Jolianne M. Rijks

BACKGROUND: Tick-borne encephalitis virus (TBEV) was detected in the Netherlands in 2015. Current monitoring through serology in deer, tick collection and reported human cases, may underestimate areas of virus circulation. Including estimates of suitability of the habitat for TBEV can guide risk-based monitoring. AIM: We aimed to improve the accuracy of the TBEV distribution map by adding estimates of TBEV habitat suitability to guide targeted tick monitoring in newly identified risk regions. METHODS: Habitat suitability for TBEV was assessed by calculating the basic reproduction number (R ₀ ) for 1 km ² grid cells aggregating various data sources for tick hosts such as mice or voles, tick abundance and TBEV transmission. The importance of different tick hosts was determined in scenario analyses. The baseline scenario was validated against data on seropositive roe deer and TBEV-positive ticks and rodents. RESULTS: The suitability (R ₀ ≥ 1) was associated with tick habitat suitability and the abundance of competent host species. Variation in competent host densities had a greater effect on R ₀ estimates than incompetent hosts. Monitoring data corresponded well with model-predicted high-risk areas and confirmed further spread of TBEV. CONCLUSION: The TBEV suitability map is a useful tool for targeted sentinel surveillance by identifying new risk areas, informing local municipal health services of endemic areas for potential human exposure. Our results support targeted efforts for awareness, preparedness and outbreak response, even in regions where TBEV has not yet been detected. Integrating One Health monitoring with spatial modelling can strengthen preparedness in emerging TBEV regions.

Climate change is one of the drivers of wildlife-borne disease emergence, as it can affect species abundance and fitness, host immunocompetence, and interactions with pathogens. To detect emerging wildlife-borne diseases, countries may implement general wildlife-disease surveillance systems. Such surveillance exists in the Netherlands. However, it is unclear how well it covers host species vulnerable to climate change and consequently disease emergence in these species. Therefore, we performed a trait-based vulnerability assessment (TVA) to quantify species vulnerability to climate change for 59 Dutch terrestrial mammals. Species vulnerability was estimated based on the magnitude of climatic change within the species distribution (exposure), the species potential to persist in situ (sensitivity), and the species ability to adjust (adaptive capacity). Using these vulnerability categories, we identified priority species at risk for disease emergence due to climate change. Subsequently, we assessed the frequency of occurrence of these priority species compared to other mammal species examined in general wildlife disease surveillance during 20082022. We identified 25 of the mammal species to be highly exposed, 24 to be highly sensitive, and 22 to have a low adaptive capacity. The whiskered myotis and the garden dormouse were highly vulnerable (i.e., highly exposed, highly sensitive, and low adaptive capacity), but they are rare in the Netherlands. The Western barbastelle, the pond bat, and the Daubentons myotis were potential adapters (highly exposed, highly sensitive, and high adaptive capacity). Species vulnerable to climate change were relatively poorly represented in current general surveillance. Our research shows a comprehensive approach that considers both exposures to climate change and ecological factors to assess vulnerability. TVAs, as presented in this study, can easily be adapted to include extra drivers and species, and we would therefore recommend surveillance institutes to consider integrating these types of assessments for evaluating and improving surveillance for wildlife-borne disease emergence.

Wild carnivore species infected with highly pathogenic avian influenza (HPAI) virus subtype H5N1 during the 2021–2022 outbreak in the Netherlands included red fox (Vulpes vulpes), polecat (Mustela putorius), otter (Lutra lutra), and badger (Meles meles). Most of the animals were submitted for testing because they showed neurological signs. In this study, the HPAI H5N1 virus was detected by PCR and/or immunohistochemistry in 11 animals and was primarily present in brain tissue, often associated with a (meningo) encephalitis in the cerebrum. In contrast, the virus was rarely detected in the respiratory tract and intestinal tract and associated lesions were minimal. Full genome sequencing followed by phylogenetic analysis demonstrated that these carnivore viruses were related to viruses detected in wild birds in the Netherlands. The carnivore viruses themselves were not closely related, and the infected carnivores did not cluster geographically, suggesting that they were infected separately. The mutation PB2-E627K was identified in most carnivore virus genomes, providing evidence for mammalian adaptation. This study showed that brain samples should be included in wild life surveillance programs for the reliable detection of the HPAI H5N1 virus in mammals. Surveillance of the wild carnivore population and notification to the Veterinary Authority are important from a one-heath perspective, and instrumental to pandemic preparedness.

