Effect Measure

There’s an epidemic of a viral disease in Florida, although you wouldn’t know it unless you were a vegetable or a farmer:

In recent years, the number of whitefly-transmitted viruses in cucurbit fields, home to crops like cucumbers, squashes, pumpkins, melons and watermelons, has increased to almost epidemic proportions in Florida.

Researchers led by plant pathologists Scott Adkins and Bill Turechek at the ARS Subtropical Plant Pathology Research Unit in Fort Pierce, Fla., are dealing with a “triple threat” to cucurbits: three major viruses, all transmitted by silverleaf whitefly, Bemisia tabaci. The host range is similar–mostly cucurbits–but the symptoms differ. And the researchers have discovered a new host for the whiteflies: green beans. (Science Daily)

The three viruses in the cucumber-squash triple threat are the Cucurbit Leaf Crumple Virus (CuLCrV), a threat to greenbeans; the Squash Vein Yellowing Virus (SqVYV), producing disease in squash and watermelon; and the Cucurbit Yellow Stunting Disorder Virus (CYSDV), a scourge of melons, cucumbers, gourds and squash.

There isn’t a living thing we know of, including tiny bacteria, that aren’t subject to viral infection. We know that viral diseases of animals can infect humans (dare I mention bird flu?), and that viral infections of bacteria can turn a harmless bacterium into a toxin producer (e.g., diphtheria). What is somewhat surprising is that I could find no human diseases caused by plant viruses. In fact I couldn’t find any animal diseases caused by plant viruses.

I have seen statements to the effect that plant viruses must mechanically breach the plant cell wall to gain entrance, a trick they pull with the help of a vector like an insect, but that doesn’t explain why it doesn’t happen in animal host cells. In fact I see references to plant viruses replicating in some insect vectors (e.g., Begomoviruses [Geminiviridae])), although it is not clear if this really does happen.

Any reader know of examples of animal or human infection with plant viruses or a reason why it cannot happen?


  1. #1 MB
    April 21, 2008

    Two papers worth looking at: F. Van der Riet, Diseases of plants transmissible between plants and man (Phytonoses) exist, Medical Hypotheses , Volume 54 , Issue 2 , Pp. 310 – 311 and Talya Kunik et. al., Genetic transformation of HeLa cells by Agrobacterium, Proceedings of the National Academy of Sciences, February 13, 2001, vol. 98, no. 4; 1871-1876.

  2. #2 Lea
    April 21, 2008

    O.K., if someone reads the papers MB referenced would you please share the results here? Thank you.

    A tiny bit off topic revere, it’s time to get back to basics and tell big agriculture to take a frakking hike. Time to consider the wisdom’s of Farmer’s Almanac and Companion Planting. (garlic with tomatoes, keeps white flys out)
    Time to use Cannabis in the Companion Planting too as it’s a NATURAL insect repellent. What’s that saying on that show I never watch, D’oh!

  3. #3 Tom DVM
    April 21, 2008

    Is the fundamental question for scientists not…

    …why do we find ourselves on genetically shifting sands in respect to all pathogens?

    …it seems that some unknown environmental stimulus…at some unknown time period in the middle-late twentieth century…has produced a paradigm shift that is now being reflected in both enhanced pathogen diversity and virulence…

    …that is surprisingly consistent across all geographic areas of the world at relatively the same time.

    Most of the twentieth century was a relatively quiescent period both for plant and animal pathogens.

  4. #4 Andrew Hill
    April 21, 2008

    For Lea.

    In the paper,

    Talya Kunik et. al., Genetic transformation of HeLa cells by Agrobacterium, Proceedings of the National Academy of Sciences, February 13, 2001, vol. 98, no. 4; 1871-1876.

    They show that the tumor forming plant pathogen, Agrobacterium, also has the ability to integrate its DNA into a mammalian cell genome. In particular, they used cells cultured from the HeLa line, therefore showing Agrobac’s ability to infect a human cell. However, they concede that the laboratory results may not be consistent with what one might find in natural conditions. But the cite two more papers where Agrobac has been suggested to cause human disease:

    Sauter, C. (1995) Lancet 346, 1433

    Chalandon, Y. , Roscoe, D. L. & Nantel, S. H. (2000) Bone Marrow Transplant

  5. #5 phytosleuth
    April 21, 2008

    A. tumefaciens is a parasitic, Gram-negative soil bacterium that causes crown gall disease (forms growth-like tumors on plants). It is commonly used in plant genetic research to transfer DNA into its tumor-inducing plasmid into a host cell and this integrates the DNA into the host cell genome. This is genetic modification. The transformation process is mediated by virulence proteins encoded in the tumor-inducing plasmid.

    Viruses are often transferred to plants by eukaryotes: insects.

    Soil bacterium seem to be in the news lately. Acinetobacter baumannii is a Gram-negative soil bacterium that has suddenly become a very resistant human pathogen.

    Can humans become infected with a plant virus? Not that I know of. But that may be too simple of a question. Not sure anyone has looked for plant viruses in animals. But people are now looking for viruses in various biomes. And there are new theories on the role of viruses in transferring genes across taxa. Luis P. Villarreal and Frank P. Ryan. Viruses as symbionts and How viruses shape the tree of life.

    Functional metagenomic profiling of nine biomes. Dinsdale et al. Vol 452; 3 April 2008; doi:10.1038/nature06810 in Nature

  6. #6 pft
    April 23, 2008

    From this, human feces may also be a source of plant viruses.


    In any event, as we genetically modify plants to be resistant to these viruses, one has to be concerned of the unintended consequences, as there seems very little independent testing being done to ensure their safety, other than FDA chanting “In Monsanto We Trust” in the church of corporatism.

  7. #7 revere
    April 23, 2008

    pft: Saw this paper when it came out. It suggests we might be a vector for plant viruses but still doesn’t say whether plant viruses can cause disease in humans. As far as I have been able to tell, no one has found this to happen and I wonder why. Have we not looked hard enough? Or is there an insurmountable biological barrier?

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