THE PIROPLASMASIDA 



287 



important place in the animal disease 

 picture as we discover new manifesta- 

 tions of their activity. 



Among recent discussions of babesi- 

 osis and its manifestations are those by 

 Curasson (1943), Sergent et al. (1945), 

 Muromtseva and Dobrokhotova (1955), 

 Henning (1956), Malherbe (1956) and 

 Antipin et al. (1959). 



Life Cycle : The trophozoites of 

 Babesia occur in the erythrocytes, where 

 they multiply by binary fission or by schi- 

 zogony. In some species, two tropho- 

 zoites are formed, which break out of the 

 erythrocytes and enter new red cells, 

 while in others tetrads composed of 4 

 trophozoites are formed. Some authors 

 place the latter in a separate genus, 

 Nuttallia. The formation of more than 4 

 trophozoites by schizogony has also been 

 described in the erythrocytes (Dschun- 

 kowsky, 1937; Ivanic, 1942; Delpy, 1946), 

 but most workers (e. g. , Reichenow, 1953) 

 consider that it is merely simulated by 

 repeated binary fissions or by multiple 

 invasion of a host cell. 



The above asexual cycle continues 

 indefinitely, the animals sometimes re- 

 maining infected for life. 



Babesia is transmitted by ticks. The 

 discovery of this fact--by Smith and Kil- 

 borne (1893) for B. bigemi)ia of cattle-- 

 was a milestone in the history of para- 

 sitology, since it was the first demonstra- 

 tion that an arthropod was the vector of 

 any disease. 



Dennis (1932) described sexual re- 

 production of B. bigemina from cattle in 

 the tick, Boophilus annulatus , and Petrov 

 (1941) did the same for B. bovis in Ixodes 

 ricinus. However, Regendanz and Reich- 

 enow (1933) denied its existence in the 

 life cycle of B. canis from the dog in 

 Derniacentor reticidatus, and Regendanz 

 (1936) and Muratov and Kheisin (1959) 

 found no evidence of sexual reproduction 

 in 5. bigemina in Boophilus microplus 

 and B. calcaratus, respectively, nor 

 could Polyanskii and Kheisin (1959) for 

 B. bovis in Ixodes ricinus . It is likely 



that Dennis and Petrov may have been 

 misled by trying to draw an analogy with 

 the life cycle of Plasuiodiitiu . Pending 

 final settlement of the question, however, 

 both accounts are given below. 



According to Regendanz and Reichenow 

 (1933), most of the B. canis ingested by 

 the female tick die in its intestine. Some 

 of them become vermiform and enter the 

 intestinal epithelial cells, coming to lie 

 against the basal membrane, and grow 

 into large amoeboid forms. These then 

 multiply by a series of binary fissions, 

 producing more than 1000 individuals in 2 

 to 3 days. These lie together loosely at 

 first, but finally fill the whole host cell. 

 They then become vermiform and pass 

 into the body cavity. 



The vermiform stages are broadly 

 rounded at the anterior end and pointed 

 posteriorly, about 16jj, long, and have a 

 gliding motion. They enter the ovary, 

 where they penetrate the eggs. Here they 

 round up and divide a few times, forming 

 very small round individuals. They do 

 not develop further in the larval tick 

 which hatches from the egg, but when it 

 molts they enter the salivary glands and 

 continue their development. This first 

 occurs in the nymphal stage, but is much 

 more active in the adults, both male and 

 female. The parasites undergo a series 

 of binary fissions and enter the cells of 

 the glandular acini. Here they multiply 

 further, becoming smaller and filling the 

 whole host cell, so that it finally contains 

 thousands of minute parasites. These 

 become vermiform, break out of the host 

 cell, come to lie in the lumen of the gland, 

 and are injected into the host when the tick 

 sucks blood. The developmental process 

 in the salivary glands takes 2 to 3 days. 



The tick larvae are not able to infect 

 new hosts. The nymphs may do so, but 

 generally it takes so long for the parasites 

 to reach the salivary glands that most 

 transmission, in this species at least, is 

 by the adults. 



Regendanz (1936) found that the devel- 

 opment of Babesia bigeniiiia from cattle in 

 the intestinal wall of Boophilus microplus 



