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Giardia and Coccidia: Two Dangerous Parasites

Cats and Dogs can be seriously affected by two dangerous parasites known as giardia and coccidia

How Giardia and Coccidia can cause major problems for your pets

Giardiasis and coccidiosis (also known as Giardia and Coccidia) are two dangerous parasites that exist in the intestinal tract of cats (mainly kittens) and dogs. The diseases can affect can affect a range of 5-15 percent of cats and dogs.

These intestinal parasites are transmitted through infected feces, exposure to infected animals or tissue, or through environmental contamination. The infections are protozoan parasites, with Giardia being specifically zoonotic (meaning that it can spread between animals and people), and cause similar infections.

While these two dangerous parasites, Giardia and Coccidia, can cause diarrhea, eventually leading to bloody stool and dehydration. Once the parasites are ingested, they move into the gastrointestinal tract, become mature, and settle in the intestine. After taking root in the intestines, inflammation can occur, which has a tendency to become life threatening, even though both diseases are treatable.

It should be noted that only Coccidia can spread to humans. Humans are actually more susceptible to contracting it from drinking untreated water, from lakes and streams.

If you have a multi-pet household (with a dog and a cat) they can both fall victim to these two dangerous parasites, Giardia and Coccidia, but they cannot pass it to one another. Cats and dogs are affected by different strains, so an infected dog poses no risk to a cat, and vice versa.

What is Giardia?

Giardia is a one-celled parasite species that can affect humans and animals through an intestinal infection, referred to as Giardiasis. Giardia is more common in kittens, and adult cats with compromised immune systems. It’s also very common in heavily populated places such as animal shelters.

Giardia Symptoms

While most cats and dogs infected with Giardia are asymptomatic, there exists specific symptoms that indicate its presence. It should be noted that these symptoms can also present as other diseases such as irritable bowel disease and even cancer. The most prevalent symptom is chronic diarrhea, which tends to be smelly, soft, pale, mushy and may have traces of mucus.

Other symptoms may include nausea, gas, vomiting, weight loss, lethargy, and dehydration.

Keep in mind that Giardia’s symptoms are not immediate. In fact, the parasite can be intestinally hosted for up to several years, before it is passed on. It’s not a life threatening affliction, but it can be very dangerous to dogs, kittens, older cats, as well as cats with a weakened immune system.

As giardia is asymptomatic, be sure to have any new cat or dog additions to your home tested for it. This should also be the case if your cat or dog spends any time outside, where it’s more likely to be contracted.

How Cats and Dogs Contract Giardia

Giardia will go through two stages. First is a motile stage (which means that it can move freely) and then a cystic stage. It’s during the cystic stage where the organism is able to transmit between hosts.

The cysts are often removed in the feces of an infected animal. They are able to thrive for several months, especially if there’s plenty of dampness and humidity outside. The cysts can be found in contaminated water or infected feces. Once ingested, giardiasis can occur as the cyst will take root in the animal’s intestines in order to feed. This is where the numerous symptoms start to occur. It can take up to 16 days for the cysts to pass in the cat’s waste.

Diagnosing Giardia in Cats and Dogs

Having a stool sample tested by your Austin vet will help determine if your pet is affected by giardia. The parasites are often visible in the stool, but, multiple samples may need to be analyzed to determine if there is an infection.

Your vet may perform a fecal flotation test, or a fecal smear test. For the fecal flotation test, the cat’s stool is put in a container with a solution, which causes any present Giardia eggs to float to the top. Here they can be collected and studied. The fecal smear test is a diagnostic test that checks for bacteria, parasites and any other organisms to help determine what may be causing diarrhea.

Treating Your Pet for Giardia

Should your cat or dog test positive for Giardia, it can be treated. Most vets will prescribe Fenbendazole, a deworming medication which can help reduce cyst shedding. This medicine is given orally over the course of five days, and it’s safe for pregnant cats. Another medication is Metronidazole which is more effective in cats than in dogs. The treatment lasts for up to seven days, and it is not safe for pregnant cats.

Some Giardia strains can be resistant to these medications, so it may be hard to eliminate it entirely. If this is the case, then your vet may have to resort to using additional medications to help stop it.

It’s also crucial to make sure that your cat is eating a low-residue diet (food with high digestible protein and low fiber) to help harden their stool. Having plenty of fresh, clean water will also help to prevent dehydration caused by diarrhea and excessive vomiting.

Clean Your House and Your Pets

Keeping your pets clean through this experience is also important. Give them a bath (if they let you) to check for any parasites and to ensure there is no fecal residue hiding in their fur.

Always keep their food and water dishes clean, and if you have a cat, make sure you scoop out the litter box and keep it clean after they go to help prevent its spread (always wear gloves when doing this, so you can avoid contracting it.)

