Toxoplasmosis


Toxoplasmosis is a severe, world-wide generalised or central nervous system disease by the Protozoan toxoplasma gondii. This protozoan parasite is found in man and many species of birds and animals. T gondii has recently been shown to be a coccidian that exists in 3 infectious forms:

1. The tachyzoite (or endozoite), the proliferative form, is present in large numbers in blood, excreta and secretions in acute disseminated infections;


2. The cystozite (or bradyzoite), the resting form, is present within encapsulated cysts, particularly in muscle and nerve tissue, in chronic infections;


3. The oocyst is the form passed only in the faeces of cats following their infection by the coccidian intestinal epithelial stages characteristic only of feline toxoplasmosis. The coccidian stages in cats appear to be crucial to the maintenance of T. gondii in nature. However the relative importance of several sources of infection for man remains to be determined, including, particularly, accidental ingestion of oocysts denied from cat faeces or the ingestion of encapsulated cysts in raw or under-cooked meat.


In human terms the clinical patterns of Toxoplasmosis can be divided into four patterns; acquired toxoplasmosis, congenital infection, retinochoroiditis and disease in the altered host. In the latter, toxoplasmosis may present as a disseminated disease.    In patients treated with immuno suppressive drugs or in patients with neoplasms of the lymphatic system.    Patients with acquired toxoplasmosis are often asymptomatic, but may present with fever, general malaise, enlarged glands, splenomegaly, headaches and a macropapular rash. Rarely, severe cases include myocarditis (inflammation of the heart muscle) and retinochoroiditis (eye problems).    Congenital transmission occurs only during acute infection – which has been detected in 1% of pregnant women. Approximately 20-40% of such adult infections are transmitted to the
foetus, resulting in some abortions and still births.   Signs of congenital toxoplasmosis are present at birth or progress during the first months of life: seizures, mental retardation, enlarged spleen and/or liver, pneumonitis, rash, fever, retinochoroiditis and cerebral calcification.    The retinochoroiditis is usually a late manifestation of asymptomatic congenital infection, with symptoms being first noted in the second or third decade of life.

The congenital disease is often fatal and if the infant survives the acute infection, he is likely to be handicapped with severe Central Nervous System and ocular lesions.    The acquired disease is usually symptomatic or mild, but acute infections in adults have been known to be fatal. Asymptomatic infections are common, serological surveys indicate that 20-80% of various populations (human and animals) are infected!

 

Diagnosis is based on the presence of changing or elevated titers of toxoplasmosis antibodies (which are very specific) and on the isolation of the parasite from infected tissues.


Toxoplasmosis organisms may be directly identified in smears of blood, bone marrow, spinal fluid or wound exudates.


Human treatment of symptomatic acute infections is pyrimethamine, trisulfapyrimidines, and folic acid for one month. Recently trimethoprim has been found effective. Steroids may also be used. Blood tests should be done weekly. Congenital toxoplasmosis should be treated whether symptomatic or asymptomatic.  Pregnant women should have their serum examined for the toxoplasmosis antibody. Those with negative titers should take precautionary measures to prevent the infection, preferably having no further contact with cats, and eating no undercooked meats or unwashed/undercooked vegetables.

 
Reference: Current Medical Diagnosis and Treatment, 1980. Marcus A Krupp, M.D. Milton J Chatton, M.D.


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