Toxoplasma gondii Infection in Dogs
Toxoplasmosis, a disease caused by the parasite Toxoplasma gondii (T. gondii), is prevalent among various warm-blooded animals and humans. Its primary host is the cat, wherein the parasite completes its life cycle within the cat’s intestinal tract before being excreted in feces and re-entering the environment. However, cats aren’t the sole source of infection.
In the United States, transmission of T. gondii often occurs through the consumption of raw meat and unwashed fruits and vegetables. Toxoplasmosis can manifest in both acute and chronic forms. The chronic form typically presents as a mild, asymptomatic condition, whereas the acute form tends to exhibit more noticeable clinical symptoms.
Symptoms and Types
While cats tend to exhibit clinical symptoms more frequently than dogs, canines can still become ill from the Toxoplasma gondii parasite, often resembling other infections like canine distemper or rabies. Young dogs with developing immune systems and those with compromised immunity are at higher risk. The following symptoms, commonly observed in infected cats, can also manifest in dogs:
- Neurological symptoms
- Seizures
- Tremors
- Depression
- Lethargy
- Uncoordinated gait
- Muscle weakness
- Partial or complete paralysis
- Respiratory issues such as shortness of breath
- Fever
- Weight loss
- Loss of appetite
- Vomiting
- Diarrhea
- Abdominal pain
- Jaundice
- Tonsillitis (inflammation of the tonsils)
- Retinitis (inflammation of the retina)
- Uveitis (inflammation of the middle part of the eye including the iris)
- Keratitis (inflammation of the cornea)
Causes
Dogs contract the T. gondii parasite through contact, which can occur by rooting in contaminated soil or by consuming cat feces.
Diagnosis
To diagnose toxoplasmosis in your dog, it’s essential to provide your veterinarian with a detailed account of your dog’s health history, including the onset and characteristics of symptoms, as well as any potential exposure to cat feces or the presence of feral cats in your surroundings. Your veterinarian will conduct a comprehensive physical examination to assess your dog’s overall health and body systems.
Standard laboratory tests, such as a complete blood count, biochemistry profile, and urinalysis, are typically performed to confirm the infection. Dogs with toxoplasmosis may exhibit abnormalities in their blood count, including low levels of white blood cells, neutrophils, and lymphocytes, indicating leukopenia, neutropenia, and lymphopenia, respectively. Conversely, as the dog recovers, an increase in white blood cell count may be observed, indicating heightened immune response.
The biochemistry profile often reveals elevated levels of liver enzymes ALT and AST, along with decreased levels of albumin, a protein found in the blood, leading to hypoalbuminemia. In rare instances, jaundice may occur alongside abnormal liver enzyme levels. Urinalysis may detect high levels of proteins and bilirubin in the urine.
Serological tests are the most reliable for making a definitive diagnosis, measuring levels of toxoplasma antigens in the body to determine the type and activity of the infection, whether acute or chronic. These tests also assess levels of antibodies IgM and IgG, which are produced in response to the toxoplasma antigen. Polymerase chain reaction (PCR) tests are used to verify the presence of Toxoplasma gondii in samples.
In more complex cases, collecting cerebrospinal fluid (CSF) for laboratory analysis may reveal increased white blood cell counts and protein concentrations, indicating infection that has reached the central nervous system.
Treatment
If your dog has severe toxoplasmosis, hospitalization for urgent treatment may be necessary, although this is uncommon and typically occurs in dogs with compromised immune systems. Intravenous fluids may be administered to address dehydration in affected dogs. Antibiotics may also be prescribed to manage the infection and halt the advancement of symptoms.
Prevention
Although cats are commonly associated with transmitting the T. gondii parasite, it’s crucial to recognize that the parasite is more frequently acquired through handling raw meat and consuming unwashed fruits and vegetables. Prevention and hygiene are key to safeguarding both yourself and your pet against this parasite. Avoid feeding your dog raw meat and prevent access to cat feces. If you have a cat, keep the litter box in a location inaccessible to the dog, as dogs may ingest cat feces.
Additional protective measures include covering outdoor sandboxes when not in use, wearing gloves while gardening, washing hands after outdoor activities, particularly with children, and using disposable gloves and possibly a face mask when changing litter boxes, especially for pregnant individuals or those with compromised immune systems. Regularly clean the litter box to minimize the risk of parasite viability and infection. Pregnant women should avoid litter box cleaning whenever possible due to potential severe complications.
Consider testing your cat for T. gondii parasite, but note that cats testing positive for antibodies are less likely to pose a transmission risk as they have developed immunity. Conversely, cats testing negative lack immunity and require more stringent preventive measures. Similarly, testing your dog for T. gondii antibodies may provide insights, but if antibodies are present, the dog has likely been previously infected and is not considered a transmission threat.
Dogs are generally not regarded as significant carriers of this parasite.
