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.

Development of a cell culture-based method for detecting infectious tick-borne encephalitis virus (TBEV) in milk products.

Tick-borne encephalitis outbreaks have been reported in Europe after consumption of raw milk products from infected animals. While molecular methods are commonly used in viral foodborne outbreak investigations due to their sensitivity, specificity and rapidity, there are very few methods to detect infectious tick-borne encephalitis virus (TBEV) in milk products for routine use/analyses. To address this gap, we developed a cell culture-based method to detect infectious TBEV in artificially contaminated raw goat milk and raw goat cheese, and evaluated the sensitivity of TBEV infectivity assays. Raw goat milk samples were spiked with TBEV to achieve inoculation levels ranging from 106 to 100 TCID50/mL, and Faisselle and Tomme cheese samples were spiked so their TBEV concentrations ranged from 9.28 × 105 to 9.28 × 101 TCID50 per 2.5g. To detect infectious TBEV, Vero cells were infected by raw goat milk. For cheese samples, after homogenisation and membrane filtration, Vero cells were infected with samples adsorbed on the filter (method A) or with samples eluted from the filter (method B). After 5 days, cytopathic effects (CPEs) were observed and TBEV replication in Vero cells was confirmed by an increase in the number of genome copies/mL that were detected in cell supernatant. Infected Vero cells exhibited CPEs for both milk and cheese samples. Infectious TBEV was detected to 103 TCID50/mL in raw milk samples and to 9.28 × 101 TCID50 from Faisselle samples using both methods A and B. For Tomme samples, method A was able to detect TBEV to 9.28 × 102 TCID50/2.5g and method B to 9.28 × 103 TCID50/2.5g. The number of positive samples detected was slightly higher with method A than with method B. To conclude, this qualitative cell culture-based method can detect infectious TBEV artificially inoculated into raw milk and cheese; it should be further evaluated during foodborne outbreak investigations to detect infectious TBEV from naturally contaminated milk and cheese.

Questing tick abundance in urban and peri-urban parks in the French city of Lyon.

BACKGROUND: In Europe, ticks are responsible for the transmission of several pathogens of medical importance, including bacteria of the Borrelia burgdorferi (s.l.) complex, the agents of Lyme borreliosis. In France, the Auvergne Rhône-Alpes region is considered a hot spot for human tick-borne pathogen infections, with an estimated annual rate of 156 cases of Lyme borreliosis per 100,000 inhabitants. Although several studies have assessed the abundance of ticks in rural areas, little consideration has been given thus far to urban green spaces in France. METHODS: This study aimed to estimate tick abundance in three parks, two urban (U1, U2) and one peri-urban (PU), in and around the city of Lyon (France). A forest in a rural area was used as a control (C). Tick sampling campaigns were performed in each site in April, May, June, July, and October 2019 using the dragging method. One hundred transects of 10 m2 each were randomly chosen in each park in places frequented by humans. The sampling sessions were carried out under semi-controlled abiotic conditions. Ticks were stored in 70% ethanol and identified to species and developmental stage under a light microscope using morphological keys. RESULTS: A total of seven ticks (nymphs and adults) were collected in the two urban parks (six in U1 and one in U2), while 499 ticks were sampled in the peri-urban park. Of the 506 ticks collected, 504 were identified as Ixodes ricinus, one as Dermacentor marginatus, and one as Ixodes frontalis. In the peri-urban park, ticks were mainly collected under the forest cover and at forest edges. Tick density under forest cover was 7.1 times higher in the control site than in the peri-urban park throughout the survey period. CONCLUSIONS: This study confirmed the presence of ticks in all of the parks surveyed, although their occurrence in the urban parks was very rare compared to the peri-urban park and the control site. These results should serve as a basis for the implementation of preventive measures.