Tick-Borne Encephalitis in Sheep, Romania

Serological evidence of human exposure to foodborne zoonotic parasites in Romanian patients and possible association with food habits and hygiene

Humans may become accidental dead-end hosts for a series of zoonotic foodborne parasites, of which Toxoplasma gondii, Echinococcus spp., Toxocara spp., and Trichinella spiralis are of major public health interest, due to their potential pathological implications. The aims of the study were to evaluate the exposure to these pathogens in north-western Romania, and to investigate their potential association to risk factors. From June 2022 to January 2024, 554 patients admitted to a tertiary hospital in north-western Romania were screened for the presence of IgG antibodies against T. gondii, Echinococcus spp., Toxocara canis, and T. spiralis by ELISA, and potential risks were assessed using a questionnaire. Overall, 225 samples (40.6%) were positive for at least one pathogen. The highest seroprevalence for IgG was found for T. gondii (33.9%), followed by Echinococcus spp. (9.1%), T. spiralis (2.9%), and T. canis (1.1%). For T. spiralis, raw meat consumption was associated with positivity. For T. gondii, increased age, rural environment, contact with cats, consumption of unwashed fruits/vegetables and drinking water from unverified sources were significantly associated to seropositivity. The present study provides new insights into the epidemiological status of zoonotic foodborne parasite in Romania, underlining the need to increase awareness on the importance of water, sanitation and food habits in relation with this neglected pathology.

Exposure of cattle to tick-borne encephalitis virus in the historical endemic zone in north-eastern France

BACKGROUND

Tick-borne encephalitis (TBE) is a severe human neuroinfection caused by TBE virus (TBEV). TBEV is transmitted by tick bites and by the consumption of unpasteurized dairy products from infected asymptomatic ruminants. In France, several food-borne transmission events have been reported since 2020, raising the question of the level of exposure of domestic ungulates to TBEV. In this study, our objectives were (i) to estimate TBEV seroprevalence and quantify antibodies titres in cattle in the historical endemic area of TBEV in France using the micro virus neutralisation test (MNT) and (ii) to compare the performance of two veterinary cELISA kits with MNT for detecting anti-TBEV antibodies in cattle in various epidemiological contexts. A total of 344 cattle sera from four grid cells of 100 km² in Alsace-Lorraine (endemic region) and 84 from western France, assumed to be TBEV-free, were investigated.

RESULTS

In Alsace-Lorraine, cattle were exposed to the virus with an overall estimated seroprevalence of 57.6% (95% CI: 52.1-62.8%, n = 344), varying locally from 29.9% (95% CI: 21.0-40.0%) to 92.1% (95% CI: 84.5-96.8%). Seroprevalence did not increase with age, with one- to three-year-old cattle being as highly exposed as older ones, suggesting a short-life duration of antibodies. The proportion of sera with MNT titres lower than 1:40 per grid cell decreased with increased seroprevalence. Both cELISA kits showed high specificity (> 90%) and low sensitivity (less than 78.1%) compared with MNT. Sensitivity was lower for sera with neutralising antibodies titres below 1:40, suggesting that sensitivity of these tests varied with local virus circulation intensity.

CONCLUSIONS

Our results highlight that cattle were highly exposed to TBEV. Screening strategy and serological tests should be carefully chosen according to the purpose of the serological study and with regard to the limitations of each method.

Tick-Borne Encephalitis Virus Prevalence in Sheep, Wild Boar and Ticks in Belgium

Tick-borne encephalitis virus (TBEV) is the most important tick-borne zoonotic virus in Europe. In Belgium, antibodies to TBEV have already been detected in wildlife and domestic animals, but up-to-date prevalence data for TBEV are lacking, and no studies have assessed its seroprevalence in sheep. Serum samples of 480 sheep from all over Belgium and 831 wild boar hunted in Flanders (northern Belgium) were therefore screened for TBEV antibodies by ELISA and plaque reduction neutralization test (PRNT), respectively. The specificity of positive samples was assessed by PRNTs for TBEV and the Louping Ill, West Nile, and Usutu viruses. TBEV seroprevalence was 0.42% (2/480, CI 95%: 0.11-1.51) in sheep and 9.27% (77/831, CI 95%: 7.48-11.43) in wild boar. TBEV seroprevalence in wild boar from the province of Flemish Brabant was significantly higher (22.38%, 15/67) compared to Limburg (7.74%, 34/439) and Antwerp (8.61%, 28/325). Oud-Heverlee was the hunting area harboring the highest TBEV seroprevalence (33.33%, 11/33). In an attempt to obtain a Belgian TBEV isolate, 1983 ticks collected in areas showing the highest TBEV seroprevalence in wild boars were tested by real-time qPCR. No TBEV-RNA-positive tick was detected. The results of this study suggest an increase in TBEV prevalence over the last decade and highlight the need for One-Health surveillance in Belgium.

