A Density Map of the Tick-Borne Encephalitis and Lyme Borreliosis Vector Ixodes ricinus (Acari: Ixodidae) for Germany

Abstract

The castor bean tick Ixodes ricinus (L.) is the principal vector for a variety of viral, bacterial, and protozoan pathogens causing a growing public-health issue over the past decades. However, a national density map of I. ricinus is still missing. Here, I. ricinus nymphs in Germany were investigated by compiling a high-resolution map depicting the mean annually accumulated nymphal density, as observed by monthly flagging an area of 100 m Input data comprise ticks collected at 69 sampling sites. The model domain covers an area of about 357,000 km (regional scale). Two negative binomial regression models were fitted to the data to interpolate the tick densities to unsampled locations using bioclimatic variables and land cover, which were selected according to their significance by the Akaike information criterion (AIC). The default model was fitted to the complete dataset resulting in AIC = 842. An optimized model resulted in a significantly better value of AIC = 732. Tick densities are very low in urban (green) areas. Maximum annual densities up to 1,000 nymphs per 100 m are observed in broad-leaved forests. The tick maps were verified by leave-one-out cross-validation. Root mean square errors of RMSE = 137 and RMSE = 126 nymphs per 100 m were estimated for the two models, respectively. These errors are of the order of the interannual variation of the tick densities. The compilation of a high-resolution density map of unfed nymphal I. ricinus for Germany provides a novel, nationwide insight into the distribution of an important disease vector.

Research paper on abiotic factors and their influence on Ixodes ricinus activity—observations over a two-year period at several tick collection sites in Germany

“…In recent studies, nymph density was investigated as a potential indicator for the risk of tick-borne diseases and for producing high-resolution risk maps for Baden-Wuerttemberg (Boehnke et al 2015) and Germany (Brugger et al 2016). These investigations emphasise that nymphs may be the most important tick stage for the transmission of pathogens.…”

In silico target network analysis of de novo-discovered, tick saliva-specific microRNAs reveals important combinatorial effects in their interference with vertebrate host physiology

“…miRNAs have yet to be described in Ixodes ticks. Ixodes ricinus is an important disease vector in Europe where they transmit viruses, bacteria, and protozoan parasites (Honig et al 2015;Vayssier-Taussat et al 2015;Brugger et al 2016). Difficulties in genome analysis have restricted our knowledge of their miRNAs (Cramaro et al 2015).…”

Murine Gammaherpesvirus 68 (MHV-68), a Newly Discovered Tick Borne Virus

“…It should be noted that ixodid tick species have multiple life stages with each feeding off a different host and often a different host species. Ixodes ticks are the most important arthropod disease vector, long been acknowledged as an important vector for a wide variety of pathogens of medical and veterinary importance, particularly the tick-borne encephalitis virus and the Lyme disease spirochetes of the genus Borrelia [86][87][88]. Their vectorial capacity is due to long-term coevolution with the pathogens that they transmit, an extended life span (up to years), and long-lasting blood feeding by all parasitic life stages [89].…”