144 COMMON DISEASES. 



horses and mules. Calves at birth are as a rule immune ; but 

 this immunity is gradually lost until at two years of age nearly 

 all are highly susceptible to the disease. Cattle reared in the 

 southern states on tick-free pastures arc as susceptible as those 

 raised in the North. 



Period of incubation. — The disease usually develops in from 

 seven to ten days after direct inoculation of a susceptible animal 

 with the blood of one infected, or that has acquired immunity from 

 a previous attack. When infection occurs in the natural way, 

 about the same time usually elapses between exposure to tick 

 infestation and the development of the disease. This period is 

 not always uniform, for in some cases no evidences of the dis- 

 ease can lie detected before fifteen to thirty days after inocula- 

 tion. However, a large percentage of cases develop within ten 

 days after inoculation. 



Symptoms. — Tt is frequently stated that tick fever occurs in 

 acute and chronic forms. The chronic form, however, usually 

 follows the acute and appears months after the acute attack. 

 These relapses or secondary attacks are not uncommon in the late 

 fall and earlv winter. It is then difficult to distinguish them 

 from ordinary debility from other causes except by the history of 

 a previous attack or by an examination of the blood. 



Fever. — In the acute type of the disease an elevation of tem- 

 perature is usually the first noticeable symptom. A temperature 

 of 107 degrees or ?o8 degrees F. is not unusual but when it 

 reaches 105 degrees or 106 degrees other symptoms usually be- 

 come apparent. While there are considerable fluctuations in tem- 

 perature it generally remains high during five to seven davs and 

 may then drop suddenly to normal or below. Many animals die 

 during the extremely high temperature, or, if the temperature 

 falls, it is only as a prelude to deaths. The period of subnormal 

 temperature is a dangerous one and collapse should be fortified 

 against. Otherwise an animal may succumb that might by proper 

 treatment be saved. 



Other symptoms. — The patient usually stands apart with the 

 head down and back arched. In severe cases or when death ap- 

 proaches, it may lie or fall down. The pulse usually runs from 

 80 to 100 and the respirations from fifty to sixtv per minute. In 

 most cases during the extremely high temperatures, the urine is 

 highly colored, sometimes becoming of port wine color or almost 



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