Seroprevalence Rates against West Nile, Usutu, and Tick-Borne Encephalitis Viruses in Blood-Donors from North-Western Romania

Introduction: West Nile virus (WNV), Usutu virus (USUV), and the tick-borne encephalitis virus (TBEV) are all arboviruses belonging to Flaviviridae family. All are characterized by vectorial transmission and sometimes associated with neuroinvasive infections. The circulation of these viruses is considered endemic in parts of Europe, with human cases reported in many countries. Among hosts, the viruses are vectored by hematophagous arthropods, such as mosquitoes (WNV, USUV) and ticks (TBEV). Considering the currently outdated knowledge regarding the epidemiology of these viruses in Romania, the aim of our study was to assess the seroprevalence rates of WNV, USUV, and TBEV among healthy blood donors in north-western Romania. Methods: Human blood samples from healthy donors were collected between November 2019 and February 2020 in six counties from the north-western region of Romania. The samples were serologically tested by ELISA and serum neutralization test. Results: Overall, we obtained a seroprevalence of 3.17% for WNV, 0.08% for TBEV, and 0% for USUV. Conclusion: Despite the low seroprevalence of WNV, USUV, and TBEV in our study, we highlight the need for continuous nationwide vector and disease surveillance and implementation of control measures. Further research is required for an optimal overview of the epidemiological status of the Romanian population regarding these flaviviruses together with countrywide awareness campaigns.

Food-Borne Transmission of Tick-Borne Encephalitis Virus—Spread, Consequences, and Prophylaxis

Tick-borne encephalitis (TBE) is the most common viral neurological disease in Eurasia. It is usually transmitted via tick bites but can also occur through ingestion of TBEV-infected milk and dairy products. The present paper summarises the knowledge of the food-borne TBEV transmission and presents methods for the prevention of its spread. The incidence of milk-borne TBE outbreaks is recorded in central, eastern, and north-eastern Europe, where Ixodes ricinus, Ixodes persulcatus, and/or Dermacentor reticulatus ticks, i.e., the main vectors of TBEV, occur abundantly. The growing occurrence range and population size of these ticks increases the risk of infection of dairy animals, i.e., goats, sheep, and cows, with viruses transmitted by these ticks. Consumers of unpasteurised milk and dairy products purchased from local farms located in TBE endemic areas are the most vulnerable to alimentary TBEV infections. Familial infections with these viruses are frequently recorded, mainly in children. Food-transmitted TBE can be monophasic or biphasic, and some of its neurological and psychiatric symptoms may persist in patients for a long time. Alimentary TBEV infections can be effectively prevented by consumption of pasteurised milk and the use of TBEV vaccines. It is recommended that milk and dairy products should be checked for the presence of TBE viruses prior to distribution. Protection of dairy animals against tick attacks and education of humans regarding the epidemiology and prophylaxis of TBE are equally important.

Alimentary Infections by Tick-Borne Encephalitis Virus

Tick-borne encephalitis virus (TBEV) causes serious the neurological disease, tick-borne encephalitis (TBE). TBEV can be transmitted to humans by ticks as well as by the alimentary route, which is mediated through the consumption of raw milk products from infected ruminants such as sheep, goats, and cows. The alimentary route of TBEV was recognized in the early 1950s and many important experimental studies were performed shortly thereafter. Nowadays, alimentary TBEV infections are recognized as a relevant factor contributing to the overall increase in TBE incidences in Europe. This review aims to summarize the history and current extent of alimentary TBEV infections across Europe, to analyze experimental data on virus secretion in milk, and to review possible alimentary infection preventive measures.

Recreational behaviour, risk perceptions, and protective practices against ticks: a cross-sectional comparative study before and during the lockdown enforced by the COVID-19 pandemic in Romania

Background

Gaining insight into the risk perceptions and the knowledge evolution of the public about emerging or changing health risks is vital for the improvement of health promotion activities. Currently, scientific evidence regarding the attitudes of the Romanian public towards ticks is scanty. This study aimed to identify how the lockdown enforced by the COVID-19 pandemic in Romania impacted the recreational behaviour, risk perceptions, and protective practices of the Romanian population regarding ticks.

