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CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE 



heart to the lungs. If many worms go through the lungs at the same 

 time they injure this organ and may produce pneumonia. This 

 roundabout journey from the intestine to the liver and thence to the 

 lungs is completed in about a week. From the lungs, the larvae 



Figure 7. — Life cycle of the horse ascarid, Parascaris equorum. The eggs shown 

 in this illustration are enlarged about 50 times. 



crawl up the windpipe until they reach the back of the mouth and 

 are then swallowed. In getting into the small intestine from the 

 stomach for the second time, they settle down and develop to maturity 

 in from about 2 to 2% months (fig. 8). 



Symptoms and lesions. — When ascarids are present in large numbers, 

 which is likely to be the case in foals and young horses, they produce 

 digestive disturbances of various sorts and may cause colic. These 

 parasites frequently become entangled with one another, resulting in 

 large masses of worms which may plug the lumen of the intestine. 

 In an extreme condition of this sort the results may be fatal. Such 

 an entangled mass of worms may even rupture the wall of the intestine 

 as a result of continuous pressure on it. These worms have also been 

 reported as being capable of perforating the wall of the intestine, 

 presumably as a result of continually pushing their heads against it. 

 In either case, a rupture of the intestinal wall would usually cause 

 the death of the horse. 



