Parasites in animals vs. plants

[dslc1000]

Hi,

Haven't posted here in a while ... hope all is well!

I've been considering various arguments in favour of a plant-based diet recently. Not being particularly competent in the field of biology however, I don't fully understand some of the health-related arguments - from either side!

To be honest, the more I think about it, the more a plant-based diet does seem like the healthy option to me. And to cut to the chase, I was wondering if the 'generalisation' that:

The more complex an organism is, the more likely it is to be a host for other organisms, such as malignant bacteria and parasites

is true, in your opinions. In other words, aren't animals, in general, more 'bacteria and parasite -ridden' than plants? After all, isn't this is the reason emphasis is placed on the importance of refrigerating meat and dairy products, and then cooking them at high temperatures (in attempts to kill any remaining harmful organisms) - while fruit and vegetables can be left for considerable periods at room temperature?

[Mokele]

I'd say, in general, yes. For parasites, each organism is an ecosystem, and you have the problem of competition. Many parasites are not only specialized to deal with a single host species and organ system, but even specific regions of that host's organ system. If you cut open fish, you find different parasites of the digestive system in different portions of the system for the same reason animals become specialists: to reduce competition.

 

Ergo, the more "niches" an animal has to parasitize, the more species of parasite will find a way in. However, this is a *very* broad generalization, with numerous counter-examples; for instance, reptiles are about as complex as mammals, but have less parasites becuase the continually warm mammal body is a much more inviting home than the body of a reptile, which varies it's temperature.

 

Also, for plants, what do you define as "parasite"? A wood-boring beetle or a termite colony could be considered a plant parasite.

 

In terms of health, the important thing is how many of those parasites can or will affect you if you eat them. Heavily parasitized species might be fine to eat if none of the parasites can survive in a human host.

 

Mokele

[ecoli]

Well, it all depends on your definition of parasite. Do consider the many insects that live inside fruits and vegetables, and feed on them to be parasites?

[jdurg]

Plants also tend to have the edge on animals in terms of generating toxic compounds that kill those who try to eat them. (Though the puffer fish does a darn good job of that).

[dslc1000]

Thanks for the replies.

I'm thinking of parasites that are too small to be visible; that can't be removed by simple washing.

Interesting points Mokele: the one about reptiles; and about how many parasites in other organisms can actually survive in humans. But aren't there cases where the parasites clearly do survive in the human host - such as tapeworms? In general, I would have thought that, with the biological similarities between mammals, there would be a huge number of parasites that could survive in both humans and their beef, pork, veal, lamb, whatever. Feel free to enlighten me though.

[Mokele]

Yes, many parasites *do* survive in humans, sometimes as part of their natural life cycles (many species go through 2 or even 3 hosts in their lives). Additionally, some can "accidentally" wind up in humans (meaning they can parasitize us, but will not be able to reproduce; like being stranded on a desert island).

 

A few parasites can also go from cold-blooded to warm-blooded hosts. But it's easier, in terms of adaptations needed by the parasite, to go from warm to warm.

 

Mokele

[Skye]

It depends on how the parasite works. A tick can survive on reptiles (blue tongued lizards often have lots of ticks when you find them) or birds or mammals because they simply jam their mouthparts in and drink the blood. On the other hand many viruses bind to specific molecules on the cell surface, and this specficity can mean they are unable to attack other species.