218 Diseases of Poultry 



where they live and breed. The most thorough study yet 

 made of this parasite and its effect on birds is that of Haiduk.^ 



Diagnosis. — This very common disease is easily recognized 

 by the enlarged roughened appearance it gives the foot and 

 shank. This appearance is shown in Fig. 41, with a normal 

 leg for comparison. 



The disease is present in most flocks unless especial care 

 has been taken to exclude it. It is slightly contagious, but 

 usually only a few birds in a flock appear to be infected. The 

 scales on the foot and leg of an affected bird are raised by a 

 crusty substance deposited beneath them. The lesions 

 usually appear first near the joints between the toes and 

 foot. The parts affected first appear to be enlarged and 

 then the scales are raised, giving the roughened appearance 

 shown in B, Fig. 41. In early stages the disease does not 

 appear to disturb the general health of the fowl. As it 

 progresses the birds become lame and sometimes the foot 

 becomes so badly diseased that joints or even whole toes 

 drop off. The photograph of a badly affected leg is shown in 

 Fig. 42. The two legs are usually affected equally. 



Etiology. — The disease is caused by the minute parasitic 

 mite Knemidocojjtes mutans (Figs. 43 and 44). 



The mites bore under the scales of the foot and leg and 

 burrow deeper and deeper into the tissue. They set up an 

 irritation which leads to multiplication of cells and the 

 exudation of serum. This accumulation forms crusty 

 deposits beneath the scales. These crusts contain many 

 depressions in which are embedded female mites containing 

 eggs. The larvae and the males are usually found beneath 

 the crusts. The relations just described are shown in Fig. 

 45 which is a picture of a section of the skin of a "scaly" 

 leg. 



1 Haiduk, T., "Die Fussrjiuder des Gefliigels." Inaug. Diss. 

 Giessen, 1909, pp. 1-58, Taf. I-VI. 



