At which temperature is the Tick-Borne Encephalitis Virus destroyed?

Question

At which temperature is the Tick-Borne Encephalitis Virus destroyed? If there is no data specifically for TBEV, is there any data for typical temperatures at which other Flaviviruses / Flaviviridae / other similar viruses are destroyed? (Or if there's nothing specific at all, then viruses in general?)

Answer 1

A very basic model of virus inactivation is exponential decay.

You can describe exponential decay with the $N(t) = N_0e^{-\lambda t}$ equation, of if you want to use half-time, then with the $N(t) = N_02^{-t/t_{1/2}}$, where $N$ is the value which reduces by time, $t$ is the time, $\lambda$ is the exponential decay constant and $t_{1/2}$ is the half-life (the time required to reduce the actual value to its half).

Exponential decay looks like this on diagrams:

• Figure 1 - exponential decay

• Figure 2 - exponential decay on log scale is linear

In the case of your TBEV virus, the $N_0$ will be the initial virus titer, the $N(t)$ will be the virus titer by a specific time, the $t$ will be the time and the $t_{1/2}$ will be the half-life, which depends on many things; TBEV strain, temperature, dry/moist heat, pH, etc...

Now real life logarithmic diagrams of TBEV thermal inactivation are linear only by the first 30 mins or so (the inactivation is exponential during that period) as you can see on Figure 3.

• Figure 3 - virus inactivation at 60°C
  2004 - West Nile virus: recent experience with the model virus approach.
  where $TCID_50$ is the tissue culture infective dose

By virus inactivation most of the articles like to use log 10 reduction factors. For example $3 lg$ or $3 log 10$ means in this context, that lowering the initial value to $10^3 = 1000$ fold.

According to this article most of the checked TBEV strains has an inactivation index (the reduction factor difference between two temperatures) around 1.7lg between 50°C and 37°C for 15 mins. So you need 15 mins at 50°C to reduce them at least $10^{1.7}=50$ fold. The reduction factor by this study was around 4lg by 37°C for 15mins (so the virus count reduces certainly not just because the heat, but other environmental factors).

Thermoresistance (Т50) of TBEV strains was tested by Ovchinnikova et al. method [17] using 24-hour cell culture grown in 96-hole plates at the presence of СО2. The thermoresistance was determined by inactivation index – difference in lg of titers of virus samples heated at 50°С during 15 minutes or unheated (4°С). In case of titers difference equal or less than 2.0 lg the strain was characterized as Т50+, from 2.1 to 3.0 lg – as medium, equal or more than 3.1 lg – as Т50-.

The values of lgTCD50/ml at 37ºС varied from 3.5 to 8.26. According to the thermoresistanse feature all tested strains were divided into three group: thermostable (Т50+) - nine strains; thermolabile (Т50-) – one strain; strains with medium thermoresistance – three strains. It should be noted that all strains isolated from I. persulcatus ticks collected in Krasnochikoiskiy district of Transbaikalia were thermostable.

• 2013 - Genetic and Biological Properties of Original TBEV Strains Group Circulating in Eastern Siberia

According to another study TBEV required 6 hours of moist heat at 60°C for inactivation of 6.6 lg.

Vapor heating of a FVII concentrate in another study (which used lyophilization, followed by adding water to achieve homogenous moistening, then heating at 60°C for 10 hours, followed by heating at 80°C for one hour in an airtight container under nitrogen gas atmosphere) was evaluated for its ability to inactivate HAV, HIV-1, TBEV, PRV, and MVM. HAV was readily inactivated within one hour at 60°C (5.9 log 10 ). TBEV required six hours of this treatment for inactivation of 6.6 log 10 , and three hours were required to inactivate 6.2 log 10 of HIV-1 and 6.9 log 10 of PRV.

• 2002 - Part 3a, Plasma and Plasma Products - Heat and Solvent/Detergent Treatments

According to this study TBEV is considered not heat resistant, so if you are worried for example about raw milk pasteurization, then I think boiling the milk for a few minutes is enough.

Due to the lipid envelope, TBEV is readily inactivated by heat treatment, detergents and organic solvents. Even though a viremic phase is common during a TBEV infection in several animal species, foodborne infection via contaminated meat or organs is unlikely due to the fast virus inactivation at elevated temperatures.

• 2011 - Scientific Opinion on an update on the present knowledge on the occurrence and control of foodborne viruses