As a “Labrador person,” I am fully aware of the irresistible draw between some dogs and water. I am also all too familiar with waterborne illnesses. Today, as many of us venture out with our pups to local parks and trails to relieve cabin fever, I want to remind you of a few waterborne illnesses that you should be mindful of as your pup makes a beeline for the water.

1. Giardiasis

Giardia is a protozoan parasite that causes an intestinal infection called giardiasis. Most dogs contract the giardia parasite from ingesting dirty water that has been contaminated by feces of another animal that carried the infection.

Once ingested, the giardia parasite travels to the dog's small intestine where they absorb nutrients and reproduce. The giardia offspring (called “cysts”) is then eliminated from the dog's body in feces. Giardia cysts can survive for months in a cool, moist environment.

It is estimated that approximately 50% of young puppies will experience giardiasis at some point during their puppyhood. As with most illnesses, puppies, seniors, and immunocompromised dogs are most at risk for developing more severe symptoms associated with giardia infection.


Symptoms of giardiasis include diarrhea that can have a very strong odor, mucus, or have a frothy quality. If left untreated for any period, giardiasis in dogs can cause dehydration and malnutrition which can lead to death.


Dogs with Giardia are usually treated with metronidazole for 7-10 days. Once treatment is complete, your vet will perform a second fecal smear to check for any remaining signs of the giardia parasite. If traces of the parasite remain, additional medications may be added to treatment.

Guarding Against Reinfection

Giardia is highly contagious and there is a possibility of spreading the disease to humans. Be sure to always wash your hands after picking up after your dog and clean up after them right away.

Once you have picked up their waste, disinfect the area using a bleach solution. You should also regularly wash your dog’s bedding, their bowls, and anything else that may come into contact with the parasite.

Cryptosporidiosis in dogs

2. Cryptosporidiosis

Cryptosporidiosis is caused by the protozoan parasite cryptosporidium. The parasite is most commonly contracted through ingestion of dirty water or food that has been contaminated with the feces of an animal with cryptosporidiosis.

Once ingested, the cryptosporidium cysts travel to the dog's small intestine where they release “spores” which are referred to as sporozoites. These sporozoites move into the outer layer of the cells in the intestine where they reproduce. These offspring then infect other cells where they produce male and female elements that fuse to create a cyst (think offspring).

This cyst then ruptures in the intestine and the lifecycle of the parasite begins again. While thin-walled cysts rupture in the intestines, thicker-walled cysts that do not rupture are eliminated in feces. These contaminated feces are then another source of infection. In a cool water environment, cryptosporidiosis cysts can survive for weeks.


Symptoms of cryptosporidiosis in dogs include diarrhea, fever, food intolerance, lethargy, exercise intolerance, weakness, and in serious cases, organ disease.


Dogs with cryptosporidiosis are usually treated by limiting food and providing fluids to avoid dehydration. In most dogs, once diarrhea subsides, symptoms resolve. Young puppies, older dogs, and immunocompromised dogs may experience more severe infection and require medication.

No single medication is consistently effective in treating cryptosporidiosis in dogs at this time, but various medications like Azithromycin, Paramomycin, and Tylosin have been beneficial.

Guarding Against Reinfection

Cryptosporidiosis is highly infectious and, like Giardiasis, it has the potential to spread to humans from dogs.

The same hygiene protocols should be carried out with cryptosporidiosis as are carried out with giardiasis, but the application of a bleach solution should be followed with an application of hydrogen peroxide because this parasite is particularly stubborn.

Schistosomiasis in dogs

3. Schistosomiasis

Schistosomiasis is caused by the parasite flatworms called schistosomes. The parasite is contracted when dogs walk through or swim in contaminated water and the worms penetrate the dog's skin.

Once ingested, the schistosomes travel to the dog's lungs and liver where they grow into adults. These adults travel through the veins run to other veins that connect to the intestines where they reproduce and lay eggs. The eggs then produce an enzyme that lets them penetrate through the intestinal veins and into the intestines.

These eggs are then shed in feces and if they come into contact with freshwater, the young parasite larvae hatch and search for a lymnaeid snail to infect. Once inside the snail, the larvae produce sporocysts that mature into larval flukes which then leave the snail and seek another host – your dog.


Symptoms of schistosomiasis in dogs include diarrhea, bloody diarrhea, vomiting, lethargy, anorexia, weight loss, increased drinking, and increased urination. Anemia may also develop and cause additional complications.


Dogs with schistosomiasis are usually treated with praziquantel at high doses for a short period or with fenbendazole for approximately 10 days with a follow-up treatment course in three weeks.