Methods

A cross-sectional, nationwide web-based questionnaire was designed and distributed via social media to evaluate if, and how, the COVID-19 lockdown impacted the behaviour of the Romanian public concerning ticks. The survey was available online from 6 May until 15 May 2020, which marked the last day of the travel ban in Romania. The collected data were processed by applying both uni- and multivariate methods.

Results

Respondents reported a higher frequency of finding ticks on themselves and their dogs during the lockdown. Bathing/showering and checking the body for ticks were the two most used protective behaviours both before and during the lockdown. Nevertheless, an overall lower usage rate of protective measures was registered during the lockdown. Almost all dog owners used a form of ectoparasite control for their dogs, and only three stopped due to lockdown-associated reasons. Respondent characteristics that were found to be positively associated with risk perceptions were being female and living in peri-urban/suburban/rural environments.

Conclusions

Despite spending less time outdoors during the lockdown, more respondents reported finding ticks on themselves or their dogs. Changes in the preferences for recreational locations, rates of protective practices usage, amount of time spent in specific areas, or tick seasonal activity might have contributed to this outcome. Concerning risk groups, men of all ages, senior citizens, and rural inhabitants should be targeted by the relevant Romanian authorities when promoting local or nationwide tick awareness campaigns.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04944-7.

Comparison of Three Serological Methods for the Epidemiological Investigation of TBE in Dogs

Tick-borne encephalitis (TBE) virus is an emerging pathogen that causes severe infections in humans. Infection risk areas are mostly defined based on the incidence of human cases, a method which does not work well in areas with sporadic TBE cases. Thus, sentinel animals may help to better estimate the existing risk. Serological tests should be thoroughly evaluated for this purpose. Here, we tested three test formats to assess the use of dogs as sentinel animals. A total of 208 dog sera from a known endemic area in Southern Germany were tested in an All-Species-ELISA and indirect immunofluorescence assays (IIFA), according to the manufacturer’s instructions. Sensitivity and specificity for both were determined in comparison to the micro-neutralization test (NT) results. Of all 208 samples, 22.1% tested positive in the micro-NT. A total of 18.3% of the samples showed characteristic fluorescence in the IIFA and were, thus, judged positive. In comparison to the micro-NT, a sensitivity of 78.3% and a specificity of 98.8% was obtained. In the ELISA, 19.2% of samples tested positive, with a sensitivity of 84.8% and a specificity of 99.4%. The ELISA is a highly specific test for TBE-antibody detection in dogs and should be well suited for acute diagnostics. However, due to deficits in sensitivity, it cannot replace the NT, at least for epidemiological studies. With even lower specificity and sensitivity, the same applies to IIFA.

Discovery and genetic characterization of a novel orthonairovirus in Ixodes ricinus ticks from Danube Delta

Different arthropod species are vectors of a wide array of arboviruses (arthropod-borne viruses) and have likely been central to viral evolution. To better understand the extent of arthropod-borne pathogens, as well as their origin and evolutionary history, it is crucial to uncover the full range of microbial agents, including viruses associated with arthropods. In this study, a collection of ticks obtained in 2016 directly from mammal and bird hosts from several rural and natural sites of Danube Delta was subjected to transcriptome sequencing and amplification assays. Vector surveillance revealed the presence of a novel orthonairovirus species, designated Sulina virus, in Ixodes ricinus ticks. Phylogenetic clustering of each viral protein consistently placed the new virus in the Orthonairovirus genus as a new genogroup closely related to Tamdy orthonairovirus, a genogroup comprising both pathogenic and tick-associated orthonairoviruses. The serological testing of engorged ticks and blood of infected hosts, along with the inoculation of vertebrate cells and mice found no specific antibodies or viral replication, suggesting that Sulina virus is an orthonairovirus associated with the virome of Ixodes ricinus. Finally, the characterization of a novel orthonairovirus identified using high throughput sequencing will advance our knowledge of interactions between viruses and tick vectors, expanding our perspective on fundamental questions regarding orthonairovirus evolution, diversity, ecology and potential of emergence as pathogens.

