Metastrongylus apri frequently lives in the bronchial tubes—usually the smaller ones—of the pig[309] and wild boar; it is also found occasionally in sheep and in man; in young pigs it is apt to set up a bronchitis, which frequently causes death.
The first communication as to the occurrence of this species in man was that of Diesing, who, in 1845, in Klausenburg, had the opportunity of examining Strongylidæ found by Jortsits in the lung of a little boy, aged 6, in Transylvania; probably also the Nematodes found in the trachea and larynx of man, and described by Rainey and Bristowe as specimens of Filaria trachealis, belong to this group; according to Chatin, Metastrongylus apri may also occur in the intestine of man; this occurrence, however, may in all probability have been due to an accidental introduction of adult worms into the intestine, and should not be attributed to an infection by the larval stage.
No experiments to induce infection have been made; it is probable, however, that infection is direct and without the aid of an intermediate host.
Sub-family. Trichostrongylinæ, Leiper, 1908.
Strongylidæ with buccal capsule absent or slightly developed, vagina short, uteri divergent (i.e., anterior and posterior), ovejectors differentiated. Parasitic in the alimentary canal. Contains the genera Trichostrongylus, Hæmonchus, Ostertagia, Nematodirus, Cooperia, Dictyocaulus.[310]
Genus. Trichostrongylus, Looss, 1905.
Very small Strongylidæ. Mouth with three small lips and nodular or punctiform papillæ. Cervical papillæ absent. Bursa entirely closed, with large lateral lobes, and median lobe not distinctly defined. Anterior[311] rays double, the branches widely divergent, one thin, the other thick, and close to the antero-median. The postero-median ray is thin and close to the postero-external. Posterior ray bifurcate, each branch bifid at the tip (fig. 311). Spicules short, spoon or spatula-like, with on the broad anterior end a lateral knob or disc and in front of the point an angular projection. Gubernaculum of a peculiar canoe or shoe shape in profile. Vulva in the hinder half of the body. Tail with two minute papillæ just in front of tip. Eggs thin shelled; when laid they show eight to thirty-two segments. Parasitic in duodenum, seldom in the stomach of herbivora.
