934 RICKETTSIA 



about which comparatively little is known, we may refer briefly to the reproduction 

 of the various rickettsial diseases in animals. 



Pathogenicity of R. prowazeki for Animals. — A febrile disease simulating typhus 

 can be reproduced in apes, monkeys, and guinea-pigs by the classical louse-borne 

 type of virus ; rabbits and rats are relatively resistant to inoculation. According 

 to Nicolle, Conor and Conseil (1911), chimpanzees are more sensitive than macaques ; 

 subcutaneous inoculation of 1 ml. of human blood is generally sufficient to infect 

 chimpanzees, but for macaques 4-5 ml. intraperitoneally are required. The blood 

 of human patients is most virulent towards the end of the fever, but it is said 

 to be virulent from 2 days before the onset to 2 days after the decline of the fever 

 (Arkwright et al. 1919-20). 



After inoculation of typhus blood into monkei/s there is an incubation period of about 

 a week, followed by a rise of temperature, which continues to ascend gradually for some 

 days, just as in man ; the temperature is mamtained for 7 to 10 days, and then falls rapidly. 

 A period of hypothermia may succeed, followed by a return to normal temperature. 

 Accompanying the fever there are general constitutional symptoms, such as anorexia, 

 ruffled coat, and conjunctival congestion ; on the 3rd or 4th day a rash sometimes breaks 

 out on the face. Death may occur. During the early part of the fever there is a leucopenia, 

 followed by a return to normal ; the leucocytes continue to rise, passing above normal 

 during convalescence, and not returning to normal till about a month after inoculation. 

 The disease can be passed indefinitely through monkeys. A single attack, provided it is 

 severe, produces a solid immunity ; but after a mild attack the immunity is less marked. 

 Instead of typhus blood, monkeys can be infected with a suspension of guinea-pig brain 

 tissue, or with ground-up lice or louse excreta. Arkwright, Bacot and Duncan (1919) 

 brought evidence to show that the monkey-louse, Pedicmus hngiceps, became infected 

 by feeding on typhus monkeys, or after rectal injeation of typhus blood, and was able to 

 transmit the disease to normal monkeys. The infected lice were found to contain rick- 

 ettsise ; Pedicini from non-inoculated monkeys never contained rickettsise. 



Guinea-pigs can be infected by virus from man, the louse, or infected guinea-pigs or 

 monkeys. The incubation period is generally 6 to 14 days, but it may extend to 26 days 

 (da Rocha-Lima 1920ffl) ; it is longer after subcutaneous than after intraperitoneal injection. 

 The disease is characterized mamly by fever. The rectal temperature rises from 102° to 

 103° F. at the end of the incubation period, remains at between 103° and 106° F. for 3 to 

 14 days, and then falls to normal. According to Griinfeld, Serebrjannaja, and Neumann 

 (1933), there is a mononuclear leucocytosis reaching its maximum as the fever decUnes ; 

 the mononuclear cells rise from 2 per cent, to between 6 and 14 per cent. The animals 

 recover, and are subsequently immune to a fresh inoculation. If killed, there is little to 

 be seen macroscopically beyond sUght enlargement and darkening of the spleen, and some- 

 times slight congestion of the testicles, which may be covered with a gelatinous exudate. 

 Microscopically, both in man and in guinea-pigs the main lesions are found in the blood 

 capillaries, especially those in the skin, skeletal muscles and central nervous system. 

 They consist of thromboses with perivascular accumulations of cells, often accompanied 

 by small haemorrhages. In the central nervous system characteristic nodules are found, 

 simulating tubercles. The primary lesion is in the endotheUal cells Iming the walls of the 

 capillaries. Rickettsiae have been demonstrated in the lesions of the skm, kidneys, testicles, 

 brain, and other organs in man (Wolbach et al. 1922). The height and duration of the 

 fever in guinea-pigs is variable, and great care should be taken before concluding that it 

 is definitely caused by the typhus virus. Ecker and Weed (1932) and Badger (1933a, b) 

 point out that symptoms very suggestive of infection with R. prowazeki or R. rickettsi 

 may be produced in guinea-pigs by certam organisms of the Proteus and Salmonella groups. 

 Cultural, serological and cross-immunity tests may all be required to estabUsh the real 

 causative agent in any given febrile condition. According to Arkwright and Bacot (1923), 



