In addition to the many species of Arthropods which are normally parasitic on man and animals, there is a considerable number of those which may be classed as accidental or facultative parasites.

Accidental or facultative parasites are species which are normally free-living, but which are able to exist as parasites when accidentally introduced into the body of man or other animal. A wide range of forms is included under this grouping.

Acarina

A considerable number of mites have been reported as accidental or even normal, endoparasites of man, but the authentic cases are comparatively few.

In considering such reports it is well to keep in mind von Siebold's warning that in view of the universal distribution of mites one should be on his guard. In vessels in which animal and other organic fluids and moist substances gradually dry out, mites are very abundantly found. If such vessels are used without very careful preliminary cleaning, for the reception of evacuations of the sick, or for the reception of parts removed from the body, such things may be readily contaminated by mites, which have no other relation whatever to them.

Nevertheless, there is no doubt but that certain mites, normally free-living, have occurred as accidental parasites of man. Of these the most commonly met with is Tyroglyphus siro, the cheese-mite.

Tyroglyphus siro is a small mite of a whitish color. The male measures about 500µ long by 250µ wide, the female slightly larger. They live in cheese of almost any kind, especially such as is a little decayed. "The individuals gather together in winter in groups or heaps in the hollows and chinks of the cheese and there remain motionless. As soon as the temperature rises a little, they gnaw away at the cheese and reduce it to a powder. The powder is composed of excrement having the appearance of little grayish microscopic balls; eggs, old and new, cracked and empty; larvÆ, nymphs, and perfect mites, cast skins and fragments of cheese, to which must be added numerous spores of microscopic fungi."—Murray.

Tyroglyphus siro, and related species, have been found many times in human feces, under conditions which preclude the explanation that the contamination occurred outside of the body. They have been supposed to be the cause of dysentery, or diarrhoea, and it is probable that the Acarus dysenteriÆ of LinnÆus, and Latreille, was this species. However, there is little evidence that the mites cause any noteworthy symptoms, even when taken into the body in large numbers.

Histiogaster spermaticus (fig.152) is a Tyroglyphid mite which was reported by Trouessart (1902) as having been found in a cyst in the groin, adherent to the testis. When the cyst was punctured, it yielded about two ounces of opalescent fluid containing spermatozoa and numerous mites in all stages of development. The evidence indicated that a fecundated female mite had been introduced into the urethra by means of an unclean catheter. Though Trouessart reported the case as that of a Sarcoptid, Banks places the genus Histiogaster with the TyroglyphidÆ. He states that our species feeds on the oyster-shell bark louse, possibly only after the latter is dead, and that in England a species feeds within decaying reeds.

Nephrophages sanguinarius is a peculiarly-shaped, angular mite which was found by Miyake and Scriba (1893) for eight successive days in the urine of a Japanese suffering from fibrinuria. Males, .117 mm. long by .079 mm. wide, females .36 mm. by. 12 mm., and eggs were found both in the spontaneously emitted urine and in that drawn by means of a catheter. All the mites found were dead. The describers regarded this mite as a true endoparasite, but it is more probable that it should be classed as an accidental parasite.

Myriapoda

There are on record a number of cases of myriapods occurring as accidental parasites of man. The subject has been treated in detail by Blanchard (1898 and 1902), who discussed forty cases. Since then at least eight additions have been made to the list.

Neveau-Lamaire (1908) lists thirteen species implicated, representing eight different genera. Of the Chilognatha there are three, Julus terrestris, J. londinensis and Polydesmus complanatus. The remainder are Chilopoda, namely, Lithobius forficatus, L. malenops, Geophilus carpophagus, G. electricus, G. similis, G. cephalicus, Scutigera coleoptrata, Himantarium gervaisi, ChÆtechelyne vesuviana and Stigmatogaster subterraneus.

The majority of the cases relate to infestation of the nasal fossÆ, or the frontal sinus, but intestinal infestation also occurs and there is one recorded case of the presence of a species in Julus (fig.13) in the auditory canal of a child.

