EtiologyThe infectious agent of psittacosis - lymphogranuloma venerum trachoma group (PLVG) is an obligate intracellular parasite and is classified as separate genera with only 2 species, viz. Chlamydia trachomatis and Chlamydia psittacii. These organisms are the members of an exclusive order Chlamydiales under the family Chlamydiaceae. The organism resembles bacteria in the composition of the cell wall, as it possesses both RNA and DNA and also multiply by binary fission. However, unlike bacteria, this multiplication occurs only within the host cells. In this respect, like viruses the organism is intracellular and can only be propagated or multiply in living cells. The elementary bodies of chlamydia stain with basic dyes and are visible as small, round red coloured dots with the light microscope when stained by the methods of Machiavello or Gimenez or modified acid-fast techniques. Their colour is purple blue in Giemenez stained preparations and appear Gram negative in Gram’s stained preparations.