Tropical Diseases/Chapter 42
CHAPTER XLII
II. PARASITES OF THE CONNECTIVE TISSUE
DRACUNCULUS MEDINENSIS, Velsch, 1674
Synonyms.—Vena medinensis; Dracunculus persarum; Gordius medinensis; Filaria dracunculus; F. medinensis; Guinea-worm.
Geographical distribution.— This important parasite is found in certain parts of India— the Deccan, Scinde, etc.— in Persia, Turkestan, Arabia, tropical Africa— particularly on the West Coast, and in a very limited part of Brazil (Feira de Santa Anna). Formerly it was supposed to be endemic in Curagoa, Demerara, and Surinam; apparently it has now disappeared from these places. Dracunculus is not equally diffused throughout this extensive area; it tends to special prevalence in limited districts, in some of which it is excessively common. In parts of the Deccan, for example, at certain seasons of the year nearly half the population is affected; and in places on the West Coast of Africa nearly every negro has one or more specimens about him. Although guinea-worm is sometimes seen in Europe, this is only in natives of, or in recent visitors from, the endemic areas. Though frequently introduced in this way, it has not become established either in Europe or in North America. We have no account of the parasite as endemic in any part of Asia east of Hindustan, in the Eastern Archipelago, in Australia, or in the Pacific islands.
Dracunculus medinensis has been reported for horses, oxen, dogs, wild cats, jackals, leopards, and other animals. Possibly some of the parasites in the lower animals described as guinea-worm may belong to quite a different species. The parasite (Figs. 146-8).—The female is reputed to attain in some instances enormous dimensions; it is probable, however, that worms of 5 or 6 ft. in length owe their size to errors of observation, two worms, or their fragments, having been regarded as one. According to Ewart, in forty carefully measured specimens the smallest was about 32·5 cm., the largest 1 m. 20 cm. in length; 90 cm. is probably an average length. The diameter of the worm is about 1·5 to
Fig. 146.—Dracunculus medinensis (reduced).
1·7 mm. The body is cylindrical, milky-white, smooth, and without markings. The tip of the tail comes to a point and is abruptly bent, thus forming a sort of blunted hook, perhaps functioning as a "holdfast." The head end is rounded off, terminating in what is known as the cephalic shield. The mouth is triangular, very small, and surrounded by six papillæ—two large and four small The alimentary canal is relatively small, being compressed and thrust to one side by the uterus; in the mature worm it is probably cæcal, for it has not been traced to an anus. Nearly the whole of the worm is occupied by the uterus, which is packed from end to end with coiled-up embryos. The vagina also may be lacking. According to Looss, the uterine tubes (he states, contrary to Leuckart, that there are two) open into the posterior part of the œsophagus by a common duct, the œsophagus prolapsing through the mouth at the time of parturition and being subsequently withdrawn. Leiper, however, has shown that the worm discharges its young by a prolapse of the uterus as described by me, and that the extrusion does not occur through the mouth, as suggested by Looss and myself, but by a rupture just outside the circumoral ring of papillæ, possibly the vagina.
Nothing definite is known of the male worm. According to Polak, the Persians have long known the male to be a smaller worm, 7-10 cm. long. They stated that at times as many as twenty of these small worms might be found coiled round a female specimen. Charles described a shorter (4 cm.) worm, regarding it as the male, which he found twice attached to the larger female worm within the sub-peritoneal connective tissue. Charles's description does not exclude the possibility that what he describes as the male worm in coïtu. was really a prolapse of the uterus through the ruptured integument. Daniels, at the post-mortem of a monkey experimentally infected by Leiper six months previously, found three immature females (30 cm. long) and two remarkably small males (22 mm.), which were obtained, one from the psoas muscle and the other from the connective tissue behind the œsophagus.
Fig. 148.—Transverse section of D. medinensis.
(Leuckart.)
Habits.—The habitat of the female guinea-worm is the connective tissue of the limbs and trunk. When mature, and prompted by instinct, she proceeds to bore her way through this tissue, travelling downwards. In 85 per cent. of cases she presents in some part of the lower extremities. Occasionally she presents in the scrotum; rarely in the arms (Fig. 149); exceptionally in other parts of the body, or even in the head. In a proportion of cases the appearance of the worm at the surface of the body is preceded by slight fever and urticaria, as described by Sutherland in 1897 and by Bartet independently in 1898. Arrived at her destination she pierces the derma. Probably in consequence of some irritating secretion, a small blister now forms and elevates the epidermis over the site of the hole, in the derma. By and by the blister ruptures, disclosing a small superficial erosion ½-¾ in. in diameter. At the centre of the erosion, which sometimes quickly heals spontaneously, a minute hole, large enough to admit an ordinary probe, can be seen. Sometimes, when the blister ruptures, the head of the worm is seen protruding from this hole; as a rule, however, at first the worm does not show. If now we douche the neighbourhood of the ulcer with a stream of cold water
Fig. 149.—Female guinea-worm lying under the skin of the forearm.