In the nose, the myriapods have been known to live for months and according to some records, even for years. The symptoms caused by their presence are inflammation, with or without increased flow of mucus, itching, more or less intense headache, and at times general symptoms such as vertigo, delirium, convulsions, and the like. These symptoms disappear suddenly when the parasites are expelled.

In the intestine of man, myriapods give rise to obscure symptoms suggestive of infestation by parasitic worms. In a case reported by Verdun and Bruyant (1912), a child twenty months of age had been affected for fifteen days by digestive disturbances characterized by loss of appetite, nausea and vomiting. The latter had been particularly pronounced for three days, when there was discovered in the midst of the material expelled a living myriapod of the species ChÆtechelyne vesuviana. Anthelminthics had been administered without result. In some of the other cases, the administration of such drugs had resulted in the expulsion of the parasite through the anus.

One of the extreme cases on record is that reported by Shipley (1914). Specimens of Geophilus gorizensis (= G. subterraneus) "were vomited and passed by a woman of 68 years of age. Some of the centipedes emerged through the patient's nose, and it must be mentioned that she was also suffering from a round worm. One of her doctors was of the opinion that the centipedes were certainly breeding inside the lady's intestines, and as many as seven or eight, sometimes more, were daily leaving the alimentary canal."

"According to her attendant's statements those centipedes had left the body in some hundreds during a period of twelve or eighteen months. Their presence produced vomiting and some hÆmatemesis, and treatment with thymol, male-fern and turpentine had no effect in removing the creatures."

The clinical details, as supplied by Dr. Theodore Thompson were as follows:

"Examined by me July, 1912, her tongue was dry and glazed. There was bleeding taking place from the nose and I saw a living centipede she had just extracted from her nostril. Her heart, lungs and abdomen appeared normal. She was not very wasted, and did not think she had lost much flesh, nor was there any marked degree of anemia."

Shipley gives the following reasons for believing it impossible that these centipedes could have multiplied in the patient's intestine. "The breeding habits of the genus Geophilus are peculiar, and ill adapted for reproducing in such a habitat. The male builds a small web or nest, in which he places his sperm, and the female fertilizes herself from this nest or web, and when the eggs are fertilized they are again laid in a nest or web in which they incubate and in two or three weeks hatch out. The young Geophilus differ but very little from the adult, except in size. It is just possible, but improbable, that a clutch of eggs had been swallowed by the host when eating some vegetables or fruit, but against this is the fact that the Geophilus does not lay its eggs upon vegetables or fruit, but upon dry wood or earth. The egg-shell is very tough and if the eggs had been swallowed the egg-shells could certainly have been detected if the dejecta were examined. The specimens of the centipede showed very little signs of being digested, and it is almost impossible to reconcile the story of the patient with what one knows of the habits of the centipedes."

In none of the observed cases have there been any clear indications as to the manner of infestation. It is possible that the myriapods have been taken up in uncooked fruit or vegetables.

Lepidopterous LarvÆ

Scholeciasis—Hope (1837) brought together six records of infestation of man by lepidopterous larvÆ and proposed to apply the name scholeciasis to this type of parasitism. The clearest case was that of a young boy who had repeatedly eaten raw cabbage and who vomited larvÆ of the cabbage butterfly, Pieris brassicÆ. Such cases are extremely rare, and there are few reliable data relative to the subject. In this connection it may be noted that Spuler (1906) has described a moth whose larvÆ live as ectoparasites of the sloth.

Coleoptera

Canthariasis—By this term Hope designated instances of accidental parasitism by the larvÆ or adults of beetles. Reports of such cases are usually scouted by parasitologists but there seems no good basis for wholly rejecting them. Cobbold refers to a half dozen cases of accidental parasitism by the larvÆ of Blaps mortisaga. In one of these cases upwards of 1200 larvÆ and several perfect insects were said to have been passed per annum. French (1905) reports the case of a man who for a considerable period voided adult living beetles of the species Nitidula bipustulata. Most of the other cases on record relate to the larvÆ of DermestidÆ (larder beetles et al.) or TenebrionidÆ (meal infesting species). Infestation probably occurs through eating raw or imperfectly cooked foods containing eggs or minute larvÆ of these insects.