Influenza A(H5N1) Virus in Sandwich Terns

Sialic acids are used as a receptor by several viruses and variations in the linkage type or C-5 modifications affect the binding properties. A species barrier for multiple viruses is present due to α2,3- or α2,6-linked sialic acids. The C-5 position of the sialic acid can be modified to form N-acetylneuraminic acid (Neu5Ac) or N-glycolylneuraminic acid (Neu5Gc), which acts as a determinant for host susceptibility for pathogens such as influenza A virus, rotavirus, and transmissible gastroenteritis coronavirus. Neu5Gc is present in most mammals such as pigs and horses but is absent in humans, ferrets, and dogs. However, little is known about C-5 content in wildlife species or how many C-5 modified sialic acids are present on N-linked glycans or glycolipids. Using our previously developed tissue microarray system, we investigated how 2 different lectins specific for Neu5Gc can result in varying detection levels of Neu5Gc glycans. We used these lectins to map Neu5Gc content in wild Suidae, Cervidae, tigers, and European hedgehogs. We show that Neu5Gc content is highly variable among different species. Furthermore, the removal of N-linked glycans reduces the binding of both Neu5Gc lectins while retention of glycolipids by omitting methanol treatment of tissues increases lectin binding. These findings highlight the importance of using multiple Neu5Gc lectins as the rich variety in which Neu5Gc is displayed can hardly be detected by a single lectin.

Tularemia Transmission to Humans, the Netherlands, 2011–2021

Background: The main objective of this study was to determine the prevalence of nine vector-borne pathogens or pathogen genera in roe deer (Capreolus capreolus) in the Netherlands, and to identify which host variables predict vector-borne pathogen presence in roe deer. The host variables examined were the four host factors ‘age category’, ‘sex’, ‘nutritional condition’ and ‘health status’, as well as ‘roe deer density’. Methods: From December 2009 to September 2010, blood samples of 461 roe deer were collected and analysed by polymerase chain reaction (PCR) for the presence of genetic material from Anaplasma phagocytophilum, Bartonella spp., Babesia spp., Borrelia burgdorferi sensu lato (s.l.), Borrelia miyamotoi, Neoehrlichia mikurensis, Rickettsia spp., and epizootic haemorrhagic disease virus (EHDV), and by commercial enzyme-linked immunosorbent assay (ELISA) for antibodies against bluetongue virus (BTV). The possible associations of host factors and density with pathogen prevalence and co-infection, and in the case of A. phagocytophilum with bacterial load, were assessed using generalized linear modelling. Results and conclusion: Analysis revealed the following prevalence in roe deer: A. phagocytophilum 77.9%, Bartonella spp. 77.7%, Babesia spp. 17.4%, Rickettsia spp. 3.3%, B. burgdorferi sensu lato 0.2%. Various co-infections were found, of which A. phagocytophilum and Bartonella spp. (49.7% of infected roe deer) and A. phagocytophilum, Bartonella spp. and Babesia spp. (12.2% of infected roe deer) were the most common. Anaplasma phagocytophilum, Babesia spp., and co-infection prevalence were significantly higher in calves than in adult roe deer, whereas the prevalence of Bartonella spp. was lower in roe deer in good nutritional condition than in deer in poor nutritional condition. Local roe deer density was not associated with pathogen presence. The high prevalence of A. phagocytophilum, Bartonella spp., and Babesia spp. is evidence for the role of roe deer as reservoirs for these pathogens. Additionally, the results suggest a supportive role of roe deer in the life-cycle of Rickettsia spp. in the Netherlands. Graphical