Fig. 53.—Demodex folliculorum, var. caninus. a, Female; b, male. Viewed from below and in profile. Magnified 300 diameters. After Mégnin.
The ectoparasitic arachnidans comprise a great variety of mites and ticks (Acaridæ and Ixodidæ) more or less proper to man, and also a number of creatures which, though hardly to be reckoned as human parasites, are apt to transfer themselves from animals to man. Little more than an enumeration of the forms is possible here. The Common Scab or Itch insect (Sarcoptes scabiei) forms the type of a great variety of arachnids, generally spoken of as different species according to the host they dwell upon. Mégnin, however, in his beautiful memoir, quoted below, regards most of the forms of this genus (found on the horse, hog, sheep, dog, wolf, and other animals) as mere varieties. In man the female Acarus burrows beneath the skin, forming galleries or curved channels, in which she deposits her eggs. The irritation produced is not alone due to these excavations, but to the presence also of a poison which the mite discharges when feeding. The Sarcoptes crustosæ of Fürstenberg, producing the Norway itch, is a variety, if, indeed, it can be called as much. Under the frightful name of Dermatophagoides Schérémétewsky two parasites found on an herpetic patient have been described as new to science by M. Bogdanoff, but Mégnin points out that these Acari are only female and young male representatives of his Chorioptes setiferus (var. bovis) respectively. In Newfoundland, Dr Le Roy de Méricourt discovered a singular species upon an officer who had come from Havannah (Tyroglyphus Méricourti, Laboulbène). It possesses enormous palpi, as in the genus Chyletus to which Robin refers it. Another ectozoon, placed by Mégnin and others amongst the lowest types of Arachnida, is the well-known Demodex folliculorum. It is a gregarious species, a dozen or more examples often being present in a single dilated hair follicle. Though disfiguring to the human face it produces little harm. M. Gruby made it out to be a very common parasite, infesting forty out of sixty persons; but Mégnin, in his brochure (l. c. infra, p. 119), shows this statement to be an exaggeration. It infests on the average not more than one in ten persons. According to Gruby, moreover, a single follicle in the dog may contain 200 of these mites, another statement which Mégnin deems unreliable. The Demodex of the dog is only a variety (fig. 53). Many other human Arachnids have been found, some of which appear to be genuine species, whilst others are accidental, so to speak. Of the former kind, perhaps we may reckon the two species discovered by Hessling (Cœlognathus morsitans and Entarsus cancriformis). Of the latter sort, those found by Busk, Simon, and Bory de St Vincent may be cited. The mite found in Simon’s case was the Dermanyssus avium, which infests cage-birds. Probably it was the same species which Bory found on a lady; but in Busk’s negro sailor the mite may have been D. gallinæ of the common fowl. Differing from the mites, proper, and also from the true ticks, are some bug-like forms called Argades. The two best known are the Miana bug of Persia (Argas persicus) and the Chinche of Columbia (A. chinche). Like their congener infesting pigeons (A. reflexus) these parasites are terrible blood-suckers. The bite of the Persian bug is so venomous as to have occasioned death. Various species of tick have been known to attack man, but the species have not been well determined. Although a human form has been described (Ixodes hominis, Koch), yet it is more probable that the species usually attacking man are the same as those known to infest the domesticated animals. In this list we may, therefore, reckon Ixodes nigra, Ix. bovis, Ix. ricinus, and Ix. reduvius. Cases in which one or other of these ticks occasioned much pain and distress are recorded by Hussem, Raspail, and Dr Cosson. Besides these there is a formidable tick well known at Angola (Ix. monbata). Its habits are like those of the common bed-bug. Severe pain comes on two hours after the person is bitten. It likewise attacks animals. The Ix. carapato is similarly troublesome in Brazil. Another very disgusting arachnid liable to attack man is the Galeodes araneoides. This large spider-like creature, two inches in length, commonly attacks camels and has an extremely venomous bite. One or more species of the dung-beetle mites (Gamasidæ) have also been known to fasten themselves on man. According to Latreille, they first get attached to the clothes of travellers, whence they pass to his body, and there shift about, producing great torment. Another disagreeable arachnid is the little harvest bug (Leptus autumnalis), which not only excites irritation during its crawling motion on the human skin, but even succeeds in burying itself near the hairs. The irritation thus produced is almost unbearable. This mite attacks various animals, especially dogs and cats. I myself once suffered severely from this species in consequence of fondling a young wild rabbit which, as I afterwards discovered, was much infested. When the parasites had reached my left arm-pit they occasioned extreme torture. I have known these autumnal spiders to produce small suppurating boils on the abdomen. I may add that Dr Tilbury Fox has brought under my notice an instance where the hexapod larva of another species (probably Trombidium cinereum) was found to have occasioned severe irritation in a child.
