ORDER I. RICKETTSIALES BUCHANAN AND BUCHANAN, 

 1938, emend. GIESZCZKIEWICZ, 1939. 



(Buchanan and Buchanan, Bacteriology, 4th ed., New York, 1938, 49; Gieszczykiewicz, 

 Bull. Intern. Acad. Polon. "Sci., Classe Math., B (1), 1939, 9-30.) 



Ri.ckett.si.a'Ies. M.L. fern. pi. n. Rickettsiaceae type family of the order; -ales ending to 

 denote an order; M.L. fern. pi. n. Rickeitsiahs the Rickettsiaceae order. 



Small, rod-shaped, coccoid and often pleomorphic microorganisms occurring as ele- 

 mentary bodies which are usually intracellular but which may occasionally be facultatively 

 or exclusively extracellular. Ma}' also develop larger "initial bodies" as intracellular, 

 spherical or less regular inclusions. Intracytoplasmic forms may be diffuse, compacted into 

 colonies or morulae and may be located in special situations. Usually non-filterable. Gram- 

 negative. Cultivated outside the host only in living tissues, embryonated chicken eggs or 

 rarely in media containing body fluids. Parasitic organisms almost always intimately as- 

 sociated with not only reticulo-endothelial and vascular endothelial cells or erythrocj^tes 

 in vertebrates, but also often in invertebrates which may act as vectors. The intracellular 

 parasites of Protozoa and other invertebrates are provisionally assigned here also. May 

 cause diseases in man or other animals or both. Seldom kill the invertebrate hosts. 



Key to the families of order Rickettsiales. 



I. Parasites, intracellular or intimately associated with tissue cells other than erythro- 

 cytes or with certain organs in arthropods; rarely extracellular in arthropods. 



A. Frequently cause diseases of vertebrates. Transmitted by arthropod vectors. 



Family I. Rickettsiaceae, p. 934. 



B. Intracellular parasites found in tissues of vertebrates. Not known to be transmitted 

 by arthropod vectors. 



Family II. Chlamydiaceae, p. 957. 

 II. Parasites, intracellular or facultatively extracellular; found characteristically in or on 

 the erythrocytes of vertebrates, exceptionally in fixed-tissue cells. 



A. Small, rod-shaped, bacteria-like cells. At least one species, when cultured, may show 

 a single, polar flagellum. Arthropod transmission established for some members of 

 the family. 



Family III. Bartonellaceae, p. 968. 



B. Very small, virus-like particles occurring in the erythrocytes of vertebrates. Trans- 

 mitted by arthropods. 



Family IV. Anaplasmataceae , p. 980. 



FAMILY I. RICKETTSIACEAE PINKERTON, 1936.* 



(Parasitology, 28, 1936, 186.) 



Ri.ckett.si.a'ee.ae. M.L. fem.n. Rickettsia type genus of the family; -aceae ending to 

 denote a family; M.L. fem.pl .n. Rickettsiaceae the Rickettsia family. 



* Revised by Dr. Cornelius B. Philip, Rocky Mountain Laboratory, Hamilton, Montana, 

 January, 1954, from the original by Dr. Ida A. Bengtson, Sixth Edition of the Manu.\l. 



934 



