Viruses are infectious agents that depend on a host cell to reproduce. Nowadays we are all familiar with different kind of viruses, such as the Coronavirus, the Tobamovirus and the Cucumber mosaic virus. But it seems that some viruses transmit more easy and are easier to eliminate than others. Why is it that some viruses are more difficult than others?

One of the parameters is the size of a virus. With the size of only 18 nm, a Tobamovirus for example is a relatively small virus. Tobamoviruses can cause necrotic lesions on leaves and have many plants as natural hosts, including tobacco, potato, tomato, and squash. The smaller a virus, the more difficult it is to eliminate. Small viruses can hide in all cracks and tears of a surface. Even when a surface looks smooth and without tears it can still harbour many pathogens. Look for example on the pictures in figure 1 where we have microscopic images of different types of “flat” surfaces. We know them as flat or smooth, but for a virus these are enormous mountains with lots of spots and crevices to hide.

Figure 1. Flat surfaces like concrete, post-it and sugar as an electro microscopic image, which show the surface is not smooth at all.

Beside the size of a virus there is also a difference in composition. There are two types of viruses, namely enveloped and non-enveloped viruses. A Tobamovirus is an example of a non-enveloped variant where a Coronavirus is an example of an enveloped virus. A Coronavirus carries an outer envelope composed of proteins and fatty material (lipid). This envelope makes them vulnerable since many disinfectants easily destroy this outer layer. Non-enveloped viruses do not carry this outer layer. In conclusion the type and size of the virus influences how easy viruses can be eliminated. This is visualised in Figure 2, which shows that the Tobamovirus is a non-enveloped virus (big bubble) with a diameter of approximately 18 nm. These characteristics make the virus relatively difficult to inactivate (score of 9 out of 10, where 10 is very difficult to inactivate).

Figure 2. Classification of virus sensitivity to disinfectants (Foulon, 2019) showing that the Tobamovirus (in red) is difficult to eliminate.

Based on the type and size of a virus it is important to select the right biocide to perform the disinfection. For the small viruses it is needed to have a perfect wetting agent included in the biocide to make sure your disinfectant will reach all cracks and crevices on the “flat” surfaces. In fact you would like the disinfectant to be crawling and reaching points where you did not even spray a drip of solution.

Intra Multi-Des GA is the fifth generation disinfectant of Intrahorti containing the highest concentration of the active ingredient glutaraldehyde in combination with four different quaternary ammonium compounds. A high amount of supporting elements is Included in Multi-des GA to make sure it has this low-viscosity property to reach the smallest viruses.

The efficacy of 0.5% 0.75% and 1% Intra Multi-Des GA for 10 minutes against Tomato mosaic virus has been assessed by an independent research facility. A solution of Infected plant sap was prepared from ToMV contaminated tomato leaves, and incubated with 0.5%, 0.75%, or 1% Intra Multi-Des GA. After 10 minutes, five tomato plants were inoculated with each mixture. Two weeks later, the inoculated plants were sampled and tested for the presence of ToMV using qPCR analysis. Negative controls were plants inoculated with 1% Intra Multi-Des GA without infectious plant sap, positive controls were inoculated with infectious plant sap without Intra Multi-Des GA.

Table 1 shows that after treatment of the inoculant with 0.5% Intra Multi-Des GA, one out of five plants was still infected. This means that under these circumstances 0.5% Intra Multi-Des GA was not able to fully deactivate the virus within 10 minutes. After treatment with 0.75% and 1% Intra Multi-des GA, no infected plants were detected, meaning that these treatments were able to inactivate the virus within 10 minutes.

Table 1. Number of infected plants after 10 minutes incubation with 0.5% 0.75% and 1% Intra Multi-Des GA.

In conclusion, even under stringent conditions of high organic content and high viral pressure 0.75% (75 ml product in 10 liter tap water) Intra Multi-Des GA is able to kill Tobamoviruses like Tomato mosaic virus (ToMV) and Tomato brown rugose fruit virus (ToBRFV). Application of the product on contaminated surfaces thus effectively prevents the spread of such viruses.