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Toxoplasmosis - Cat and Dog (view source)
Revision as of 19:21, 12 August 2010
, 19:21, 12 August 2010→Description
==Description==
==Description==
''Toxoplasma gondii'' is an obligate, intracellular protozoa that is capable of infecting most mammals. Cats and other felids are the definitive host for ''T. gondii'', and all other mammals, including dogs, are intermediate hosts.
''Toxoplasma gondii'' is an obligate, intracellular protozoa that is capable of infecting most mammals including man. Cats and other felids are the definitive host for ''T. gondii'', and all other mammals, including dogs, are intermediate hosts.
Toxoplasma gondii is an obligate intracellular coccidian parasite that can infect virtually all
species of warm-blooded animals, including people. Domestic cats and other Felidae are the
definitive hosts. All nonfeline hosts are intermediate hosts. There are three infectious stages:
sporozoites in oocysts, tachyzoites (actively multiplying stage), and bradyzoites (slowly multiplying
stage) enclosed in tissue cysts. Oocysts are excreted in feces, whereas tachyzoites and
bradyzoites are found in tissues.
The three major modes of transmission are congenital infection, ingestion of infected tissues,
and ingestion of oocyst-contaminated food or water . Other minor modes of transmission include
transfusion of fluids or transplantation of organs.
Enteroepithelial Life Cycle
This cycle is found only in the definitive feline host. Most cats are thought to become infected
by ingesting intermediate hosts infected with tissue cysts. Bradyzoites are released in the stomach
and intestine from the tissue cysts when the cyst wall is dissolved by digestive enzymes.
Bradyzoites penetrate the epithelial cells of small intestine and give rise to schizonts initiate the
five types (ABE) of predetermined asexual stages and merozoites released from schizonts form
male and female gamonts. After fertilization a wall is formed around the fertilized macrogamont to
form an oocyst. Oocysts are round to oval, 10 � 12 �m, and are unsporulated (uninfective) when
passed in feces. After exposure to air and moisture for 1 to 5 days, oocysts sporulate and contain
two sporocysts, each with four sporozoites.
The entire enteroepithelial (coccidian) cycle of T. gondii can be completed within 3 to 10 days
after ingestion of tissue cysts and occurs in up to 97% of naive cats. However, after ingestion of
oocysts or tachyzoites, the formation of oocysts is delayed until 18 days or more, and only 20% of
cats fed oocysts will develop patency.
Felids are the only definitive hosts of T gondii ; both wild and domestic cats therefore serve as the main reservoir of infection. There are 3 infectious stages of T gondii ; tachyzoites (rapidly multiplying form), bradyzoites (tissue cyst form), and sporozoites (in oocysts).
Felids are the only definitive hosts of T gondii ; both wild and domestic cats therefore serve as the main reservoir of infection. There are 3 infectious stages of T gondii ; tachyzoites (rapidly multiplying form), bradyzoites (tissue cyst form), and sporozoites (in oocysts).
T gondii is transmitted by consumption of infectious oocysts in cat feces, consumption of tissue cysts in infected meat, and by transplacental transfer of tachyzoites from mother to fetus. T gondii initiates enteroepithelial replication in unexposed cats after ingestion of uncooked meat containing tissue cysts. Bradyzoites are released from tissue cysts by digestion in the stomach and small intestine, invade intestinal epithelium, and undergo sexual replication, culminating in the release of oocysts (10 µm diameter) in the feces. Oocysts are first seen in the feces at 3 days after infection and may be released for up to 20 days. Oocysts sporulate (become infectious) outside the cat within 1-5 days, depending on aeration and temperature, and remain viable in the environment for several months. Cats generally develop immunity to T gondii after the initial infection and therefore shed oocysts only once in their lifetime.
T gondii is transmitted by consumption of infectious oocysts in cat feces, consumption of tissue cysts in infected meat, and by transplacental transfer of tachyzoites from mother to fetus. T gondii initiates enteroepithelial replication in unexposed cats after ingestion of uncooked meat containing tissue cysts. Bradyzoites are released from tissue cysts by digestion in the stomach and small intestine, invade intestinal epithelium, and undergo sexual replication, culminating in the release of oocysts (10 µm diameter) in the feces. Oocysts are first seen in the feces at 3 days after infection and may be released for up to 20 days. Oocysts sporulate (become infectious) outside the cat within 1-5 days, depending on aeration and temperature, and remain viable in the environment for several months. Cats generally develop immunity to T gondii after the initial infection and therefore shed oocysts only once in their lifetime.