Brumpt cites a curious case of accidental parasitism by a coleopterous larva belonging to the genus Necrobia. This larva was extracted from a small tumor, several millimeters long, on the surface of the conjunctiva of the eye. The larvÆ of this genus ordinarily live in decomposing flesh and cadavers.

Dipterous LarvÆ

Myasis—By this term (spelled also myiasis, and myiosis), is meant parasitism by dipterous larvÆ. Such parasitism may be normal, as in the cases already described under the heading parasitic Diptera, or it may be facultative, due to free-living larvÆ being accidentally introduced into wounds or the body-cavities of man. Of this latter type, there is a multitude of cases on record, relating to comparatively few species. The literature of the subject, like that relating to facultative parasitism in general, is unsatisfactory, for most of the determinations of species have been very loose. Indeed, so little has been known regarding the characteristics of the larvÆ concerned that in many instances they could not be exactly determined. Fortunately, several workers have undertaken comparative studies along this line. The most comprehensive publication is that of Banks (1912), entitled "The structure of certain dipterous larvÆ, with particular reference to those in human food."

Without attempting an exhaustive list, we shall discuss here the more important species of Diptera whose larvÆ are known to cause myasis, either external or internal. The following key will serve to determine those most likely to be encountered. The writers would be glad to examine specimens not readily identifiable, if accompanied by exact data relative to occurrence.

Eristalis—The larvÆ of Eristalis are the so-called rat-tailed maggots, which develop in foul water. In a few instances these larvÆ have been known to pass through the human alimentary canal uninjured. Hall and Muir (1913) report the case of a boy five years of age, who had been ailing for ten weeks and who was under treatment for indigestion and chronic constipation. For some time he had vomited everything he ate. On administration of a vermifuge he voided one of the rat-tailed maggots of Eristalis. He admitted having drunk water from a ditch full of all manner of rotting matter. It was doubtless through this that he became infested. It is worth noting that the above described symptoms may have been due to other organisms or substances in the filthy water.Piophila casei, the cheese-fly (fig.99), deposits its eggs not only in old cheeses, but on ham, bacon, and other fats. The larvÆ (fig.98) are the well-known cheese skippers, which sometimes occur in great abundance on certain kinds of cheese. Indeed, some people have a comfortable theory that such infested cheese is especially good. Such being the case, it is small wonder that this species has been repeatedly reported as causing intestinal myasis. Thebault (1901) describes the case of a girl who, shortly after consuming a large piece of badly infested cheese, became ill and experienced severe pains in the region of the navel. Later these extended through the entire alimentary canal, the excrement was mixed with blood and she suffered from vertigo and severe headaches. During the four following days the girl felt no change, although the excretion of the blood gradually diminished and stopped. On the fourth day she voided two half-digested larvÆ and, later, seven or eight, of which two were alive and moving.

That these symptoms may be directly attributed to the larvÆ, or "skippers," has been abundantly shown by experimental evidence. Portschinsky cites the case of a dog fed on cheese containing the larvÆ. The animal suffered much pain and its excrement contained blood. On post mortem it was found that the small intestine throughout almost its entire length was marked by bloody bruises. The papillÆ on these places were destroyed, although the walls were not entirely perforated. In the appendix were found two or three dead larvÆ. Alessandri (1910) has likewise shown that the larvÆ cause intestinal lesions.

According to Graham-Smith, Austen (1912) has recorded a case of myasis of the nose, attended with a profuse watery discharge of several weeks duration and pain, due to the larvÆ of Piophila casei.AnthyomyiidÆ—The characteristic larvÆ of two species of Fannia (= Homalomyia or Anthomyia, in part) (fig.101) are the most commonly reported of dipterous larvÆ causing intestinal myasis. Hewitt (1912) has presented a valuable study of the bionomics and of the larvÆ of these flies, a type of what is needed for all the species concerned in myasis. We have seen two cases of their having been passed in stools, without having caused any special symptoms. In other instances their presence in the alimentary canal has given rise to symptoms vaguely described as those of tapeworm infestation, or helminthiasis. More specifically, they have been described as causing vertigo, severe headache, nausea and vomiting, severe abdominal pains, and in some instances, bloody diarrhoea.

