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Toxoplasmosis - Cat and Dog (view source)
Revision as of 11:17, 13 August 2010
, 11:17, 13 August 2010→Laboratory Tests
Demonstration of antibodies in serum is indicative of exposure to ''T. gondii'', but does not necessarily show active infection. This could be overcome by testing for ''T. gondii'' antigen or immune complexes, but these methods are currently only available to researchers. Several techniques are commercially available for detection of antibody, including ELISA,
Demonstration of antibodies in serum is indicative of exposure to ''T. gondii'', but does not necessarily show active infection. This could be overcome by testing for ''T. gondii'' antigen or immune complexes, but these methods are currently only available to researchers. Several techniques are commercially available for detection of antibody, including ELISA,
immunofluorescent antibody testing, Sabin-Feldmann dye test, and agglutination tests. Although these tests are theoretically able to detect all classes of immunoglobulin against ''Toxoplasma gondii'' in many species, it seems that feline serum positive for IgM only often reads as a false negative<sup>5, 6</sup> and so careful interpretation is necessary, particularly since the IgM antibody class appears to correlate more closely to clinical disease than IgG<sup>7</sup>. IgG antibody persists at high levels for at least six years after infection, and so a single IgG measurement is not particularly useful for clinical diagnosis. A rising IgG titre may be more suggestive of active toxoplasmosis: however, IgG is not produced until 2-3 weeks post-infection which may be too late to be useful in acute cases, and many animals with chronic toxoplasmosis will not be assayed until IgG is already at its maximal titre. A more practically useful form of serology is examination of IgM in aqueous humour or cerebrospinal fluid. IgM, in contrast to IgG and IgA, has only been detected in the aqueous humour and CSF of cats with clinical disease <sup>5, 6</sup>. Thereforem, an IgM titre of above 1:64 is highly suggestive of recent of active ''T. gondii'' infection.
immunofluorescent antibody testing, Sabin-Feldmann dye test, and agglutination tests. Although these tests are theoretically able to detect all classes of immunoglobulin against ''Toxoplasma gondii'' in many species, it seems that feline serum positive for IgM only often reads as a false negative<sup>5, 6</sup> and so careful interpretation is necessary, particularly since the IgM antibody class appears to correlate more closely to clinical disease than IgG<sup>7</sup>. IgG antibody persists at high levels for at least six years after infection, and so a single IgG measurement is not particularly useful for clinical diagnosis. A rising IgG titre may be more suggestive of active toxoplasmosis: however, IgG is not produced until 2-3 weeks post-infection which may be too late to be useful in acute cases, and many animals with chronic toxoplasmosis will not be assayed until IgG is already at its maximal titre. A more practically useful form of serology is examination of IgM in aqueous humour or cerebrospinal fluid. IgM, in contrast to IgG and IgA, has only been detected in the aqueous humour and CSF of cats with clinical disease <sup>5, 6</sup>. Therefore, an IgM titre of above 1:64 is highly suggestive of recent of active ''T. gondii'' infection.
''T. gondii'' oocysts may be demonstrated in cat faeces. This diagnostic procedure is not of value in dogs, since as intermediated hosts they do not prodice oocysts. Oocysts are roughly 10 x 12 microns in size and can be seen microscopically following a flotation technique. It is not possibly to visibly differentiate between ''Toxoplasma'' oocysts and those from other, non-pathogenic coccidia such as ''Hammondia hammondi' and ''Besnoitia darlingi'': laboratory animal innoculation is necessary for this. Unfortunately, most cats with clinical toxoplasmosis have already finished shedding oocysts, and so faecal examination is of little use ase a stand-alone diagnostic test. However, it will evaluate the zoonotic risk posed by cats showing signs of toxoplasmosis.
Finally, a positive response to treatment for toxoplasmosis may aid in its diagnosis.
for any cat with clinical signs referable to toxoplasmosis.
===Diagnostic Imaging===
===Diagnostic Imaging===