Toxoplasmosis

Toxoplasmosis

Causative Agent

Toxoplasmosis is a disease caused by the protozoan parasite, Toxoplasma gondii.

Click on the image to enlarge.

Life cycle of Toxoplasma gondii.

Distribution

Geographic:

Seasonality:

Hosts, Transmission and Life Cycle

Hosts:

Domestic or wild cats are the definitive host for this parasite with feral cats being the main “reservoir” for this parasite. Cougars in British Columbia have been reported to harbor this parasite.
Other wildlife in BC and North America known to act as intermediate hosts and to have suffered clinical effects of toxoplasmosis include:
- moose, pronghorn antelope, mule deer, white-tailed deer
- black bear, red fox, skunk, opossum, mink, small mammals
Toxoplasmosis is also a potentially serious zoonotic disease. A waterborne epidemic occurred in 1995 in Victoria, BC and affected a number of humans.

Transmission and Life Cycle:

Refer to above life cycle diagram
Cats ingest cysts of T. gondii that are contained in the tissues of intermediate hosts. Cysts then disintegrate within the stomach and small intestine.
After multiplication and reproduction within the walls of the intestines, egg-like “oocysts” are passed in the feces. Oocysts can survive in the environment for several months and are extremely resistant to disinfectants, freezing, and drying.
Within a few days in the external environment oocysts become infective and are ingested incidental to feeding or drinking in areas contaminated with cat feces.
Cysts form in the tissues of intermediate hosts; primarily in muscle and nervous tissue and to a lesser extent in lungs, liver and kidney. Cysts may persist for years.
The cycle continues when a cat consumes meat contaminated with cysts.
Humans may enter this cycle either by consuming meat contaminated with cysts or through ingestion of food or water contaminated by cat feces.

Signs and Symptoms

Outward signs are rarely observed in cats or the intermediate hosts.
In humans symptoms may include:
- fever
- fatigue
- muscle pains and sore throat
- in more severe cases, inflammation of the brain, eyes, birth defects and even death can occur in patients with suppressed immune systems.

Meat Edible?

Meat is edible if cooked thoroughly at 67°C.
When skinning infected animals, care should be taken as viable parasites may be present even if the infected animals shows no outward signs of disease.

Human Health Concerns and Risk Reduction

Health Concerns

Toxoplasmosis is of considerable risk to pregnant women as T. gondii can be readily transmitted from the mother through the placenta to the developing fetus.
Complications in the developing fetus may lead to diminished vision, mental deficiencies, convulsions and hydrocephalus (enlargement of the skull caused by fluid accumulation).
Some of these complications may not appear until later in life.

Risk Reduction

Hands, utensils and cutting surfaces should be washed with soap and water after handling meat.
Thoroughly cook meat (see above).
Pregnant women should avoid contact with cat litter boxes, soil, raw meat and aborted animals.
Cats should be fed dry, canned or cooked food, not allowed to “hunt” out of doors, and not allowed to “scavenge” from household garbage.
When gardening, gloves should be worn and vegetables thoroughly washed prior
consumption.

Samples for Diagnosis

Microscopic and immunologic examination of secretions, excretions, body fluids and other tissues collected either at necropsy or through biopsy of live tissue will help to determine the presence of T. gondii.
Whole carcasses should be submitted for necropsy.