Comparative characterization of Leporipoxvirus members’ reproduction in continuous cell culture

Examination of the virus-cell interactions is of both scientific and practical importance. Our study was aimed at comparative characterization of rabbit myxoma virus and Shope fibroma virus biological properties that manifested during the virus reproduction in RK-13/2-03 clonal continuous rabbit kidney cell culture. It was demonstrated that the viruses varied in infection development and cytopathic effect duration in RK-13/2-03 cell culture. Apparent lesions in cell monolayers infected by myxoma virus and fibroma virus at similar multiplicity of infection and cultivation temperature were observed on day 2 and day 3 of cultivation, respec- tively, as well as maximum cell lesions with evident degeneration were observed on day 3 and day 6 of cultivation, respectively. Myxoma virus was accumulated at titre of 6.25–6.50 lg TCID50/0,2 cm3, and Shope fibroma virusа was accumulated at titre of 5.50−5.75 lg TCID50/0.2 cm3. Shope fibroma virus demonstrated such infectivity during three passages and myxoma virus demonstrated such infectivity during twenty passages. Prepared cultures were identified as myxoma virus and Shope fibroma virus with molecular genetic analysis. Tests of the viruses for their antigenic relatedness showed that antibodies against myxoma virus were able to neutralize Shope fibroma virus also. NT titres of antibodies against both viruses were similar (1:8). RK-13/2-03 cell culture was found to be highly permissive to Shope fibroma virus that had been isolated from the diseased rabbit and not been an attenuated variant

Spatial multi-criteria decision analysis for modelling suitable habitats of Ornithodoros soft ticks in the Western Palearctic region

Ticks are economically and medically important ectoparasites due to the injuries inflicted through their bite, and their ability to transmit pathogens to humans, livestock, and wildlife. Whereas hard ticks have been intensively studied, little is known about soft ticks, even though they can also transmit pathogens, including African Swine Fever Virus (ASFV) affecting domestic and wild suids or Borrelia bacteria causing tick-borne relapsing fever (TBRF) in humans. We thus developed a regional model to identify suitable spatial areas for a community of nine Ornithodoros tick species (O. erraticus, O. sonrai, O. alactagalis, O. nereensis, O. tholozani, O. papillipes, O. tartakovskyi, O. asperus, O. verrucosus), which may be of medical and veterinary importance in the Western Palearctic region. Multi-Criteria Decision Analysis was used due to the relative scarcity of high-quality occurrence data. After an in-depth literature review on the ecological requirements of the selected tick community, five climaterelated factors appeared critical for feeding activity and tick development: (i) a spring temperature exceeding 10 °C to induce the end of winter soft tick quiescent period, (ii) a three-months summer temperature above 20 °C to allow tick physiological activities, (iii) annual precipitation ranging from 60 mm to 750 mm and, in very arid areas, (iv) dry seasons interrupted by small rain showers to maintain minimum moisture inside their habitat along the year or (v) residual water provided by perennial rivers near habitats. We deliberately chose not to include biological factors such as host availability or vegetation patterns. A sensitivity analysis was done by performing multiple runs of the model altering the environmental variables, their suitability function, and their attributed weights. To validate the models, we used 355 occurrence data points, complemented by random points within sampled ecoregions. All models indicated suitable areas in the Mediterranean Basin and semidesert areas in South-West and Central Asia. Most variability between models was observed along northern and southern edges of highly suitable areas. The predictions featured a relatively good accuracy with an average Area Under Curve (AUC) of 0.779. These first models provide a useful tool for estimating the global distribution of Ornithodoros ticks and targeting their surveillance in the Western Palearctic region

Suitable habitats for Palearctic Ornithodoros soft ticks

Ticks are economically and medically important due to injuries to livestock directly caused by their bite and their ability to transmit pathogens to humans and animals. While hard ticks (Ixodidae) have been extensively studied, the ability of soft ticks (Argasidae) to transmit pathogens to humans and domestic animals remains underestimated (Gray, Estrada-Pena, and Vial 2014). These ticks are nonetheless medically important, especially those belonging to the Ornithodoros genus. In the Palearctic region, five Ornithodoros tick species are considered able to transmit borreliae that cause Tick-Borne Relapsing Fever (TBRF) in humans, with many ocular, encephalitic, arthritic and pregnancy complications (Rebaudet and Parola 2006). The detection of human TBRF cases caused by Borrelia hispanica between 2002 and 2012 in Spain confirmed that the risk of human contamination through soft tick bites in Europe is real (Croche Santander et al. 2015). In the same region, the Iberian tick species O. erraticus was confirmed as a competent vector and natural reservoir for the virus of African Swine Fever (ASF) (Boinas et al. 2011). Knowing the spatial distribution of ticks is essential to assess the risk for pathogen transmission by ticks, so we set out to map suitable habitats for Ornithodoros ticks. In the Palearctic, presence data for Ornithodoros ticks are scarce and largely historical, and absence data are mostly unavailable (Vial 2009). Due to the relative scarcity of high-quality occurrence data, a GIS-based Multi-Criteria Decision Analysis was chosen to describe the range of environmental conditions enabling ticks to survive, grow and reproduce. Based on ecological knowledge on Palearctic Ornithodoros ticks distilled from an in-depth literature review, five criteria were identified. Two criteria were linked to temperatures allowing feeding activity and tick development. The three other criteria were related to the moisture availability for tick survival and development, either from precipitation, ambient humidity or other environmental factors that may provide sufficient moisture in arid zones. In order to incorporate uncertainty, a sensitivity analysis was done by performing different runs of the model and varying the environmental variables describing the respective criteria, the suitability response curves for each of the variables and the weights attributed to the different criteria for each run. Only in the final step, the available presence/absence data were used to validate the results. All models indicated similar trends. Several highly suitable areas were identified along the southern frontier between Portugal and Spain as well as the eastern coast of Spain from Catalonia to Andalusia. Also highlighted were the coastal areas in Sardinia, Sicilia and eastern Italy, as well as eastern Greece and western Turkey. To the east, the estimated distribution extended to the Ukrainian and south-west Russian region above the Black Sea. The models were based on climate variables and did not aim to assess local heterogeneity. Nonetheless, this remains one of the rare examples where a knowledge-based approach was used to produce distribution maps for ticks. This approach compensated both for the scarcity of the presence data and the fuzzy nature of the knowledge available on the ecology of these Ornithodoros tick species. The high values of the accuracy measures, as well as major congruence between the different models for predicting suitable and highly suitable areas, inspired confidence in this methodology and the resulting suitability maps. This makes it a very useful tool to target the surveillance of Ornithodoros ticks and assess the risk for Tick Borne Relapsing Fever throughout Europe