One of the most striking cases is that reported by Blankmeyer (1914), of a woman whose illness began fourteen years previously with nausea and vomiting. After several months of illness she began passing larvÆ and was compelled to resort to enemas. Three years previous to the report, she noticed frequent shooting pains in the rectal region and at times abdominal tenderness was marked. There was much mucus in the stools and she "experienced the sensation of larvÆ crawling in the intestine." Occipital headaches were marked, with remissions, and constipation became chronic. The appetite was variable, there was a bad taste in the mouth, tongue furred and ridged, and red at the edges. Her complexion was sallow, and general nervousness was marked. As treatment, there were given doses of magnesium sulphate before breakfast and at 4 P. M., with five grain doses of salol four times a day. The customary parasiticides yielded no marked benefit. At the time of the report the patient passed from four to fifty larvÆ per day, and was showing some signs of improvement. The nausea had disappeared, her nervousness was less evident, and there was a slight gain in weight.

The case was complicated by various other disorders, but the symptoms given above seem to be in large part attributable to the myasis. There is nothing in the case to justify the assumption that larvÆ were continuously present, for years. It seems more reasonable to suppose that something in the habits of the patient favored repeated infestation. Nevertheless, a study of the various cases of intestinal myasis caused by these and other species of dipterous larvÆ seems to indicate that the normal life cycle may be considerably prolonged under the unusual conditions.

The best authenticated cases of myasis of the urinary passage have been due to larvÆ of Fannia. Chevril (1909) collected and described twenty cases, of which seven seemed beyond doubt. One of these was that of a woman of fifty-five who suffered from albuminuria, and urinated with much difficulty, and finally passed thirty to forty larvÆ of Fannia canicularis.

It is probable that infestation usually occurs through eating partially decayed fruit or vegetables on which the flies have deposited their eggs. Wellman points out that the flies may deposit their eggs in or about the anus of persons using outside privies and Hewitt believes that this latter method of infection is probably the common one in the case of infants belonging to careless mothers. "Such infants are sometimes left about in an exposed and not very clean condition, in consequence of which flies are readily attracted to them and deposit their eggs."MuscinÆ—The larvÆ of the common house-fly, Musca domestica, are occasionally recorded as having been passed with the feces or vomit of man. While such cases may occur, it is probable that in most instances similar appearing larvÆ of other insects have been mistakenly identified.

Muscina stabulans is regarded by Portschinsky (1913) as responsible for many of the cases of intestinal myasis attributed to other species. He records the case of a peasant who suffered from pains in the lower part of the breast and intestines, and whose stools were mixed with blood. From November until March he had felt particularly ill, being troubled with nausea and vomiting in addition to the pain in his intestines. In March, his physician prescribed injections of a concentrated solution of tannin, which resulted in the expulsion of fifty living larvÆ of Muscina stabulans. Thereafter the patient felt much better, although he suffered from intestinal catarrh in a less severe form.

CalliphorinÆ—Closely related to the SarcophagidÆ are the CalliphorinÆ, to which group belong many of the so-called "blue bottle" flies. Their larvÆ feed upon dead animals, and upon fresh and cooked meat. Those of Protocalliphora, already mentioned, are ectoparasitic on living nestling birds. Larva of Lucilia, we have taken from tumors on living turtles. To this sub-family belongs also Auchmeromyia luteola, the Congo floor maggot. Some of these, and at least the last mentioned, are confirmed, rather than faculative parasites. Various species of CalliphorinÆ are occasionally met with as facultative parasites of man.

