Borrelia Infections in Ageing Ticks: Relationship with Morphometric Age Ratio in Field-Collected Ixodes ricinus Nymphs

Abstract

In Europe, Ixodes ricinus plays a major role as a vector of Borrelia burgdorferi sensu lato (s.l.) spirochaetes, the causative agents of Lyme borreliosis, among other pathogens. In unfed ticks, Borrelia spirochaetes experience prolonged nutrient restriction. However, only few studies exist with regard to Borrelia infections in unfed ticks of different physiological ages. Changing body dimensions of unfed ticks, due to the consumption of energy reserves, allow physiological age estimation. The present study investigated the relationship of morphometric age with Borrelia prevalence and spirochaete load in 1882 questing I. ricinus nymphs, collected at two different locations in northern Germany in 2020. In addition, Borrelia species composition was investigated by employing a reverse line blot (RLB) probe panel suitable for the detection of ten different B. burgdorferi s.l. species, as well as the relapsing-fever spirochaete B. miyamotoi. Overall, Borrelia prevalence was 25.8% (485/1882). Whilst there was no statistically significant difference in Borrelia prevalence between the different morphometric age groups, Borrelia infection intensity as determined by probe-based quantitative real-time PCR significantly declined with increasing morphometric age. Borrelia species differentiation by RLB was successful in 29.5% of positive ticks, and revealed B. afzelii as the dominating species (65.0% of the differentiated infections). Additionally, B. garinii, B. valaisiana, B. burgdorferi sensu stricto, B. spielmanii, and B. miyamotoi were detected.

Diversity of Borrelia burgdorferi sensu lato in ticks and small mammals from different habitats

“…The other genospecies— B. valaisiana (6/69), B. lusitaniae (3/69), B. burgdorferi s.s. (2/69) and B. spielmanii (2/69)—were found only in ticks, and have been described before in ticks from Germany at similar frequencies [ 59 , 60 ]. The diversity of the detected genospecies was higher [ 14 , 31 , 58 ] or similar to that of other studies carried out in Germany, Belarus, and Romania [ 59 – 62 ]. The reason for this might be the association of certain genospecies with the abundance of their respective reservoirs.…”

“…B. afzelii was predominant in ticks (37/69) and small mammals (7/8), followed by B. garinii [which was found in ticks (16/69) and small mammals (1/8)]; similar results have been previously reported [ 31 , 58 ] for Germany and elsewhere in Europe [ 53 ]. The other genospecies— B. valaisiana (6/69), B. lusitaniae (3/69), B. burgdorferi s.s. (2/69) and B. spielmanii (2/69)—were found only in ticks, and have been described before in ticks from Germany at similar frequencies [ 59 , 60 ]. The diversity of the detected genospecies was higher [ 14 , 31 , 58 ] or similar to that of other studies carried out in Germany, Belarus, and Romania [ 59 – 62 ].…”

Infected Ixodes scapularis Nymphs Maintained in Prolonged Questing under Optimal Environmental Conditions for One Year Can Transmit Borrelia burgdorferi ( Borreliella genus novum ) to Uninfected Hosts

“…High mobility and the ability to grab moving objects is the expected behavior of questing nymphs that also have higher metabolic activity and lipid energy stored to be spent toward host-seeking in natural conditions ( 19 – 21 ). At 6 weeks post molting from infected engorged larva, when nymphal ticks usually begin host-seeking, we found a significantly higher B. burgdorferi nymphal infection prevalence (NIP) as well as a 10× increase in B. burgdorferi load in the host-seeking questing nymphs in contrast to the ticks that remained in diapause ( Fig.…”

Infected I. scapularis nymphs maintained in prolonged questing under optimal environmental conditions for one year can transmit B. burgdorferi to uninfected hosts

“…High mobility and the ability to grab moving objects is the expected behavior of questing nymphs that also have higher metabolic activity and lipid energy stored to be spent toward host-seeking in natural conditions [19, 20] [21]. At 6 weeks post molting from infected engorged larva, when nymphal ticks usually begin host-seeking, we found a significantly higher B. burgdorferi nymphal infection prevalence (NIP) as well as a 10X increase in B. burgdorferi load in the host-seeking questing nymphs in contrast to the ticks that remained in diapause (Fig 1).…”