The larvæ of the Linguatulidæ bore through the intestinal wall and reach the liver, more rarely the mesenteric glands, etc.; they here become encysted and enter a sort of pupal stage in which they lose their limbs; after several moultings and gradual growth the second larval stage, having the appearance of the adult Linguatula, sets in. About five to six months after infection the creatures have become 4 to 6 mm. long, possess eighty to ninety rings, which have a series of fine points on their posterior border; the mouth and intestine are formed, the sexual organs mature and the two pairs of hooks are near the mouth. This larval stage (fig. 372) has been known for a long time, but it was regarded as an independent species of animal, and therefore had a separate name (Linguatula serrata, Fr.; Pentastoma denticalatum, Rud., etc.).
Later these Linguatula larvæ make an attempt to escape from their hosts, and this, of course, can only be effected by means of an active migration; they leave the cysts, and according to their respective positions in the abdominal or pleural cavities they reach the bronchi or the intestine, and finally pass out; they may be again sniffed up by dogs and settle in their nasal cavities. Still this outward migration does not appear to be necessary for further development. A portion of the larvæ gain access to the nasal cavities directly through the trachea, and thus herbivorous mammals certainly become directly infected. In most cases the infection of dogs, wolves and foxes, that is, of carnivorous mammals, takes place through consuming the bodies of mammals, or parts of them, such as the liver and lungs, which are affected with the second larval form; in any case most larvæ obtain access first to the stomach of their host, from here they make an active migration through the œsophagus to the oral and nasal cavities, in which they settle. It is possible also that the same larvæ which are free in the oral cavity when the food is being eaten migrate into the nasal cavities. After being stationary a fresh skin is formed and the spine-bearing cuticula are thrown off. The male attains its full size in the fourth, and the female in the sixth month. The duration of life is stated to be from fifteen months to several years.
Fig. 373.—Linguatula rhinaria: on left, eggs in gelatinous covering, 110/1. On right, first larval stage. 300/1. (After M. Koch.)
L. rhinaria has been observed in man in the adult as well as in the larval condition (Pentastoma denticulatum). Zenker first called attention to the occurrence of the larva in man, having found it nine times in the liver in 168 autopsies. Heschl found it twice in Vienna in twenty autopsies, Virchow found it in Würzburg and Berlin, Wagner in Leipzig (10 per cent.), and Frerichs in Breslau five times in forty-seven autopsies. The parasite is much less frequent in Switzerland. According to Klebs, one case occurs in 900 autopsies, and according to Zaeslin two cases occurred in Basle to 1,914 autopsies. In the Seamen’s Hospital in Kronstadt P. denticulatum has been found six times in 659 autopsies. It was almost always the liver that contained one or a few specimens. The parasite was very rarely found in the kidney or spleen, or encysted in the intestinal wall. The adult L. rhinaria is far more rarely observed in man.
A case reported by Landon that related to a blacksmith of Elbing is particularly interesting. This man accompanied the campaign of 1870; he soon, however, fell ill with pains in the liver, accompanied by icterus and intestinal disorders. Soon after the war, and after the symptoms were reduced to icterus and weakness, bleeding of the nose set in and continued with slight intermissions for seven years; an unpleasant sensation of pressure in the left nasal cavity set in, with inflammatory swelling of the mucous membrane. At last, in the summer of 1878, when the pressure in the nose had considerably increased, a Linguatula was expelled from the nose with a violent attack of sneezing, and lived for three days longer in water. The bleeding of the nose then ceased and the patient soon recovered. There can be no doubt that the first illness was connected with the invasion in the liver of numerous larvæ of Pentastoma, and disappeared after their encystment; one or a few of these must subsequently have found its way to the nose and settled there.
Genus. Porocephalus.
Porocephalus constrictus, v. Siebold, 1852.
Syn.: Nematoideum hominis, Diesing, 1851; Pentastomum constrictum, v. Sieb., 1852; Porocephalus constrictus, Stiles, 1893.