Prevention, Immunization. 777 



In the United States and North America the destruction of ticks was inaug- 

 urated on a large scale in 1906. On this occasion 220,780 cattle were infested with 

 ticks in 29,315 examined herds, and 328,064 were found to be free (Steddom). 

 The procedure consists in placing the herds for three weeks in enclosed pastures 

 free of ticks, until the young ticks become mature ana drop to the ground. Then 

 the animals are driven to another uninfected pasture, and their former stands are 

 disinfected. It is also aimed to clear the cattle pasture from ticks by keeping the 

 cattle away for about six months, when the ticks are destroyed by starvation, or 

 large pasture areas are burned over in the spring. 



Immunization. As cattle recovering from the disease ac- 

 quire a long-lasting immunity in North America (Schroeder) 

 and Australia (Gray), cattle brought from non-infected terri- 

 tories into affected localities are infected artificially with blood 

 of calves born in infected territories or of recovered cattle, 

 which, as a rule contain piroplasma sparingly. After such 

 inoculations the animals become sick after 8 to 10 days, some- 

 times with symptoms of anemia, hemoglobinuria, frequently 

 also with bloody diarrhea, and at the same time the number 

 of red blood corpuscles, some of which may contain typical 

 piroplasma, diminishes 10% or more. This symptom disap- 

 pears after 8 to 10 days; after a month, however, a second 

 reaction usually appears, which lasts 8 to 10 days, and 

 the red blood corpuscles contain only atypical piroplasma 

 in very small numbers (Theiler). If cattle so treated are 

 driven to infected pastures after the lapse of about two 

 months, a number of animals resist the natural infection, in 

 tlie others, however, fever appears again as a result of the 

 tick bites. In most of the animals recovery finally takes place, 

 but a certain percentage succumb to the disease (Francis). 

 Inasmuch as this percentage is considerably smaller than the 

 loss observed from non-inoculated animals under the same 

 conditions, the inoculation appears to be advantageous in 

 strongly infested localities, in spite of the fact that the inocula- 

 tion itself causes disturbance of nutrition, and sometimes even 

 direct losses. 



Blood from older cattle which have recovered shortly before 

 from the disease is also suitable for immunization, and gives 

 similar results. 



The immunizing action of the blood from animals shortly before 

 recovered has been confirmed through experiments, by Smith & Kil- 

 horne, also Schroeder in North America, Francis in Texas, Hellens in 

 Finland, Koch in Africa, Theiler in Kossell, Schiitz, Weber & Miessner 

 in Germany. 



In Germany the immunization is carried out with blood of artificially infected 

 calves, and has recently been employed extensively in practice; until the end of 

 1909, 6,153 cattle were immunized, principally in Prussia. According to the reports 

 on 4,261 inoculated cattle, 1.97% became mildly and 0.49% severely affected, and 

 recovered, and 0.09% died or were slaughtered. Besides, during pasturing 2.98% 

 became mildly, 0.54% severely affected and recovered, 0.54% died or were slaugh- 

 tered. The percentage in young stock amounted to only 0.04%, in adults 1.46%. 

 In 10 herds of the immunij'ed animals 4.14% were mildly, 0.46% severely affected; 

 of those not immunized 19.63% mildly, and 7.48% severely affected (Schmitt). 

 Satisfactory results are reported by Graffunder and Bugge. Less satisfactory 



