Nematodes in your home
by Holly M. Bik
Nematodes are small, squiggly worms that most often get confused with other things (much to my dismay). They’re not earthworms (or even closely related), but like their segmented counterparts they also flourish in all kinds of dirt. Nematodes are the underdog of worms. That’s usually because they’re not thought to be very interesting. The most common species don’t have any bristles, circular rings, or body patterns. They’re not visible to the naked eye; if you squint closely at a nematode on a microscope slide you might just confuse it with a speck of dust. The most apt description I can conjure is to say that nematodes look “pointy at both ends.” But such a bland turn of phrase does nematodes a severe disservice—underdogs are unsung heroes, and this group of worms is no different.
My fascination with nematodes really happened by accident (and yours might too) – what started as an interest in deep-sea biology turned into an obsession with the unseen, microscopic species that live in the mud on the ocean bottom. Nematodes under the microscope look like little sea monsters, eyeless and snakelike, with twisted bristles splaying everywhere and mouths packed with jagged teeth. But these beasts aren’t restricted to the oceans. Nematodes’ ability to invade and thrive in every corner of the globe is what makes these creatures truly astounding.
You’re probably already well acquainted with my roundworm friends. Pet owners will be especially accustomed to constant vigilance against nematodes—heartworm pills are specifically prescribed to prevent against infections of Dirofilaria immitis. The nematode Trichinella spiralis is also the reason you should be wary of undercooked pork. Once a person eats infected meat, these worms will bore through the intestinal wall and camp out within human muscle tissue, surrounding themselves with a protective capsule. Many parents will be familiar with pinworm, a much less worrisome (and easily treatable) intestinal infection of Enterobius nematodes that commonly afflicts children. Sticky pinworm eggs are laid on the anus and are quickly transmitted to other areas of the skin—and then to toys, bedsheets, and unsuspecting playgroups. Another set of nematodes are devastating parasites in developing nations, but are nearly unheard of in Western countries—Ascaris, Filarial nematodes, and hookworm persistently infect millions of people worldwide.
Inspecting dirt under a microscope may result in a renewed dedication to washing your household produce. I, for one, will never look at vegetables the same way again. Soil is one of the places where nematodes thrive best—roundworms are experts at recycling nutrients as they go about their daily routine of munching on bacteria, fungi, and other organic matter. Pull up a carrot, and you can be sure that nematodes are silently lurking amongst the hanging clumps of soil. Gardening enthusiasts can even buy packets of live, beneficial nematodes to spread across their lawns or compost heaps (think of these worms as probiotics for your plants). Even the most famous nematode of them all, Caenorhabditis elegans (the first multicellular organism to have its genome sequenced) makes its home on rotting fruit. Of course, some species prosper a little too well in soil. Globodera, Meloidogyne and Heterodera are agricultural pests that frequently wreak havoc on potatoes, tomatoes and soybeans. Because of the high economic costs and impact to industrial food supply chains, a substantial body of scientific research in the USA is focused on such nematode crop parasites.
I’ve saved the most cringeworthy part for last: not even tap water is free from nematodes. Drinking water is filtered as best as possible, but small worms are hard to keep tabs on (And it isn’t just the worms, tap water also contains rotifers, copepods and many kinds of bacteria). We still don’t know where they come from (Your pipes? Your well? The reservoir that pipes out your town’s water?), but recent research suggests that if you fill a glass with water these worms will be likely there, swimming. And it is not just one species; your tap water may have a diversity of worms. In that water, the worms may feed on even smaller life forms. Once, I barely knew about nematodes; now I know I can find them, eating, mating and thriving nearly anywhere, even in the swirl of a glass of the very liquid we imagine to be most devoid of life.
It is impossible to avoid interacting with nematodes whether on the floor of your house, the skin of your friend or anywhere else. Meanwhile, while we know that nematodes are nearly everywhere, we don’t know what most of them are doing. Are there nematodes on your skin right now? Probably. Does anyone know what they are doing; almost certainly not. I like the idea that I might be covered in and drinking worms, so long as I don’t think about it too much; my ancestors drank worms. Yours did too. What is unusual is not that they are there, sip after sip, but rather that we have only just found out.
1Buse HY, Lu J, Struewing IT, Ashbolt NJ. (2013) Eukaryotic diversity in premise drinking water using 18S rDNA sequencing: implications for health risks. Environ Sci Pollut Res. doi: 10.1007/s11356-013-1646-5
About the Author
Holly Bik is a marine biologist focusing on computational approaches and environmental sequencing at the UC Davis Genome Center. Her current research uses high-throughput technologies (Illumina, 454) to study the community structure and phylogeography of nematodes and other microbial eukaryotes in marine sediments, with a specific focus on deep-sea habitats. Holly is a strong advocate of integrative biology, aiming to merge expertise and synthesize historically disparate fields such taxonomy, molecular biology, computer science and design. She regularly contributes to Deep Sea News and tweets at @Dr_Bik.