Life History.—In the stomach of the mosquito the larvæ cast their sheath in the thickened blood in one to two hours. In twenty-four hours the majority have reached the thoracic muscles, where development proceeds. They are at first immobile and of a “sausage” form (110µ by 13 µ), with a short spiky tail. In three to five days the œsophagus is formed, the larva now being 0·5 mm. long. The larva appears to moult at this time. After the gut is formed papillæ, three or four in number, appear at the tail end. In two to three weeks the larvæ are 1·5 mm. long. They now leave the thorax and reach the labium, but they may be found in various parts of the body, e.g., the legs. They bore through Dutton’s membrane and so arrive on the surface of the skin, which they rapidly enter. Their development in man is unknown, but it may be very long, as children are not infected till 4 to 5, or even 10 years old, but this may be due to unknown causes.

Development takes place in numerous mosquitoes. Anophelines: Myzomyia rossii, Pyretophorus costalis, Myzorhynchus sinensis, Myzorhynchus barbirostris, Myzorhynchus peditæniatus.

Culicines: Culex pipiens, Culex fatigans, Culex skusei, Culex gelidus, Culex sitiens, Culex albopictus, Stegomyia fasciata, Stegomyia pseudoscutellaris, Stegomyia gracilis, Stegomyia perplexa, Mansonioides uniformis, Mansonioides annulipes, Scutomyia albolineata, Tæniorhynchus domesticus.

Partial development takes place in other species.

Pathology.—Among the conditions which Filaria bancrofti is believed to produce are lymphangitis, varicose glands, especially inguinal and epitrochlear, chyluria, chylocele, lymph scrotum, orchitis, abscess, and elephantiasis. The evidence that these so-called “filarial diseases” are produced by F. bancrofti is (1) geographical and statistical; (2) pathological. Bahr has contributed evidence of the former kind from his researches in Fiji, on which we may base the following statements:—

(1) The prevalence of filarial diseases is proportional to the prevalence of Mikrofilaria bancrofti in the blood. Thus in four villages examined by him he got the following figures:—

(2) Out of 257 people with Mf. bancrofti in the blood, 153 were suffering from filarial diseases, i.e., 59 per cent.

(3) Whereas of 672 people without Mf. bancrofti in the blood, only 263 were suffering from filarial diseases, i.e., 37·6 per cent.

(4) Again out of 416 people suffering from filarial disease, 153 showed Mf. bancrofti in their blood, i.e., 36·7 per cent.

It is generally assumed that all people suffering from filarial disease show at some (presumably early) stage larvæ in the blood; but we do not consider that this must necessarily be so. It appears to us quite possible that living adult filariæ may be present in the body, producing disease, without their larvæ appearing in the blood. The absence of larvæ from the blood in 63·3 per cent. of persons suffering from filarial disease is, however, generally explained otherwise. The adults which occur in enlarged glands, etc., get eventually destroyed by inflammatory reaction, so that larvæ are no longer being produced, while the enlarged gland, etc., which the adults have produced remains. This explanation assumes that the larvæ of the original worm die in the circulation or elsewhere, e.g., kidney, but we have no evidence as to the duration of life of larvæ in the human body; but also it assumes that a person cannot be reinfected with filaria, for otherwise there is no reason why the diseased should not be infected in the same proportion as the non-diseased. But assuming the explanation to be true, it would explain why a diseased population show larvæ in only about one-third of the cases. It must be borne in mind also that the figures are rather small.

Pathology.—In order to explain the effects which do or may be expected to occur from obstruction of lymphatics, it is necessary to have an accurate knowledge of the distribution and connections of lymphatic vessels (and glands) and the anastomoses of these vessels. We can only briefly summarize our knowledge here.

We should recall also that considerable destruction or obstruction of lymphatics or glands may occur without necessarily producing any lymphatic obstruction, at least, of a permanent nature, e.g., when a mass of lymphatic glands is destroyed by a bubo in the groin or, again, when a carcinomatous mass of glands is removed from the axilla. Again, to take the case of chyluria—where it is generally assumed that obstruction must occur higher up than the point at which the intestinal lacteals enter the juxta-aortic glands—this disease may occur, e.g., in temperate regions, quite apart from such obstruction. It is true that some of these cases of chyluria are not cases of chyle in the urine, but, as little or no fat is present, lymphuria. These do not require the above assumption, but seeing that true chyluria may apparently occur without such obstruction, we should be cautious about explaining this and other symptoms on the basis of obstructions which theory may demand, for only too often there are no post-mortem facts at our disposal.