Chrysomyia macellaria, the screw worm fly (fig.107), is the fly which is responsible for the most serious cases of human myasis in the United States. It is widely distributed in the United States but is especially abundant in the south. While the larvÆ breed in decaying matter in general, they so commonly breed in the living flesh of animals that they merit rank as true parasites. The females are attracted to open wounds of all kinds on cattle and other animals and quickly deposit large numbers of eggs. Animals which have been recently castrated, dehorned, or branded, injured by barbed wire, or even by the attacks of ticks are promptly attacked in the regions where the fly abounds. Even the navel of young calves or discharges from the vulva of cows may attract the insect.

Not infrequently the fly attacks man, being attracted by an offensive breath, a chronic catarrh, or a purulent discharge from the ears. Most common are the cases where the eggs are deposited in the nostrils. The larvÆ, which are hatched in a day or two, are provided with strong spines and proceed to bore into the tissues of the nose, even down into or through the bone, into the frontal sinus, the pharynx, larynx, and neighboring parts.

Osborn (1896) quotes a number of detailed accounts of the attacks of the Chrysomyia on man. A vivid picture of the symptomology of rhinal myasis caused by the larvÆ of this fly is given by Castellani and Chalmers: "Some couple of days after a person suffering from a chronic catarrh, foul breath, or ozÆna, has slept in the open or has been attacked by a fly when riding or driving,—i.e., when the hands are engaged—signs of severe catarrh appear, accompanied with inordinate sneezing and severe pain over the root of the nose or the frontal bone. Quickly the nose becomes swollen, and later the face also may swell, while examination of the nose may show the presence of the larvÆ. Left untreated, the patient rapidly becomes worse, and pus and blood are discharged from the nose, from which an offensive odor issues. Cough appears as well as fever, and often some delirium. If the patient lives long enough, the septum of the nose may fall in, the soft and hard palates may be pierced, the wall of the pharynx may be destroyed. By this time, however, the course of the disease will have become quite evident by the larvÆ dropping out of the nose, and if the patient continues to live all the larvÆ may come away naturally."

For treatment of rhinal myasis these writers recommend douching the nose with chloroform water or a solution of chloroform in sweet milk (10-20 per cent), followed by douches of mild antiseptics. Surgical treatment may be necessary.

SarcophagidÆ—The larvÆ (fig.105) of flies of this family usually feed upon meats, but have been found in cheese, oleomargerine, pickled herring, dead and living insects, cow dung and human feces. Certain species are parasitic in insects. Higgins (1890) reported an instance of "hundreds" of larvÆ of Sarcophaga being vomited by a child eighteen months of age. There was no doubt as to their origin for they were voided while the physician was in the room. There are many other reports of their occurrence in the alimentary canal. We have recorded elsewhere (Riley, 1906) a case in which some ten or twelve larvÆ of Sarcophaga were found feeding on the diseased tissues of a malignant tumor. The tumor, a melanotic sarcoma, was about the size of a small walnut, and located in the small of the back of an elderly lady. Although they had irritated and caused a slight hÆmorrhage, neither the patient nor others of the family knew of their presence. Any discomfort which they had caused had been attributed to the sarcomatous growth. The infestation occurred in mid-summer. It is probable that the adult was attracted by the odor of the discharges and deposited the living maggots upon the diseased tissues.

According to KÜchenmeister, Sarcophaga carnaria (fig.106), attracted by the odor, deposits its eggs and larvÆ in the vagina of girls and women when they lie naked in hot summer days upon dirty clothes, or when they have a discharge from the vagina. In malignant inflammations of the eyes the larvÆ even nestle under the eyelids and in Egypt, for example, produce a very serious addition to the effects of small-pox upon the cornea, as according to Pruner, in such cases perforation of the cornea usually takes place.

Wohlfartia magnifica is another Sarcophagid which commonly infests man in the regions where it is abundant. It is found in all Europe but is especially common in Russia, where Portschinsky has devoted much attention to its ravages. It deposits living larvÆ in wounds, the nasal fossÆ, the ears and the eyes, causing injuries even more revolting than those described for Chrysomyia.