Factors driving the abundance of ixodes ricinus ticks and the prevalence of zoonotic I. ricinus-borne pathogens in natural foci

Environmental factors may drive tick ecology and therefore tick-borne pathogen (TBP) epidemiology, which determines the risk to animals and humans of becoming infected by TBPs. For this reason, the aim of this study was to analyze the influence of environmental factors on the abundance of immature-stage Ixodes ricinus ticks and on the prevalence of two zoonotic I. ricinus-borne pathogens in natural foci of endemicity. I. ricinus abundance was measured at nine sites in the northern Iberian Peninsula by dragging the vegetation with a cotton flannelette, and ungulate abundance was measured by means of dung counts. In addition to ungulate abundance, data on variables related to spatial location, climate, and soil were gathered from the study sites. I. ricinus adults, nymphs, and larvae were collected from the vegetation, and a representative subsample of I. ricinus nymphs from each study site was analyzed by PCR for the detection of Borrelia burgdorferi sensu lato and Anaplasma phagocytophilum DNA. Mean prevalences of these pathogens were 4.0% ± 1.8% and 20.5% ± 3.7%, respectively. Statistical analyses confirmed the influence of spatial factors, climate, and ungulate abundance on I. ricinus larva abundance, while nymph abundance was related only to climate. Interestingly, cattle abundance rather than deer abundance was the main driver of B. burgdorferi sensu lato and A. phagocytophilum prevalence in I. ricinus nymphs in the study sites, where both domestic and wild ungulates coexist. The increasing abundance of cattle seems to increase the risk of other hosts becoming infected by A. phagocytophilum, while reducing the risk of being infected by B. burgdorferi sensu lato. Controlling ticks in cattle in areas where they coexist with wild ungulates would be more effective for TBP control than reducing ungulate abundance.

African swine fever virus transmission cycles in Central Europe: evaluation of wild boar-soft tick contacts through detection of antibodies against Ornithodoros erraticus saliva antigen.

BACKGROUND African swine fever (ASF) is one of the most complex viral diseases affecting both domestic and wild pigs. It is caused by ASF virus (ASFV), the only DNA virus which can be efficiently transmitted by an arthropod vector, soft ticks of the genus Ornithodoros. These ticks can be part of ASFV-transmission cycles, and in Europe, O. erraticus was shown to be responsible for long-term maintenance of ASFV in Spain and Portugal. In 2014, the disease has been reintroduced into the European Union, affecting domestic pigs and, importantly, also the Eurasian wild boar population. In a first attempt to assess the risk of a tick-wild boar transmission cycle in Central Europe that would further complicate eradication of the disease, over 700 pre-existing serum samples from wild boar hunted in four representative German Federal States were investigated for the presence of antibodies directed against salivary antigen of Ornithodoros erraticus ticks using an indirect ELISA format. RESULTS Out of these samples, 16 reacted with moderate to high optical densities that could be indicative of tick bites in sampled wild boar. However, these samples did not show a spatial clustering (they were collected from distant geographical regions) and were of bad quality (hemolysis/impurities). Furthermore, all positive samples came from areas with suboptimal climate for soft ticks. For this reason, false positive reactions are likely. CONCLUSION In conclusion, the study did not provide stringent evidence for soft tick-wild boar contact in the investigated German Federal States and thus, a relevant involvement in the epidemiology of ASF in German wild boar is unlikely. This fact would facilitate the eradication of ASF in the area, although other complex relations (wild boar biology and interactions with domestic pigs) need to be considered.

Sex-biased differences in the effects of host individual, host population and environmental traits driving tick parasitism in red deer

The interactions between host individual, host population, and environmental factors modulate parasite abundance in a given host population. Since adult exophilic ticks are highly aggregated in red deer (Cervus elaphus) and this ungulate exhibits significant sexual size dimorphism, life history traits and segregation, we hypothesized that tick parasitism on males and hinds would be differentially influenced by each of these factors. To test the hypothesis, ticks from 306 red deer-182 males and 124 females-were collected during 7 years in a red deer population in south-central Spain. By using generalized linear models, with a negative binomial error distribution and a logarithmic link function, we modeled tick abundance on deer with 20 potential predictors. Three models were developed: one for red deer males, another for hinds, and one combining data for males and females and including "sex" as factor. Our rationale was that if tick burdens on males and hinds relate to the explanatory factors in a differential way, it is not possible to precisely and accurately predict the tick burden on one sex using the model fitted on the other sex, or with the model that combines data from both sexes. Our results showed that deer males were the primary target for ticks, the weight of each factor differed between sexes, and each sex specific model was not able to accurately predict burdens on the animals of the other sex. That is, results support for sex-biased differences. The higher weight of host individual and population factors in the model for males show that intrinsic deer factors more strongly explain tick burden than environmental host-seeking tick abundance. In contrast, environmental variables predominated in the models explaining tick burdens in hinds.