Survival of Tick-Borne Encephalitis Virus in Goat Cheese and Milk

Tick-borne encephalitis: A comprehensive review of the epidemiology, virology, and clinical picture

Tick-borne encephalitis virus (TBEV) is a flavivirus commonly found in at least 27 European and Asian countries. It is an emerging public health problem, with steadily increasing case numbers over recent decades. Tick-borne encephalitis virus affects between 10,000 and 15,000 patients annually. Infection occurs through the bite of an infected tick and, much less commonly, through infected milk consumption or aerosols. The TBEV genome comprises a positive-sense single-stranded RNA molecule of ∼11 kilobases. The open reading frame is > 10,000 bases long, flanked by untranslated regions (UTR), and encodes a polyprotein that is co- and post-transcriptionally processed into three structural and seven non-structural proteins. Tick-borne encephalitis virus infection results in encephalitis, often with a characteristic biphasic disease course. After a short incubation time, the viraemic phase is characterised by non-specific influenza-like symptoms. After an asymptomatic period of 2-7 days, more than half of patients show progression to a neurological phase, usually characterised by central and, rarely, peripheral nervous system symptoms. Mortality is low-around 1% of confirmed cases, depending on the viral subtype. After acute tick-borne encephalitis (TBE), a minority of patients experience long-term neurological deficits. Additionally, 40%-50% of patients develop a post-encephalitic syndrome, which significantly impairs daily activities and quality of life. Although TBEV has been described for several decades, no specific treatment exists. Much remains unknown regarding the objective assessment of long-lasting sequelae. Additional research is needed to better understand, prevent, and treat TBE. In this review, we aim to provide a comprehensive overview of the epidemiology, virology, and clinical picture of TBE.

The Consumption of Raw Goat Milk Resulted in TBE in Patients in Poland, 2022 "Case Report"

The alimentary route is the second most important route of tick-borne encephalitis infection. In Poland, the last TBE case due to the consumption of unpasteurized milk or dairy products of infected animals was recorded in 2017 as the fourth documented outbreak of TBEV infection in the country. In this study, two patients infected with TBEV through consumption of unpasteurized goat's milk from one source are described from a cluster of eight cases. In August and September 2022, a 63- and 67-year-old woman were hospitalized at the Infectious Diseases Clinic of the Institute of Rural Health (Lublin, Poland). The patients denied been recently bitten by a tick, and neither had been vaccinated against TBEV. The disease had a biphasic course. In the first case, the patient suffered from a fever, spine pain, and muscle weakness and paresis of the lower left limb. The second patient suffered from fever, vertigo, headaches, abdominal pain, and diarrhoea. The results of IgM and IgG antibodies were positive in both cases. After three weeks hospitalization, the patients were discharged in good condition. In one case, slight hearing impairment was observed. Vaccination and avoiding the consumption of unpasteurized milk remain the most effective ways to prevent tick-borne encephalitis.

Comparison of Extraction Methods for the Detection of Tick-Borne Encephalitis Virus RNA in Goat Raw Milk and Cream Cheese

Infection with the tick-borne encephalitis virus (TBEV) can cause meningitis, meningoencephalitis and myelitis in humans. TBEV is an enveloped RNA virus of the family Flaviviridae, which is mostly transmitted via tick bites. However, transmission by consumption of virus-contaminated goat raw milk and goat raw milk products has also been described. Only a few methods have been reported for the detection of TBEV in food so far. Here, we compare different virus extraction methods for goat raw milk and goat raw milk cream cheese and subsequent detection of TBEV-RNA by RT-qPCR. Langat virus (LGTV), a naturally attenuated TBEV strain, was used for artificial contamination experiments. Mengovirus and the human coronavirus 229E were compared to assess their suitability to serve as internal process controls. Out of three tested extraction protocols for raw milk, sample centrifugation followed by direct RNA extraction from the aqueous interphase yielded the best results, with a recovery rate (RR) of 31.8 ± 4.9% for LGTV and a detection limit of 6.7 × 10³ LGTV genome copies/ml. Out of two methods for cream cheese, treatment of the samples with TRI Reagent® and chloroform prior to RNA extraction showed the best RR of 4.7 ± 1.6% for LGTV and a detection limit of 9.4 × 10⁴ LGTV genome copies/g. RRs of Mengovirus and LGTV were similar for both methods; therefore, Mengovirus is suggested as internal process control virus. The developed methods may be useful for screening or surveillance studies, as well as in outbreak investigations.

