Toxoplasmosis

Toxoplasmosis is a fairly uncommon disease that affects all type of mammals and birds. When it does occur, it is a serious disease. Toxoplasmosis is caused by a single-celled protozoan parasite called Toxoplasma gondii. Although disease caused by Toxoplasma is uncommon, many animals have immunity to the disease that they acquired during a prior exposure.



 That is, the majority of animals are exposed to the organism and develop immunity to it without developing any disease. Life Cycle Wild and domestic felines are the only animals in which Toxoplasma can fully live out their life cycle and in which sexually mature forms of the parasite occur. Because of this cats are called the definitive host of Toxoplasma. Cats are also the only true reservoir of this parasite in Nature. Cats play an important roll in transmitting Toxoplasma to other species including humans. In humans and all species other than cats, only non-sexual (asexual) stages of Toxoplasma occur. Raw or undercooked meat is a common way for the infection to be passed from animal to animal or animal to man. The Toxoplasma organism has three stages, tachyzoite, oocyst and cyst. After eat any one of these stages in an infected small mammal or bird, the intestinal lining of cats becomes infected. Cats are the only species of animal that develop this intra-intestinal form of the parasite. The oocysts that are shed from these cells pass out of the cat with its feces. This infection persists only for a few weeks before the cat itself becomes immune to the disease. After being passed in the feces, these oocysts sporulate and become infectious for any human or animal that accidentally eats them. These sporulated oocysts are tightly encapsulated in an impervious membrane that resists drying and heat. They survives for up to a year in damp shaded soils. While the cat is hosting this parasite, some of the Toxoplasma oocysts within the intestine burrow deeper within the lining where they divide into tachyzoites. These tachyzoites leave the intestine and spread throughout the body multiplying and causing the systemic or extra-intestinal phase of the disease. When the cat’s immune system has produced sufficient antibody against these Toxoplasma, the organisms are walled off as dormant oocysts in muscle and nerve tissue throughout the body. A few cats never produce sufficient antibody and so, chronically shed infective oocysts into their environment with their stool. These cysts remain in the host cat for the remainder of its life. In all other species the intestinal stage is lacking. These animals and man share only the extra-intestinal portion of the disease and, if they survive, harbor dormant cysts in their brain and muscle for the rest of their lives. Most cats become infected through eating creatures that contain dormant toxoplasma cysts and most other animals become infected by ingesting prey animals or material contaminated with cat feces. In a few cases infection is passed from animal to animal and cat to cat through the womb. This is called congenital infection and it is quite uncommon. Symptoms of Toxoplasmosis Most cats that become infected with Toxoplasmosis show no clinical evidence of the disease. A few stressed cats, kittens and immature adults do develop transient disease related to their infection. Cats that are positive for feline leukemia or feline immunodeficiency virus are more at risk for developing the active diseases. Early in this disease, cats are listless and depressed. They may refuse to eat and they run a fever. As the disease progresses these cats often develop signs of lung congestion and pneumonia. The organism can invade the liver causing yellow mucus membranes (jaundice), vomiting and diarrhea. Inflammation of other body organs such as the pancreas and lymphatic tissue also occurs. In some cases the nervous system and eyes are attacked causing blindness, aimless meandering, walking in circles, personality changes, incoordination, seizures and loss of urine and bowel control. These central nervous system signs can be mistaken for rabies, lead or arsenic poisoning.