Ticks are obligate, bloodsucking, nonpermanent ectoparasitic arthropods. Among them, Ixodes ricinus is a classic example of an extreme generalist tick, presenting a highly permissive feeding behavior using different groups of vertebrates as hosts, such as mammalian (including humans), avian and reptilian species (Hoogstraal & Aeschlimann, 1982; Dantas-Torresa & Otranto, 2013). This ecological adaptation can account for the broad geographical distribution of I. ricinus populations, which extends from the western end of the European continent to the Ural Mountains in Russia, and from northern Norway to the Mediterranean basin, including the North African countries - Morocco, Algeria and Tunisia (https://ecdc.europa.eu/en/disease-vectors/surveillance-and-disease-data/tick-maps). The contact with different hosts also promotes the exposure/acquisition and transmission of various pathogenic agents (viruses, bacteriae, protists and nematodes) of veterinary and medical relevance (Aeschlimann et al., 1979). As one of the prime ticks found on humans, this species is implicated in diseases such as Lyme borreliosis, Spotted Fever Group rickettsiosis, Human Anaplasmosis, Human Babesiosis and Tick-borne Encephalitis (Velez et al., 2023). 

The climate change projections drawn for I. ricinus, in the scenario of global warming, point for the expansion/increase activity in both latitude and altitude (Medlock et al., 2013). The adequacy of vector modeling is relaying in the proper characterization of complex biological systems. Thus, it is essential to increase knowledge on I. ricinus, focusing on aspects such as genetic background, ecology and eco-epidemiology on a microscale but also at a country and region level, due to possible local adaptations of tick populations and genetic drift. 

In the present systematic revision, Perez et al. (2023) combine old and recently published data (mostly up to 2020) regarding I. ricinus distribution, phenology, host range and pathogen association in continental France and Corsica Island. Based on a keyword search of peer-reviewed papers on seven databases, as well as other sources of grey literature (mostly, thesis), the authors have synthesized information on: 1) Host parasitism to detect potential differences in host use comparing to other areas in Europe; 2) The spatiotemporal distribution of I. ricinus, to identify possible geographic trends in tick density, variation in activity patterns and the influence of environmental factors; 3) Tick-borne pathogens detected in this species, to better assess their spatial distribution and variation in exposure risk. 

As pointed out by both reviewers, this work clearly summarizes the information regarding I. ricinus and associated microorganisms from European France. This review also identifies remaining knowledge gaps, providing a comparable basis to orient future research. This is why I chose to recommend Perez et al (2023)'s preprint for Peer Community Infections. 

REFERENCES

Aeschlimann, A., Burgdorfer, W., Matile, H., Peter, O., Wyler, R. (1979) Aspects nouveaux du rôle de vecteur joué par Ixodes ricinus L. en Suisse. Acta Tropica, 36, 181-191.

Dantas-Torresa, F., Otranto, D. (2013) Seasonal dynamics of Ixodes ricinus on ground level and higher vegetation in a preserved wooded area in southern Europe. Veterinary Parasitology, 192, 253- 258.
https://doi.org/10.1016/j.vetpar.2012.09.034

Hoogstraal, H., Aeschlimann, A. (1982) Tick-host specificity. Mitteilungen der Schweizerischen Entomologischen Gesellschaft, 55, 5-32.

Medlock, J.M., Hansford, K.M., Bormane, A., Derdakova, M., Estrada-Peña, A., George, J.C., Golovljova, I., Jaenson, T.G.T., Jensen, J.K., Jensen, P.M., Kazimirova, M., Oteo, J.A., Papa, A., Pfister, K., Plantard, O., Randolph, S.E., Rizzoli, A., Santos-Silva, M.M., Sprong, H., Vial, L., Hendrickx, G., Zeller, H., Van Bortel, W. (2013) Driving forces for changes in geographical distribution of Ixodes ricinus ticks in Europe. Parasites and Vectors, 6. https://doi.org/10.1186/1756-3305-6-1

Perez, G., Bournez, L., Boulanger, N., Fite, J., Livoreil, B., McCoy, K., Quillery, E., René-Martellet, M., Bonnet, S. (2023) The distribution, phenology, host range and pathogen prevalence of Ixodes ricinus in France: a systematic map and narrative review. bioRxiv, ver. 1 peer-reviewed and recommended by Peer Community in Infections. https://doi.org/10.1101/2023.04.18.537315