(Photograph by P. H. Bohr.)
expressed from a sponge and, as the water falls, watch the little hole in the centre of the erosion, we shall see in a few seconds a droplet of fluid—at first clear, later milky—well up through the hole and flow over the surface. Sometimes, instead of this fluid, a small, beautifully pellucid tube, about 1 mm. in diameter, doubtless the uterus of the worm prolapsed through her head parts, is projected through the hole in response to the stimulus of the cold water. When this tube has been extruded an inch or thereabouts, it suddenly fills with an opaque whitish material, ruptures and collapses, the fluid spreading over the surface of the erosion. If a little of the fluid, either that which has welled up through
Fig. 150.—Embryos of D. medinensis. (Microphotograph by Mr. H. B. Bristow.)
the hole, or that which has escaped from the ruptured tube, is placed under the microscope, it is seen to contain myriads of dracunculus larvæ lying coiled up, almost motionless, with their tails projecting in a very characteristic manner (Fig. 150). If now a drop of water be instilled below the cover-glass the larvæ may be observed to unroll themselves and, in a very short time, to swim about, more suo, with great activity. Manifestly these larvæ come from a guinea-worm lying in the tissues and communicating with the surface through the little hole in the derma. If the douching be repeated after an hour or longer a further supply of larvæ can be obtained; and this can be continued from time to time until the worm has emptied herself. Apparently the cold applied to the skin of the host stimulates the worm to contract and thereby force out her uterus, inch by inch, until it is completely expelled. When the protruded portion of uterus ruptures, under the pressure of the vis a tergo, it shrivels up, dries, and thus effectually seals up the end of that part of the organ which is still inside the worm, thereby preventing what might be inopportune and too prodigal discharge of larvæ.
Fig. 151.—D. medinensis.
a, Side view; b (After Looss.) front view.
The larva (Fig. 151).—The larvæ are not cylindrical; they are distinctly flattened. In swimming they move by a sort of side-to-side lashing of the tail, and tadpole-like motion of the body. The movements are intermittent; sudden, short swims alternating with brief pauses. When progressing, the greater transverse axis of the body is perpendicular to the plane travelled over; but when, from time to time, the little worms pause, they gradually roll over on to their flat surfaces. As soon as they come to rest on the flat they suddenly recover themselves with a jerk, and turn quickly on to their edges and begin swimming about again. This series of movements is constantly repeated.
The larva of D. medinensismeasures about 15 to 25 mm. in length by 0·50 to 0·75 mm. at its greatest breadth. The head is somewhat tapered and then abruptly rounded off. The tail is long, slender, but not quite sharply pointed. The alimentary canal can be readily detected. Towards the root of the tail two peculiar gland-like organs, placed opposite to each other,
can be made out. The cuticle is very distinctly transversely striated.
In clean water the larva remains alive for six days; in muddy water, or in moist earth, it will live from two to three weeks. If slowly desiccated it does not die; it may be resuscitated by placing it again in a little water.
Intermediary host.—If, by way of experiment, we place some dracunculus larvæ along with Cyclops quadricornis in a watch-glass we shall find that, after a few hours, the larvæ have transferred themselves to the interior of the body cavity of the cyclops, where they can be seen moving about, coiling and uncoiling themselves, with considerable activity (Fig. 152). As many as fifteen or twenty young guinea-worms may be counted in each of the little crustaceans, which, unless the infection is excessive, seem in no way inconvenienced. After a time the embryos so transferred undergo a metamorphosis. They cast their skins two or three times, get rid of their long swimming tails, acquire a cylindrical shape and, ultimately, along with increased size, develop a tripartite arrangement of the extreme posterior end, which recalls a similar arrangement of the tail of F. banecrofti and of F. recondita towards the termination of the stay of the former nematode in the mosquito, and of the latter in the dog-flea (Grassi).
Mode of infection.— The metamorphosis of D. medinensis in cyclops was discovered by Fedschenko in Turkestan. His observations I have been able to confirm in England; but, owing to the colder climate of the latter country, in English cyclops the metamorphosis takes somewhat longer to complete— eight or nine weeks, instead of five weeks as in Turkestan. Fedschenko supposed that the cyclops containing the larvae of the guinea-worm, on being swallowed by man in drinking-water, was digested; and that the parasite, being then set free, worked its way into the tissues of its new and definitive host; but all the experiments he made to bring about infection by means of ingestion of cyclops containing dracunculus larvæ gave a negative result. These failures led to the belief that the larvæ might have to undergo further changes before it was fitted for life in man. Considering the peculiar geographical limitations of this helminthiasis, and the very general distribution of cyclops, such an arrangement seemed likely enough.* [1]
Recently, Leiper has shown that when an infected cyclops is transferred to a 0.2 per cent, solution of hydrochloric acid it is immediately killed, but the larvæ, so far from being destroyed, are aroused to great activity, and eventually escape into the fluid, in which they swim freely. From this he conjectured that under natural conditions man becomes infected through the ingestion of infected cyclops, the gastric juice acting on cyclops and larva in the same way as the hydrochloric acid in his experiment. In order to prove this he fed a monkey on bananas concealing cyclops which had been infected for five weeks, and which contained fully developed larvæ. Six months later, when the monkey died, five worms were found in its connective tissues, all possessing the anatomical characteristics of D. medinensis.
The evidence is now fairly complete that the life span of the female dracunculus extends to about one year, conforming probably to the habits of certain species of cyclops which, under natural conditions, serve as its intermediary host. It is not to be supposed that every species of cyclops is an effective intermediary; for, were this the case, guinea- worm would have a much wider geographical range.
