342 



SARCOCYSTIS, TOXOPLASMA AND RELATED PROTOZOA 



Geographic Distribution: Worldwide, 



Prevalence : Perrin (1943) found 

 Enceplialitozuon in the brains of 5 of 502 

 Swiss mice, 2 of 283 Wistar strain albino 

 rats, and 1 of 291 guinea pigs at the Na- 

 tional Institutes of Health, Bethesda, Md. 

 It has been encountered sporadically by a 

 number of workers in laboratory rabbits, 

 mice and rats (Frenkel, 1956; Perrin, 

 1943). In most cases it has been found 

 during routine histologic examination of 

 animals being studied for some other pur- 

 pose. 



Plowright (1952) described 3 cases in 

 a litter of foxhounds in England, and Plow- 

 right and Yeoman (1952) found it in a litter 

 of puppies in Tanganyika. They also re- 

 viewed the literature on previous reports 

 of what may have been the same organism 

 in dogs. Jungherr (1955) found it in a 

 cottontail rabbit. 



Morphology : The trophozoites meas- 

 ure 2.0 to 2. 5 by 0. 8 to 1. 2 fi in tissue 

 sections and up to 4. by 2. 5 fx (mean, 

 2. by 1 . 2 /J, ) in smears (Perrin, 1943a). 

 They are straight to slightly curved rods 

 with both ends bluntly rounded but one end 

 a little larger than the other. The body 

 is sometimes slightly constricted at or 

 near its midpoint. Round or oval forms 

 occasionally occur. The nucleus is com- 

 pact, round, oval or bandlike, about 1/4 

 to 1/3 the size of the parasite, and is not 

 central. Pseudocysts containing up to 

 100 or more trophozoites are found within 

 the nerve cells, macrophages or other 

 tissue cells. Both they and the tropho- 

 zoites are rarely extracellular. 



Life Cycle : The mode of multiplica- 

 tion is unknown. The organism can be 

 transmitted from the mouse, rabbit, rat 

 or guinea pig to other laboratory animals 

 by intracerebral, intravenous, intraper- 

 itoneal or other parenteral inoculation of 

 infected brain, liver, spleen or peritoneal 

 exudate (Perrin, 1943a). It has been 

 found in the urine. Congenital infection 

 undoubtedly occurs in mice (Perrin, 1943) 

 and probably in rabbits (Smith and Flor- 

 ence, 1925) and dogs (Plowright, 1952). 



Pathogenesis : E. cuniculi causes 

 encephalitis and systemic disease asso- 

 ciated with nephritis in rabbits and pup- 

 pies, and an inapparent infection in labor- 

 atory rodents. The great majority of cases 

 in rabbits are also inapparent, being dis- 

 covered on histologic examination carried 

 out for some other reason. Its true im- 

 portance in dogs is unknown, since it has 

 been seen very rarely in them. 



Encephalitozoonosis is usually a mild, 

 chronic, infection in rabbits, altho paral- 

 ysis and death may occur. The principal 

 lesions in the brain are tiny, focal granu- 

 lomata made up of epithelioid cells sur- 

 rounding a tiny area of necrosis. In fatal 

 cases there may be large necrotic areas 

 and perivascular lymphocytic cuffing. The 

 parasites may occur in or around the ne- 

 crotic areas. Similar granulomatous 

 lesions may be present in the kidneys and 

 other organs. In the kidneys they occur 

 principally in the epithelial cells of the 

 collecting tubules, which they distend and 

 finally rupture, passing out in the urine 

 (Smith and Florence, 1925). 



In mice and rats the principal lesions 

 are meningoencephalitis and, in experi- 

 mentally infected animals, abdominal en- 

 largement with ascites. Nodular, granu- 

 lomatous lesions, sometimes with central 

 necrosis, occur thruout the brain. There 

 is slight to moderate focal perivascular 

 infiltration by lymphocytes and a few large 

 mononuclear and plasma cells in the men- 

 inges and also in the brain. The parasites 

 may be either within or at the margins of 

 the lesions or even in normal brain tissue 

 at a distance from them. There may be 

 moderate to marked interstitial lymphocytic 

 infiltration in the kidneys, primarily in the 

 cortex. The tubular epithelium may be de- 

 generate or proliferative in the areas of 

 infiltration, and parasites may occur either 

 in the epithelial cells or within the collect- 

 ing tubules. Similar areas of infiltration 

 may be seen in other organs (Perrin, 1943). 



According to Frenkel (1955), treatment 

 with cortisone exacerbates the disease in 

 mice. The parasites proliferate exten- 

 sively in most organs, and the mice may die. 



