Veterinary session

Pathogen carrier hard ticks are known to show different spatio-temporal occurrence compared to uninfected individuals of the same species. To the best of our knowledge, this was not reported in the case of Dermacentor spp.. Dermacentor reticulatus is the more widespread species of the genus in Europe. It is frequently found in urban biotopes, where it is a vector of Babesia canis, an important protozoan parasite of dogs. Literature data from Central-Eastern Europe attest, that clinical cases of canine babesiosis are more frequent in the spring time, despite the fact that the peak activity of D. reticulatus is during the autumn. Therefore the present study was initiated to ascertain if a "biased seasonal pattern" exists among B. canis-infected D. reticlatus ticks.

Ticks were collected in two urban habitats of Budapest (from August, 2014 until June, 2015). The size of all ticks was measured, and the mean size of overwintering adults (3.7 mm) was considered as the cut-off to separate small and large ticks. This was followed by DNA extraction from randomly selected 23 ticks (males + females) per month. The latter samples were analysed for the presence of B. canis with PCR and sequencing.

In the two habitats 852 D. reticulatus adults were collected. Taken together, 8.23% of ticks were PCR positive for piroplasms. In all of them B. canis canis (abbreviated as B. canis onwards) was identified with sequencing. Two 18S genotypes were shown to be present: "A" and "B". In habitat-1 B. canis-infected ticks were only found in the spring (April and May). The mean size of ticks started to decrease in April, corresponding to the emergence of B. canis. In this habitat all five babesia-carrier ticks were small. In habitat-2 B. canis-infected ticks were significantly more frequently detected during the winter and spring, than in the autumn. In this habitat the mean size of ticks started to decrease in December, corresponding to the period with increasing numbers of B. canis-infected ticks in the winter and spring. The prevalence of infected ticks was the highest (43.48%) in late February. In the winter-to-spring period 19 small, and nine large size babesia-carrier ticks were found. In this way, taking into account both habitats, significantly more small, than large size D. reticulatus adults were shown to harbour B. canis. In addition, a month-dependent time-shift was also noted in the appearance of the two B. canis 18S genotypes: the less pathogenic "A" predominating earlier, and the more pathogenic "B" later.

D. reticulatus indviduals, which moult to adult in the spring, are known to be smaller in size, therefore the majority of ticks infected with B. canis in the present study were freshly moulted adults, and only the minority overwintered. One possible explanation for this phenomenon is that babesia-carrier ticks might have different behaviour. Similar observations have already been reported for other tick-pathogen associations.