Biological peculiarities explained.— The little we now know of the life-history of the guinea-worm explains many things that were formerly mysterious. We now understand why the parasite, on attaining maturity, makes for the legs and feet; these are the parts of the human body most likely, in tropical countries, to come in contact with puddles of water, the medium in which cyclops— the intermediary host —lives. We can understand, also, why it is that the contact of water with the skin of the host causes the guinea-worm to expel her young; and we can understand the rationale of the douching so much practised by the natives of certain of the endemic districts in their attempts at extraction. The water-carriers in India are said to be very subject to guinea-worm, which, in their case, is prone to appear on the back— that is, the part of the body against which the water-skin lies when being carried. On this fact has been based an hypothesis that the young guinea- worm enters by the skin. I would interpret the fact, if fact it be, by suggesting that the mature guinea- worm, conformably to her instinct, seeks out that part of the body most in contact with water, which, in the case of the Indian water-carrier, is his back.
Premature death of parasite.— Occasionally the guinea-worm fails to pierce the integument of her host; sometimes she dies before arriving at maturity. In either case she may give rise to abscess; or she may become cretified, and in this condition may be felt, years afterwards, as a hard convoluted cord under the skin of the leg, or be discovered only on dissection. (Fig. 149.)
Treatment.— Formerly it was the custom, so soon as a guinea-worm showed herself, to attach the protruding part to a piece of wood and endeavour to wind her out by making a turn or two of this daily. Sometimes these attempts succeeded; just as often, the worm snapped under the strain. The consequences of this accident were often disastrous. Myriads of young escaped from the ruptured ends into the tissues, and violent inflammation and fever, followed by abscess and sloughingj ensued; weeks, or months perhaps, elapsed before the unhappy victims of this rough surgery were able to get about. Too often serious contractions and ankyloses from loss of tissue and inflammation, and even death from septic trouble, resulted.
If a guinea-worm be protected from injury, and the part she occupies frequently douched with water, her uterus will be gradually and naturally forced out inch by inch and emptied of embryos. Until this process is completed she resists extraction; possibly the hook at the end of her tail assists her to maintain her hold. When parturition, in from fifteen to twenty days, is completed, the worm is absorbed or tends to emerge spontaneously. A little traction, if practised then, may aid extrusion. Traction, however, must not be employed so long as the embryos are being emitted. The completion of parturition can be easily ascertained by the douching experiment already described.
Emily, a French naval surgeon, has introduced a system of managing guinea- worm cases which bids fair to shorten treatment and obviate the serious risks of the old winding-out system. By means of a Pravaz's syringe he injects the body of the worm, if she chances to be protruding, with solution of bichloride of mercury, 1 in 1,000. This kills the parasite; after twenty-four hours, extraction is usually easily effected. If the worm has not shown herself externally, but can be felt coiled up under the skin, he injects as near the coils as possible, and through several punctures, a few drops of the same solution. This, too, kills the parasite. Her body is then absorbed, as a piece of aseptic catgut would be, without inflammation or reaction of any description; or she may be cut down on, and easily extracted. Others have confirmed the value of Emily's method, which saves much time and suffering and, with due care, is devoid of risk.
Prophylaxis.— From what has been stated with regard to the role of cyclops, it is evident that the prevention of guinea-worm is merely a question of protection of drinking-water from pollution by the subjects of guinea-worm infection. Leiper has shown that by raising by a few degrees the temperature of the water in which cyclops are living these crustaceans are killed. He suggests heating by a portable steam generator the water in wells and water-holes known to be sources of guinea- worm infection, as a prophylactic measure. Alcock has found that the addition of a trace of potash to the water is equally effective.
LOA LOA (Guyot, 1778)
Synonyms.— Dracunculm oculi; Filaria loa; F. oculi; F. subconjunctivalis; F. diurna; F. bourgi.
History.— Loa loa (Fig. 153) has been known for more than three hundred years. Although undoubtedly of African origin, the earlier-described cases were in negroes in the West Indies who must have acquired their parasites in West Africa prior to their deportation as slaves to America. For long the worm was regarded as an immature dracunculus. Since the characters of the parasite have been more carefully studied this view can no longer be held, and L. loa is now thoroughly established as a distinct species.
" In 1891 I found in the blood of two negroes— one from the Lower Congo, the other from Old Calabar—certain microfilariæ morphologically closely resembling that of F. bancrofti, but differing from the latter inasmuch as they came into the peripheral circulation during the day and disappeared from it during the night. As in one of these negroes L. loa had formerly been seen in his eye, I suggested that the new microfilaria, which I named F. diurna, was the hæmatozoal larval form of L. loa. This view was supported by the fact that in fragments of a loa which I received from Leuckart the contained embryos appeared to be identical in every respect with F. diurna. Nevertheless, I failed in several cases of L. loa infection to find mf. diurna in the blood.
In 1901 Dutton, Annett and Elliot had the opportunity of studying F. diurna in its own habitat in West Africa, and came to the conclusion that my hypothesis as regards the relationship of F. diurna and L. loa was erroneous, contending that F. diurna was none other than mf. bancrofti whose normal periodicity had been disturbed by the peculiar habits of those West African negroes who, they tell us, spent their nights in orgies.
Fig. 153.—Loa loa (nat. size).
Sambon, refuting the theory of the Liverpool Commission, again pointed out the similarity of mf. diurna to the larvæ still contained within the uterus of L. loa, and explained that the lack of contemporaneousness between mf. diurna and L. loa in the same patient is probably due to the fact that this long-lived parasite does not produce its young until after a long period of wanderings, when, having attained full maturity, it retires into deeper structures for parturition. He pointed out that the majority of filariæ removed whilst wandering beneath the skin of patients were more or less immature forms; that in young children L. loa is, as a rule, the only form found, whilst in adults mf. diurna is the commonest finding, with frequently the history of a previous loa and finally that F. equina of horses and asses, also found in or about the eyes of the host in its immature or barely mature stages, descends into the peritoneal cavity for parturition when fully mature.
