AVIAN TOXOPLASMA

ctfaulkn at utkvx.utk.edu ctfaulkn at utkvx.utk.edu
Fri Jun 2 00:04:57 EST 1995


In Article <01HR4J2007DU90OIKO at grove.iup.edu>
BLZWBCB at grove.iup.edu writes:
> 
>Antibody titres are an indirect measure of the intensity of infection.  They
>represent the dilution of the blood sera.  A bird that is antibody positive 
>at 1:500 vs. a bird that is antibody positive at 1:25 will have sustained a 
>higher infection.  

	Although it is true that an Ab titer is an indirect measure of
infection w/ T. gondii, it is not necessarily a measure of infection 
intensity.  In a study of T. gondii infection is experimentally infected
chickens (Dubey 1993, Am Jour Vet Res 1671) there was no apparent difference
in optical density values between chickens fed 1,000 oocysts and chickens fed
10,000 oocysts. OD values increased up to day 27, and then remained stable
until day 58 Post Infec, supporting the notion of a rising Ab titer over time.
Thus, a low titer of 25 (reciprocal of the lowest dilution w/ a positive
reaction) may actually mean that the animal is only recently infected, and not
sustaining a minor infection (i.e. low numbers of infective organisms). So it 
is necessary to monitor the infection status over time (usually 2 to 4 weeks)
to doccument a rising Ab titer.

Measurement of T. gondii Ab in birds is difficult, and not all immunodiagnostic
tests are suitable. For example, the Sabin-Feldman dye test does not work, 
IHA (Indirect Hemagglutination) and LAT (Latex Agglutination) have very low
sensitivity and frequently result in titers that are 4 to 8 dilutions lower
than those obtained by the MAT (Modified Direct Agglutination) which uses 
Fromalin-fixed whole Tachyzoites as antigen.  This means that a bird with 
a Ab titer of 256 by the MAT would probably be undetected by IHA or LAT. 

Other people who have worked with avian toxoplasmosis are Drs.
David Lindsay at Auburn Univ, and Sharon Patton at the Univ of Tennessee,
if you are serious about have your birds for T. gondii Abs. I'm sure either of
those individuals will be glad to share their expertise with you.  Good luck!


**********************************
*      Charles T. Faulkner       *   Get your facts first and then you
*  Univ of Tennessee, Knoxville  *   can distort them as much as you please.
*   (ctfaulkn at utkvx.utk.edu)     *                   Mark Twain
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