Bibliography (No. 38).—Alibert, ‘Maladies de la Peau,’ Paris, 1833.—Audouin, V., art. “Arachnida,” in ‘Todd’s Cyclop.,’ vol. i, 1836.—Beneden, Van (et Gervais), ‘Zool. Med.,’ 1859.—Bourguignon (et Delafond), in ‘Rec. Vét.,’ 1856.—Idem, in ‘Mém. de l’Institut.,’ 1862.—Cobbold, “Case of Leptus producing Boils,” in ‘Worms,’ p. 140, London, 1872.—Gamgee, ‘Our Domestic Animals in Health and Disease,’ Edin., 1861.—Gerlach, ‘Kraetze und Räude,’ 1857.—Hebra, in ‘Oester. Jahrb.,’ 1864.—Hering, ‘Die Kraetzmilben,’ Stuttgard, 1845.—Krabbe, “Husdyrenes paras. Mider.,” ‘Tidssk. f. Vet.,’ Rœk. 2, Bd. iii.—Küchenmeister, l. c., 1855, s. 412 (good figs.).—Mégnin, ‘Monographie de la tribu des Sarcoptides psoriques.’ (This work contains a full bibliography and numerous beautiful plates; see also Review in the ‘Veterinarian,’ Aug., 1877, p. 563).—Idem, “Mémoire sur un nouveau Symbiote (Chorioptes, Gerv.),” ‘Journ. de l’Anat. et de la Physiol.,’ 1872.—Idem, “Mém. sur un nouvel Acarien,” ibid., 1873.—Idem, “Mém. sur les Hypopes,” ibid., 1874.—Idem, “Mém. sur l’organisation et la distribution zoologique des Acariens de la famille des Gamasidés,” ibid., 1876.—Idem, “Mém. sur les métamorphoses des Acariens en général, et en particulier sur celles des Trombidions,” ‘Ann. des Sci. Nat.,’ 1876.—Idem, “Des conditions de la contagion de la gale des animaux à l’homme,” ‘Arch. générales de Méd.,’ 1876.—Idem, “Mém. sur le Demodex folliculorum (Owen),” ‘Journ. de l’Anat. et de la Physiol.,’ 1877.—Moquin-Tandon, ‘Elém. de Zool. méd.’ (Hulme’s edit., p. 302–328), 1861.—Williams, in his ‘Veterinary Surgery’ (good figs., reproduced from Gamgee’s translation of ‘Gerlach,’ &c.), 1872.
SECTION IV.—Part IV.—Crustacea (Gammaridæ).
Although multitudes of small Crustaceans are parasitic upon fishes, and some few of them adhere to oceanic mammals (Cetacea), I am sceptical as to the parasitism of Crustacea either in or upon man. Many of the Amphipodous Gammari lead a sort of free parasitic existence, and they are themselves very liable to harbor larval parasites. As regards human parasitism from this source the only records known to me are those quoted below.
Bibliography (No. 39).—Banon, “Freshwater Shrimp, or Gamarus pulex (said to have been passed per anum),” ‘Rep. of Path. Soc. of Dublin,’ in ‘Dub. Med. Press,’ April 6, p. 351, 1864.—Bartels, “Gamarus pulex in the Human Subject, with a postscript by Troschel,” trans. by Dr E. P. Wright, from ‘Verhandl. des Naturhist. verein. der Preuss. Rheinl. und Westph.,’ in ‘Dubl. Med. Press,’ 2nd ser., vol. ix, p. 407, 1864.—Wright, E. P., ‘Remarks on Dr Banon’s Case’ (see Bartels).
SECTION IV.—Part V.—Insecta (Coleoptera, Diptera, Hemiptera, Aphaniptera).
Whilst very many flies, bugs, lice, and fleas persecute animals, not a few of them also attack man. Several of the species are genuine parasites, others are semi-parasitic, and others, again, are altogether outside the border-land of parasitism in the ordinary sense of the term. In fact, it becomes difficult to say where the line of parasitism should be drawn. I cannot, however, ignore all notice of the insect tormentors, whether strictly parasitic or not.
At least fifty different species have been regarded as playing the rôle of parasitism in man. Amongst the Coleopterous parasites none is more authentic than Blaps mortisaga. At least half a dozen such cases have occurred. Mr Hope’s catalogue of insects producing parasitism in man gives three examples of scolechiasis from this source. Sir J. R. Cormack published a fourth case, and I have recorded a fifth. In this instance I received the living larva from Dr Horne, of Barnsley, who procured it from an infant eleven weeks old. In my ‘Introductory Treatise’ I have alluded to the case of the girl Riordan, who not only passed per anum upwards of 1200 larvæ, but also several perfect insects. The case was first reported by Pickells, Thomson, and Bellingham. One of the other authentic cases, in which only a few larvæ were present, was recorded by Patterson, of Belfast, and the third case by Bateman. Mr Hope’s ‘Catalogue’ originally appeared in the ‘Transactions of the Entomological Society,’ being afterwards published in the pages of the ‘London Medical Gazette,’ 1837. Patterson’s case was also, I believe, first communicated to the Entomological Society.