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Ascaris Parasitic Worms: Phylum & Classification

Instructor: Sarah Phenix
In this lesson we will explore the parasitic worms of the genus Ascaris, which are part of the phylum Nematoda. We will also see what relation they have with humans.

Ascaris Parasitic Worms

You read that right, in this lesson we will talk about parasitic worms, specifically a genus called Ascaris. So we've all heard the term 'parasite', but what does it actually mean? Well, a parasite is an organism that feeds off of or lives within another organism, called a host, to the detriment of that host organism.

Now, since we are specifically talking about parasitic worms, rather than, say flies (such as mosquitos), fish (such as the toothpick fish), or insects (like a flea or tick), we can use the term helminth, which specifically refers to parasitic worms.

Ascaris lumbricoides, giant intestinal worms
Ascaris lumbricoides, Giant Intestinal Worms

Classification in Phylum Nematoda

So, we've established that Ascaris is a genus of helminth. They belong to the Kingdom Animalia (just like us), and the Phylum Nematoda (from the Greek 'nematos' meaning 'thread'). Nematoda is the phylum containing all roundworm species. But, in spite of the fact that nematodes are 'roundworms', that does not mean that all worms that are round in shape are nematodes. The term nematoda actually refers, not to their body shape, but to their digestive tract, which is tube-like with tapered openings at either end.

Nematodes are pseudocoelomates, meaning they have a 'fake' coelom. A coelom is a body cavity that surrounds the digestive track. In nematodes, their pseudocoelom, or fluid filled cavity, isn't encased in mesoderm but makes direct contact with their intestinal wall.

Cross-section of coelomate and pseudocoelomate
Coelomate V Pseudocoelomate

What should also be noted is that not all nematodes are parasitic, although, of the approximately 12,000 known species (some estimate that there may be as many 500,000 species because so little is known of their diversity), about half are of the parasitic persuasion.

Parasitic Action of Ascaris Worms

Of the 17 species of known Ascaris worms, the two most common species are Ascaris suum and Ascaris lumbricoides, and these helminths can both be found occupying human hosts- gross, right? With that said, A. suum prefers pigs (both domestic and wild alike) but they will certainly take up residence in you or I if given the chance.

Ok, so how would they get the chance to invade our bodies? Well, these are a brand of wriggly beast referred to as soil-transmitted helminths, meaning that their unwitting hosts become infected by consuming contaminated soil. Now, I'm sure that might sound pretty silly- it's likely been a long time since you put a fist-full of soil in your mouth but, what about an unwashed fruit or vegetable? I bet you didn't think about that. With that said, let's not swear off strawberries, carrots, and tomatoes just yet- these soil-transmitted helminths are generally localized to areas with poor sanitation as well as areas using human feces for fertilizer.

Oh, did I not mention anything about human feces yet? Probably not, as I'm sure you'd remember that one. So how does the term human feces even come into play here? Well, Ascaris take up residence in the small intestines, where they mature and reproduce. A single mature female can lay up to 200,000 eggs…per day! Then she relies on the unwitting host to generously disperse her eggs through excrement, which she hopes will infect a new host.

Adult Ascaris worms can reach lengths of up to 14 inches in length and their eggs can survive up to 10 years in the soil. It's thought that Ascaris currently infect somewhere between 1-2 billion people worldwide, with the greatest population residing in sub-Saharan Africa, Latin America, and Asia.

Ascaris lumbricoides
Ascaris lumbricoides

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