Evolution of tick populations in urban and peri-urban parks
Ticks are arthropod vectors of pathogens, since they are capable of transmitting viruses, bacteria and, consequently, diseases, both to human beings and to domestic animals (pets and livestock) and wild animals. Of the different tick families, those usually found in the vegetation, called “exophilic ticks”, are those that entail a greater risk to people and domestic animals.
This indicator shows the possible presence of ticks and the evolution of existing populations throughout the study period in several urban and peri-urban parks of Bilbao, Donostia and Gasteiz.
- Of the 19 tick species identified to date in the Basque Country, Ixodes ricinus is the most abundant and widely distributed Lyme disease vector.
- This species is active much of the year, decreasing its activity during the colder times of the year.
Relationship of the indicator with the climate change
The climatic characteristics of each zone-region condition the presence of its own flora and fauna, and likewise, the existence of some species of ticks or others, as well as their abundance and periods of activity (seasonality) (Barandika et al., 2011). Therefore, variations in climatic conditions can cause a change in both environment and tick populations, either in an increasing sense, if the new conditions are more favourable, or in a decreasing sense, if they are less suitable (Gale et al., 2012). Eventually, along the years, climate change could cause some “native” species to disappear, and new species to appear, carrying new pathogens to which hosts are not used to, causing changes in the currently existing host-vector-pathogen balance.
Thus, due to climatic effects, the increase in temperature during the winter period may favor that species of ticks which currently show a lesser and even no activity is this period, become more active, as could be the case of I. ricinus. This situation is taking place in European countries, where new climatic conditions are favouring the appearance of this tick species in regions where they did not previously exist (Jore et al., 2014). It can also favor the increase or arrival of new species that require a warmer climate for their development, such as the species of the genus Hyalomma (Estrada-Peña et al., 2021). There may also be changes in the duration of the biological cycle of ticks, shortening the periods of diapause caused by the cold, which would favor the increase in the number of ticks.
All this may affect the periods of risk of acquisition of the existing diseases, and even the appearance of new pathogens, such as the case of the Crimean Congo haemorrhagic fever virus transmitted by ticks of the genus Hyalomma (Estrada-Peña et al., 2021).
The knowledge which currently exists in the Basque Country about the populations of ixodid ticks mainly refers to mountain areas and recreational areas, and not so much to areas closer to urban centres, such as urban and peri-urban parks. Often, these parks may present flora and fauna that favor the development of tick populations. This is the reason why, over three years (2022-2024), sampling will be carried out in several parks located in the three Basque capitals.
The abundance index allows to observe if ticks are present and the activity they show month by month throughout the year. Changes in this index over the years will display the evolution of tick populations. Data from several sampling years in the vegetation of urban and peri-urban areas will be needed to know the temporal trend of this indicate.
Of the 19 species of ticks identified up to date in the Basque Country, it is Ixodes ricinus (vector of Lyme disease), the most abundant and widely distributed species. This species is active throughout most of the year, decreasing its activity during the colder times of the year. On the opposite side we have the species Hyalomma marginatum, as the least abundant and most reduced distribution species in the Community, located only in the southern half of the Arabian Territory, where the climate is warmer and less humid.
The indicator will show the abundance of exophilic ticks and the evolution of populations in the urban and peri-urban parks of the three Basque capitals. This indicator is based on the number of ticks collected from the vegetation per square metre of sampled area, expressed as a percentage (%).
To collect ticks from the vegetation, the cloak method is used, which consists of dragging a blanket or similar piece of cloth, over the vegetation, allowing the ticks to cling to the cloth in a similar way as they would be attached to the skin of a possible host which would pass through there. The blanket crawls for a certain distance, stopping every few meters to collect the captured specimens. At the end of the sampling, the collected ticks are counted and identified in the laboratory. The sampling area (m²) is calculated based on the distance travelled (m) and the size of the blanket used (m).
As an indicator of the evolution of the tick population, the following index is calculated:
\[\text{Abundance Index (IA)} = {\text{No.of ticks collected} \over \text{Sampling area (m ²)}} x 100\]
The abundance index may be used for the ensemble of ticks captured (Figure 1), for each of the identified species, and even for the different stages (larvae, nymphs and adults) caught (Figure 2).
Figure 1.
Figure 2.
Fuente: Pexels - Erik Kartis
Barandika, J.F., Olmeda, S.A., Casado-Nistal, M.A., Hurtado, A., Juste, R.A., Valcarcel, F., Anda, P., Garcia-Perez, A.L. 2011. Differences in questing tick species distribution between Atlantic and continental climate regions in Spain. J Med Entomol. 48, 13-19. https://doi.org/10.1603/me10079.
Estrada-Peña, A., D'Amico, G., Fernandez-Ruiz, N. 2021. Modelling the potential spread of Hyalomma marginatum ticks in Europe by migratory birds. Int J Parasitol. 51, 1-11. https://doi.org/10.1016/j.ijpara.2020.08.00410.1016/j.ijpara.2020.08.004.
Gale, P., Stephenson, B., Brouwer, A., Martinez, M., de la Torre, A., Bosch, J., Foley-Fisher, M., Bonilauri, P., Lindstrom, A., Ulrich, R.G., de Vos, C.J., Scremin, M., Liu, Z., Kelly, L., Munoz, M.J. 2012. Impact of climate change on risk of incursion of Crimean-Congo haemorrhagic fever virus in livestock in Europe through migratory birds. J Appl. Microbiol. 112, 246-257. https://doi.org/10.1111/j.1365-2672.2011.05203.x.
Jore, S., Vanwambeke, S.O., Viljugrein, H., Isaksen, K., Kristoffersen, A.B., Woldehiwet, Z., Johansen, B., Brun, E., Brun-Hansen, H., Westermann, S., Larsen, I.L., Ytrehus, B., Hofshagen, M. 2014. Climate and environmental change drives Ixodes ricinus geographical expansion at the northern range margin. Parasit Vectors. 7, 11. https://doi.org/10.1186/1756-3305-7-11. PMC3895670.
The Basque Country
Ixodes ricinus, Lyme disease vector
Most abundant and widespread specie