Now a great question that came in through the, the AUA forum was,
can plants be vectors of disease?
Now, and the question was specifically posed in terms of vectors for
of disease for humans, but more broadly I think the question is very interesting.
You know, can plants act as vectors of disease and
how do they interact in that role?
>> So definitely plants are good vectors for some viruses of insects.
There hasn't, I'm not aware of any documented case where a plant
has been a vector for a human disease although there are some kinds of
food poisoning like some of the e coli, that, you know-
>> Mm-hm. >> Had a problem in spinach and
lettuce in recent years.
Evidently, those can be taken up by plants through the roots, and get into the plant.
So, there can be bacterial examples.
>> Mm-hm. >> For viruses some of,
there are some really cool stories about viruses being vectors for, or
plants being vectors for insect viruses.
So my favorite one is the rosy apple aphid.
So this aphid has two morphs.
A winged state and a non, a non winged state.
And the winged ones obviously can move from plant to plant.
When they land on a plant they they are infected with the virus and
they deposit the virus in the plant.
The virus doesn't replicate in the plant, but it moves through that leaf.
And then the aphid begins to have offspring, and
its offspring don't have wings because they're not infected with the virus.
So the virus is not transmitted vertically.
And they're bigger and they have more offspring and, but
then pretty soon the plant gets really, really crowded, and
eventually, one of those offspring will take up the virus.
Just by happenstance there's a little bit of virus in the plant because it
was adopt, it was deposited in the original, by the original aphid.
And when they take it up, then they develop the wings and
they move off to a new plant and start the whole process over.
So that's definitely a mutualistic virus for
the aphids because it gives them a way to move.
>> So it provides a trigger for high population density, right?
>> Right. >> So that presumably that's a degradation
of the food source that then would suggest that the aphids should move on.
>> Yeah so, but, so the way that it happens is by,
because eventually somebody will take up, up the virus.
>> So, I think in animal diseases we tend to think of a vector as somewhere where
the pathogen actually multiplies within that vector as opposed to transporters,
which would just carry.
So in the case of the cabbage and
the things, they're just carrying E.coli or something like that.
>> Right, that's right, it's not replicating.
>> But in some of them, would there be replication?
>> It would, insect, yes.
So there are a number of plant insect viruses, and
actually we've never been sure whether they're insect viruses or
plant viruses because they replicate in both hosts.
>> Yes.
>> Like tomato spotted wilt virus.
>> Yes.
>> One of the worst virus, viruses in the world right now.
I mean its, it infects almost everything.
>> Oh.
>> And it replicates in its insect hosts and in the plant hosts.
>> Yeah. >> So who's the bacteria and
who's the host?
You know, they're kind of both.
But, in general, that's not very common.
In plant viruses, most of them,
what we call vectors, don't, they don't have any replication.
>> Okay. That's interesting.
>> So there's an interest, interesting distinction, of course, as,
as you said, but there are some cases where humans do
get diseases from replication of a parasite in the plant.
And really great examples are fungi replicating on
the plant's materials that we then eat.
So, ergo.
>> That's true. >> Mm-hm.
>> is a really wonderful example,
it's called Saint Anthony's fire in Europe.
It caused these tremors and, and,
and problems in the, the appendages.
It was suggested to be the cause of Asian madness.
As we saw in Salem in the 1600s because people ate infected rye.
It is, the fungus inside it is the same fungus from
which we originally derived LSD from back in the 1930s.
So what the fungus is doing is living inside the raw ear of corn or different
plants producing a lot of alkaloids, which have an effect on mammalian herbivores.
So the plant has cooperation with the fungus to
prevent being eaten by herbivore.
When we eat it, the consequence of which is we,
we have these hallucinations >> Hm.
>> And the last example was in France in 1952 when we
saw this mass outbreak because somebody illegally sold infected rye.
And, and one great story from that, or maybe not so
great is some 12 year old trying to kill her mother with a kitchen knife,
because she, the whole town had this mass hallucination.
It's really a compressive agent.
>> Mm hm.
>> But not a traditional vector story.
>> [LAUGH] [CROSSTALK].
>> So, it's a fungal types then that's causing the disease.
>> Yeah. >> So
the fungus isn't actually infecting the humans per se.
>> No. >> But it's the toxins that's produced.
>> Yeah. >> Yeah.