Toxoplasmosis in Dogs

Vladimir Negron
Feb 09, 2010
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Toxoplasma gondii Infection in Dogs

Toxoplasmosis infection is caused by a parasite called Toxoplasma gondii (T. gondii). It is one of the most common parasitic diseases, and is known to affect nearly all warm-blooded animals and humans.

Cats are recognized as the primary host, as the parasite completes its life cycle in the cat's intestinal tract, passing back into the environment through the feces. However, cats are not the only source of infection.

In the U.S., the main source for T. gondii transmission is raw meat and unwashed fruits and vegetables. Both acute and chronic forms of toxoplasmosis exist, where the chronic form is usually a low-grade disease without any clinical symptoms, and the acute form is more symptomatic.

Symptoms and Types

Cats are more commonly seen with clinical symptoms than dogs. Still, dogs can be made ill from this parasite, and may mimic other infections, such as canine distemper or rabies. At increased risk are young dogs with developing immune systems, and dogs that have impaired immunity. The following symptoms are known to occur in infected cats, and may also be seen in dogs:

  • Neurological symptoms
  • Seizures
  • Tremors
  • Depression
  • Lethargy
  • Uncoordinated gait
  • Muscle weakness
  • Partial or complete paralysis
  • Respiratory problems like shortness of breath
  • Fever
  • Weight loss
  • Loss of appetite
  • Vomiting
  • Diarrhea
  • Abdominal Pain
  • Jaundice
  • Inflammation of tonsils (tonsillitis)
  • Inflammation of retina (retinitis)
  • Inflammation of middle part of the eye including iris (uveitis)
  • Inflammation of the cornea (keratitis)


Dogs become infected through contact with the T. gondii parasite, which may be acquired from rooting in infected soil or from ingesting cat feces.


You will need to give a detailed history of your dog's health, onset and nature of symptoms, and possible incidents that might have precipitated this condition, such as contact with cat feces, or prevalence of feral cats in the yard space. Your veterinarian will perform a thorough physical exam to evaluate your dog's body systems and to evaluate the overall health of your dog. Routine laboratory tests -- such as a complete blood count, biochemistry profile, and urinalysis -- are also used to confirm infection.

For example, dogs with toxoplasmosis may show an abnormally low number of white blood cells (leukopenia), low neutrophils (neutropenia), and low lymphocytes (lymphopenia) in the complete blood count.

Conversely, during recovery, the complete blood count may reveal an increased number of white blood cells, an indication of the increased activity of the infection fighting white blood cells.

The biochemistry profile usually reveals abnormally high levels liver enzymes ALT (alanine aminotransferase ) and AST (aspartate aminotransferase). Moreover, the level of albumin (the protein normally present in the blood) is also found to be at decreased levels in some dogs with toxoplasmosis; a medical condition known as hypoalbuminemia. In some rare cases, jaundice is seen with disturbed liver enzymes ALT and AST. The urinalysis may reveal abnormally high level of proteins and bilirubin in the urine sample.

Serological tests are the most reliable tests for making a definitive diagnosis. By measuring the levels of toxoplasma antigens in the body, your veterinarian can determine the type of infection, and whether it is active, dormant, recent (acute), or long term (chronic).

Serological tests will also help in determining the levels of antibodies IgM and IgG. Antibodies are proteins that are normally present in the body or produced in response to an antigen (in this case toxoplasma) for the purpose of neutralizing the antigen. Determination of antigen and antibody levels will help your veterinarian make the confirmatory diagnosis. The polymerase chain reaction test is a reliable test for verifying the presence of Toxoplasma gondii in samples.

More advanced diagnostic testing includes taking a collection of cerebrospinal fluid (CSF). Laboratory testing of CSF may reveal an abnormally high number of white blood cells (WBCs) and protein concentrations in patients with infection that has reached the central nervous system.

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