2 LEAFLET NO. 5, U. S. DEPARTMENT OF AGRICULTURE 



cations, often with pus production, sometimes follow the invasion 

 of the lungs by the young worms, and these infections share the 

 responsibility for stunted growth ot pigs. 



Investigations and experiments have also shown that pigs are most 

 susceptible to infection and suffer most seriously from the infection 

 during the first few weeks of life. As they grow older they become 

 more resistant, have fewer worms, and suffer less from both the young 

 worms in the lungs and the older ones in the intestine. Little pigs, 

 therefore, require special protection. 



Sources of Infection 



Pigs become infected by swallowing the eggs of the parasite. 

 These worm eggs are of microscopic size and are found in the manure 



■~fo /mrfcrrrfy m ado/* <? morif/iS. >'r> 



s.oas and am swafiave?. 



A'o-'fn eyas conte/n-.y you/i<? >vc-~>s 

 are acted up from ground and stva/ 

 Sowed fS-se Ato. .?„ ' 



(7) 



After a fe-v rJays n /ungs, yds"? 



,.-. s r"7.'/. dr -v. !/-.-jz- ce r-^ -t-jc 



ofmoufr, ar>: s *'a.>; orf'ea 'See '/c : 



rarr) h,;a'' ycuni ,;-?rm go fo 'jy.> 4 

 i?) dead '/eiseJs and ' ^/Vrv'seyero/" '"""' 



,mf />;r,yer ^Ser 



(~3 , i "'.:'*r dyeryaung worms qo rt> near? '/ 

 (See No 4 J 



Fig. 1. — The course traveled by the roundworm in the pig. The worm eggs are swal- 

 lowed by the pig and hatch in the intestines; the young worms go by way of the 

 blood vessels to the liver and then to the lungs; here they leave the blood vessels 

 and enter the air passages ; go up the windpipe to the mouth and are swallowed ; 

 return to the intestines where they develop to adult worms ; and the female worms 

 produce eggs which pass out in the manure and start a new journey through the 

 pig which swallows them 



of infested hogs or on and in the soil of places that have been occu- 

 pied by infested hogs and hence contaminated by their droppings. 

 It has been estimated that one full-grown female worm in the intes- 

 tine of a hog may contain as many as 26,000,000 to 27,000,000 eggs. 

 At the time they are passed out of the body of the hog in the drop- 

 pings the eggs are not infective. But in a few weeks or months, 

 depending on the weather and various other conditions, the egg 

 develops to a stage at which it contains a tiny worm, and it is then 

 ready to infect the pig which swallows it. The eggs are very resist- 

 ant to cold weather and drought ; they are not killed by most chemical 

 disinfectants, and are very long-lived (some may live as long as five 

 years). Not all adult hogs harbor intestinal worms, even though ex- 

 posed to infested soil; commonly, however, the parasites may be 

 found in one out of three hogs of breeding age. Worms which can not 

 be distinguished from the swine ascarid are also not uncommon in 



