively. However, CFU in the Cultures kept at 4degreesC dropped from log 6.78 CFU/ml at day 0 to below detection after 84 days. The presence of catalase in the agar resulted in higher CFU. and at day 84. log, 1.95 CFU/ml still was detectable. No colonies were observed at day 125. The presence of viable-but-nonculturable (VBNC) cells in the 4degreesC Cultures was confirmed using SYTO9 viability staining. Viable Cell numbers were log 1.77 higher than CFU on plates with catalase. At day 84 and after 125 days, log 3.70 viable cells per ml still were I present. Shifts in subpopulations differing in viability were found by flow cytometric sorting of 4degreesC-treated cells stained with SYTO9 (healthy) and propidium iodide (PI, compromised). The SYTO9-stained cell fractions dropped from 99 to 39%, and the PI-stained fractions increased from 0.7 to 33.3% between days 0 and 125. At 20degreesC. the SYTO9-stained fraction remained stable at 99% until day 132, SYTO9-stained cells sorted from 4degreesC Cultures at day 100 were injected into tomato plants. Upon incubation for 30 days, these plants did not show wilting. However. more than log 4.19 CFU and log 8.17 cells were recovered from these plants. Cells from colonies isolated from the nonwilted plants did not regain their virulence as demonstrated by Subsequent injection into several mew, sets of tomato plants. Cells from 4degreesC cultures injected at day 125 were not able to cause wilting of, or proliferate in, tomato plants. The threat posed by VBNC R. solanacearum cells upon incubation at 4degreesC was thus ephemeral because cells lost their capacity to cause disease after 125 days

Field evaluation of a novel synthetic odour blend and of the synergistic role of carbon dioxide for sampling host-seeking Aedes albopictus adults in Rome, Italy

Background Despite the expanding worldwide distribution of Aedes albopictus and its increasing relevance as arboviral vector, current methods to collect adult specimens are not optimal. Improved approaches are thus needed to monitor their density and pathogen infections, and to establish baseline data for control interventions. A widely used device is the BG-Sentinel (BG-trap) which mostly targets host-seeking females attracted by release of CO2 and/or a synthetic odour blend (the BG lure). We compared the attractiveness of this blend to that of the Mbita (MB5) lure, a new synthetic blend of proven efficiency in attracting Afrotropical malaria vectors, and evaluated the additional effect of CO2 to the two odour baits. Findings We carried out 6x6 Latin square experiments in two Ae. albopictus-infested areas in Rome, baiting the BG-traps as follows: CO2, BG lure, MB5 lure, BG lure¿+¿CO2, MB5 lure¿+¿CO2, no bait. CO2 was derived from yeast-fermented sugar. Overall, 949 females and 816 males were collected. Baited traps collected significantly more females than unbaited ones. Traps baited with either lures in combination with CO2 were more effective than those baited with CO2 alone. No significant differences were observed in female captures between traps baited with any of the two lures, nor between the two lures, independently from the addition of CO2. The use of BG lure¿+¿CO2 significantly increased males catches compared to unbaited traps. Conclusions The results suggest a broad significance of the MB5 lure for sampling medically important mosquito species and highlight the high efficacy of the combination of lures¿+¿CO2 for female Ae. albopictus and of BG lure¿+¿CO2 for males, leading to consider CO2 as an essential additional cue for the sampling of this species

Geographic and Temporal Variations in Population Dynamics of Ixodes ricinus and Associated Borrelia Infections in The Netherlands

In a countrywide investigation of the ecological factors that contribute to Lyme borreliosis risk, a longitudinal study on population dynamics of the sheep tick Ixodes ricinus and their infections with Borrelia burgdorferi sensu lato (s.l.) was undertaken at 24 sites in The Netherlands from July 2006 to December 2007. Study sites were mature forests, dune vegetations, or new forests on land reclaimed from the sea. Ticks were sampled monthly and nymphal ticks were investigated for the presence of Borrelia spp. I. ricinus was the only tick species found. Ticks were found in all sites, but with significant spatial and temporal variations in density between sites. Peak densities were found in July and August, with lowest tick numbers collected in December and January. In some sites, questing activities of I. ricinus nymphs and adults were observed in the winter months. Mean monthly Borrelia infections in nymphs varied from 0% to 29.0% (range: 0%–60%), and several sites had significantly higher mean nymphal Borrelia infections than others. Four genospecies of Borrelia burgdorferi s.l. were found, with B. afzelii being dominant at most sites. Borrelia infection rates in nymphal ticks collected in July, September, and November 2006 were significantly higher (23.7%, p