Toxoplasmosis in Dogs

Dogs may act as a mechanical factor in transmitting toxoplasmosis to humans by rolling in foul-smelling substances and by ingesting fecal material. Just remember that 50% of stray dogs and dogs carry T.gondii antibodies, which means that they have been infected and may transmit the parasite to you.

Toxoplasmosis: Infection Dangerous for Dogs and Humans

Toxoplasmosis is the most common parasitic infection worldwide. The organism that causes toxoplasmosis is Toxoplasma gondii.

Toxoplasma gondii infects a wide range of warm-blooded vertebrates including humans and is one of the world's most successful parasites. As a member of the phylum Apicomplexa, T. gondii is used as a model for understanding infection by a variety of related parasites such as Plasmodium and Cryptosporidium. Apicomplexans have a unique ability to directly penetrate their host cell, without the need for host uptake mechanisms. Invasion occurs very rapidly and avoids triggering of the respiratory burst in macrophages. Within the host cell, the parasite resides in a modified vacuole that resists destruction, while intimately associate with host cell structures. Active secretion of parasite proteins results in modification of the vacuole, rendering it permeable to small molecules. Within this porous vacuole the parasite acquires nutrients from the host, allowing rapid replication, and eventual consumption of the host cell prior to leaving the host cell. Understanding the complex biology of intracellular survival by T. gondii has bearing on the mechanisms of host resistance during both acute and chronic infection.²

Role of Dogs in Transmitting Toxoplasmosis

In dogs, toxoplasmosis is rare. It usually occurs in young dogs infected with distemper or other viral infection. In other cases, dogs develop disease without any other present infectious disease. It appears that many cases that were once considered to be toxoplasmosis in dogs are actually neosporosis - infectious disease of dogs caused by Neospora caninum. The dogs pass parasite cysts in the feces which are ingested through contaminated food and water by cattle, sheep, goats, horses and some other animals. Tissue cysts develop in these animals and dogs become infected by ingesting raw tissue containing these cysts.

Signs of Toxoplasmosis

Testing shows that many dogs are infected and are carriers of this parasite, but mostly puppies and young dogs develop the disease with clear clinical signs. These signs may include hepatitis, pneumonia and ulcerative dermatitis. Infection of the central nervous system and musculature may result in behavioral changes, limb shaking, blindness, circling, muscle pain, progressive paralysis and finally death. Younger animals may have limb paralysis.

Diagnosis of Toxoplasmosis

Diagnosis is difficult and usually requires complex testing. The disease resembles many other infections such as distemper and rabies. In some cases treatment is effective with medications used to treat toxoplasmosis. However, your dog may develop very serious complications affecting nervous system and muscles.

Determining when Toxoplasma infection occurred in a pregnant woman is particularly important because infection before conception poses no substantial risk for transmission of infection to the fetus; however, infection after conception does pose such risk. Although most infants infected with Toxoplasma show no symptoms after birth, they are most likely to develop symptoms later in life that include, vision loss, seizures and mental disability.

Prevention of Toxoplasmosis

References:
1. Parasitic Disease Information
2. Invasion and Intracellular Survival by Toxoplasma. In: Protozoans in Macrophages. Audra Charron, Sebastian Hakansson and Dana Mordue