25 July 2014

Where’s the site for the parasite?

I’ve had the good fortune to have a glut of papers appear, thanks in part to the publication of symposium proceedings I helped organized with Kelly Weisnersmith. One of the papers in the symposium proceedings is the follow-up to Carreon and colleagues (2011), which I described here. (My goodness, was that three years ago already?)

In our previous paper, we showed that living inside the neural tissue of shrimp were these little baby tapeworms:

After Nadia Carreon (pictured) finished her bachelor’s degree, she volunteered to stay and try to push the project forward a little further before she went off to graduate school.  (Nadia will will soon be finishing a master’s degree at University of Texas Brownsville.)

We decided to have a first pass at trying to answer the question of where the parasites were located in the shrimp nervous system. I knew the basic landmarks of the crustacean nervous system, and the general function of different parts of the nervous system. If parasites were infecting one region but not another, we would have a reasonable first explanation for why.

We did this work a couple of years back, so why is it only being published now? For two reasons. First, projects often sit waiting for a student to pick them up. I don’t have the sort of research lab doctoral students, post-docs, or technicians, so progress comes in fits and starts.

Second, and more importantly, there things that I hoped to add to this paper to make it a richer and deeper story. (This is a recurring theme in my writing. It happened with another recent paper, too. Note to self: don’t let the perfect be the enemy of the good.)

First, I wanted to analyze the position of parasites in the brain, not just the abdominal ganglia. There are fewer parasites in the brain, though, so it would take longer to build up a coherent picture, which is why we started where we did. Checking the position in the brain will have to wait for another paper.

Second, I wanted to section the nervous tissue, and look at those at higher power; under an electron microscope, say. This would help us to see where the larval tapeworms are sitting in three dimensions, not just two. The higher magnification might also help us get a better sense of how the neurons are displaced around the tapeworms, and whether the tapeworms were damaging the tissue.

One reviewer said it would be nice to have these sections. I agreed, but Nadia had left, no other student had picked up the project, I don’t have sectioning skills, and we have no histology core with technicians who might help with something like that. There was no telling how long it might be before I could get sections, so this paper went forward without them. that will be in a later paper (I hope!)

Speaking of which, one reviewer suggested something very helpful. We show in this paper that there are more tapeworms in the ganglia than the nerve cord between them. We show that in the first figure.

The reviewer suggested correcting for the number of parasites by the volume of tissues. Doing this required a quick couple of measurements from photographs I already had, and some quick back of the envelope calculations. And it made the difference in infection even more striking: more parasites in the ganglia than the nerve cord, even though the ganglia are smaller than the cord!

Although I describe it in the text, I could have shown this figure in the paper, which would have emphasized the differences all the more:

Even when you are happy about a paper coming out, you will always know there are things that could have made it better. At least I share the better graph here.

By the way, thanks to the support of my department, this paper is open access and free for all to read!


Nadia and I dedicated this paper to the late Luis Colom. I am glad we we able to give some personal recognition to Dr. Colom. Dr. Colom’s influence on UTB (and, eventually, UTRGV) looks like it be a lastng one, judging from this picture Nadia shared yesterday:

Related posts

823 days: a tale of parasite publication
Luis Colom, the peer I never met


Carreon N, Faulkes Z, Fredensborg BL. 2011. Polypocephalus sp. infects the nervous system and increases activity of commercially harvested white shrimp (Litopenaeus setiferus). Journal of Parasitology 97(5): 755-759. http://dx.doi.org/10.1645/GE-2749.1

Carreon N, Faulkes Z. 2014. Position of larval tapeworms, Polypocephalus sp., in the ganglia of shrimp, Litopenaeus setiferus. Integrative and Comparative Biology 54(2): 143-148. http://dx.doi.org/10.1093/icb/icu043

No comments: