Article written by Dr Cait Hope, SASH Tuggerah Emergency Clinician Lead.
Coccidia is a microscopic intestinal parasite that can cause serious illness—especially in puppies and dogs with weakened immune systems.
In this article, we’ll explore what Coccidia is, how dogs become infected, the symptoms to watch out for, and how it’s diagnosed and treated. We’ll also explain how contagious it is, whether humans are at risk, and how you can help protect your dog from this common but potentially dangerous parasite.
What is Coccidia in Dogs?
Coccidia are microscopic, single-celled parasites that live in the intestinal lining of dogs. Infections caused by these parasites are known as coccidiosis.
Coccidiosis typically refers to gastrointestinal infections with Cystoisospora (previously known as Isospora) spp. At least four different genera of coccidia can infect dogs:
- Cystoisospora canis
- C. ohioensis
- C. neorivolta
- C. burrowsi
These parasites invade and damage the intestinal cells, potentially disrupting digestion and nutrient absorption.
While many dogs may carry Coccidia without showing any signs (called subclinical infections), young puppies, senior dogs, and those with weakened immune systems are more likely to develop clinical signs, such as diarrhea, dehydration, and vomiting. If left untreated, severe cases can be life-threatening—especially in vulnerable dogs.
Stress, concurrent infections, overcrowding and/or unsanitary environments may also contribute to infection risks.
How Do Dogs Get Coccidia?
Dogs become infected with Coccidia by ingesting the immature form of the parasite, called oocysts. These are shed in the faeces of infected animals and can survive for long periods in the environment. Oocysts must “sporulate” in the environment to be infective.
Sporulation can take from 8 hours to 2 days, and cannot occur in temperatures >45*C. If a susceptible dog ingests the sporulated oocysts, the oocysts will release ‘sporozoites’ that invade the intestinal lining cells and set up a cycle of infection in neighboring cells.
Common Ways Dogs Can Contract Coccidia
- Ingesting contaminated faeces: This is the most common source, particularly in shared areas like parks, kennels, or shelters.
- Contact with contaminated soil or surfaces: Oocysts can remain infective for weeks or months on the ground, in grass, or on objects.
- Grooming themselves: Dogs may lick their paws or fur after walking on contaminated ground.
- Drinking contaminated water or eating infected food: Shared or unclean water bowls and food sources can transmit the parasite.
- Eating infected prey: Mice and other small animals can carry Coccidia, and hunting or scavenging dogs may become infected this way.
Symptoms of Coccidia
Not all infected dogs will show signs of illness, but when symptoms do appear—particularly in puppies or immunocompromised dogs—they can include:
- Watery or bloody diarrhea
- Dehydration
- Weight loss
- Lethargy
- Abdominal pain or bloating
- Vomiting (in more severe cases)
- Loss of appetite
Severe infections can lead to serious complications, especially in young or fragile dogs, and may even be fatal if not treated promptly.
Many dogs that are infected with coccidia do not have any clinical signs. When the coccidial oocysts are found in the stool of a dog without diarrhea, they are generally considered a transient, insignificant finding.
How is Coccidia Diagnosed?
Diagnosing Coccidia usually involves a veterinary faecal examination (faecal float), where your vet will analyse a stool sample under a microscope to check for Coccidia oocysts. Sometimes clinical disease can occur before oocyst shedding, so repeat faecal exams may be needed, especially if symptoms persist.
Diagnosis is straightforward but must be done quickly to avoid progression of the infection—especially in high-risk dogs.
Healthy dogs may pass oocysts in faeces, so a positive result doesn’t necessarily indicate cause of disease.
Treatment for Coccidia in Dogs
If your dog is diagnosed with coccidiosis, treatment may involve:
- Antiprotozoal medication: Prescription drugs like sulfonamides or triazines are commonly used to eliminate the parasites.
- Rehydration support: Dogs with significant diarrhea or vomiting may need fluids, either orally or intravenously (via a drip). Severely anaemic patients may need a blood transfusion.
- Repeat treatments: In some cases, a second course of medication may be required if symptoms return.
- Environmental cleaning: To prevent reinfection, clean your dog’s environment thoroughly. Disinfect hard surfaces with a diluted bleach solution and wash bedding, toys, and food bowls.
Is Coccidia Contagious With Other Dogs?
Yes, Coccidia is highly contagious to other dogs. Infected dogs can shed oocysts in their stool, which can then infect other dogs that come into contact with contaminated surfaces or faeces.
Puppies, kennelled dogs, and dogs in shelters are especially vulnerable due to close contact and shared environments. Prompt diagnosis and isolation of infected dogs help reduce the risk of spreading the infection.
Is Coccidia Contagious With Humans?
The types of Coccidia that infect dogs are generally species-specific, meaning they pose little to no risk to humans. That said, good hygiene practices are always important.
How to Prevent Coccidia
Prevention focuses on hygiene, routine checks, and reducing exposure to contaminated environments. Key prevention strategies include:
- Prompt removal of faeces: Pick up after your dog immediately to reduce environmental contamination.
- Disinfect living areas regularly: Use a diluted bleach solution to clean kennels, crates, and bowls.
- Avoid shared water bowls or food in public areas: Prevent your dog from drinking from puddles or communal dishes.
- Limit exposure to infected animals or areas: Be cautious when visiting places like shelters or pet boarding facilities.
- Prevent scavenging and hunting: Keep your dog from eating rodents or digging in contaminated soil.
What to Do if You Suspect Coccidia
If your dog is showing signs such as persistent diarrhea, vomiting, loss of appetite, or lethargy, it’s time to contact your vet. Even if the symptoms seem mild at first, Coccidia can quickly become dangerous—especially for puppies and older or immunocompromised pets.
Don’t wait to see if symptoms resolve on their own. Early veterinary intervention leads to a faster, more successful recovery and helps stop the spread to other animals.
Protect Your Dog from Coccidia
Coccidia is a common but potentially serious parasite that can severely affect young, old, or vulnerable dogs. Recognising the symptoms early—such as diarrhea, lethargy, or weight loss—and seeking prompt veterinary care can make all the difference.
If you’re concerned your dog may have Coccidia, don’t hesitate to get help. At SASH, our experienced veterinary team is available 24/7 to support your pet in any emergency or when your regular vet is unavailable.
Call us anytime, even if you’re unsure whether your dog needs to be seen—our friendly team is happy to guide you.
