Cryptosporidiosis in Dogs

What is cryptosporidiosis?

Cryptosporidiosis is a gastrointestinal infection in humans and animals caused by a microscopic, one-celled parasitic organism called Cryptosporidium. The parasite occurs worldwide and can be found in water, food, soil, or any other contaminated surface. Cryptosporidium is a very small form of coccidia.

Cryptosporidium can cause illness in animals and people, especially watery diarrhea. However, most dogs and people infected with Cryptosporidium do not have any signs of illness.

How do dogs get cryptosporidiosis?

Dogs get cryptosporidiosis when they eat something contaminated by Cryptosporidium, including feces, prey animals, water, and food. Cryptosporidium lives in the intestines and sometimes in the stomach of infected animals and people (the hosts). 

When Cryptosporidium reproduces inside the host, it creates two different kinds of oocysts (small “packages” of the parasite). One kind is thin-walled and further infects the host intestine; the other is much thicker-walled and is released into the environment in the host’s feces.

When an animal ingests an oocyst, the package opens and the parasites infect the intestinal cells, starting the process again in a new host. Thick-walled cysts can be difficult to filter out of water due to their tiny size, and they are extremely resistant to environmental stress. They may survive steaming, freezing, thawing, drying, or exposure to chemical disinfectants. As few as 10 oocysts can cause illness in people or pets.

What are the clinical signs of cryptosporidiosis?

When Cryptosporidium is found in the stool of a healthy, adult dog that does not have diarrhea, it is generally considered a temporary, insignificant finding. However, in puppies and immunosuppressed adult dogs, Cryptosporidium could be life-threatening. Signs may include:

• Diarrhea (typically watery, yellowish, smelly, and may be chronic or random)
• Weight loss 
• Loss of appetite (anorexia)

How is cryptosporidiosis diagnosed?

Cryptosporidiosis can be difficult to diagnose because a routine fecal flotation test may fail to detect the tiny oocysts. Your veterinarian may recommend one or more specialized tests:

• Special stains may reveal the presence of Cryptosporidium in a stool sample.
• DNA testing can be so sensitive that it detects parasites that are unrelated to your pet’s clinical signs. 
• An ELISA test is available that detects specific Cryptosporidium proteins in a fecal sample, but it may not consistently detect the parasite.

Your veterinarian will interpret the test results, along with your pet’s clinical signs, and recommend appropriate treatment when needed.

How is cryptosporidiosis treated?

Most infections in healthy animals do not require specific treatment. 

• If dehydration or severe diarrhea is present, supportive treatment with medications (such as azithromycin, paromomycin, tylosin, or nitazoxanide) and intravenous fluids may be needed. 
• In severe cases, or if a patient is immunocompromised, antibiotics may be prescribed to try to control the infection, although no medication has been found to eliminate Cryptosporidium.
• A highly digestible diet, probiotics, and added dietary fiber may help resolve diarrhea more quickly. 
• Your veterinarian may recommend follow-up fecal testing and other testing, depending on your dog’s health status. 

Cryptosporidium oocysts can infect an animal immediately after they pass into the environment, so you should quickly remove and dispose of any feces. 

What is the prognosis for cryptosporidiosis?

The prognosis for cryptosporidiosis is good in most cases. Debilitated or geriatric animals, and those with incompetent immune systems, are at increased risk of complications.

Can my dog transmit cryptosporidiosis to me or my family?

It is possible, but the risk is generally low. The risk depends on the species of Cryptosporidium involved.

• Cryptosporidium canis, the species normally found in dogs, is very unlikely to cause disease in humans. However, people with weakened immune systems are at greater risk.
• Cryptosporidium parvum, the species normally found in cattle, is more likely to cause disease in humans. It can also spread between people and between people and animals. Dogs may be able to spread this species to humans, but this has not been proven. 
• Cryptosporidium hominis infects people only.

If your dog is diagnosed with cryptosporidiosis, it is essential to clean and disinfect their environment and practice good personal hygiene to reduce the risk of accidental spread. Wash your hands thoroughly with soap and water, as alcohol-based hand sanitizers are not generally effective against Cryptosporidium. People with weakened immune systems, including those with AIDS or cancer and those undergoing chemotherapy, should use extreme care, especially when handling feces or administering medications.

Decontaminating the environment can be difficult because no disinfectant is completely effective against Cryptosporidium. A 3% hydrogen peroxide solution may be the most effective option when it is left on surfaces for 20 minutes before rinsing. Follow your veterinarian’s instructions and the directions on the product label. Your veterinarian may also recommend applying bleach before hydrogen peroxide, but make sure the bleach is thoroughly rinsed off before you apply the hydrogen peroxide. Never mix bleach and hydrogen peroxide.