Later, an association was discovered between L. loa and the disease known as Calabar swellings, and, also, between Calabar swellings and mf. diurna. Moreover, as a considerable number of cases of L. loa concurring with mf. diurna have now been recorded by Prout, Henley, Brurnpt, Wurtz, Penel, Kerr, and myself, and as the concurrence of the geographical range of the two forms of parasitic infection has been fairly well made out, there can be little doubt that L.loa and mf. diurna are respectively the mature and larval form of the same species.
Geographical distribution.— We have no definite knowledge of the extent and details of the geographical range of L. loa. It appears to be widely distributed throughout tropical West Africa from Sierra Leone to Benguella. In some parts— as in Old Calabar, Cameroons, and the Ogowé River —a very large proportion of the inhabitants are affected. How far it penetrates into the interior of the continent is as yet unknown. I have seen several cases in Europeans from the Upper Congo within a few miles of Stanley Falls. Brumpt records its presence in Kassai, approximately 600 miles from the coast, on one of the chief tributaries of the Congo. The larval form (mf. loa) has been found twice by Cook in Uganda, although such isolated findings cannot be taken as landmarks, seeing that L. loa is a long-lived parasite and its hosts may have contracted the infection years previously, and at a distance from the place at which it was recognized. At the time of the slave trade numerous cases were reported from the West Indies and South America, but always in negroes from Africa, and their occurrence ceased with the abolition of slavery. The suggestion that about 1795 there existed an endemic centre for this parasite in San Domingo is based on very doubtful evidence. Nowadays, cases are occasionally seen in Europe and America, in both negroes and whites, but only in persons who have frequented those parts of Africa inhabited by the parasite. Possibly, on account of the opening of new trade routes and of the more frequent intercourse between the natives, L. loa may greatly extend its range in Africa. Zoological distribution.— Hitherto L. loa has not been seen by reliable observers in animals, but, according to Plehn, the natives of Cameroons assert that it occurs in goats and sheep.
The parasite (Figs. 154, 155). L. loa is especially characterized among the nematodes of man by the presence of numerous rounded, smooth, translucent protuberances of the cuticle, 12-16 μ in diameter and rising 9-11 μ above the general surface. These chitinous bosses vary greatly in number and arrangement on different specimens and are, as a rule, more numerous on the female. Their distribution is very irregular. In the male they are wanting at the extremities, beginning about 1.5-2.5 mm. from the mouth and tail- tip respectively. In the female they usually extend to the posterior extremity and may also be found on the cephalic end.
The body is filiform, cylindrical, whitish, semi-transparent. Anteriorly it tapers somewhat abruptly to the mouth, which is terminal, small, simple, unarmed, and apparently destitute of papillæ. There is no distinctly marked neck, but there is a sort of shoulder about 0.15 mm. from the mouth, and at about this level are two small papillæ, one corresponding to the dorsal, the other to the ventral median line.
The posterior extremity of the female is straight, attenuated, and broadly rounded off (Fig. 156). That of the male is slightly curved ventrally and provided with two lateral expansions of the cuticle (0.7 mm. long by 0.029 mm. broad), situated nearer the ventral than the dorsal surface. In the middle of the ventral surface, between the lateral alæ, and about 0.080 mm. from the tail-tip, is the opening of the ano-genital orifice, from which two unequal spicules may be seen protruding. The opening is surrounded by thick labia. On either side, and somewhat asymmetrically placed, are four large globular and pedunculated papillæ closely approximated and decreasing in size antero-posteriorly. Farther back, and nearer to the middle line, is a fifth symmetrical pair of very small, conical, postanal papillæ with broad base and acuminated point. (Fig. 157.) Leiper has reported the existence of three additional paired papillæ.
The adult male worm measures 30-34 mm. in length, and presents a maximum breadth of 0.350-0.430 mm. in the anterior part of the body. The posterior part tapers gradually towards the tail. The measurements of the adult female have not been satisfactorily determined. The specimens so far examined, extracted from under the skin or from about the eyes of patients, varied greatly in length*[2] 20 mm. (Blanchard); 27 mm. (Leuckart); 32.3 mm. (Manson); 50 mm. (Annett, Dutton and Elliot); 52 mm. (Looss); 55 mm. (Ozzard); 60 mm. (Brumpt); 70 mm. (Maurel). The alimentary tube begins at the oral cavity, which is funnel-shaped and surrounded by a strong muscular mass. It consists of a slender œsophagus without bulb, of an intestine attaining a width of about 65 μ towards the middle of the body, and of a short, attenuated rectum.
The male reproductive organ is first encountered about 3 mm. from the cephalic extremity, where it ends in a pointed blind sac. Anteriorly it is very sinuous and winds round the alimentary canal; posteriorly it straightens, attains a diameter of 85-105 μ, and terminates by a vesicula seminalis filled with more or less spherical spermatozoa 6-8 μ in diameter.
Fig. 154.—L. loa, female. (Partly after Looss.)
