326 ANEMIA 



tions prove negative. Animals other than chickens are not 

 susceptible to the disease. 



Pathogenesis. The method of development of infectious 

 leukemia has not been definitely proved. The virus of the 

 disease by irritation produces an increase in the number of 

 white blood cells in the capillaries of the spleen, bone-marrow 

 and liver. 



Pathology. The most pronounced lesions are found in the 

 spleen, liver and marrow of the bones. The spleen and 

 liver are much enlarged, and the bone-marrow reddened and 

 congested. The lymph glands are also enlarged occasionally. 

 The blood is lighter in color than normal (less hemoglobin) 

 and contains a larger proportion of leukocytes than normally. 

 General anemia is apparent by the wasted tissues. 



Symptoms. The period of incubation is approximately 

 thirty to sixty days. The disease develops very slowly and 

 insidiously. Some cases may assume an acute form, the 

 birds succumbing in about two weeks. The early indications 

 are anemia as indicated by the paleness of the comb and 

 wattles and a decided loss in weight. Later as the disease 

 continues there is a tendency for hemorrhages to take place 

 even from slight wounds, indicating a hemorrhagic diathesis. 



Examination of the blood reveals the true condition. 

 There will be found a great increase in white corpuscles and 

 a material reduction in the number of red. The latter may 

 be reduced to one-fourth their normal number. The hemo- 

 globin content of the blood is also reduced giving it a pale 

 color and reducing its staining properties. 



The condition when chronic develops gradually and the 

 chicken often dies from exhaustion. 



Course. The course of the disease is quite variable. Many 

 cases apparently run a very rapid course after the appearance 

 of the first symptoms, lasting from one to three weeks. 

 Others may linger longer or from one to four months. 



Diagnosis. The diagnosis can be established only by 

 necropsy and a microscopic examination of the blood to deter- 

 mine the ratio of the white to the red corpuscles. Differen- 

 tial diagnosis may be difficult, but considering the lesions 



