Bulk Milk Tank Samples Are Suitable to Assess Circulation of Tick-Borne Encephalitis Virus in High Endemic Areas

The Prevalence of Tick-Borne Encephalitis Virus in Wild Rodents Captured in Tick-Borne Encephalitis Foci in Highly Endemic Lithuania

Wild rodents are considered to be one of the most important TBEV-amplifying reservoir hosts; therefore, they may be suitable for foci detection studies. To investigate the effectiveness of viral RNA detection in wild rodents for suspected TBEV foci confirmation, we trapped small rodents (n = 139) in various locations in Lithuania where TBEV was previously detected in questing ticks. Murine neuroblastoma Neuro-2a cells were inoculated with each rodent sample to maximize the chances of detecting viral RNA in rodent samples. TBEV RNA was detected in 74.8% (CI 95% 66.7-81.1) of the brain and/or internal organ mix suspensions, and the prevalence rate increased significantly following sample cultivation in Neuro-2a cells. Moreover, a strong correlation (r = 0.88; p < 0.05) was found between the average monthly air temperature of rodent trapping and the TBEV RNA prevalence rate in cell culture isolates of rodent suspensions, which were PCR-negative before cultivation in cell culture. This study shows that wild rodents are suitable sentinel animals to confirm TBEV foci. In addition, the study results demonstrate that sample cultivation in cell culture is a highly efficient method for increasing TBEV viral load to detectable quantities.

Phylogenetic characterisation of tick-borne encephalitis virus from Lithuania

The Baltic states are the region in Europe where tick-borne encephalitis (TBE) is most endemic. The highest notification rate of TBE cases is reported in Lithuania, where the incidence of TBE has significantly increased since 1992. A recent study reported 0.4% prevalence of TBE virus (TBEV) in the two most common tick species distributed in Lithuania, Ixodes ricinus and Dermacentor reticulatus, with the existence of endemic foci confirmed in seven out of Lithuania's ten counties. However, until now, no comprehensive data on molecular characterisation and phylogenetic analysis have been available for the circulating TBEV strains. The aim of this study was to analyse TBEV strains derived from I. ricinus and D. reticulatus ticks collected from Lithuania and provide a genotypic characterisation of viruses based on sequence analysis of partial E protein and NS3 genes. The 54 nucleotide sequences obtained were compared with 81 TBEV strains selected from the NCBI database. Phylogenetic analysis of the partial E and NS3 gene sequences derived from 34 Lithuanian TBEV isolates revealed that these were specific to Lithuania, and all belonged to the European subtype, with a maximum identity to the Neudoerfl reference strain (GenBank accession no. U27495) of 98.7% and 97.4%, respectively. The TBEV strains showed significant regional genetic diversity. The detected TBEV genotypes were not specific to the tick species. However, genetic differences were observed between strains from different locations, while strains from the same location showed a high similarity.

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.

Detection of Influenza D-Specific Antibodies in Bulk Tank Milk from Swedish Dairy Farms

Influenza D virus (IDV) has been detected in bovine respiratory disease (BRD) outbreaks, and experimental studies demonstrated this virus's capacity to cause lesions in the respiratory tract. In addition, IDV-specific antibodies were detected in human sera, which indicated that this virus plays a potential zoonotic role. The present study aimed to extend our knowledge about the epidemiologic situation of IDV in Swedish dairy farms, using bulk tank milk (BTM) samples for the detection of IDV antibodies. A total of 461 and 338 BTM samples collected during 2019 and 2020, respectively, were analyzed with an in-house indirect ELISA. In total, 147 (32%) and 135 (40%) samples were IDV-antibody-positive in 2019 and 2020, respectively. Overall, 2/125 (2%), 11/157 (7%) and 269/517 (52%) of the samples were IDV-antibody-positive in the northern, middle and southern regions of Sweden. The highest proportion of positive samples was repeatedly detected in the south, in the county of Halland, which is one of the counties with the highest cattle density in the country. In order to understand the epidemiology of IDV, further research in different cattle populations and in humans is required.

Dairy milk from cow and goat as a sentinel for tick-borne encephalitis virus surveillance

Tick-borne encephalitis (TBE) is one of the most severe human tick-borne diseases in Europe. It is caused by the tick-borne encephalitis virus (TBEV), which is transmitted to humans mainly via bites of Ixodes ricinus or I. persulcatus ticks. The geographical distribution and abundance of I. ricinus is expanding in Sweden as has the number of reported human TBE cases. In addition to tick bites, alimentary TBEV infection has also been reported after consumption of unpasteurized dairy products. So far, no alimentary TBEV infection has been reported in Sweden, but knowledge about its prevalence in Swedish ruminants is scarce. In the present study, a total of 122 bulk tank milk samples and 304 individual milk samples (including 8 colostrum samples) were collected from dairy farms (n = 102) in Sweden. All samples were analysed for the presence of TBEV antibodies by ELISA test and immunoblotting. Participating farmers received a questionnaire about milk production, pasteurization, tick prophylaxis used on animals, tick-borne diseases, and TBE vaccination status. We detected specific anti-TBEV antibodies, i.e., either positive (>126 Vienna Units per ml, VIEU/ml) or borderline (63-126 VIEU/ml) in bulk tank milk from 20 of the 102 farms. Individual milk samples (including colostrum samples) from these 20 farms were therefore collected for further analysis. Our results revealed important information for detection of emerging TBE risk areas. Factors such as consumption of unpasteurized milk, limited use of tick prophylaxis on animals and a moderate coverage of human TBE vaccination, may be risk factors for alimentary TBEV infection in Sweden.