Different Types of Serologic Reactivity to Bedsonia (Psittacosis Group) Antigen in Various Hosts. Discussion of Some Related Problems

Abstract

About 450 Bedsonia-positive serum samples from acutely sick, convalescent or apparently healthy humans and animals have been investigated by both CF and CFI tests with an ornithosis antigen prepared in our laboratory. Sera of humans (with three exceptions) and sera of horses, reacted in the CF test only. Sera of sheep (with one exception), as well as sera of pigs and cattle, showed either a positive CF or a positive CFI test. Sera of pigeons showed either positive CF or positive CFI tests or both. The sera of other birds (ducks, geese, hens and turkeys) reacted positively in the CFI test only (apparently an inherent characteristic of those orders). Significantly different types of serologic reactivity have been observed in various groups of Bedsonia-positive sheep. Sera which were positive in both CF and CFI tests showed a zone in the CF test mostly of the same height as the titer revealed in the CFI test. Sera positive in the CF test only have been mixed in various proportions with pigeon serum shown to be positive by the CFI test only, and the mixtures have been titrated by both tests. Results suggest the following conclusion: both types of antibodies (complete and incomplete), if contained in the same serum specimen or mixed in various proportions, may compete for the antigen resulting in a partial or complete suppression of their respective activities as manifested by positive CF test only with no zoning, by negative CF test and positive CFI test, or by positive CF test with zoning and positive CFI test, mostly with titers equaling the height of the zone revealed in the CF test. Similarly, as the specificity of the CF titers can be verified by testing the sera vs various antigens of unrelated specificity, also specificity of the CFI titers has been checked by setting up CFI tests vs indicator systems of unrelated specificity. By means of several checkerboard titrations we have verified the well known observations that pigeon sera when titrated in the presence of larger doses of antigen show lower prozones in the CF test, and the titers obtained in the CFI test are lower if larger doses of antigen are used in the indicator system. A simple test is proposed to determine if the so-called type III serologic reactivity (positive CF test with a prozone and a positive CFI test) is induced due to the presence of complete antibodies in an excess, or to the presence of incomplete antibodies as well as the complete ones. Both serologic and epizootologic observations presented here seem to indicate the presence of the virus of enzootic abortion of ewes in Yugoslavia. Other observations concerning CF serology of the Bedsonia group of viruses are discussed.