Pathogenesis. 71 



Infection in the barn is also possible. A porous and con- 

 tinually moist soil of improperly arrano-ed hog pens, also 

 the soil of the stables of other animals, the moist soil in the 

 neighborhood of drinking places, stagnant water in the latter, 

 offer a chance for the further development of embryos which 

 are coughed up by infected animals. Indeed, lungworm disease 

 has repeatedly been observed in young pigs which have never 

 left the pen (Schultz, Moussu, Marek), or in cattle kept perma- 

 nently in the barn (Kasparek, Sclieiliel). Sucking animals may 

 occasionally infect themselves from the udders of their mothers 

 which have become infected through contaminated straw. Ex- 

 ceptionally an infection may occur through dry feed contami- 

 nated with desiccated but living larvae. 



The brood of the worms is usually taken up into the body 

 of the host in spring, at the beginning of pasturing; newer ob- 

 servations, however, permit the conclusion that infection may 

 also occur in summer and even late in the fall (Schultz). Ac- 

 cording to Docter, field hares infect themselves in fall. Eepeated 

 invasions are not at all rare. 



Direct contagion does not occur; experiments to infect 

 healthy animals through the introduction of bronchial mucus 

 containing embryos into the respiratory passages or into the 

 stomach, or by the intravenous introduction of embryos and 

 ova (Leuckart, Schlegel), were not successful. 



Susceptibility. Young animals who have at least reached 

 an age of several weeks are preferably affected. The observa- 

 tion of Kasparek, according to which calves one and one-half 

 to eight days old were affected, has remained unique. Older ani- 

 mals are aifected more rarely in direct proportion to advancing 

 age. Sometimes, however, sheep and goats are affected equally 

 and independently of age, especially in infection with Str. cap- 

 illaris. The clinical sjmiptoms are, however, usually much 

 milder in older animals. 



Pathogenesis. With the ingestion of food and drink the 

 larvae get into the stomach, and from there, during rumination 

 or by active wandering toward the pharynx, they g;et into the 

 respiratory passages. Ztirn, Spinola and Csokor claim that the 

 worm brood may "also get directly into the air passages by the 

 inhalation of dust from contaminated pools and marshes. The 

 idea that the larvae may get directly into the lungs with the 

 blood current has been' generally abandoned. Joest, however, 

 believes that this mode of invasion, with a subsequent migration 

 of the brood from the lung into the bronchi, cannot be entirety 

 denied. Strongylus larvae which get into the bronchi, prolial^ly 

 invade then the smaller bronchi, some also the pulmonary alveoli, 

 and produce, partly by their motion, partly by their metabolic 

 products, an inflaiinnation of the invaded bronchi (bronchitis 

 verminosa) or of the alveoli. Since the invasion is usually not 

 very intense, and since the degree of inflammation and the num- 