Presence of antibodies against tick-borne encephalitis virus in sheep in Tunisia, North Africa

BACKGROUND

Tick-borne encephalitis virus (TBEv) is a flavivirus that circulates in a complex cycle involving small mammals as amplifying hosts and ticks as vectors and reservoirs. The current study aimed to investigate the presence of TBEv in Tunisian sheep. A sample of 263 adult sheep were selected from 6 localities where Ixodes ricinus is well established. Sera were screened using ELISA for TBEv IgG detection, then the doubtful and positive sera were tested by the seroneutralisation test (SNT) and screened for West Nile Virus (WNv) IgG for cross-reaction assessment.

RESULTS

The ELISA for TBEv IgG detected one positive serum and 17 borderlines. The SNT showed one positive serum among the 18 tested, giving an overall antibody prevalence of 0.38% (95% CI = 0.07-2.12%). All but one serum tested negative to WNv ELISA. None of the sheep farmers reported neurological signs among sheep or humans in their households.

CONCLUSIONS

The results may indicate the circulation of TBEv for the first time in Tunisia and in North Africa. Further studies based on either virus isolation or RNA detection, are needed to confirm the presence of TBEv in North Africa.

Revealing new tick-borne encephalitis virus foci by screening antibodies in sheep milk

Background

Tick distribution in Sweden has increased in recent years, with the prevalence of ticks predicted to spread towards the northern parts of the country, thus increasing the risk of tick-borne zoonoses in new regions. Tick-borne encephalitis (TBE) is the most significant viral tick-borne zoonotic disease in Europe. The disease is caused by TBE virus (TBEV) infection which often leads to severe encephalitis and myelitis in humans. TBEV is usually transmitted to humans via tick bites; however, the virus can also be excreted in the milk of goats, sheep and cattle and infection may then occur via consumption of unpasteurised dairy products. Virus prevalence in questing ticks is an unreliable indicator of TBE infection risk as viral RNA is rarely detected even in large sample sizes collected at TBE-endemic areas. Hence, there is a need for robust surveillance techniques to identify emerging TBEV risk areas at early stages.

Methods

Milk and colostrum samples were collected from sheep and goats in Örebro County, Sweden. The milk samples were analysed for the presence of TBEV antibodies by ELISA and validated by western blot in which milk samples were used to detect over-expressed TBEV E-protein in crude cell extracts. Neutralising titers were determined by focus reduction neutralisation test (FRNT). The stability of TBEV in milk and colostrum was studied at different temperatures.

Results

In this study we have developed a novel strategy to identify new TBEV foci. By monitoring TBEV antibodies in milk, we have identified three previously unknown foci in Örebro County which also overlap with areas of TBE infection reported during 2009–2018. In addition, our data indicates that keeping unpasteurised milk at 4 °C will preserve the infectivity of TBEV for several days.

Conclusions

Altogether, we report a non-invasive surveillance technique for revealing risk areas for TBE in Sweden, by detecting TBEV antibodies in sheep milk. This approach is robust and reliable and can accordingly be used to map TBEV “hotspots”. TBEV infectivity in refrigerated milk was preserved, emphasising the importance of pasteurisation (i.e. 72 °C for 15 s) prior to consumption.

Tick-borne encephalitis virus (TBEV) antibodies in animal sera - occurrence in goat flocks in Germany, longevity and ability to recall immunological information after more than six years

Background

TBE is an important tick-borne viral zoonosis in Europe and some parts of Asia. Humans can become infected by tick bite and in some cases also by consumption of nonpasteurized raw milk and raw milk products from ruminants. Serological investigations of milking flocks can help to assess the risk of TBEV infection for humans. 735 blood samples from 50 goat flocks from four federal states of Germany were tested by TBEV-VNT to assess a potential risk for TBEV infection.

There are some gaps in the knowledge about immunity in animals, for example with regard to the longevity of TBEV immunity. Two goats and two sheep were immunized and TBEV antibody titers could be detected for up to 7 years.

Furthermore, nothing is known about a possible long-lasting immunological memory that could quickly be reactivated by an additional contact to TBEV. Seven years after the first immunization two goats and two sheep as well as two naïve goats and two sheep were boostered and TBEV antibody titers followed.

Results

Only one sample in each of the three states was TBEV-antibody positive (VNT), albeit with low titers. However, in Baden-Württemberg seven samples were positive, among them four goats of the same flock.

TBEV-antibody positive titers were detected in goats for up to 6 years and 10 months, in sheep for up to 4 years and 7 months.

Seven years after immunization a clear immunological recall occurred in response to administration of one dose of vaccine in two goats and two sheep.

