Do you enjoy gardening like I do? Well, I used to never enjoy getting out there to turn soil, rake grass and trim branches or pop off dead blossoms. But, over the last few years, I can't wait to get out to do that because I know of the rewards I will get when the afternoon sun heats up the air bringing forth beautiful blooms and a beautiful green carpet where I can sit myself down and enjoy my park like surroundings. It will also bring more bees, butterflies and insect eating birds and hummingbirds to my place of solitude and with the air alive and serenading birds it brings rest and relaxation.
However, after studying entomology, plant physiology and phycology at HSU, I have a new knowledge and respect for all those critters that are best studied under a microscope. Gardening is a great hobby and brings a lot of enjoyment in the end, but it can also cause physiological affects to the human body, if the gardener is not careful when working with soils, roots, branches and the like. Parasitic animals are alive and active in those soils, on roots and on branches. When first looking at a cup of soil there appears nothing on the surface. But, put that same cup under a dissecting microscope and that top soil comes alive as it quivers and shakes with hundreds of minute and parasitic animals living their life in that habitat.
What is interesting that I never once ever really questioned where those 'wild' animals go to rid themselves of their wastes. I do know by the rancid odor amongst my flowers and bushes that some feline came and either sprayed or used my soil as a litter box. But, where do the raccoons, opossums, occasional fox, skunks and other smaller mammals go to relieve themselves? Well, why not where that cat or dog just went? And, so there parasitic animals await the next warm blooded hand to attach themselves to move from the outside to get to inside through a small cut that the owner wasn't aware of. And, those parasites cause a heap of trouble for your intestines and body organs and not to mention those specific parasites that can stay a life time and make their way to the brain bringing death to the host. But, do you have to eat that soil to get infected?
Eating dirt doesn’t necessarily mean picking up soil and deliberately putting it in your mouth: we accidentally ingest dirt when we put dirty fingers in our mouths, or eat uncooked vegetables that have not been very thoroughly scrubbed. Soil particles may even be picked up by the wind and inhaled.
Put simply, worm eggs and protozoan cysts and oocysts can’t be present in soil unless animals put them there. The commonest ones are passed in the stools of infected animals. If they are present in soil, it means that animal feces have contaminated the ground.
Nematodes
Nematodes are found in almost all habitats, but are often overlooked because most of them are microscopic in size. For instance, a square yard of woodland or agricultural habitat may contain several million nematodes. Many species are highly specialized parasites of vertebrates, including humans, or of insects and other invertebrates. Other kinds are plant parasites, some of which can cause economic damage to cultivated plants. Nematodes are particularly abundant in marine, freshwater, and soil habitats. One study in Colorado estimated that nematodes consumed about as much grass as a prairie dog colony.
Soil is an excellent habitat for nematodes, and 100 cc of soil may contain several thousand of them. Because of their importance to agriculture, much more is known about plant-parasitic nematodes than about the other kinds of nematodes which are present in soil. Most kinds of soil nematodes do not parasitize plants, but are beneficial in the decomposition of organic matter. These nematodes are often referred to as free-living nematodes. Juvenile or other stages of animal and insect parasites may also be found in soil. Although some plant parasites may live within plant roots, most nematodes inhabit the thin film of moisture around soil particles. The rhizosphere soil around small plant roots and root hairs is a particularly rich habitat for many kinds of nematodes.
Nematodes are roundworms in the Phylum Nematoda. Various authorities distinguish among 16 to 20 different orders within this phylum. Only about 10 of these orders regularly occur in soil, and four orders (Rhabditida, Tylenchida, Aphelenchida, and Dorylaimida) are particularly common in soil. More than 15,000 species and 2,200 genera of nematodes had been described by the mid-1980s. Although the plant-parasitic nematodes are relatively well-known, most of the free-living nematodes have not been studied very much. Therefore there is a high probability that most soil habitats will contain nondescribed species of free-living nematodes. Identification of these groups is extremely difficult, and there are only a few nematode taxonomists in the world who can formally describe new species of free-living nematodes to science. Therefore most nematode ecologists identify soil nematodes only to family or genus.
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| Nematodes inside a grub (top of body) |
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| Healthy and nematode-infected white grubs |
Feeding Habits
Soil-inhabiting nematodes can also be classified according to their feeding habits. This classification is particularly useful to ecologists in understanding the positions of nematodes in soil food webs. Several important feeding groups of nematodes commonly occur in most soils. In addition, algivores (feed on algae) and various stages of insect and animal parasites occasionally are found in soil. The nematode feeding groups are called trophic groups by some authors.
