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Hygiene: plant viruses and COVID-19

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Based on the philosophy; avoiding plant disease is better than control, PQS develops best practices in horticulture with focus on hygiene. With the recent human virus outbreak of COVID-19, questions raise if the products used in the horticulture is doing its work for human viruses too. In this post, I would like to give insight of the differences between plant and human viruses but also how different disinfectants interact or may interact with viruses.

Plant viruses and human or animal viruses have a similar construction. They consist of a DNA or RNA particle (a genetic code) surrounded by a protein mass; the capsid protein structure. The biggest difference of plant and human-viruses are their pathways of how to infect organisms. No plant pathogen has been found to infect humans (means multiplication in human cells) and cause disease and vice versa. No human virus has been able to infect a plant.

Plant viruses always need a vector to enter the plant cell. The DNA of the plant virus code for cellulase, the predominant component of cell walls. But let us first look at CoVID-19 (as far as we know the disease by now).

The COVID-19 has a lipid membrane around its DNA particle and protein sheet. This enables the virus to melt with the fatty acids in the human cells. This frees up the virus to penetrate the human cell and start multiplying. In fact, the virus “orders” the human cell to make more of itself. By doing so, the human cell will eventually collapse when full of new virus particles enabling to spread within the body. How exactly is being investigated; we still have a lot to learn about this new virus. Let’s go back to plant viruses….

Plant viruses are brought in the plant tissue by insects puncturing the plant cell. This can also be done by nematodes, fungi or by activities of humans. Examples of human introduction: accidentally breaking branches, leaf-hairs or on purpose when modulating the plant. It requires contact with an infected plant first before being able to transmit it to the growing crops. One of the new tomato viruses, Tomato Brown Rugose Fruit Virus or ToBRFV in short,  is one of the typically human transmitted viruses. And by the way, tomato leaves have plenty of leaf hairs that readily break off even when just walking the crop. The further development of the virus in the plant is approximately the same. The plant virus induces the plant cell to make more of itself. The plant sap stream brings virus particles throughout the plant.

Now is the question, do both types share the same efficacy towards disinfectants? The answer is both yes and no. Mechanisms to control viruses are indeed the same, however, differences in efficacy exists. Generally speaking, we need to have more aggressive disinfectants for plant viruses. Plants have substances that are alike disinfecting agents. Just think of vitamin C, a product made by plants, effective for flu but does not do anything with plant viruses.

First step for both types is to wash hands. For the COVID-19, a nice animation has been made of how the soap connects to the fatty acid membrane of the virus and disintegrates1. The purpose of hand washing for plant pathogens is to wash off any plant sap of other plants and therefore avoiding introduction of plant viruses into a greenhouse.

But, what about disinfecting agents? There is fairly recent work done on the effect of disinfectants of a bacteriophage (= a virus that infects bacteria), that demonstrated that different strains of the virus were more affected by disinfectants than others2. A good example is the control of COVID-19, the WHO recommended to use a hand sanitizer, when no water and soap is available. The 70% ethanol is enough to control the virus, but not plant virus es like ToBRFV. This is most likely due to the fatty acids surrounding COVID-19. Disinfectants that demolishes the capsid protein structure or products that damages the genetic code will work for both plant as well as human viruses. However, there may be need in a different concentration or time of exposing the virus to the disinfectant to be working properly. In my working life, I have been largely involved in experimenting different time*dose responses when exposing plant viruses. Products like quaternary ammonium, chlorine, hydrogen peroxide at various concentration to eradicate the pathogen from surfaces have been investigated recently for its efficacy for COVID-193. These products are also used with success in the horticulture. Although concentration of the disinfecting agents may need to be higher for plant viruses then for human viruses. And despite ethanol does not work for plant viruses, there is still benefit to use as hand sanitizer. It avoids introduction of bacterial and fungal plant pathogens.

In short: avoiding introduction of plant viruses entering the greenhouse certainly contributes to eradicating COVID-19 in surfaces. Washing of hands for both plant virus as well as human virus remains key.

For further reading:

  1. A nice animated gif on the mode of action of soap can be found in the link below. It demonstrated very simple of how soap connect to the virus particle and disintegrates. It makes it difficult for the virus to attach itself to the human cell:
  2. Wigginton et al, 2012. Virus Inactivation Mechanisms: Impact of Disinfectants on Virus Function and Structural Integrity. Environmental Science & technology 2012; 46: 12069-12078.
  3. Kampf et al 2002. Persistence of coronaviruses on inanimate surfaces and their inactivation with biocidal agents. Journal of Hospital Infection 104 (2020) 246-251.

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