Differences in Genetic Diversity of Mammalian Tick-Borne Flaviviruses

The genetic diversities of mammalian tick-borne flaviviruses are poorly understood. We used next-generation sequencing (NGS) to deep sequence different viruses and strains belonging to this group of flaviviruses, including Central European tick-borne encephalitis virus (TBEV-Eur), Far Eastern TBEV (TBEV-FE), Langat (LGTV), Powassan (POWV), Deer Tick (DTV), Kyasanur Forest Disease (KFDV), Alkhurma hemorrhagic fever (AHFV), and Omsk hemorrhagic fever (OHFV) viruses. DTV, AHFV, and KFDV had the lowest genetic diversity, while POWV strains LEIV-5530 and LB, OHFV, TBEV-Eur, and TBEV-FE had higher genetic diversities. These findings are compatible with the phylogenetic relationships between the viruses. For DTV and POWV, the amount of genetic diversity could be explained by the number of tick vector species and amplification hosts each virus can occupy, with low diversity DTV having a more limited vector and host pool, while POWV with higher genetic diversities has been isolated from different tick species and mammals. It is speculated that high genetic diversity may contribute to the survival of the virus as it encounters these different environments.

Prevalence of foodborne and zoonotic viral pathogens in raw cow milk samples

Foodborne and zoonotic viral pathogens are responsible for substantial morbidity and mortality worldwide. These viruses can be transmitted through foods such as dairy products to humans and cause several acute and chronic diseases. This study aimed to investigate the prevalence and profile of different foodborne and zoonotic viruses in raw cow milk samples. We collected 492 raw cow milk samples from local dairy markets in Qazvin, Iran. Then we evaluated the presence of hepatitis A virus, noroviruses, rotavirus, astrovirus, bovine leukaemia virus (BLV) and tick-borne encephalitis virus (TBEV) in samples using conventional and nested reverse transcription-polymerase chain reaction methods. We found that 34.95, 7.72, 25.81, 14.63, 66.86, 12.80 and 21.34% of raw milk samples were contaminated with norovirus GI, norovirus GII, hepatitis A virus, rotavirus, astrovirus, BLV and TBEV viruses, respectively. Interestingly, the samples collected from the city's south area revealed a higher prevalence of foodborne and zoonotic viruses. Astrovirus and its combination with norovirus GI were the most prevalent virus profiles. Also, the highest correlations were observed among the presence of rotavirus and hepatitis A viruses (0.36) and TBEV and norovirus GII (0.31). Considering the prevalence rate and virus profiles of different foodborne and zoonotic viruses in raw milk samples, hygiene practices and the pasteurization process are strongly suggested to be conducted throughout the cow milk production chain and in dairy industries to prevent infections with these pathogens.

Tick-Borne Encephalitis Virus RNA Found in Frozen Goat's Milk in a Family Outbreak

Tick-borne encephalitis (TBE) is one of the commonest arthropod-borne viral diseases in Middle-East Europe and North Asia. The main reservoir of the virus is comprised of small rodents and domestic mammals with the common tick (Ixodes) being the usual vector. The clinical spectrum of TBE ranges from mild meningitis to severe meningoencephalomyelitis. This disease can lead to severe sequelae and has a mortality up to 2% in Europe. Even though the majority of cases are transmitted through bites of infected ticks, infections through ingestion of contaminated milk and dairy products from farms in endemic areas have been reported. We report a family outbreak of a febrile disease, initially suggestive of human-to-human infection, during the early summertime in Austria. Tick-borne encephalitis was diagnosed following consumption of unpasteurised goat’s milk and the virus was subsequently detected in frozen milk samples. Although this is a rare manifestation of TBE, this case series shows that TBE should be included in the differential diagnosis of an outbreak of febrile disease, and a careful clinical history with reference to unpasteurized dairy products is crucial in order to prevent further disease spread. The best preventive measure is active immunisation of people living in, or travelling to, endemic areas.