In the female the vulva forms a small eminence at about 2·5 mm. from the anterior extremity. The vagina, 9 mm. long and 95 μ wide, branches off into two long tubes extending almost throughout the entire length of the body. These tubes, the narrow ends of which are the ovaria, contain eggs in all stages of development, as well as free larvæ 0·253-0·262 mm. in length by 0·0047-0·005 mm. in breadth.
Structure of the larval form.—Microfilaria loa (= diurna) is very similar in size (298 μ by 7·5 μ) and structure to microfilaria bancrofti. Like the latter, it is enclosed within a "sheath," its tail is pointed, and it has the same V and tail spots. (Figs. 96, 97.)
Their respective periodicities are very characteristic; more so, apparently, in the case of mf. loa than in that of mf. bancrofti; for, whereas by inverting the sleeping habits of a subject of F. bancrofti infection it is easy to invert or disturb the periodicity of the microfilariæ, this cannot be done in the case of mf. loa. Unfortunately, I can adduce only one experiment in support of this remarkable circumstance; but that experiment was a very thorough and carefully conducted one, and extended over a considerable period. During all the time the patient (who had had several L. loa excised at different times and who was still showing signs of their presence) slept during the day and kept awake during the night; nevertheless, the microfilariæ
Fig. 155.—L. loa, male. (Partly after Looss.)
continued to appear in vast numbers in the peripheral blood during the day, but were only very rarely found in it during the night.
Although in the fresh liquid blood it is practically impossible to distinguish, with the microscope alone, the living mf. loa from the living mf. bancrofti, in dried and stained films certain more or less pronounced differences can be made out. (1) In such preparations mf. bancrofti is usually disposed in sweeping and graceful curves such as a skilled penman might make (Plate XI., Fig. 1); mf. loa, on the other hand, assumes a stiff, ungraceful, almost angular attitude like the flourishes made by a schoolboy (Plate XI., Fig. 2). (2) The tail end of mf. loa is often disposed in a series of sharp flexures, giving it in some instances a corkscrew-like appearance, the extreme tip being always sharply flexed. (Plate XI., Fig. 6.) (3) The nuclei of the central column of cells of mf. loa are larger and stain less deeply than those of mf. bancrofti, and, as a rule, the cephalic end of the column is more abruptly terminated in the former. Although in most slides one or two specimens may be hard to diagnose, on the average of a series of preparations the foregoing distinctions are recognizable. Fülleborn by special staining methods points out various minor differences (see Fig. 98), amongst which the large genital cell is a marked feature. He proposes the measurement of various fixed points (Fig. 128) as a standard of differentiation of the various microfilariæ.
Life-history.—Of the life-history of L. loa little is positively known. As the larval form comes into the peripheral
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| Fig. 156.—Posterior extremity of L. loa, female. (After Looss.) |
Fig. 157.—Posterior extremity of L. loa, male. (After Looss.) |
circulation of the human host, it is very probable that, like mf, bancrofti, it is liberated by some blood-sucking insect; and, seeing that it approaches the surface of the body only during the day-time, this is undoubtedly a blood-sucker of diurnal habit.
Several years ago I called attention to the so-called mangrove flies as possible intermediaries, specifying as the most probable Chrysops dimidiata (Fig. 158). This conjecture Leiper has ascertained to have been well founded. During a recent visit to West Africa, with the object of ascertaining the intermediary host of L. loa, he examined many blood-sucking insects, including mosquitoes and a variety of other insects. He found that in Chrysops dimidiata and in C. silacea rapid and uniform developmental changes of mf. loa were effected, similar to those of mf. bancrofti in the mosquito. Later observations by Kleine, working in the Cameroons, tend to confirm those of Leiper. As to the way in which L. loa is acquired we must await further information. It would appear that, after it has entered the human body, development is very slow, and that probably full maturity is not attained until after several years. In many cases the parasite did not show itself until 3, 4 and 4½ years after the patient had left the endemic area. In one case the parasite was extracted from the eye 13 years after the patient had left Africa; in another the worm or worms appeared at irregular intervals during 15 years. Manifestly it is long-lived. An interesting and suggestive evidence of slow development is that, while the immature active worm is often seen in children,
Fig. 158.—Chrysops dimidiata (v. d. Wulp), ♀. (Drawn by W. McDonald.)
the larval form in the blood is found as a rule only in adults. Annett, Dutton and Elliot, in 390 native children of all ages up to about 18 years, examined in a district where L. loa was exceedingly common in adults, found mf. loa once only, in a boy aged 11. Meinhof reports a case in which the period elapsing between infection with F. loa and the appearance of embryos in the blood was at least 7 years.
Slow development and a different habitat at different stages are not peculiar to L. loa only. F. equina of the horse and ass and F. labiato-papillosa of deer and cattle wander about the subdermal connective tissues and frequently occur in the eyes during their semi-adult stage, but repair to the peritoneal cavity when fully mature. The larvæ of both are found in the blood of the respective hosts, and Noè has shown recently that F. labiato-papillosa is fostered and transmitted, like F. bancrofti and F. immitis, by an insect intermediary, to wit, the stinging-fly (Stomoxys calcitrans), amongst the cephalic muscles of which it undergoes development.
