The adult Pentastoma tænioides is characterised by the possession of a vermiform, lancet-shaped body, flattened at the ventral surface, attenuated posteriorly, and marked transversely by about ninety rings (fig. 50, 1 and 2). The cephalo-thoracic segments are continuous with the body, each supporting a pair of strong retractile chitinous claws; four in all. The head is truncated, furnished with an oval mouth, armed with a horny lip. The integument of the body is perforated with numerous respiratory openings or stigmata. These are wanting in the cephalic segment. In the larval state (══ Pent. denticulatum) the body is armed with numerous rows of small, sharply pointed spines. The adult female measures from three to four inches in length, but the male is only about an inch long. The genital aperture of the female is situated at the extremity of the tail, that of the male being placed at the front part of the abdomen in the middle line. The mode of reproduction is oviparous, accompanied by a subsequent and complete metamorphosis.
In the mature condition this parasite infests the nostrils, and frontal sinuses of the dog and wolf, and also, though more rarely, the nasal cavities of the horse and sheep. In the pupal and larval states it sometimes occurs in the abdominal and thoracic cavities of the human body, but it is more frequently found in herbivorous mammals, such as the sheep, deer, antelope, peccary, porcupine, guinea-pig, hare, and rat. According to Creplin, it infests the domestic cat. In these animals and in man the young worms occupy little cysts within or upon the peripheral parts of the liver and lungs. I have occasionally found them free in the cavities of the abdomen and pleura.
In the course of the development of this entozoon, Leuckart recognises four well-marked stages. The first is that of the embryo with a boring apparatus. In the second stage, the embryo has become transformed into a motionless pupa. The third is the ordinary larval condition characterised by numerous rows of small spines in addition to two pairs of double claws. The fourth is the sexually-developed stage, furnished with a simple hook-apparatus, and without integumentary denticles. “Our Pentastomes, therefore,” says Leuckart, “exhibit two kinds of larval forms, an earlier and later one, such as takes place in other animals; this also occurs even in insects (Strepsiptera and Meloidæ), only that, in our case (i.e. in Pentastoma), both do not immediately follow one another, but are separated by a resting condition, which I have designated as the pupa stage. In choosing this name I do not mean to express a complete identity of this intermediate state with the pupal sleep of insects.”
Fig. 51.—Upper third of the body of Pentastoma denticulatum. Original.
So far as my own observations extend, the pupa, in its later stages, closely resembles the free larva; but, as Leuckart points out, the earlier stages are very different. The embryo, after encystation, repeatedly casts its skin, and during the intervals of these several successive moultings, the young animal makes rapid growth, accompanied by a series of structural changes. Passing through these it at length acquires the perfected larval state (P. denticulatum).
As regards the occurrence of this entozoon in the human body, the best account is that given by Frerichs. As quoted in my previous work from Murchison’s edition of Frerichs’ well-known clinical treatise, the German savant remarks:—“The Pentastoma is a parasite which has only recently been discovered in the human subject, but it is, nevertheless, far more common in the human liver than the echinococcus. It is devoid of clinical importance, because it does not give rise to any functional derangements. Pruner (‘Krankheit des Orients,’ 1847, s. 245) was the first who pointed out the existence of the Pentastoma in the human liver. On two occasions he found an encysted parasite in the liver of negroes at Cairo, the nature of which, however, he did not accurately determine. Bilharz and Von Siebold (‘Zeitschr. für Wissench. Zoologie,’ Bd. iv, s. 63) recognised in it a new variety of Pentastoma, to which he gave the name of P. constrictum. In Germany the Pentastoma was found in the human liver by Zenker (‘Zeitschr. f. ration. Med.,’ 1854, Bd. v, s. 224); it occurs, however, not only in this gland, but also in the kidneys, and in the submucous tissue of the small intestine (Wagner). The parasite is by no means rare with us. Zenker, at Dresden, succeeded in finding it nine times out of 168 autopsies; Heschl, at Vienna, met with it five times out of twenty autopsies; Wagner, at Leipsig, once in ten. According to Virchow, it is more common in Berlin than in Central Germany. During six months at Breslau I met with it in five out of forty-seven dead bodies. The Pentastoma-endemic in Germany is not identical with that which occurs in Egypt; the former is the P. denticulatum of Rudolphi.” This clear statement of Frerichs is valuable; but, as Murchison has also pointed out, there is some discrepancy between Frerichs and Küchenmeister’s record of Zenker’s experience. According to Küchenmeister, Zenker met with the Pentastoma thirty times in 200 autopsies.
Although from a purely clinical point of view, and speaking generally, this worm, as Frerichs says, can claim little attention, yet, as we shall see (when treating of the parasites of the dog), it occasionally proves fatal to the canine bearer. Not only so, it may even occasion severe inconvenience to the human bearer. Quite recently a remarkable instance of this kind occurred in Germany, some notice of which appeared in the ‘Medical Times and Gazette,’ Jan. 4th, 1879, as follows:
“Dr Landon of Elbing (‘Berl. Klin. Wochenschrift,’ No. 49, 1878) relates the case of a workman, aged forty-two, who soon after the Franco-German campaign of 1870 was laid up with pain in the hepatic region, jaundice, and gastric disturbance, which symptoms persisted more or less until 1874, when he came under Dr Landon’s care with an attack apparently of perihepatitis. It then appeared that since 1871 he had also suffered from severe attacks of epistaxis, which occurred often twice in the same day. The patient complained of a feeling of painful pressure in the left nasal cavity, but with the speculum nothing but a moderate degree of inflammatory swelling could be detected. Suddenly, at Easter, 1878, a parasite was dislodged from the left side of the nose by a violent sneeze, and from that moment the epistaxis has not occurred. Its cause proved to be the Pentastoma tænioides.”