Borrelia spirochetes in European exotic farm animals

Ticks transmit a broad spectrum of pathogens, threatening both animal and human health. Tick survival and proliferation are strongly dependent on host selection and suitability. The hard tick Ixodes ricinus, which is widespread throughout most of Europe, is a host generalist capable of feeding on many different vertebrate species. Pasture-kept exotic farm animals may be at a high risk for tick and tick-borne pathogens infestations but research characterizing this is currently lacking. This study focused on the detection of Borrelia spirochetes (including Borrelia miyamotoi) in exotic farm animals. Using nested-PCR with Borrelia-specific primers, 121 serum samples from 54 exotic farm animals of several species bred in four different farms in Bohemia and Moravia (Czechia) were tested. Positive samples were sequenced for the identification of Borrelia species. The prevalence of Borrelia DNA in the samples ranged from 13 to 67%, depending on the sampling site. The sequencing results confirmed the DNA presence of multiple spirochete species from the Borrelia burgdorferi sensu lato complex. Only one sample from an ostrich (Struthio camelus) was found to be positive for Borrelia myiamotoi. The results show that exotic farm animals can serve as hosts for hard ticks and can be infected by Borrelia spirochetes, transmitted by hard ticks. Therefore, these animals could play a relevant role in maintaining Borrelia spirochetes in nature.

A One-Health Approach to Investigating an Outbreak of Alimentary Tick-Borne Encephalitis in a Non-endemic Area in France (Ain, Eastern France): A Longitudinal Serological Study in Livestock, Detection in Ticks, and the First Tick-Borne Encephalitis Virus Isolation and Molecular Characterisation

Tick-borne encephalitis virus’ (TBEV) geographic range and the human incidence are increasing throughout Europe, putting a number of non-endemic regions and countries at risk of outbreaks. In spring 2020, there was an outbreak of tick-born encephalitis (TBE) in Ain, Eastern France, where the virus had never been detected before. All patients but one had consumed traditional unpasteurised raw goat cheese from a local producer. We conducted an investigation in the suspected farm using an integrative One Health approach. Our methodology included (i) the detection of virus in cheese and milk products, (ii) serological testing of all animals in the suspected farm and surrounding farms, (iii) an analysis of the landscape and localisation of wooded area, (iv) the capture of questing ticks and small mammals for virus detection and estimating enzootic hazard, and (v) virus isolation and genome sequencing. This approach allowed us to confirm the alimentary origin of the TBE outbreak and witness in real-time the seroconversion of recently exposed individuals and excretion of virus in goat milk. In addition, we identified a wooded focus area where and around which there is a risk of TBEV exposure. We provide the first TBEV isolate responsible for the first alimentary-transmitted TBE in France, obtained its full-length genome sequence, and found that it belongs to the European subtype of TBEV. TBEV is now a notifiable human disease in France, which should facilitate surveillance of its incidence and distribution throughout France.

Orf Virus Detection in the Saliva and Milk of Dairy Goats

Orf is a zoonotic and highly contagious disease caused by Orf virus (ORFV) infection. Orf outbreaks in sheep and goats usually lead to high culling rate and mortality in newborn kids and lambs, posing a great threat to the development of goat and sheep industry. Human Orf occurs via direct contact with infected animals or fomites. While this disease is traditionally thought to spread through direct contact, whether other transmission routes exist remains unclear. Herein, we report the detection of ORFV in the saliva and milk of dairy goats without clinical Orf symptoms. Further analyses showed that these ORFV are infectious, as they can induce characteristic cytopathic changes in primary mammary and lip cells. Importantly, these ORFV can induce typical Orf lesions after inoculation in ORFV-free dairy goats. This is the first study showing that live, infectious ORFV can be isolated from the saliva and milk of asymptomatic goats, highlighting novel potential transmission routes of ORFV. These findings provide a novel idea for the prevention and control of Orf spread.

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.