Bacterivores. Many kinds of free-living nematodes feed only on bacteria, which are always extremely abundant in soil. In these nematodes, the "mouth", or stoma, is a hollow tube for ingestion of bacteria. This group includes many members of the order Rhabditida as well as several other orders which are encountered less often. These nematodes are beneficial in the decomposition of organic matter.
Fungivores. This group of nematodes feeds on fungi and uses a stylet to puncture fungal hyphae. Many members of the order Aphelenchida are in this group. Like the bacterivores, fungivores are very important in decomposition.
Predators. These nematodes feed on other soil nematodes and on other animals of comparable size. They feed indiscriminately on both plant parasitic and free-living nematodes. One order of nematodes, the Mononchida, is exclusively predacious, although a few predators are also found in the Dorylaimida and some other orders. Compared to the other groups of nematodes, predators are not common, but some of them can be found in most soils.
Omnivores. The food habits of most nematodes in soil are relatively specific. For example, bacterivores feed only on bacteria and never on plant roots, and the opposite is true for plant parasites. A few kinds of nematodes may feed on more than one type of food material, and therefore are considered omnivores. For example, some nematodes may ingest fungal spores as well as bacteria. Some members of the order Dorylaimida may feed on fungi, algae, and other animals.
Unknown. Since free-living nematodes have not been studied very much, the food habits of some of them are unknown. The microscopic size of these animals presents additional difficulties. For example, it can be very difficult to distinguish whether a nematode is feeding on dead cells from a plant root or on fungi growing on the cell surface. Sometimes a nematode showing this feeding behavior may be classified simply as a root or plant associate.
Free-living nematodes are very important and beneficial in the decomposition of organic material and the recycling of nutrients in soil. Nematode bacterivores and fungivores do not feed directly on soil organic matter, but on the bacteria and fungi which decompose organic matter. The presence and feeding of these nematodes accelerate the decomposition process. Their feeding recycles minerals and other nutrients from bacteria, fungi, and other substrates and returns them to the soil where they are accessible to plant roots.
There are 15,000 known species of roundworms, also known as nematodes, and another half a million roundworms waiting to be discovered and studied. That would make roundworms the second most diverse group of animals. The first would be arthropods. Certain species of roundworms can lay more than 200,000 eggs in one day. Most species of roundworms have separate sexes, but there are a few that have both male and female gonads.
Most parasitic roundworm diseases are transmitted to humans through soil. There can be thousands of roundworms in one handful of soil. The roundworms can be ingested by unwashed hand to mouth or the roundworms can enter through the skin. Some of the most common parasitic roundworms in humans are: Enterobius Vermicularis (Pinworms), Ascaris Lumbricoides (Large Intestinal Roundworms), Trichuris Trichiura (Whipworm), Necator and Ancylostoma (Hookworms), Strongyloides Stercolralis, and Trichinella Spiralis. Other roundworms affecting humans are: Dracunculiasis (Guinea Worm), Wuchereria Bancrofti, Brugia Malayi, Brugia Timori, Toxocara Canis, and Toxocara Cati. Wuchereia Bancrofti, B. Malayi, and B. Timori cause Lymphatic Filariasis (Elephantiasis). Toxocara Canis (dog roundworms) and Toxocara Cati (cat roundworms) cause a disease called Toxocariasis.
Once the eggs are ingested in the body, the roundworm larvae travels through the liver, lungs, and other organs. In most cases, these "wandering worms" cause no symptoms or apparent damage. It is when the larvae moves into the nerves or lodge themselves in the eye that they can cause permanent damage or even blindness. This condition is called visceral larva migrans.
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| Nematode Life Cycle |
Finally, make sure that you practice good hygiene habits after working with your soil and other gardening activities. After all, to better enjoy the outside and all your work is better out there than inside battling the disease that can come about once infected by those nematodes.
For more information:
http://www.dowagro.com/soil/products/tomatoes-se/attacking.htm
http://www.my-grape-vine.com/blog/the-role-irrigation-has-on-fungus-diseases-and-nematodes-in-vineyards/
http://classes.seattleu.edu/biology/biol235/hodin/nematodePriapulidGroup/nematodes/parasite.htm
http://www.fcps.edu/islandcreekes/ecology/predatory_nematode.htm
http://www.firehow.com/2011010923084/how-to-control-nematodes-in-a-vegetable-garden.html
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