Publications

4508

Abstract BACKGROUND: Rickettsia spp. are human pathogens that cause a number of diseases and are transmitted by arthropods, such as ixodid ticks. Estonia is one of few regions where the distribution area of two medically important tick species, Ixodes persulcatus and I. ricinus, overlaps. The presence of the nidicolous rodent-associated I. trianguliceps has also recently been shown in Estonia. Although there is no data available in Estonia on human disease caused by tick-borne Rickettsia spp., the presence of three Rickettsia species in non-nidicolous ticks was also previously reported. The aim of this study was to detect, identify and partially characterize Rickettsia species in nidicolous and non-nidicolous ticks attached to rodents.RESULTS: Larvae and nymphs of I. ricinus (n = 1004), I. persulcatus (n = 75) and I. trianguliceps (n = 117) removed from rodents and shrews caught in different parts of Estonia were studied for the presence of Rickettsia spp. by nested PCR. Ticks were collected from 314 small animals of 5 species (Myodes glareolus (bank voles), Apodemus flavicollis (yellow necked mice), A. agrarius (striped field mice), Microtus subterranius (pine voles) and Sorex araneus (common shrews)). Rickettsial DNA was detected in 8.7% (103/1186) of the studied ticks. In addition to R. helvetica previously found in questing ticks, this study reports the first identification of the recently described I. trianguliceps-associated Candidatus R. uralica west of the Ural Mountains.

AbstractCarrot cultivation in Europe is suffering from infections with “Candidatus Liberibacter solanacearum” (CLso), a psyllid‐transmitted bacterial pathogen. In this study, field experiments were carried out in Finland to separately measure the effects of psyllid feeding damage and CLso infection on the carrot root growth and to reveal the dynamics of the spreading of CLso within the field. Most of the experiments were carried out during the summers 2016 and 2017, and a follow‐up sampling was performed in 2018. Carrot psyllid (Trioza apicalis) flight activity was monitored and carrots were sampled at 25 points within the field. Early in the season a clear spatial correlation was found between the sampling sites showing the psyllid feeding damage, that is, leaf‐curling, up to the range of 40–60 m, indicating aggregation behaviour of the psyllids. No CLso infections were detected in the first sampling, which was performed before the psyllid flight peak in both years. Later, a positive correlation between the psyllid feeding damage and the CLso titre was observed. An increase in the CLso titre occurred approximately a month after the psyllid flight peak, and this increase correlated with the accumulating effective temperature sum. In 2016, both the psyllid feeding damage and CLso infection had a significant effect on the carrot root weight. The effect of CLso titre on root weight was nonlinear, that is, it intensified rapidly at the highest bacterial titres. During the colder summer of 2017 the CLso titres did not reach high enough levels in the plants to cause substantial visible symptoms and root growth reduction. Thus, it seems that in the Nordic conditions the effect of CLso infection on carrot yield is strongly dependent on the weather conditions during the growing season.