Increasing awareness for tick-borne encephalitis virus using small ruminants as suitable sentinels: Preliminary observations

Abstract

Tick-borne encephalitis virus (TBEV) is one of the most common zoonotic vector-borne infections in Europe. An appropriate awareness is crucial to react quickly and efficiently to protect humans from this pathogen. From winter 2017 until spring 2018 serum samples were collected from 71 small ruminant flocks (3174 animals) in five German federal states. The sera were examined for TBEV antibodies by ELISA and serum neutralization test. In the TBEV risk areas, there was a coincidence in 14 districts between seropositive small ruminants and the occurrence of human TBE cases in 2017. In eight districts, the TBEV infection could not be detected in small ruminants although human cases were reported. In contrast, in five districts, small ruminants tested TBEV seropositive without notified human TBE cases in 2017. A changing pattern of TBEV circulation in the environment was observed by the absence of antibodies in a defined high-risk area. In the non-TBE risk areas, seropositive small ruminants were found in five districts. In two districts with a low human incidence the infection was missed by the small ruminant sentinels. An intra-herd prevalence of 12.5% was determined in a goat flock in the non-TBE risk area in 2017, two years prior the first autochthone human case was reported. All sheep and goats in this flock were examined for TBEV antibodies for three years. Individual follow-up of twelve small ruminants was possible and revealed mostly a short lifespan of TBEV antibodies of less than one year. The probability to identify TBEV seropositive sheep flocks was enhanced in flocks kept for landscape conservation or which were shepherded (p < 0.05). Our preliminary observations clearly demonstrated the successful utilization of small ruminants as sentinel animals for TBEV.

Keywords: Goat; Public health; Sentinels; Sheep; Surveillance; Tick-borne encephalitis virus.

Fig. 1

Administrative districts of Germany sectioned according to the risk for humans to acquire TBEV infection and the location of districts with small ruminant flocks participating in this TBEV antibody study. Districts within TBEV risk areas are coloured in yellow, non-risk areas are uncoloured. This classification is based on human TBE cases notified between 2002 and 2017 [22]. In total, 71 small ruminant farms in five German federal states (Schleswig-Holstein: SH, Lower Saxony: LS, North Rhine-Westphalia: NRW, Baden-Wuerttemberg: BW, Bavaria: BAV) participated in the study. The district Emsland, coloured in red, is the first TBEV risk area in the federal state of LS since 2019 (in this district no small ruminants were sampled). Districts with participating small ruminant flocks within the TBEV risk areas are coloured in blue, districts with participating small ruminant flocks within the non-TBEV risk areas are coloured in green. The black stars indicate the localisation of the flocks with seropositive TBEV small ruminants, GÖ = district of Göttingen, MSP = district of Main-Spessart, and Sallandse Heuvelrug a TBEV hot spot in the Netherlands. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)