Giardia & Toxoplasmosis: Common Protozoan Parasites Seen in Dogs and Cats

Many pet owners will have heard of the condition Giardia and/or Toxoplasmosis, but are unfamiliar with what these infections exactly are, what symptoms they give, and how they can be prevented. Giardia and Toxoplasmosis are caused by protozoan parasites. Protozoan parasites are not worms, bacteria or viruses, but a one-celled parasitic species. So let’s have a closer look at these common Protozoan Parasites seen in cats and dogs.

Giardia Lamblia / Giardia

Giardia Lamblia is a common protozoa parasite seen in cats and dogs and will lead to an intestinal infection named Giardiasis, also called Giardia. Dogs and cats aren’t the only animals that can get Giardia, it’s also seen in other animals and humans can also get infected. Giardia Lamblia has two forms, a fragile feeding form living in the intestine of the infected animal, and a hardy cystic form which is shed in the faeces. This cystic form can live up to several months in the environment. 

Dogs and cats that get infected with Giardia don’t always show symptoms. If they do show symptoms these are usually foul smelling diarrhea or vomiting. A Giardia infection may also lead to weight loss, intermittent diarrhea (diarrhea that comes and goes) and fatty stool. Stool may have a greenish color and occasionally may contain blood. Giardia is usually not life-threatening, unless the animal is very young, very old or immunocompromised. Pets can carry and transmit the infection without developing symptoms themselves.  

Infection with Giardia happens when a pet comes into contact with contaminated soil or water. The cysts get ingested, and when a pet is susceptible (often seen when already sick and/or stressed), the cyst will transform into its feeding form and attach itself to the intestine wall of the animal to feed. The more cysts in the environment of the animal and the more cyst ingested, the higher the risk will be of developing the infection. Giardia outbreaks are often seen in settings like shelters because animals usually are already stressed, and the density of animals is high which can lead to more cysts in the direct environment.

Positive rapid test for Giardiasis 
Positive rapid test for Giardiasis 

Giardia can be treated with medication. Alongside the medication a strict cleaning and hygiene protocol will need to be followed to prevent reinfection from cysts that may have gotten into the environment. Clean up the stool of your pet straight away. Also bathe your pet regularly to remove any cysts that might have gotten stuck into their fur. Wash their bedding regularly and clean their living area. For disinfection of the environment you can use chlorine bleach at a dilution of 1:32 or 1:16, or 1 to 2 cups in a gallon of water (60-120 ml/L). Make sure to dry area’s well as Giardia cysts are vulnerable to drying. Prevention of Giardia is through proper hygienic measurement like cleaning of the environment, bathing of the pet when infected, and hand washing for humans to prevent the ingestion of contaminated material like soil, food or water.

Toxoplasma Gondii / Toxoplasmosis

The disease Toxoplasmosis is caused by the one-celled protozoan parasite Toxoplasma Gondii.  Toxoplasmosis is an infection that almost all warm-blooded animals can get, including our dogs and cats. Humans can also get infected with toxoplasmosis and the infection is dangerous when pregnant as it can infect the foetus in utero. When a foetus gets infected this can lead to hearing and vision loss, and developmental disabilities later in life. Most healthy adults will not develop any health problems when infected unless immunocompromised.

Unlike the cat who is a primary host, dogs and humans can contract the infection but do not shed the Toxoplasma Gondii oocysts in their faeces. They are a so-called intermediate host. Intermediate hosts do not shed the cysts in their stool, but can pass on the infection if their infected meat is eaten. This way of transmission is seen if cats eat infected rodents, or if we consume infected under cooked meat from livestock. 

An infection with Toxoplasma Gondii rarely leads to symptoms in healthy adults, unless the disease toxoplasmosis develops. This is often the case in very young animals or animals that are immunocompromised. The most common symptoms of toxoplasmosis are lethargy, loss of appetite and fever. Other symptoms may occur depending if the infection is chronic or acute, like pneumonia, jaundice, blindness, personality changes, circling, head pressing, difficulty eating, seizures, and incontinence. 

Toxoplasmosis can be treated with antibiotics. Prevention in humans can be achieved through hygienic measurements like washing hands, cleaning stool in litter boxes straight away, and making sure food that is eaten is properly washed or heated. When pregnant, prevent cleaning litter boxes if possible. In pets prevention is achieved through hygienic measurements like removing stool in a timely manner and prevention of eating contaminated meat like rodents.

Important note regarding toxoplasmosis and being pregnant

Some people consider placing their cats for adoption once they are pregnant or wish to get pregnant because of the risk toxoplasmosis poses/will pose to their unborn baby. This is totally unnecessary as the chance of picking up Toxoplasma Gondii from your cat is incredibly small, even more so if they are an indoor cat only. Indoor cats won’t have access to infected rodents or will come into contact with contaminated soil or faeces. 

Cats that do get infected only shed the T. Gondii oocysts for a very short time after infection (2 weeks) and in almost all cases at only the first time of being exposed to Toxoplasmosis Gondii. The chance your cat will pick up their first infection in the exact time frame you are pregnant is small.

It also takes 24 hours for stool that has the oocysts to become infectious. By removing stool from your cat straight away, wearing gloves and washing hands, you can greatly minimise the risk of an infection. Cat bites, scratches and stroking of the fur of an infected cat are very unlikely ways of picking up an infection as this is not where the parasite is carried. 

The main source of infection with toxoplasmosis for humans is through eating infected under cooked meat and consuming insufficiently washed infected fruits and vegetables. Another common way to pick up an infection is through gardening without gloves and insufficiently washing your hands afterwards. 


Through this article we hope to have informed pet owners about Giardia and Toxoplasmosis in pets, how to recognize an infection, and what can be done to prevent a (re)infection. We also hope we have cleared up some confusion that some people may have about toxoplasmosis in relation to being pregnant. 

If you would like to know more about our pet care services feel free to contact our team. They will be happy to help.

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