Ability of Adult Dermacentor reticulatus Ticks to Overwinter in the Temperate Climate Zone

Year-round tick exposure of dogs and cats in Germany and Austria: results from a tick collection study

BACKGROUND

Ticks and tick-borne diseases play a major role in companion animal health. Additionally, the European tick fauna is changing, for instance due to the spread of Dermacentor reticulatus, displaying a higher likelihood of winter activity than Ixodes ricinus. Therefore, we investigated current tick infestations in dogs and cats in Germany and in parts of Austria and the seasonal infestation risk.

METHODS

Overall, 219 veterinary practices were invited to collect ticks from cats and dogs on a monthly basis. Ticks were morphologically identified and female I. ricinus specimens were measured to estimate attachment duration.

RESULTS

In total, 19,514 ticks, 17,789 (91.2%) from Germany and 1506 (7.7%) from Austria, were received between March 2020 and October 2021, with 10,287 specimens (52.7%) detached from dogs, 8005 from cats (41.0%) and 1222 from other species (6.3%). In Germany, the most common tick species collected from dogs were I. ricinus (78.0%) and D. reticulatus (18.8%), while cats mainly harboured I. ricinus (91.3%) and I. hexagonus (5.5%) and only few D. reticulatus (0.6%). In Austria, collected I. ricinus reached similar proportions in dogs (90.4%) and cats (95.3%), followed by D. reticulatus in both dogs (5.2%) and cats (1.5%), with I. hexagonus (0.9%) collected only marginally from cats. The average infestation intensity amounted to 1.62 ticks/dog and 1.88 ticks/cat. The single to multiple infestation ratio was 79.1% to 20.9% in dogs and 69.0% to 31.0% in cats, with cats being significantly more often multiple infested than dogs, while the proportion of mixed-species infestations was 2.0% for both dogs and cats. The average attachment duration of female I. ricinus specimens amounted to 78.76 h for dogs and 82.73 h for cats. Furthermore, year-round tick exposure was confirmed, with 108 D. reticulatus and 70 I. ricinus received on average per month during December 2020 to February 2021.

CONCLUSIONS

The study shows a year-round tick infestation risk, with activity of both D. reticulatus and I. ricinus during winter, and confirms the widespread occurrence of D. reticulatus in Germany. Additionally, long average attachment durations and frequent multiple infestations underline the need for adequate year-round tick control, even during the winter months.

The Influence of Southwestern Virginia Environmental Conditions on the Potential Ability of Haemaphysalis longicornis, Amblyomma americanum, and Amblyomma maculatum to Overwinter in the Region

Simple Summary

A tick’s ability to survive in cold, harsh winter conditions is influenced by numerous factors including the tick species, the variability in temperature, and the suitability of the overwintering habitat (containing insulation to retain heat). We investigated the influence of elevation and insulation coverage on the survivability of three newly invading ticks, Amblyomma americanum, Amblyomma maculatum, and Haemaphysalis longicornis and one native tick species already established in southwestern Virginia, Dermacentor variabilis. For the invasive species, we found that life stage was the only determining factor in survival for Haemaphysalis longicornis and Amblyomma americanum, whereas, Amblyomma maculatum survival was largely influenced by insulation coverage. Dermacentor variabilis survivability was not affected by elevation or insulation coverage in this study.

Abstract

Ticks are susceptible to environmental conditions and, to ensure survival during winter conditions, they adopt a wide variety of physiological and behavioral adaptations including utilization of a suitable niche with insulation (e.g., leaf coverage). To investigate the potential overwintering survival of three tick populations emerging within Appalachian Virginia (Haemaphysalis longicornis, Amblyomma americanum, and Amblyomma maculatum), both a laboratory experiment assessing super-cooling points and a two-factor (elevation and insulation coverage) field experiment assessing overwintering survivability were conducted across a natural southwestern Virginian winter (2020–2021). Dermacentor variabilis adults were included in this study as an example of a well-established species in this region known to overwinter in these conditions. Our study indicated that A. americanum and H. longicornis wintering tolerance is based on life stage rather than external factors such as insulation (e.g., leaf litter) and elevation. Amblyomma maculatum was more likely to survive without insulation. The ability to withstand the extreme temperatures of new regions is a key factor determining the survivability of novel tick species and is useful in assessing the invasion potential of arthropod vectors.

Seasonal activity of Dermacentor reticulatus ticks in the era of progressive climate change in eastern Poland

Dermacentor reticulatus ticks are one of the most important vectors and reservoirs of tick-borne pathogens in Europe. Changes in the abundance and range of this species have been observed in the last decade and these ticks are collected in areas previously considered tick-free. This may be influenced by progressive climate change. Eastern Poland is an area where the local population of D. reticulatus is one of the most numerous among those described so far. At the same time, the region is characterized by a significant increase in the mean air temperature in recent years (by 1.81 °C in 2020) and a decrease in the average number of days with snow cover (by 64 days in 2020) and in the number of days with frost (by 20 days in 2020) on an annual basis compared to the long-term average. The aim of our research was to investigate the rhythms of seasonal activity and the population size of D. reticulatus in the era of progressive climate change. To this end, questing ticks were collected in 2017-2020. Next, the weather conditions in the years of observation were analyzed and compared with multi-year data covering 30 years preceding the study. The research results show that, in eastern Poland, there is a stable population of D. reticulatus with the peak of activity in spring or autumn (up to a maximum of 359 individuals within 30 min of collection) depending on the year of observation. Ticks of this species may also be active in winter months. The activity of D. reticulatus is influenced by a saturation deficit.