Conclusion

It can be concluded that in the tested flocks the risk of an alimentary TBEV infection was low. However, in one single flock a considerably higher risk must be assumed.

Antibody titers in goats and sheep can last very long after contact to TBEV, albeit at a low level. This should be taken into consideration in cases where the risk of an alimentary infection is assessed in a flock by serological investigations.

The immunological recall gives rise to the suspicion that the immunological memory after a first contact to TBEV lasts for many years, probably lifelong.

Tick-borne encephalitis virus in cows and unpasteurized cow milk from Norway

Tick-borne encephalitis virus (TBEV) is recognized as the most important zoonotic tick-transmitted virus in Europe. TBEV is mainly transmitted to humans through bites from TBEV-infected ticks (Ixodes ricinus and Ixodes persulcatus). However, alimentary infection after consumption of unpasteurized milk and cheese from domestic ruminants has been reported. There is little information about TBEV in ruminants in Norway. The objectives of this study were to analyse unpasteurized cow milk for TBEV RNA and to study the presence of IgG antibodies to TBEV in the same animals. A total of 112 milk and blood samples were collected from cows from five different farms spread from southern to northern Norway. The milk samples were analysed by an in-house reverse transcription (RT) real-time polymerase chain reaction and confirmed by pyrosequencing. Serum samples were screened by a commercial enzyme-linked immunosorbent assay and verified by a TBEV-specific serum neutralization test. We found TBEV RNA in unpasteurized milk collected from farms in the municipalities of Mandal, Skedsmo and Brønnøy in 5.4% of the tested animals. Specific antibodies to TBEV were only detected in Arendal, where 88.2% of the tested animals were positive. Further studies on milk containing TBEV RNA should be performed to conclude if TBEV found in unpasteurized milk in Norway is infectious, which could be of great importance in a One Health perspective.

The Role of Mammalian Reservoir Hosts in Tick-Borne Flavivirus Biology

Small-to-medium sized mammals and large animals are lucrative sources of blood meals for ixodid ticks that transmit life-threatening tick-borne flaviviruses (TBFVs). TBFVs have been isolated from various organs obtained from wild-caught Myodes and Apodemus species in Europe and Asia. Thus, these rodents are well-established reservoirs of TBFVs. Wild-caught Peromyscus species have demonstrated seropositivity against Powassan virus, the only TBFV known to circulate in North America, suggesting that they may play an important role in the biology of the virus in this geographic region. However, virus isolation from Peromyscus species is yet to be demonstrated. Wild-caught medium-sized mammals, such as woodchucks (Marmota monax) and skunks (Mephitis mephitis) have also demonstrated seropositivity against POWV, and virus was isolated from apparently healthy animals. Despite the well-established knowledge that small-to-medium sized animals are TBFV reservoirs, specific molecular biology addressing host-pathogen interactions remains poorly understood. Elucidating these interactions will be critical for gaining insight into the mechanism(s) of viral pathogenesis and/or resistance.

Tick-borne pathogens in tick species infesting humans in Sibiu County, central Romania

Romania has a highly diverse tick fauna. Consequently, a high diversity of tick-transmitted pathogens might be a potential threat to humans. However, only a limited number of tick species regularly infest humans, and pathogens present in such species are therefore of particular interest from a medical perspective. In this study, 297 ticks were collected from humans during 2013 and 2014. Ixodes ricinus was the predominant tick species, accounting for 272 specimens or 91.6% of the ticks in the study. Nevertheless, other tick species were also found to infest humans: Dermacentor marginatus constituted 7% of the ticks found on humans (21/297), Haemaphysalis punctata 1% (3/297), and Haemaphysalis concinna 0.3% (1/297). Ticks were tested by PCR for a wide range of tick-borne pathogens. In total, 11.8% of the ticks carried human pathogenic bacteria, while no viral or protozoan pathogens were detected. The most frequently detected pathogen was Rickettsia spp., occurring in 5.4% of the ticks (16/297) and comprising three species: Rickettsia (R.) raoultii, R. monacensis, and R. helvetica. Borrelia s.l. occurred in 3% (9/297) of the ticks. "Candidatus Neoehrlichia mikurensis" occurred in 1.7% (5/297) and Anaplasma phagocytophilum in 1.3% (4/297). Anaplasma bovis was detected in an H. punctata and Borrelia miyamotoi in an I. ricinus. These results point to the need for further studies on the medical importance of tick-borne pathogens in Romania.