CLASSIFICATION 937 



met with by Donatien and Lestoquard (1937a) in their study of an epidemic of 

 conjunctivitis among sheep in Algeria. The organism has not been fully examined ; 

 from its description it appears rather large ; no arthropod vector is known ; and 

 it is doubtful whether it belongs to the RicJcettsia group. According to Giroud 

 and Panthier (1939) there is no such organism as R. conjiinctivce ; the bodies that 

 have been mistaken for it are the result of bacteria undergoing phagocytosis, and 

 can be found in the conjunctiva of normal cattle. 



R. canis, R. ovina, and R. bovis.— These organisms, which were described by 

 Donatien and Lestoquard (1935, 1936a, b, 19376) in Algeria, are believed to be 

 parasites of the mononuclear cells. R. canis is said to be responsible for a severe 

 dise'ase of dogs ; the other two species are said to give rise to a relatively mild 

 disease in their respective hosts. There is evidence that infection is transmitted 

 by ticks. Whether they are true micro-organisms and, if so, whether they belong 

 to the Rickettsia group, or should be classified in some other genus, must await 

 further study. Again, their relation to the intracellular bodies found by Kurloff 

 in the mononuclear cells of the guinea-pig's blood is doubtful (see Mochovski 1937). 



Classification. — Most of our knowledge on the relationship of the pathogenic 

 rickettsiee to each other has been gleaned from an examination of the sera of 

 patients and experimentally inoculated rabbits and from cross-immunity experi- 

 ments in animals. The results of these will be more conveniently dealt with in 

 Chapter 83. Suffice it to say here that, excluding R. quintana about which our 

 information is very slight, the rickettsiae pathogenic to man may be classified 

 broadly into four groups : the typhus group, the spotted fever group, the tsutsu- 

 gamushi group and the Q fever group. Within each of these groups there are 

 types of Rickettsia, sometimes with a circumscribed geographical distribution, that 

 differs from each other in their insect host, in their virulence for man and for 

 experimental animals, and in their apparent antigenic structure. Whether these 

 types should be regarded as species or as varieties of the main type it is at present 

 impossible to decide. (For general reviews on the rickettsiae see Arkwright 1924, 

 Wolbach 1925, 1941, Cowdry 1926, Pinkerton 1942, and for useful technical 

 information on their study see Clavero and Gallardo 1943). 



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