Some people love the feel of the garden dirt in their hands as they weed or work the soil. Do you always know what's in the soil, or who's been there before you? Pets and wild animals often find garden soil a perfect ‘litter pan' and will deposit their ‘leftovers', sometimes burying them well so the evidence is not always clear. This animal fecal matter can contain all sorts of potential pathogens, but the most serious of which are the internal parasites some of these animals might be infected with. Though not all are zoonotic (contagious to people) some are and some are potentially very dangerous. The following article is a discussion of some of these potential problems one might encounter in their garden soils.
As a veterinarian I am often reminding pet owners to wash their hands after cleaning the litter box or handling their pet's droppings. We routinely deworm for a number of parasites that are common among pets, some of which are very important zoonotic creatures. Round worms, hookworms, tapeworms and a variety of protozoan parasites can be present in your pet's stools and some of these are problems if you happen to ingest them yourself. And wildlife such as skunks and raccoons can add their own mix of possible parasite zoonoses to the garden soils. Most of the time my comments to clients are directed at their children, as most adults are a bit more cautious and aware of animal fecal matter and much more likely to clean up after handling it. But children can end up playing in sand boxes or garden soil that was previous used by their cat, a neighbor's cat, the dog, or some other animal that was visiting the garden overnight. And some adults like to garden without gloves in areas of the garden these animals might have frequented. Just remember that your cat may have decided that your planters are a handy litter box.
Round worms, or Ascarids, are very common parasites in dogs, cats and some wild life. These parasites, as is true with all those discussed in this article, have a direct life cycle, meaning all one has to do is eat the eggs laid by the worm and the next host will get the infection (no intermediate host needed as is the case with some parasites). We routinely deworm all cats and dogs in my practice for this parasite as it is ubiquitous, particularly in nursing mothers and their puppies. Roundworms are not difficult to get rid of in a dog or cat, but their eggs are quite durable and can survive in the environment for a long time (years). All a dog or cat need do is ingest some stool or contaminated dirt (or lick off their paws after stepping in some stool) and they get the infection. Round worms travel about their bodies, hiding in lung or liver tissue, and then moving to the intestines to lay eggs and make more worms. This traveling through tissues in the proper host causes very little problems as the round worms have evolved to live relatively ‘peacefully' in the proper hosts. Human incidental ingestion of these eggs (from not washing hands properly, for example) can lead to something called visceral larval migrans. This is when the little larvae find themselves in the wrong host (us) and ‘get lost'. They can end up just about anywhere (liver, lungs, eyes or brain) and cause problems wherever they go. If they end up in the eye or brain, they can cause severe neurologic problems that can be very difficult to treat, and often cause permanent damage (blindness, brain damage etc.). Raccoon and skunk roundworms are just as bad if even not more dangerous, and these can do the same sorts of damage to our own pets as they do to us, as your dog, cat or rabbit are the incorrect hosts for those species (a good reason to try to keep raccoons and skunks out of your yard). So wash your hands well if you garden barehanded!
Hookworms are a common problem in the more humid climates of the US though occasionally they may be found in pets in almost any part of the world. These are also intestinal parasites with direct life cycles and are found most commonly in young puppies and kittens, or nursing mothers. These pose a slightly different problem when found in the soil. The eggs are not as serious a threat if ingested accidentally, but hookworm eggs will often hatch in soils and these first stage larvae (too small to easily see with a naked eye) can travel straight through skin tissue to re-enter their proper hosts (dog or cat) or their improper hosts (us). This sort of infection is called cutaneous larval migrans. It can cause a horrific urticaria (itching and inflammation) in the skin, and some species can get as far as our intestinal tract causing diarrhea and pain there as well. So to avoid this situation, one might consider working in the soil with garden gloves and not even use bare hands at all. If you do go bare-handed, wash your hands immediately. Those gardening in drier climates (such as in my own in southern California) have less to worry about with this particular parasite.
Most parasites gardeners should be concerned about are the ones that have direct life cycles (fecal-oral transmission); Round worms and Hookworms are spread from mother to babies primarily by nursing (and often in utero)
Protoazoan parasites can be zoonotic as well and the most infamous of these one can encounter in garden soil is Toxoplasma, a parasite potentially spread about in cat feces. Though this is not a very common parasite, it rarely causes much disease in the pet cat, so one might have no idea if their cat was infected or not, even if fecal exams were done regularly by your veterinarian. And even if you know your cat is not infected, stray cats can also get into the garden and bury their remains there. Toxoplasma is primarily a danger to pregnant gardeners as this parasite can cause abortions and miscarriages in the improper host (us). That is why one's veterinarian may insist on a pregnant client to not clean the litter box or dig about in the garden without gloves.
Giardia is a very common parasite all over the world and is infamous in causing severe diarrhea in travelers to foreign countries. There is still a lot of controversy whether dog and cat Giardia can cause disease in humans though the most recent publications are saying that it is not a true zoonotic disease. We humans have our own Giardia species which is very contagious to us, but it appears we are probably not susceptible to dog and cat Giardia. Still, many websites and sources of veterinary information insist Giardia is a zoonotic disease, so one should probably be safe than sorry when it comes to this one. Clean your hands if your pets are using the same garden soil you are digging around in.
Giardia is usaully spread about in standing water, and then it is later deposited in your garden or lawn
I am always digging out soil from under my nails and coming in from outdoors with dirt somewhere on my body. But I always clean my hands well before sticking them in my mouth, and I strongly recommend all you gardeners do the same, particularly if you have garden pets or wildlife. And dirt doesn't taste all that good anyway.