288 



THE PIROPL«iSM.\SIDA 



corresponded completely with that of B. 

 canis in Derniacentor reticulaliis. After 

 numerous binary fissions, the protozoa 

 turn into the motile, vermiform stage and 

 enter the developing eggs of the female 

 tick, where development continues. He 

 found no evidence of sexual stages. 



Muratov and Kheisin (1959) described 

 a similar process for B. bigonina in 

 Boophilus calcaralus, except that they 

 said that schizogony occurs. They studied 

 only the stages in the females and their 

 eggs. On the day after the tick drops from 

 its host, the protozoa begin to reproduce 

 in its intestine by binary fission or by 

 schizogony, producing club-shaped forms 

 which penetrate into the epithelial cells of 

 the intestine. Here they develop and un- 

 dergo atypical multiple fission, character- 

 ized by asynchronous segmentation, into 

 amoeboid or round agamonts. These be- 

 come club- or cigar-shaped, penetrate 

 other intestinal cells and repeat the asex- 

 ual cycle. The dividing stages in the intes- 

 tinal cells are up to 30 to 45 ji in diameter 

 and produce about 250 daughter parasites. 



Some of the club-shaped stages enter 

 the body cavity and divide further. They 

 penetrate all the organs of the female, 

 including the ovary, and continue to divide. 

 In the ovary they enter the eggs and divide 

 by binary or multiple fission just as in the 

 intestine, producing round or amoeboid 

 agamonts which turn into club-shaped 

 stages. Their number increases as the 

 eggs develop, and they are distributed 

 thruout the organs of the developing larvae. 

 Muratov and Kheisin found no evidence of 

 copulation or sexual reproduction. 



Polyanskii and Kheisin (1959) found 

 essentially the same pattern for B. bovis 

 in Ixodes ricinus. They said that it re- 

 produces by binary fission or schizogony 

 in the tissues of the tick and in the eggs 

 of infected females, and found no stages 

 of sexual reproduction or sporogony. 



Quite a different process was des- 

 cribed by Dennis (1932) for B. bigemina 

 in Boophilus annulatus . According to him, 

 when a female tick ingests blood, most of 

 the parasites in the blood are destroyed, 

 but some of them turn into vermiform bod- 



ies about 6|i long which he considered to be 

 gametes and which he called isogametes 

 because they all look alike. They move 

 actively by bending or gliding. Two of them 

 unite to form a motile, club-shaped zygote 

 or ookinete 7 to 12/i long. The ookinetes 

 pass thru the intestinal wall, enter the 

 ovaries and then the eggs. Here they round 

 up to form sporonts 7. 5 to 12)i in diameter. 

 The sporonts grow, and then divide by mul- 

 tiple fission into 4 to 32 amoeboid sporo- 

 blasts. The nuclei of the sporoblasts divide 

 repeatedly, forming small, multinucleate, 

 amoeboid sporokinetes which are distribu- 

 ted thruout the tissues of the developing tick 

 embryo. The sporokinetes vary in shape, 

 being round, elongate, club- or ribbon- 

 shaped, and may be as much as 15fi long. 

 They contain a varying number of granular 

 nuclei 0.4jll in diameter. In the course of 

 the embryonal development of the tick, the 

 sporokinetes multiply, probably by plasmo- 

 tomy. All the tissues of the tick may be 

 invaded, and sometimes the cytoplasm of 

 a host cell is almost entirely supplanted by 

 the parasites, particularly in the salivary 

 glands. Toward the end of the tick's de- 

 velopment, some sporokinetes produce 

 sporozoites, which are the infectious stage. 

 Others produce them only after the larva 

 has hatched. The sporozoites resemble 

 minature trophozoites; they are piriform 

 and have a blepharoplast. They are par- 

 ticularly numerous in the salivary glands, 

 in the coelenchymatous tissue at the base 

 of the legs and around the viscera. They 

 are inoculated into the blood with the sa- 

 liva when the tick feeds. 



Petrov (1941) described a similar 

 process for B. bovis in Ixodes ricinus. 

 According to him, the isogametes fuse in 

 the tick's intestine to form an ookinete 

 which passes thru the intestinal wall and 

 enters a developing ovum. Here it rounds 

 up, forms sporoblasts, and these in turn 

 form sporozoites which pass to the sali- 

 vary glands. The larvae, nymphs and 

 adults of the succeeding generation can all 

 transmit the parasite. 



It should be said that Reichenow (1953) 

 considered some of the stages described 

 by Dennis to be normal, intracellular sym- 

 bionts (cf. Buchner, 1953; Koch, 1956) 

 rather than Babesia. 