  • removing any cat or dog feces from your yard…bag it and toss it.
  • try to limit your pet’s access to any outdoor areas such as trails and parks while they have giardia, to help prevent it from spreading.
  • if you have pools of standing water in your property, do your best to remove them. Get rid of any open containers, and use dirt to fill in puddles if at all possible.
  • keep your pets indoors and away from any contaminated water.
  • clean your house on a constant basis to prevent any additional bouts of giardia from occurring.

Is Giardia contagious to humans or other pets?

Giardia is highly contagious between cats, and transmission is also possible between cats and dogs. The exact strain found in humans is not the same as the one found in cats, but it’s always better to play it safe and assume there is a chance of contracting it, even if that chance is limited. So take the necessary precautions when handling an infected cat or dog, as well as when you’re cleaning up the cat’s litter box, food and water bowls, and toys.

What is Coccidia?

Like giardia, coccidia are parasites that live in the intestines. Coccidia is fairly common in dogs and cats, usually affecting puppies and kittens. A coccidia infection can cause severe disease and even death, especially in kittens and puppies, while some infected animals show no symptoms at all.

Coccidia are are single-celled organisms (protozoa), so they aren’t worms and can’t be killed with deworming pills. There are different types of coccidia that can infect different animals. For example, Isospora is the variety of Coccidia that infects dogs and cats, but it doesn’t seem to affect humans.

Coccidia can only cause issues within their own host species, meaning that dogs with are able to spread it among other dogs. The same goes for cats that are affected with it; it can only be spread among cats and no other species.

How Coccidia is Spread Among Dogs

Feces is the main culprit is spreading coccidia among dogs. As our pets like to eat everything, by consuming contaminated soil, feces and whatever else they encounter, is a key factor in how the disease spreads. Consuming small animals such as insects or mice can help transmit the disease, especially if they’re infected with Isospora organisms.

Once Coccidia makes contact with the feces, the infection is not immediate. The parasites are initially nonsporulated, meaning that they aren’t at full maturity. Once the cat or dog defecates outdoors and it’s had time to fester, then it becomes mature or sporulated, which has the ability to affect other animals who make contact with it. Sporulated coccidia do not die off right away; they can live up to a year outside.

Coccidia Symptoms

Once the mature coccidia are ingested, they unleash additional stages that can infest the animal’s intestines. It is this damage to their intestinal cells that wreaks havoc on their system and produces the various symptoms, including:

  • Diarrhea
  • Weight loss
  • Loss of appetite
  • Vomiting
  • Death (in severe cases)

Puppies, kittens, and adult animals with compromised immune systems are at the highest risk of developing coccidia.

Diagnosing Coccidia

Coccidia are diagnosed by examining a stool sample under a microscope. Unfortunately, sometimes an infected animal may have what’s called a false-negative test result (where no coccidia is apparent although the animal is infected), so repeated fecal tests may be needed to narrow down what’s causing the illness. Coccidia can also exist in the feces of animals that show no symptoms.

Coccidia Treatments

Coccidia can be treated with medication, primarily sulfadimethoxine, an antimicrobial medication that is used to treat numerous infections. Full treatment can last from a few days to a few weeks, depending on how severe the infection is.

During treatment, it’s important to keep your home as clean and sanitary as possible. Steam cleaning floors and carpets can play a major role in preventing the chance of re-infection, especially if you have both cats or dogs.

Also in regards to other medications, treatments that kill hookworms, roundworms, and other pet parasites do not affect coccidia. Flea, tick and heartworm preventive treatments also do not remove or prevent coccidia.


Because coccidia in stool take several hours to become effective, it’s crucial to remove any feces (inside or outside) to help prevent the spread of infection. Keeping your pets inside will help reduce and eliminate any chance of exposure and infection. Make sure your dog or cat, especially if they’re very young, has a periodic fecal test by your Austin vet.

Why Giardia and Coccidia are Dangerous to Kittens

Unfortunately, these two dangerous parasites, giardia and coccidia, are common in kittens during their weaning stage. If the mother is infected, she can actually pass the infection to her kittens through her milk. Most kittens tend to respond well to treatment and slowly improve. As they grow and develop a stronger immune system, they will reduce the chance of falling victim to these parasites.

In the case of giardia, this is not usually life-threatening, however it can affect kittens, older cats, and cats with immunity issues caused by Feline Immunodeficiency Virus (FIV) or Feline Leukemia Virus (FeLV) infections. Dogs and cats can actually be asymptomatic carriers, without ever showing any symptoms or signs, whereas younger animals may show some clinical signs.

While Giardia and Coccidia can be treatable, these two dangerous parasites should not go untreated. Please contact ATX Animal Clinic if you suspect that your cat or dog is showing any of these symptoms, or if you think that they may have contracted giardia or coccidia.