Guarding Against Reinfection

Schistosomiasis cannot be directly transmitted from another dog since infection requires the presence of larval flukes that emerge from water snails. To prevent the spread of schistosomiasis it is important to clean up after your dog immediately so that eggs are unable to continue their lifecycle.

Leptospirosis in dogs

4. Leptospirosis

Leptospirosis is caused by spiral-shaped bacteria called leptospires. The leptospire bacteria are most frequently spread through the water as well as warm wet soil via direct or indirect contact.

Merck Animal Health professionals advise that leptospires can enter the body through water-softened skin or the mucous membranes of the nose, eyes, or mouth. Once in the bloodstream, the leptospires travel to the kidneys and reproduce. They can also travel to other organs and tissues where they continue to multiply.

Leptospires in the dog's kidneys are expelled via urine. This urine then contaminates water or soil where it can infect other animals. Leptospires can be shed in an infected dog's urine for months following infection.


Symptoms of leptospirosis in dogs include anorexia, fever, weight loss, lethargy, depression, abdominal pain, diarrhea, vomiting, bloody urine, respiratory distress, and acute renal failure.


Dogs with leptospirosis are usually treated with Doxycycline or for fragile dogs, penicillin treatment may precede a two-week course of Doxycycline. Dogs that have recently been exposed to leptospirosis are also often treated with Doxycycline prophylaxis for two weeks. Supportive care may also be necessary in addition to IV fluids.

Guarding Against Reinfection

Leptospirosis is a zoonotic disease meaning that it can be passed from animals to humans, so it’s particularly important to wear gloves when cleaning up after your dog and to use strong disinfectant on any area where your dog has urinated.

A leptospirosis vaccine is also available for dogs in areas where leptospirosis has been seen and for dogs at high risk of contracting the disease. This vaccination should be given annually when necessary.

Protothecosis in dogs

5. Protothecosis

Protothecosis caused by Prototheca spp. Algae. Infection with protothecosis in dogs is rare but occurs when the organism enters the body through wounds to the skin (cutaneous protothecosis) or through ingestion (systemic protothecosis).

Prototheca spp. Algae prefer warm and humid climates like those found in the southern United States. This alga is most frequently found in sewage, tree slime, and animal waste as well as in soil and water that has come into contact with these substances.

Protothecosis has a lifecycle very similar to that of cryptosporidiosis.


Symptoms of protothecosis in dogs include bloody diarrhea, vomiting, weight loss, inflammation of the eye, blindness, skin ulceration, thickening of the skin, lymph gland swelling, loss of muscle control, seizures, paralysis, head tilting, circling, and problems with gait.

Dogs with a compromised immune system are much more susceptible to protothecosis. Protothecosis can infect other animals and humans, but it is not spread between humans and animals.


Protothecosis is exceptionally difficult to treat and prognosis for dogs with this disease is grim. Treatments may include antifungal drugs and antibiotics which can slow down the progression of the disease. In the case of cutaneous disease, affected areas of skin may be surgically removed.

There is no “surefire” cure for this disease and rarely are treatments successful. When treatments do resolve symptoms, those treatments are required for two to four months and in some cases, they may be a lifelong requirement.

Guarding Against Reinfection

Protothecosis can spread through the feces of infected dogs, so you must wear gloves and pickup thoroughly after your dog as well as disinfect the area with a bleach solution.

Keeping Waterborne Illnesses at Bay

The best means of keeping waterborne illnesses at bay is to keep your dog away from stagnating and standing water. This type of water provides the perfect breeding ground for parasites and bacteria.

If you have a water-loving dog, try visiting areas with moving water instead or set up a dog pool in your backyard and fill it with fresh water on EVERY use and be sure to empty it fully after use.

Other things you should do to help to keep your dog free from waterborne illness include:

  • Staying on top of your dog’s monthly preventative medications.
  • Keeping your dog up to date on vaccinations and being aware of optional vaccinations that are recommended for your geographical area, for example, the Leptospirosis vaccine which protects against infection by Leptospira bacteria.
  • Keeping your dog away from animal feces (yes, goose poop, I’m talking about you!)
  • Do not let your dog drink from standing water.
  • At the first sign of gastrointestinal distress or symptoms that may indicate parasite or bacterial infection, take your dog to the vet immediately. The longer parasites and bacteria are left untreated, the more damage they can cause to your dog’s internal organs and their overall health.

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Diana currently lives and works in London, UK and she's been an animal lover and dog owner since she was a child. After graduating high school, she focused on getting her degree in English to become a writer with a focus on animals, pets and dogs.