Giardia: When Nasty Parasites Happen to Good Dogs (And Sometimes Cats)

A couple of weeks ago, I had an exchange with a friend that went something like this:

Friend: My dog is vomiting a lot. She’s had some pretty nasty diarrhea off and on over the last couple of weeks, and while we don’t think she’s eaten anything toxic or anything that could be causing a blockage in her digestive system, she does love to sample a lot of puddle water – and we’ve had quite a lot of this lately, since the snow has started to melt.

Me: Ohhhh this really sounds like giardia. Better get puppers to the vet asap!

This is a very simplified version of the conversation we had, but the main points are worth noting: dog is presenting with quite a bit of vomiting, has had some nasty bouts of diarrhea, and drinks from puddles. All of this put me in mind of something I learned well as a vet tech: there are certain times of the year when you will see a lot of patients showing up with giardia infections. Early spring is one of those times, as snow begins to melt, and then forms large puddles that take a long time to dry up. The problem is exacerbated as temperatures rise, and rain begins to fall, providing an environment of continually puddling water that allows parasites to thrive. Your pet might spy one of these puddles and give thanks for the delicious watering hole that they’ve discovered (yuk), but the results of consuming this water can be fairly awful, and make for a pretty sick fur child.

Giardia cyst. Credit:

Giardia is a parasite that loves a nice wet environment to hang out in. Seen under a microscope, giardia will show up as either cysts (roundish egg shapes) or trophozoites, organisms which (famously, in veterinary circles) look like tiny little aliens or perhaps deep sea creatures. Either form, when it is living inside your dog or cat (or you – more on this in a moment), will cause your pet to get really, really sick. Symptoms are pretty much exactly as described above – there is lots of diarrhea, which will often be bloody or full of mucus, and your pet may vomit. The vomiting is one of the reasons your vet might suspect giardia more than other types of parasitic infection; for whatever reason, this bug often causes a lot of nausea that shows up not just in the form of your pet having a poor appetite, but in profuse vomiting. Because of this, pets can lose body fluids and become very dehydrated quite quickly with giardia, causing them to feel worse, and making it more urgent that you don’t delay in seeking medical assistance. Further reasons for concern: giardia is easily spread and is a hardy parasite that can be difficult to kill, meaning that other pets in your home can easily become infected – and so can you. Giardia affects humans as it does our pets, so make sure that you are scrubbing your hands well and thoroughly laundering any soiled blankets, towels, etc. in your home.

Giardia trophozoite. Credit: schmidty4112 via flickr

The good news about giardia: diagnosis of giardiasis is usually routine, and treatments for this parasite are simple, highly effective, and relatively inexpensive .Your vet will first need a stool sample from your pet to confirm that giardia is present. Analysis of the stool sample, called a fecal analysis, also allows your vet to rule out any other parasites your pet may have picked up. You can help the vet tech who will run this test to find these little giardia beasts by providing the nastiest sample your pet produces. (For example, if your dog has diarrhea and some of the poop contains blood and mucus but some of the poop does not, bring the more disgusting looking sample in for testing. The worse the sample looks, the more likely it is to have ample amounts of parasitic organisms for your vet tech to discover.) Once giardia is confirmed, your vet will prescribe an antibiotic that will kill the parasite and halt the diarrhea. Pro-tip: do NOT administer over-the-counter medications to your pet until your vet has been able to examine him or her. Doing this can cause much more trouble for your pet in the long run, and it can limit the medications that your vet can safely prescribe. Anti-nauseant medication may also be prescribed, and depending on how dehydrated your pet is, a course of subcutaneous fluids may be injected under the skin. This will help your pet to replenish body fluids, which goes a long way towards making them feel better overall.

Your vet may recommend a brief time of fasting for your pet, until the prescribed medications have a bit of a chance to do their work. You will then be able help your pet to heal by feeding a very bland diet made up of small, frequent meals, for several days. There are a few different options for this type of diet, but the best loved and most common is a mixture of rice and chicken. Make sure the rice is plain, white rice, and that chicken is breast meat, broiled or baked with skin removed and nothing added to it. You want to make up a diet that is bland and low in fibre, so that you can provide good nutrition to your pet, but also rest the gut somewhat as it heals.* Once your pet is having solid bowel movements and is no longer vomiting, you can begin to slowly transition them back to their regular diet, over the course of several days.

Drinking clean water like a good doggo. Credit: Pixabay

To prevent your pet from developing giardiasis, avoid areas with free-standing water, particularly during early spring, when melting snow creates large puddles that do not dry out quickly. If you cannot avoid these areas, try to prevent your pet from drinking this water, or from licking it off their paws. A quick rinse of the feet when you come back into your house can prevent giardia from causing a major problem in your home! If you’re going to be outside for any great length of time, bring fresh water with you for your pet to drink. Additionally, I would add that it’s a great idea to avoid dog parks or other areas where many pets might congregate or pass by during this time of year. If a dog with a giardia (or other) infection comes out to play, it can easily spread infection to any other animal that comes to play. Many of my former patients would notice the onset of symptoms after visiting their local dog park, especially during the earlier spring months. (It’s also important to note that dog parks often provide an ideal environment for the spread of illness in general, and this can happen at any time. Infectious organisms can exist pretty much anywhere, it’s certainly easier to avoid them by staying away from high traffic areas like the dog park.)

*This diet is great for both cats and dogs; however, many cats do not respond well to home cooked foods. If your cat will not eat food you have prepared, speak to your veterinary staff about a bland canned food diet that they would recommend. Every vet clinic will have a couple of different options for a chicken and rice diet that your cat can safely eat while they recover. As always, if your pet has any particular dietary special needs, speak with your vet about what to feed them.