This slow development of L. loa would seem to account for the very frequent failure to find the microfilaria in the blood in cases in which mature parasites have been extracted, a circumstance which has been brought forward as an argument against the theory that mf. diurna is really the offspring of L. loa. Some time ago I was consulted by a lady who for seven years had been troubled with L. loa, and Calabar swellings, and had had three loas removed at different times from the neighbourhood of the eye. On examining her day blood I found it full of innumerable specimens of mf. diurna. That these microfilariæ were diurna was fully established by a series of carefully conducted observations carried on day and night for upwards of a week. The patient informed me that she believed the medical man who seven years before had extracted one of the loas from her eye had probably the specimen in his possession still. This I had an opportunity of examining. It was a mature female crowded with embryos in all stages of development, including free larval forms such as were found in the blood. It transpired that I had already, many years before, examined this specimen, and that, being interested in the subject, I had written for specimens of the day blood of this patient soon after the extraction had been made. On referring to my note-book I found a record of the result of my examination of this blood, and that no microfilariæ were then found. From this it is evident that the mature L. loa may be E resent in the tissues, and yet that embryos may be absent :om the blood. I cannot suggest an explanation of what is apparently an anomaly; but the fact is definitely ascertained, and explains how it is that in many of the recorded cases of loa infection the embryos have been absent from the general circulation. It may be that it is not until the gravid female arrives at some organ or tissue that she deposits her young in such a position that they can get access to the circulation, and that the wanderings for which these worms are so remarkable are an effort to attain this situation. It would be well for those who have the opportunity to look for the parasite at autopsies, especially in the serous cavities. Quite recently Penel stated that he had found mf. loa in the saliva and urine of a patient who presented this larval filaria in the peripheral circulation.
As yet it is impossible to estimate accurately the number of adult loas present in any given infection, although in advanced cases some idea of this might be got from the number of microfilariæ in the peripheral blood. As a rule it is safe to conclude that the particular loa that may show itself about the eye or elsewhere is only one of many. Thus, in 1903, Brumpt, at the post-mortem of a negro whose blood con- tained micro filariæ (for which, under the impression that it was a new species, he suggested the name of F. bourgi), found in the tissues of the heart five adult worms. Four of these were cretified, but the fifth was alive and contained embryos similar to those in the blood. This worm he subsequently identified as a L. loa. In the following year Wurtz found mf.'diurna, in the blood of a Congolese negro suffering from sleeping sickness. On the death of the patient he made a most careful post-mortem examination, and found two adult loas in the subcutaneous connective tissue of the arm. On the dissection being continued by Penel, over thirty additional specimens, male and female, were discovered under the skin of the limbs. There are not a few instances on record in which two or more loas have been extracted from the same patient. We may, therefore, be practically certain that in nearly every instance of this kind of filariasis the infection is multiple.
There is evidence that after the death of L. loa calcification takes place, as in F. bancrofti.
Pathogenesis.— As already stated, L. loa daring the period of its growth and development in man makes frequent excursions through the subdermal connective tissues. It has been noticed very frequently beneath the skin of the fingers, and it has been excised from under the skin of the back, from above the sternum, from the left breast, the lingual frænum, the loose skin of the penis, the eyelids, the conjunctiva, the anterior chamber of the eye. Ziemann says that it may wander about the scalp. The parts most frequently mentioned are the eyes, and, although the worm may have attracted more attention when in this situation, it seems as though it has a decided predilection for the eye and its neighbourhood. A patient informed me that the average rate at which a loa travelled was about an inch in two minutes. Both he and others have told me that warmth, such as in sitting before a fire, seemed to attract them to the surface of the body. As a rule, the migrations of the parasite give rise to no serious inconvenience, but they may cause prickings, itching, creeping sensations, and, occasionally, transient œdematous swellings, "Calabar swellings," in different parts of the body. When the parasite appears under the conjunctiva it may cause a considerable amount of irritation and congestion; there may be actual pain even, associated with swelling}} and inability to use the eye and, perhaps, tumefaction of the eyelids. Should a loa wander into the vicinity of such a situation as the rima glottidis or the urethra the consequences might be serious.
Bernard states that in operations for hydrocele he found L. loa encysted in the tunica vaginalis, and opines that they may be a cause of that condition; and Ouzilleau claims to have found them frequently in operations on the genitalia. Leiper has found cretitied specimens in the mesentery and parietal peritoneum.
CALABAR SWELLINGS
Under this name Thompstone described certain fugitive swellings which are of frequent occurrence in parts of tropical West Africa— southern Nigeria to Benguella and inland to the Upper Congo. They are found in natives and Europeans alike. I have seen many cases in Englishmen, especially in officials from the neighbourhood of Old Calabar. Thompstone says " the swellings are about the size of half a goose egg, painless, though somewhat' hot both objectively and subjectively, not pitting on pressure, and usually disappear in about three days. They come suddenly and disappear gradually, and occur in any part of the body." Thompstone never saw more than one swelling at a time. They recur at irregular intervals and, it may be, during many years after the patient has returned to Europe, In some instances the swellings seem to be induced by the rubbing provoked by the irritation accompanying the presence of a L. loa just under the skin, in other instances they develop spontaneously. When occurring in the hand, or about the forearm, they may give rise to a sensation of powerlessness and soreness as if the part had received a blow. They never suppurate.
Although in a large proportion of cases L. loa larvæ cannot be found, in others either the parent worm has shown itself on the eye, or its microfilariæ have been detected in the blood. The latter circumstance, together with the geographical feature of the endemicity of these swellings and their clinical characters, makes it practically certain that they are somehow produced by L. loa. On the supposition that the swelling might be caused by the emission of her larvae by a parent loa into the connective tissue. I endeavoured in one case, by aspirating the centre of the swelling with a hypodermic syringe, to substantiate this speculation; the result was negative, bub a second attempt on another patient yielded great numbers of microfilariæ in the lymph abstracted. Notwithstanding this success it cannot be affirmed that the mechanism of the production of Calabar swellings has been solved.
