Under the skin: Ixodes ticks in the subcutaneous tissue of red foxes (Vulpes vulpes) from Germany

Vector competence of Ixodes ricinus instars for the transmission of Borrelia burgdorferi sensu lato in different small mammalian hosts

BACKGROUND

Many pathogens and parasites can infect multiple host species, and the competence of different hosts as pathogen reservoirs is key to understanding their epidemiology. Small mammals are important hosts for the instar stages of Ixodes ricinus ticks, the principal vector of Lyme disease in Europe. Small mammals also act as reservoirs of Borrelia afzelii, the most common genospecies of the Borrelia burgdorferi sensu lato (s.l.) spirochetes causing Lyme disease in Europe. However, we lack quantitative estimates on whether different small mammal species are equally suitable hosts for feeding I. ricinus and whether they show differences in pathogen transmission from host to tick.

METHODS

Here, we analysed the feeding success and prevalence of B. burgdorferi s.l. infections in 12,987 instar I. ricinus found on captured small mammals with known infection status in Norway (2018-2022).

RESULTS

We found that larvae were more likely to acquire a blood meal from common shrews (Sorex araneus, 46%) compared to bank voles (Myodes glareolus, 36%) and wood mice (Apodemus sylvaticus, 31%). Nymphs tended to be more likely to acquire a blood meal from wood mice (66%) compared to bank voles (54%). Common shrews harboured few nymphs (n=19). Furthermore, we found that larvae feeding on infected bank voles (11%) were more likely to be infected with B. burgdorferi s.l. than larvae on infected common shrews (7%) or wood mice (4%).

CONCLUSIONS

Our study provides quantitative evidence of differences in suitability for the instar stages of I. ricinus across taxa of small mammals and highlights how even known small mammal host species can differ in their ability to feed ticks and infect larval ticks with the pathogen causing Lyme disease.

Subcutaneous Ticks in Wild Carnivores: Any Host-Related Differences?

Ticks under the skin have been shown in different canid species such as red fox, domestic dog, and raccoon dog. Despite being increasingly reported in Europe in the last decade, the biological mechanisms associated to subcutaneous ticks (SCT), as well as the predisposing factors, are not yet clear. The main goal of this study was to investigate the presence of SCT in wild carnivores in Northwestern Italy. Sixty-three wild carnivores were examined, and SCT were submitted to histological examination or stored in ethanol for morphological and molecular identification. A portion of the cox1 gene and 16S rDNA were amplified, and positive PCR products were sequenced. Fifty-one small brown-coloured nodules of about 2 × 3 mm containing ticks in different decomposition stages were observed in 11 out of 30 foxes. Seven ticks were classified as Ixodes ricinus, while 14 ticks were determined only at the genus level (Ixodes spp.), and in two ticks no morphological key was applicable due to the advanced degradation status. By PCR, the rDNA fragment of six ticks (26.1%, 95% CI: 12.6-46.5%) was amplified, and BLAST analysis revealed a 99-100% nucleotide similarity to I. ricinus. At the histological examination, the inflammatory response varied from a mild to a moderate mixed infiltrate, primarily composed by neutrophils and lymphocytes. The results of this study confirm foxes as the main wild reservoir for SCT. The absence of SCT in other carnivores (badgers and martens) is in accordance with other studies. Ixodes ricinus is the most frequently reported tick species, corroborating the idea that longirostral ticks might be more frequently associated to SC embedment than brevirostral ticks.

