Complement Fixation, Precipitin, Adhesion, Mercuric Chloride and Wassermann Tests in Equine Trypanosomiasis of Panama (Murrina)
Authors: Taliaferro William H. , Taliaferro Lucy Graves 
Published: January 2023

Summary
The data presented give a comparison of complement fixation, precipitin, red blood cell adhesion and mercuric chloride tests with thick blood film findings in two herds of horses and mules some of each of which were infected with T. hippicum. One herd contained 103 animals which were never treated (tables 1 to 6), and the other contained 122 animals which were treated (tables 7 to 10).
The untreated herd showed a striking correlation between in-infection of the animal and positiveness of all the tests. Thus, in one series of 103 serums where parallel tests were run, of 15 serums from demonstrably infected animals 12 were positive in all four tests, and the other three were positive in three tests (2 were negative with the mercuric chloride and one with the complement fixation) and of 88 serums from animals in which trypanosomes were never found, one was positive in all four tests, four were positive in two tests (1 in precipitin and adhesion, 2 in adhesion and mercuric chloride and 1 in mercuric chloride and complement fixation), 30 were positive in one test (1, 4, 7 and 18 in complement fixation, precipitin, adhesion and mercuric chloride, respectively) and 53 were negative in all four tests (table 6). A few cases of piroplasm and one case of filaria did not cause pseudo-positive reactions in any of the tests (table 5). Another series of tests on approximately one-third of the herd furnished corroborative data. Wassermann tests on this herd gave 1 (++) positive and 102 negative reactions. In general, all of the specific tests (complement fixation, precipitin and adhesion) on the untreated herd were more consistent and reliable (tables 1 to 3) than the non-specific mercuric chloride test (table 4) while the Wassermann test was almost completely non-reactive.
The treated herd, on the contrary, showed no correspondence between past infection of the animal and reactivity of the test. Thirty-five of the animals had been positive at some time within fifteen months, but all had been negative for from three to eleven months at the time of the tests (with the exception of one animal which was positive at the time the complement fixation tests were run). In one series of 77 serums, where all four tests were run, of 33 serums from formerly infected animals none was positive in all or even in three of the tests, 2 were positive in two tests (precipitin and mercuric chloride), 15 were positive in one test (1 in complement fixation, 1 in adhesion and 13 in mercuric chloride) and 16 were negative, and of 44 serums from animals in which trypanosomes were never found, 4 were positive in two tests (1 in both the adhesion and mercuric chloride and 3 in the precipitin and mercuric chloride), 18 were positive in the mercuric chloride alone and 22 were negative in all four tests (table 10). Additional tests on approximately one-third of the herd furnished corroborative data. On the whole, all of the specific tests (complement fixation, precipitin and adhesion) on the treated herd tended to be non-reactive (tables 7 and 8) whereas the non-specific mercuric chloride test tended to be reactive (table 9), but in neither group could the reactivity or lack of reactivity be correlated with past infection.