Can Plants be Vectors of Disease?

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Do curso por The Pennsylvania State University

Epidemias - A Dinâmica das Doenças Infecciosas

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The Pennsylvania State University

Epidemias - A Dinâmica das Doenças Infecciosas

568 ratings

Not so long ago, it was almost guaranteed that you would die of an infectious disease. In fact, had you been born just 150 years ago, your chances of dying of an infectious disease before you've reached the tender age of 5 would have been extremely high. Since then, science has come a long way in understanding infectious diseases - what they are, how they spread, and how they can be prevented. But diseases like HIV/AIDS, Malaria, Tuberculosis, or the flu are still major killers worldwide, and novel emerging diseases are a constant threat to public health. In addition, the bugs are evolving. Antibiotics, our most potent weapon against bacterial infections, are losing their power because the bacteria are becoming resistant. In this course, we'll explore the major themes of infectious diseases dynamics. After we’ve covered the basics, we'll be looking at the dynamics of the flu, and why we're worried about flu pandemics. We'll be looking at the dynamics of childhood diseases such as measles and whooping cough, which were once considered almost eradicated, but are now making a comeback. We'll explore Malaria, and use it as a case study of the evolution of drug resistance. We'll even be looking at social networks - how diseases can spread from you to your friends to your friends' friends, and so on. And of course we’ll be talking about vaccination too. We’ll also be talking about how mobile phones, social media and crowdsourcing are revolutionizing disease surveillance, giving rise to a new field of digital epidemiology. And yes, we will be talking about Zombies - not human zombies, but zombie ants whose brains are hijacked by an infectious fungus. We're looking forward to having you join us for an exciting course!

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Ask Us Anything Videos

The videos accessible in this module are responses to questions that have been posed in previous sessions of this course. We invite you to look around here as an additional resource to answer questions you might have yourself or explore topics that pique your interest.

Marilyn Roosinck and What’s Different about Plant Epidemiology?8:19

Can Plants be Vectors of Disease?4:33

What are Other Determinants of Susceptibility?5:56

Can Pathogens Change Host Function?5:57

Immune System Conflict6:08

Conheça os instrutores

Dr. Ottar N. Bjornstad
Professor of Entomology and Biology
Department of Biology
Dr. Rachel A. Smith
Associate Professor
Department of Communication Arts & Sciences and Human Development & Family Studies
Dr. Mary L. Poss
Professor of Biology
Department of Biology
Dr. David P. Hughes
Assistant Professor of Entomology and Biology
Department of Biology
Dr. Peter Hudson
Willaman Professor of Biology
Department of Biology
Dr. Matthew Ferrari
Assistant Professor of Biology
Department of Biology
Dr. Andrew Read
Alumni Professor in the Biological Sciences, and Professor of Entomology
Center for Infectious Disease Dynamics
Dr. Marcel Salathé
Assistant Professor of Biology
Department of Biology

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.

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