ONCHOCERCA VOLVULUS, Railliet and Henry, 1910
Synonym.— Filaria volvulus, Leuck., 1893.
History.— Onchocerca volvulus was discovered by a German medical missionary, who noticed peculiar worms in two tumours the size of a pigeon's egg, which he had removed, one from the scalp, the other from the chest of Gold Coast negroes. The tumours were forwarded to Leuck art, who described and named the parasite Filaria volvulus in 1893. In 1899 Labadie-Lagrave and Deguy found an immature female filaria, which Blanchard identified as 0. volvulus, in a small tumour removed from the arm of a soldier, who must have contracted the infection six years previously whilst campaigning in Dahomey. Labadie - Lagrave and Deguy were able to show that the parasite occupied a lymphatic vessel. In 1901 Prout described two cases from Sierra Leone. Brumpt, during his travels through Central Africa, had the opportunity of examining numerous cases. Recently Fülleborn, Parsons, and Clapier have added considerably to our knowledge of this parasite. Other species, such as 0. gibsoni, are parasitic in cattle and give rise to small nodes in beef. It has been suggested by Cleland that this species is transmitted by Stomoxys.
Geographical distribution.— The earlier cases were reported from the West Coast of Africa —Sierra Leone, Gold Coast, Dahomey. Brumpt met with his cases along the Welle between Dongon and M'Binia. He believes that in that region 0. volvulus affects about 5 per cent, of the riverine population. He saw cases on the Himbri, and he refers to others on the Kibali and on several of the tributaries of the Welle. Cooke met with cases in Uganda, Fülleborn in Cameroons, Parsons in northern Nigeria. Clapier reports many cases in French Guinea.
The parasite.—According to Parsons, the adult male is 20-32 mm. in length by 0.2 mm. in breadth. The body is white, filiform, tapezing at both ends. The head is rounded and has a diameter of 0.04 mm. The cuticle is transversely striated. The mouth is unarmed. The alimentary canal is straight and ends in a subterminal anus. The tail terminates in a single spiral, and is bulbous at the tip. There are two pairs of preanal papillæ, two pairs of postanal papillæ, and an intermediate single large papilla. Two unequal spicules may be seen protruding from the cloaca.
According to Braun, the adult female measures 60-70 mm. in length by 0.36 mm. in breadth; more recent measurements are much less, 35-40 mm. in length (Schafer). The head is rounded and truncated; it measures 0.04 mm. in diameter. The tail is curved. The striations of the cuticle are not so distinct as in the male. The egg possesses a peculiar striated shell.
The larva measures about 300 μ. in length; it has no " sheath." The body tapers from about the last fifth of its length and terminates in a sharply pointed tail. At about the anterior fifth of the body there is a gap in the central column of cells (V spot).
At least four males and two females are present in every tumour.
Pathogenesis.— 0. volvulus is found in peculiar subcutaneous fibrous tumours, the size of a pea to that of a pigeon's egg. The same patient may present one or several of these tumours. The regions of the body most frequently affected are those in which the peripheral lymphatics converge. Thus the tumours are usually found in the axilla, in the popliteal space, about the elbow, in the suboccipital region, and in the intercostal spaces. They are never adherent to the surrounding structures and can be easily enucleated. They are formed of a dense mass of connective tissue, which enwraps the parasites and encloses small cystlike spaces filled with a greyish viscous substance consisting almost entirely of microfilariæ. The position of the adult worms within these tumours is very remarkable. The greater length of the coiled-up bodies of the females is embedded in the connective stroma; consequently they cannot be extracted unless in fragments. The males lie in the little cyst-like cavities in the tumours, and can be turned out entire. The posterior extremity of the male with its copulating organs, and the anterior extremity of the female with its vaginal opening, are free and contiguous in one of the spaces.
The formation of the tumours is elucidated by Labadie-Lagrave and Deguy's case. These authors found an immature female 0. volvulus in a lymphatic vessel partly obstructed by an infiltration of fibrin and leucocytes. It appears, therefore, that the presence of the parasites within the lymphatics gives rise to an inflammatory process, and that the consequent fibrinous deposit envelops the parasites, obliterates the lumen of the vessel, and ultimately isolates the affected tract. According to the natives, the tumours may last indefinitely, and they seldom ulcerate or suppurate.*[3] Some old patients told Brumpt that their tumours had been present since childhood. (See Juxta-articular Nodules, p. 919.)
Ouzilleau concludes from some remarkable but unconfirmed observations that in the Mbomou region, Equatorial Africa, where F. bancrofti is absent or very rare, but elephantiasis, lymphocele, and lymph-scrotum very common, 0. volvulus is the cause of these diseases in that district. Microfilaria volvulus, he states, is invariably present in the enlarged inguino-crural glands.
Life-history.— Nothing is known of the life-history of this filaria. Recently, larvæ, presumably those of 0. volvulus, have been found in the peripheral circulation by Fülleborn, Simon, Ouzilleau, and Rodenwaldt. Brumpt, from the examination of numerous sections of filarial tumours, is confident that the microfilariæ leave the cysts. He has seen them round the periphery of the tumours, and believes they may reach the lymphatics and thence the general circulation. He even suggests that the infection is transmitted by some blood-sucking insect, and, considering its riverine distribution, he points more especially to the glossinæ.