Hard Ticks (Ixodidae) from Wildlife in Liguria, Northwest Italy: Tick Species Diversity and Tick-Host Associations

Hard ticks’ geographical distribution and abundance are influenced by wildlife population. This work presents the results of the identification of ticks retrieved from wild animals in the framework of a Regional Plan of Monitoring and Surveillance of Wildlife health. The frequency of distribution of ticks in different hosts and their geographical patterns were also investigated. Ticks were collected from game animals (Sus scrofa, Capreolus capreolus, Dama dama, and Rupicapra rupicapra) during two hunting seasons (2018–2019 and 2019–2020) in the four provinces of the Liguria region in northwest Italy. In the same period, ticks were also collected from carcasses of Vulpes vulpes, Canis lupus, Meles meles, and Asio otus received for necropsy. Tick species were identified according to taxonomic keys. A total of 819 ticks, removed from 259 animals, were found and identified. Overall, Ixodes ricinus was the dominant species (62.6%), followed by Dermacentor marginatus (24.5%), Rhipicephalus sanguineus s.l. (12.5%), Haemaphysalis punctata (0.2%), and Ixodes hexagonus (0.1%). I. ricinus was also the prevalent species in roe deer and in fallow deer and the only species collected from the three wolf carcasses examined. In contrast, D. marginatus was the dominant species in S. scrofa. This last tick species was also more frequent in one province (Imperia), whereas Ixodes spp. were more common in another one (Savona). Wild animals proved to be useful for characterizing and monitoring tick population.

Tick infestation on medium-large-sized mammalian hosts: are all equally suitable to Ixodes ricinus adults?

Background

In Europe, the generalist tick, Ixodes ricinus, is the main vector of several tick-borne pathogens causing diseases in humans and livestock. Understanding how different species of hosts limit the tick population is crucial for management. In general, larger ectoparasites are expected to select hosts with larger body size. Consistent with this, larval and nymphal I. ricinus can feed on a wide range of different-sized vertebrates, while the adult female stage is expected to rely on a medium–large-sized host for reproduction. However, we still have a limited understanding of whether medium-sized hosts other than roe deer can serve as hosts to adult ticks, and other factors than size may also affect host selection.

Methods

To increase our understanding of the suitability of the different species of medium-sized hosts for adult ticks, we sampled mainly roadkill mammals from within the questing season of ticks. We counted life stages of ticks on roe deer (Capreolus capreolus) (n = 29), red fox (Vulpes vulpes) (n = 6), badger (Meles meles) (n = 14) and red squirrel (Sciurus vulgaris) (n = 17) from spatially overlapping populations in Norway, and analysed variation between species across different body parts with a mixed-effects negative binomial model (with and without zero-inflation).

Results

Red squirrel hosted a high density of larval and nymphal I. ricinus, but only one individual had adult female ticks. Roe deer hosted by far the largest number of adult ticks. Badgers had very few ticks, possibly due to their thick skin. Red foxes had intermediate numbers, but a high proportion of subcutaneous, dead ticks (69.3%), suggesting they are not very suitable hosts. Body mass predicted the presence of adult I. ricinus ticks. However, species was a better predictor than body mass for number of ticks, suggesting there was species variation in host suitability beyond body mass per se.

Conclusions

Our study provides evidence that roe deer are indeed the main suitable reproduction host to adult I. ricinus ticks, and are likely a key to host limitation of the tick population in this northern ecosystem.

Graphic abstract

Subcutaneous ticks: a first report in a golden jackal, and their absence in non-canid carnivores

BACKGROUND

Ticks are hematophagous arthropods which normally attach to the surface of the host's skin. Their aberrant presence in the subcutaneous tissue of a few carnivores, predominantly foxes, has been reported. However, there have been no reports of this phenomenon in other carnivores such as mustelids or golden jackals. Our aim was to investigate the host spectrum for this aberrant localization of ticks.

METHODS

Between 2015 and 2020, a total of 198 carcasses of 12 species of carnivore were examined by parasitological necropsy. When a subcutaneous tick was found, the nodule was removed, carefully dissected, and stored in ethanol. The morphological identification of the subcutaneous tick was carried out to species level.

RESULTS

A single subcutaneous tick was found in one carcass, that of a golden jackal (Canis aureus). The tick was identified as a female Ixodes ricinus. All the other carcasses were negative for the presence of subcutaneous ticks.

CONCLUSION

To our knowledge, this is the first report of a subcutaneous tick in a golden jackal. This finding broadens the host spectrum of subcutaneous ticks, and reinforces the idea that, among carnivores, this phenomenon only occurs in canids.