Giardia in dogs and cats

The Giardia Parasite: Symptoms and Treatment

Introduction

If your (young) dog or cat develops diarrhea, there can be many causes. It could be food sensitivity, a gastrointestinal virus, bad bacteria, or an intestinal parasite. Giardia falls under the latter category. It is a very small intestinal parasite that can be found worldwide. There are many different types and subtypes, which usually infect only a few or even just one species of animal. Therefore, infected dogs and cats typically cannot infect each other, but in some cases, they can. In very rare instances, the parasite can even transfer to humans.

The Giardia parasite looks quite funny: it has multiple tails and seems to have two eyes. With its whip-like tails, it moves around in the intestines of an animal. A mature, moving Giardia parasite can only survive in the intestines of a dog or cat. To survive outside the host, it exits the animal in a cyst along with the stool. This cyst can remain infectious for a long time, especially if the environment is wet and cold. In warmer temperatures and dry climates, the cysts dry out faster.

Infection

The moving Giardia parasites sometimes exit the animal with the stool, but they are not usually the cause of most infections. The cysts are mainly responsible for transmission; they can survive for a long time. They are also excreted in the stool.

A study from the United States shows that 5 to 15% of cats and dogs are infected with Giardia, especially younger animals under 6 months of age. Shelters are also notorious places for Giardia. There are so many animals together that this parasite can easily spread, and Giardia is very contagious. Good hygiene is therefore even more important in such places.

An animal infected with Giardia does not always show signs of illness. Only half of the infected animals develop diarrhea. The other half may be infected without showing symptoms and can also transmit the parasite. The most common route of infection is by eating food or drinking water contaminated with cysts. Each cyst contains two Giardia parasites, which break out when they reach the gastrointestinal tract. They are not fully mature at first and grow a bit more before moving around or attaching to the intestinal wall. What happens next is quite remarkable: an adult parasite can split into two, producing more of the parasite. Before leaving the intestines, two parasites enter a cyst, which is excreted in the stool and can infect other animals (or the same animal again).

How the parasites cause illness in dogs and cats is still not fully understood. One theory is that they produce toxic substances, disrupt the gut flora, and induce inflammation. This damages the gut’s ability to absorb nutrients, leading to diarrhea.

Symptoms

Half of the infected animals show no symptoms. The other half (mainly younger animals) may show the following signs:

Abdominal pain: which can range from mild discomfort to severe cramps
Diarrhea: usually mushy to watery, very foul-smelling, slimy, sometimes a bit greasy, and may contain blood
Weight loss: especially if the animal has been sick for a longer period
A dull coat and a generally sickly appearance
They usually do not have a fever!

Diagnosis

If a dog or cat becomes sick and develops diarrhea, they may have Giardia. A veterinarian can determine if this is the case or if there is another issue. The vet will first ask about the animal’s symptoms and perform a physical examination. It is important to palpate the abdomen well. A dog or cat with Giardia often experiences abdominal pain, which may cause them to tense their abdominal muscles or whine when the vet presses on the abdomen. There may also be a lot of gas in the intestines, making the abdomen feel very bloated. The sounds from the intestines may provide more information, and these can be heard using a stethoscope.

This examination alone cannot definitively diagnose the problem, but it will guide the veterinarian in the right direction. Blood tests or X-rays typically do not reveal clear abnormalities that would immediately suggest Giardia. The best approach when Giardia is suspected is a stool test. With a quick test on a stool sample, it can be clarified within 10 minutes why the dog or cat has diarrhea. To get the most reliable results, stool should be collected over 3 days. The Giardia parasites are not always excreted in the same amounts each time, so the parasite might be missed if only one stool sample is tested.

Other tests include microscopy and a PCR test. In microscopy, a stool sample is examined under a microscope; however, the parasite may be easily missed. A PCR test also uses stool samples and measures the DNA of the Giardia parasite. This test is very sensitive because the parasite does not need to be intact.

Treatment

If a dog or cat is infected with Giardia and becomes ill, treatment is necessary. The animal cannot get rid of the parasite on its own. Even in animals without symptoms, treatment may be chosen to prevent them from becoming sick or to avoid spreading the parasite to others. The treatment aims to stop diarrhea and kill the parasites. This can be quite challenging. The parasites may be very strong, or there may be additional infections, such as other parasites or bacteria. There are several medications available to combat the infection(s), and sometimes a combination of medications or trial and error is needed before the animal fully recovers.

Supporting treatments include fiber-rich food, and there are medications to thicken the stool, preventing dehydration and weight loss. In severe cases, an animal may need an IV if it is very dehydrated, especially in very young or very sick animals.

All animals that have been in contact with an infected dog or cat or live together with them in the same house must be treated simultaneously. Otherwise, a different animal will get infected, becoming a new source of infection. A dog or cat does not become immune to Giardia, so they can get reinfected. They can also reinfect themselves. It is crucial to thoroughly clean (and disinfect with bleach or ammonia) the environment. This means cleaning and disinfecting all surfaces where the animal goes, washing their bedding and toys at 60 degrees, and, of course, cleaning their food and water bowls and litter box. Items that cannot be washed or cleaned with soap can be disinfected with a steam cleaner. Animals that have been soiled with feces should be bathed.

Prognosis

Most animals recover completely. The prognosis is therefore good. Giardia is rarely fatal, except if an animal is sick for a long time, and diarrhea is not addressed. Very young animals are at higher risk in these cases. It is also possible for an animal to become a carrier of the parasite. In this case, the parasite remains in the animal’s intestines and is excreted in the stool while the animal often shows no or only mild symptoms. Once an animal becomes a carrier, it almost never fully clears the parasite. However, the animal can still live a normal life. It is advisable not to house them with other dogs or cats to prevent them from becoming sick or carriers. If this is unavoidable, it can be accepted, but it is not advisable to house very young animals with them, as they usually become much sicker.

There is often a chance that an animal will reinfect itself if there are still some Giardia cysts left in the environment. As a rule, an animal and its environment are considered Giardia-free if the animal’s stool is normal for three months. After this period, it is very unlikely that the dog or cat will become sick from the same parasite again or that any parasites will remain in the intestines and/or environment. However, it is always possible for an animal to get infected again later in life.

Prevention

As you can see, you’d rather prevent Giardia than treat it. Full prevention is nearly impossible, but here are a few tips:

Don’t let a dog drink water outside or from a shared water bowl.
It’s wise (and almost everywhere required) to clean up after an infected dog immediately.
For cats, it becomes trickier if they are allowed outside.
If a dog or cat gets infected, it is best to treat them as quickly as possible to reduce the chances of them becoming carriers. However, this is not always preventable.
In Humans

Humans have their own species of Giardia, but it is occasionally possible for a person to become infected by their own dog or cat. The symptoms are similar, and it can make you quite sick. Therefore, it’s smart to wash your hands thoroughly if you’ve petted a pet with Giardia or cleaned up their stool.