Virus Detection in Questing Ticks is not a Sensitive Indicator for Risk Assessment of Tick‐Borne Encephalitis in Humans

Abstract

Tick-borne encephalitis virus (TBEV) is the most important tick-transmitted arbovirus causing human disease in Europe, but information on its endemic occurrence varies between countries because of differences in surveillance systems. Objective data are necessary to ascertain the disease risk for vaccination recommendations and other public health interventions. In two independent, separately planned projects, we used real-time RT-PCR to detect TBE virus in questing ticks. In Poland, 32 sampling sites were selected in 10 administrative districts located in regions where sporadic TBE cases were reported. In Germany, 18 sampling sites were selected in two districts located in a region with high TBE incidence. Altogether, >16,000 ticks were tested by real-time RT-PCR, with no sample testing positive for TBEV. A systematic search for published studies on TBEV prevalence in ticks in Poland and Germany also suggested that testing large numbers of collected ticks could not consistently assure virus detection in known endemic foci. Although assignment of results to administrative regions is essential for TBE risk mapping, this was possible in only 10 (investigating 22,417 ticks) of 15 published studies (>50,000 ticks) identified. We conclude that the collection and screening of ticks by real-time RT-PCR cannot be recommended for assessment of human TBE risk. Alternative methods of environmental TBEV monitoring should be considered, such as serological monitoring of rodents or other wildlife.

Prevalence of tick-borne encephalitis virus (TBEV) RNA in Dermacentor reticulatus ticks from natural and urban environment, Poland

“…On the other hand, studies on D. reticulatus from Podlaskie voivodeship, an endemic TBE area, conducted using real-time PCR yielded the MIR (minimum infection rate) score of only 0.33 % (Kondrusik et al 2010). It has to be emphasized, however, that according to Stefanoff et al (2013) the results of assays for the presence of TBEV in ticks tend to be higher when nested RT-PCR instead of real-time PCR is used as the method for viral RNA detection. Furthermore, in the current study, the level of TBEV infection was higher in D. reticulatus than so far noted in I. ricinus .…”

“…In Poland, D. reticulatus occurs mostly in north-eastern part of the country, although western migration of this species has been observed since the nineties of the XX century (Karbowiak and Kiewra 2010) and recently it has been found also in Upper and Lower Silesia (SW Poland) (Cuber et al 2013; Kiewra and Czułowska 2013). Even though the role of I. ricinus in TBEV transmission in Europe as well as TBEV infection level of these ticks is becoming better understood (Hubálek and Rudolf 2012; Stefanoff et al 2013), there is significantly less data concerning D. reticulatus . Studies on D. reticulatus and other ticks of this genus experimentally infected with TBEV show proliferation of this virus in the ticks (Alekseev et al 1996; Řeháček et al 1987).…”

Goats as sentinel hosts for the detection of tick-borne encephalitis risk areas in the Canton of Valais, Switzerland

“…The disadvantage is that testing ticks for TBEV is time-consuming and expensive. Due to the low prevalence of TBEV in ticks (0.1–5.0% [14, 15]), and the high variability of TBEV prevalence in space and time, there is much interest in developing alternative methods to assess the human risk of TBE [33]. One such method is the detection of TBEV-specific antibodies in sentinel vertebrate hosts.…”

Wichtige, durch Vektoren übertragene Infektionskrankheiten beim Menschen in Deutschland

“…Dies reflektiert vermutlich, dass eine nachhaltige Etablierung des FSME-Virus in einem Naturherd spezifischerer Bedingungen bedarf [66,67] als bei der Lyme-Borreliose [68]. So ist die Durchseuchung von Zecken mit dem FSME-Virus gering; in einer Übersicht von Zeckenuntersuchungen in Deutschland zwischen 1990 und 2010 lag sie meist bei <2% mit einer Spanne von 0-5,2%; höhere Werte wurden allerdings in gesogenen Zecken beobachtet [69]. FSME-Risikogebiete befinden sich in Baden-Württemberg, Bayern, Südhes-sen, Thüringen und vereinzelt in Rheinland-Pfalz und dem Saarland (.…”