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

Abstract

A reliable surveillance strategy of tick-borne encephalitis virus (TBEV) is necessary to ensure adequate disease control measures. However, current approaches assessing geographical TBEV circulation are ineffective or have significant limitations. In this study we investigated a total of 1363 goat and 312 sheep bulk tank milk samples for the presence of TBEV. Samples were collected from systematically selected farms in Lithuania every 4–5 days from April to November in 2018 and 2019. To validate results, we additionally tested 2685 questing ticks collected in the vicinity of milk collection sites. We found 4.25% (95% CI 3.25–5.47) and 4.48% (95% CI 2.47–7.41) goat and sheep milk samples to be positive for TBEV, respectively. Furthermore, geographical distribution of TBEV in milk samples coincided with the known TBE endemic zone and was correlated with incidence of TBE in humans in 2019. When sampling time coincides, TBEV detection in milk samples is as good a method as via flagged ticks, however bulk milk samples can be easier to obtain more frequently and regularly than tick samples. The minimal infectious rate (MIR) in ticks was 0.34% (CI 95% 0.15–0.64). Therefore, our results confirm that testing milk serves as a valuable tool to investigate the spatial distribution of TBEV at higher resolution and lower cost.

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

“…According to various studies, the reported minimal infection rate (MIR) in ticks ranged from 0.1 to 1.8% [20,32,33]. Nevertheless, recent studies confirmed widespread TBEV distribution in the country based on the prevalence rate of antibodies against TBEV in horses (37.5%) and virus presence in horse serum samples (3.9%), as well as in goat (4.3%) and sheep (4.5%) milk samples collected in endemic localities in Lithuania [34,35]. Moreover, in a recent study, TBEV-specific antibodies were detected in 21.6% and TBEV RNA in 18.6% of randomly collected blood serum samples of dogs residing in the secondlargest city in Lithuania.…”

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

“…Research conducted at the Institute of Rural Health in Lublin confirmed the presence of TBE virus in sheep’s milk at 22%, in goat’s milk at 20%, and in cow’s milk at 11%; however, it should be noted that the milk samples came mainly from animals grazing on pastures, where the risk of tick bites is higher than in farm breeding [ 22 ]. Despite this, most milk sample testing focuses on specific food outbreaks rather than epidemiological screening; therefore, the percentage of positive results will vary in different countries [ 23 ]. In Lithuania, the percentage of positive results of bulk-tank milk from sheep and goats has been confirmed at the level of 4.3% and 4.5%, respectively [ 23 ].…”

“…Despite this, most milk sample testing focuses on specific food outbreaks rather than epidemiological screening; therefore, the percentage of positive results will vary in different countries [ 23 ]. In Lithuania, the percentage of positive results of bulk-tank milk from sheep and goats has been confirmed at the level of 4.3% and 4.5%, respectively [ 23 ].…”