Toxoplasma gondii
Oocyst
The infective form of T. gondii, the oocyst is round to slightly oval measures 10 to 15 ?m long by 8 to 12 ?m wide. The transparent oocyst contains two sporocysts, each with four sporozoites. A clear and colorless, two-layered cell wall borders the organism
Tachyzoites
The actively multiplying crescent – shaped Tachyzoites range in size from 3 to 7 ?m by 2 to 4 ?m . one end of the organism often appears more rounded than the other end . each tachyzoite equipped with a single centrally located nucleus , surrounded by a cell membrane .
Bradyzoites
The typical bradyzoite basically has the same physical appearance as the tachyzoite, only smaller in size. These slow – growing, viable forms gather in clusters inside a host cell develop a surrounding membrane, and form a cyst in a variety of host tissues and muscles outside of the intestinal tract. Such cysts may contain as few as 50 and up to as many as several thousand bradyzoites. A typical cyst measures from 12 to 100 ?m in diameter.
Life cycle
The definitive host in the Toxoplasma life cycle is the cat (or other felines). Upon ingestion of Toxoplasma cysts present in the brain or muscle tissue of contaminated mice or rats, the enclosed bradyzoites are released in the cat and quickly transform into tachyzoites. Both sexual and asexual reproduction occurs in the gut of the cat. The sexual cycle results in the production of immature oocysts, which are ultimately shed in the stool. The oocysts complete their maturation in the outside environment, a process that typically takes from 1 to 5 days. Rodents, particularly mice and rats, serve as the intermediate hosts, ingesting the infected mature Toxoplasma oocysts while forging for food. The sporozoites emerge from the mature oocyst and rapidly convert into actively growing tachyzoites in the intestinal epithelium of the rodent.
Clinical symptoms
Toxoplasmosis a common infection with the protozoan intracellular parasite Toxoplasma gondii. It is marked in its inborn form by liver and brain involvement with calcium in the brain (cerebral calcification), convulsions, blindness, too-small head and fluid on the brain (microcephaly and hydrocephaly), and mental retardation. The acquired form is marked by rash, disease of the lymph nodes (lymphadenopathy), fever, malaise, central nervous system disorders, swelling of the heart wall (myocarditis), and swelling of lung tissue (pneumonitis). ) Cats acquire the organism by eating infected birds and mice. Lumps (cysts) of the organism are carried from cat feces to humans or by human ingestion of inadequately cooked meat containing the lumps. Infection through the placenta occurs only during acute infection of the mother. The other route of human infection occurs when contaminated blood is transfused into an uninfected person.
Laboratory diagnosis
The primary means of diagnosing T.gondii infections is by serological test methods . the recommended test for the determination of IgM antibodies present in congenital infections is the double-sandwich enzyme linked immunosorbent assay (ELISA) method. The actual demonstration of T.gondii trophozoites (tachyzoites) and cysts (filled with bradyzoites) involves tedious microscopic examination of infected human tissue samples or the inoculation of laboratory animals.