338 



SARCOCYSTIS, TOXOPLASMA AND RELATED PROTOZOA 



pseudocyst wall is composed of a thin 

 inner layer containing several flattened, 

 giant nuclei and a thick, homogeneous or 

 concentrically laminated outer wall. The 

 trophozoites in the pseudocysts are cres- 

 centic or banana-shaped, with 1 end pointed 

 and the other rounded. According to Pols 

 (1954) the trophozoites in blood, lung and 

 testis smears of experimentally infected 

 rabbits measure 5 to 9 by 2 to 5 fi and are 

 usually elongate oval and slightly pointed 

 at one end. Banana-shaped and crescentic 

 forms are found more rarely. The nucleus 

 is more or less central. 



Life Cycle : The natural mode of 

 transmission is unknown, but it is prob- 

 ably thru ingestion. Hofmeyr (1945) gave 

 circumstantial evidence that the infection 

 is spread thru contaminated watering 

 troughs in South Africa, Jellison, Fuller- 

 ton and Parker (1956) transmitted the re- 

 lated B. jellisoni to house mice by feeding 

 trophozoites from cysts of infected deer- 

 mice or from peritoneal fluid of infected 

 house mice. 



Cuille and Chele (1937), Barrairon 

 (1938) and Pols (1954) transmitted B. 

 besnoiti to cattle by intravenous injection 

 of blood from cattle in the primary stage 

 of the disease. Pols also infected an ox 

 by intraperitoneal injection and rabbits 

 by intravenous, intraperitoneal and sub- 

 cutaneous injection of blood. He passed 

 the protozoon from a rabbit thru 2 gener- 

 ations of cattle and back to a rabbit. 

 Later (1954a) he reported having passed 

 it thru 19 serial passages in the rabbit. 

 He was unable to infect mice, rats and 

 guinea pigs. 



The incubation period in the cattle 

 infected by Pols varied from 6 to 10 days, 

 and that in the rabbits from 6 to 16 days. 

 It was followed by a thermal reaction 

 which lasted 2 to 5 days. Cysts were 

 found in the skin of naturally and artifi- 

 cially infected cattle 6 to 28 days after the 

 beginning of the temperature reaction. 



Pols (1954a) described cyst formation 

 in experimentally infected rabbits. The 

 initial stages were seen as early as 16 to 

 18 days after inoculation. When a tropho- 

 zoite invades a histiocyte, a vacuole is 



formed around it. The trophozoites in 

 tissue sections measure about 3 by 1. 5 /i, 

 and the vacuoles are about 8/j, in diameter. 

 The trophozoites multiply by binary fission; 

 Pols saw a few cases of multiple fission 

 but they were so rare that he considered 

 them aberrant. It is possible that the troph- 

 ozoites may actually divide by endodyogeny, 

 since Goldman, Carver and Sulzer (1958) 

 stated that this takes place in B. jellisoni. 



The nucleus of the host cell begins to 

 divide at the same time that the tropho- 

 zoites do, forming a multinucleate cell. 

 As the parasites multiply within the vac- 

 uole, the latter becomes larger and the 

 host cell c3d;oplasm is compressed to form 

 a narrow rim. This is the middle layer of 

 the pseudocyst wall. Within it is an inner 

 membrane which can be seen only if 2 

 trophozoites have invaded the same host 

 cell, in which case it forms a thin line be- 

 tween the resultant cysts; it is uncertain 

 whether it is formed by the parasite, the 

 host or both. Concentric layers of colla- 

 genous fibers are laid down around the host 

 cell to form a hyaline capsule around the 

 whole; this is the outer layer of the pseudo- 

 cyst. 



Pathogenesis : The most complete 

 description of bovine besnoitiosis has been 

 given by Hofmeyr (1945). He found it in 

 cattle of all ages from 6 months up. Aged 

 animals were also affected. He recognized 

 3 stages in the course of the disease: 



The febrile stage . The first sign of 

 besnoitiosis is fever, up to 107° F but 

 usually lower. The animal develops a 

 photophobia and stays in the shade. The 

 hair loses its luster, especially along the 

 buttocks, limbs, flanks, lower abdomen 

 and neck. Marked anasarca develops, 

 especially along the lower line but some- 

 times over the whole body. The swellings 

 are warm and tender. The animals have 

 a stiff gait and are reluctant to move. The 

 pulse is fast, respiration is rapid, and 

 rumination decreases or ceases. Diarrhea 

 is sometimes present, and abortions are 

 not uncommon. The lymph nodes, espe- 

 cially the prescapular and prec rural ones, 

 are enlarged. Lachrymation and hyper- 

 emia of the sclera are present. The cor- 

 nea is studded with whitish, elevated specks 



