PARASITIC PROTOZOA 363 



000,000, and in many parts of the world it is almost impossible 

 to keep cattle because such a large per cent, of them die of 

 the disease. The parasite, Babesia bigeminum, that causes the 

 disease is transmitted by the common cattle tick, or Texas 

 fever tick, Mar gar opus annulatus, in the United States, and by 

 closely related species in other countries. The infection is not 

 direct, that is, the tick does not feed on one host, then pass 

 directly to another, carrying the disease germs with it. Unlike 

 many other ticks the Texas fever tick does not leave its host 

 until it is fully developed. When the female is full grown 

 and gorged she drops to the ground and lays from 1000 to 

 4000 eggs from which the minute "seed ticks" soon hatch. 

 These make their way to some nearby blade of grass or shrub 

 and at the first opportunity attach themselves to any cattle 

 that may pass that way. 



If the mother tick feeds on an animal that is infected with 

 Texas fever some of the parasites that she takes into the body 

 will find their way into her eggs, and the young ticks that hatch 

 from these will be infected and ready to transmit the disease 

 to their host. 



It has been found that the Southern cattle in the regions 

 where the ticks occur normally usually have a mild attack of 

 the disease when they are young, and although they may be 

 infected with the parasite all the rest of their life it does not 

 affect them seriously. But these cattle are a source of danger 

 when taken into a region where the ticks do not occur naturally, 

 for the larvae that issue from the eggs laid by the infected adult 

 ticks may attack non-immune cattle which soon sicken and die. 



At present in the United States no cattle south of a certain 

 quarantine line are allowed to be taken north except under 

 very strict regulations. It has been demonstrated that by a 

 system of feed-lots and pasture rotation many infested regions 

 may be made perfectly safe. The aim is to let all of the ticks 

 drop to the ground on land where they may be destroyed or 

 left to starve. When it is necessary to treat cattle that are 

 badly infested with ticks, large vats are built and filled with a 

 dipping solution and the cattle are then driven through it. 

 Many different kinds of solutions have been used for this pur- 