Sparganum mansoni (Cobbold, 1883)
Synonyms.—Ligula mansoni; Bothriocephalus liguloides; B. mansoni; Dibothrium mansoni.
This parasite, the larva of a cestode belonging to the family Dibothriocephalidæ, and, provisionally, to the artificial collective group Sparganum,[4] was discovered
Fig. 159.—Sparganum.
a, Natural size: b, anterior extremity; c, posterior extremity. Extracted from an abscess in a Masai. (After Sambon.)
in 1882 by the writer in making the post-mortem examination of a Chinaman in Amoy. So far only the larval form is known, the size varying according to stage of development. The following measurements have been given: length, 8 to 36 cm.; breadth, 0·1 to 12 mm.; thickness, 0·5 to 1·75 mm. My own specimens measured about 30 to 35 cm. in length, by about 2·5 mm. in breadth. During life they are extremely elastic; after immersion in alcohol they contract and wrinkle. The anterior end is broader than the posterior, is rounded, and presents a papilliform projection on which is found the compressed and more or less completely invaginated head. (Fig. 159.) The body is flat, unsegmented, and transversely wrinkled. On the ventral surface there is, as a rule, a distinct longitudinal median groove; on the dorsal surface there may be two longitudinal grooves. No sexual organs are present.
In my case the parasites (11) lay under the peritoneum in the neighbourhood of the kidneys and iliac fossæ, and (1) apparently free in the pleural cavity. They were more or less coiled up and irregularly disposed in the subperitoneal fascia, looking like ribbon-strings of fat until turned out, when they exhibited feeble yet distinct movements. Scheube found a specimen in the urethra of a Japanese. Ijima and Murata also found the same parasite in the urethra, the worm appearing during micturition with its head projecting from the urethra and occluding it. Thrice very young specimens have been found in Japan lying beneath the conjunctiva and producing swellings the size of a bean. In one of the Japanese cases the parasite was found in the subcutaneous connective tissue of the thigh, where during nine years it gave rise to indolent tumours that recurred fairly regularly every summer at about the same spot; it seemed to change its position very readily, disappearing in about ten days. At the time of its last appearance the swelling attained the size of a fist; an abscess formed from which the worm was extracted. A similar parasite, identified by Sambon, was likewise extracted from an abscess on the thigh of a Masai, in German East Africa, by Baxter; and another was found by Daniels in a Carib in British Guiana.
Nothing is known of the life -history of this worm.Leuckart conjectures that the definitive host is probably a carnivorous animal closely associated with man, possibly the dog, the cat, or perhaps the pig. Looss believes that it is an aquatic animal (a bird or a fish), because the parasite appears to endeavour to leave the body of its intermediary host. Analogy and structure suggest that on entering the definitive host the body of the parasite disappears and a tapeworm strobila develops from the posterior part of the surviving head and neck, as in Cysticercus fasciolaris of the mouse, or in the plerocercoid of Dibothriocephalus latus.
Ocular spargauosis.—Casaux and others have recently called attention to the marked frequency in and about the Tonkin delta of the condition they
Fig. 160.—Different forms of Sparganum proliferum. (After Ijima.)
designate ocular sparganosis. Pain, redness, œdema of the upper eyelid, with lachrymation and marked ptosis, lead to an examination and the discovery of an almond-sized indurated nodule. Incision of this reveals a small yellowish fatty mass which on section is found to contain a coiled-up S. mansoni. It is probable that in these cases similar parasites are present in other regions of the body.
Sparganum proliferum (Ijima, 1905)
Synonyms.—Plerocercoides prolifer, Plerocercus prolifer.
History.—Sparganum proliferum has been reported but once, from Tokyo, Japan. It was found encysted in the subcutaneous tissue in man.
According to Ijima, who describes it, this larva (Fig. 160) may attain 1-12 mm. in length by 2.5 mm. in breadth. The anterior is narrower and more motile than the posterior end, and may exhibit an apical depression which possibly serves as a sucker. The body, with the exception of the head, contains a number of roundish calcareous corpuscles, and in older specimens there are also reserve-food bodies irregularly distributed. These larvæ can multiply by transverse fission. They give rise to supernumerary heads, which become independent. There are no genital organs.
In the single case reported, thousands of parasites were present. In a small piece of skin, 11 cm. 2 , Ijima found as many as 60. The worms occupied small roundish or ovoid cysts (1 to 8 mm. long by 2 to 5 mm. in width) in the subcutaneous cellular tissue. The cysts could be enucleated quite easily, and contained one or more parasites. They had been present for over two years, causing an enlarged condition of the thigh and an acne-like appearance of the skin. The patient was 33 years old, and, eight years previously, had suffered from intestina tæniasis.
- ↑ * One German observer has stated that he succeeded in communicating guinea- worm to a monkey by applying living embryos to the skin of the animal.
- ↑ * If the record of Guy on (1864) that his specimen was 15 cm. long does not rest on an error in transcribing or printing, it shows that the fully grown female is really much larger than we know at present from the extracted subcutaneous specimens.
- ↑ * Schäfer has recently reported finding, in the Cameroons, portions of undoubted 0. volvulus in deep muscular abscesses.
- ↑ This group includes larval stages of bothriocephaloid worms which have not reached a stage of development enabling determination of genus.