Velez, R., De Meeûs, T., Beati, L., Younsi, H., Zhioua, E., Antunes, S., Domingos, A., Ataíde Sampaio, D., Carpinteiro, D., Moerbeck, L., Estrada-Peña, A., Santos-Silva, M.M., Santos, A.S. (2023) Development and testing of microsatellite loci for the study of population genetics of Ixodes ricinus Linnaeus, 1758 and Ixodes inopinatus Estrada-Peña, Nava & Petney, 2014 (Acari: Ixodidae) in the western Mediterranean region. Acarologia, 63, 356-372. https://doi.org/10.24349/bvem-4h49

Zoonotic pathogens, those transmitted from animals to humans, constitute a major public health risk with high associated global economic costs. Diseases associated with these pathogens represent more than 60% of emerging infectious diseases and predominantly originate in wildlife (1). Over the last decades, the emergence and re-emergence of zoonotic pathogens have led to an increasing number of epidemics, as illustrated by the current Covid-19 pandemic. There is ample evidence that human impact on native ecosystems such as deforestation, agricultural development, and urbanization, is linked to spillover of pathogens from animals to humans (2). However, research and calls to action have mainly focused on the importance of surveillance and prevention of zoonotic emergences along landscape interfaces, with special emphasis on tropical forests and agroecosystems, and studies and reviews pointing out the zoonotic risk associated with cities are scarce.  Additionally, cities are sometimes wrongly seen as one homogeneous ecosystem, almost exclusively human, with a Northern hemisphere-biased perception of what a city is, which fails to take into account the ecological and socio-economic diversities that can constitute an urban area.

Here, Dobigny and Morand (3) aim to draw attention to the importance of urban ecosystems in zoonotic risk and advocate that further attention should be paid to urban, peri-urban and suburban areas. In this well-organized and well-documented review, the authors show, using updated literature, that cities are places where massive contacts occur between wildlife, domestic animals, and human inhabitants (thus constituting spillover opportunities), and that it is even likely that human and wildlife contact in urban centers is more prevalent than in wild areas, perhaps contrary to intuition. Indeed, cities currently constitute the most important environment of human life and are places for millions of close interactions between humans and animals, including pets and domestic animals, wild animals through the intrusion of wild urban-adapted species (e.g., some bat, rodent, or bird species among others), manipulation and consumption of wildlife meat, and the existence of wildlife meat markets, which all constitute a major risk for zoonotic spillover. In cities, lab escapees of zoonotic pathogens also exist, and trends of adaptation to urban ecological conditions of many vectors of primary health importance is also a concern. The authors further argue that cities are predominant places for both epidemic amplification of human-human transmitted pathogens, because they are places with high human densities and population growth, and for dissemination of reservoirs, vectors and pathogens, as they are transport hubs. Dobigny & Morand further predict, likely correctly, that cities may be important places for pathogen evolution.  Finally, they propose actions and recommendations to limit the risk of zoonotic spillover events from urban ecosystems and future directions for research aiming at assessing this risk. 

The reviewers found the manuscript well-organized and presented, timely, and bringing novel contributions to the field of zoonotic emergence. I strongly recommend this article, which should benefit a large audience, particularly in the context of the current Covid-19 pandemics and the ongoing One Health initiatives aiming at preventing future zoonotic disease emergence (4). 

References

(1) Jones KE, Patel NG, Levy MA, Storeygard A, Balk D, Gittleman JL, Daszak P (2008) Global trends in emerging infectious diseases. Nature, 451, 990–993. https://doi.org/10.1038/nature06536

(2) White RJ, Razgour O (2020) Emerging zoonotic diseases originating in mammals: a systematic review of effects of anthropogenic land-use change. Mammal Review, 50, 336–352. https://doi.org/10.1111/mam.12201

(3) Dobigny G, Morand S (2022) Zoonotic emergence at the animal-environment-human interface: the forgotten urban socio-ecosystems. Zenodo, 6444776, ver. 3 peer-reviewed and recommended by Peer Community in Infections. https://doi.org/10.5281/zenodo.6444776

(4) Morand S, Lajaunie C (2021) Biodiversity and COVID-19: A report and a long road ahead to avoid another pandemic. One Earth, 4, 920–923. https://doi.org/10.1016/j.oneear.2021.06.007