Lymphangitis: What this is due to is unknown. There is no actual evidence of the occurrence of adults in the inflamed vessel. Complete disappearance, not to reappear, of (non-periodic) mikrofilariæ from the blood has been shown by Bahr and others to occur within twenty-four hours after an attack of lymphangitis, orchitis adenitis or simply a high temperature. This mysterious phenomenon requires explanation. If the mikrofilariæ were being killed by the attack, their dead bodies should still be found in the blood; or if the adults were being killed, for all we know to the contrary, the larvæ might well survive. We consider there is no evidence that either are affected, but that for some reason, as little understood as in periodicity, the larvæ now remain in the organs.

Abscess: In Fiji, by Bahr, they have been found in the substance of various muscles, e.g., quadriceps extensor, latissimus dorsi, serratus magnus, in the popliteal space, groin, axilla, and over the internal condyle of the humerus, and in the upper extremity they are frequently infected with cocci. They not infrequently contain fragments of dead adult filariæ. Their mode of origin is not clear. They form nearly 30 per cent. of cases of filariasis in Fiji. Of 95 cases, 41 showed mikrofilariæ in blood, 54 did not.

Hydrocele and enlarged testis: In Fiji they form about 10 per cent. (36 out of 343) of cases of filariasis. The fluid is usually sterile; mikrofilariæ were present in the fluid in 1 out of 11 cases. In the wall numerous calcified adult filariæ may be found. The walls consist chiefly of hypertrophied muscle with fibrous tissue, dilated blood-vessels and lymphatics, the lining epithelium of which appears to be absent; of 38 cases 14 had mikrofilariæ in the blood, 24 had not. Most of the cases are associated with elephantiasis of the scrotum (11 out of 12 cases).

Enlarged glands form over 40 per cent. (153 out of 343) of cases of filariasis, so that they are the commonest expression of filariasis met with in Fiji. The glands are enlarged, fibrotic, and the trabeculæ are thickened. The lymphatics are thickened or represented merely by fibrous tissue. The gland also shows dilated blood-vessels and numerous spaces filled with lymph. Giant-cells are common in those glands which contain remnants of filariæ. Masses of lymphocytes enclosed by inflammatory or fibrous tissue are common. Eosinophile cells are also extremely common, not only in the fibrous tissue of the glands, but in other inflammatory or fibrotic conditions: in other organs living or calcified filariæ are “usually” present. Only about 33 per cent. show mikrofilariæ in the blood. The epitrochlear gland is frequently enlarged in Fiji.

Breinl has examined enlarged glands and finds loose vascular fibrous tissue with lymphocytic invasion. In parts, the lymphocytes collect into areas 200 µ to 800 µ in diameter. The lymph tissue surrounding the spermatic cord showed abundance of vessels—(1) large, (2) small. The large had thick walls and wide lumina. In other cases the lumina were nearly filled by a thrombus of newly formed, fine, loose connective tissue.

Varicose glands: In about 7 per cent. (24 out of 343 cases) of filariasis, mikrofilariæ are found in the blood in 50 per cent. (12 out of 24).

Elephantiasis.—Elephantiasis scroti is associated with hydrocele in 50 per cent. of cases (12 out of 23); in 65 per cent. of cases (15 out of 23) there are associated enlarged glands in one or both groins, though also hydrocele and enlarged glands occur without elephantiasis scroti. In 13 out of 27, i.e., about 50 per cent., cases of elephantiasis in various regions, no associated enlargement of glands is found. Elephantiasis forms in Fiji less than 10 per cent. of cases of filariasis. Mikrofilariæ are present in the blood in 36 per cent. (12 out of 33) of cases.

Chyluria.—Exceedingly rare in Fiji. Theory would demand an obstruction above the point of entry of the lacteals, viz., the pre-aortic lymphatic glands, but in cases in temperate regions it may occur without any such lesion. In some of these cases the fluid is not chyle (fat absent), but presumably lymph. A discussion of the mode of production of chyluria, lymph scrotum, elephantiasis, etc., is at present premature; theory has far outrun fact. Too much stress had been laid on the mechanical action of the worms to the almost total exclusion of their (or possibly their larval) toxic action. The above analysis has been made in the hope of acquiring more extended observations similar to those made by Bahr.

Geographical Distribution.—Filaria bancrofti is known in nearly all tropical countries. It occurs in India, China, Indo-China, Japan, Australia, Queensland, the Islands of Polynesia (with the exception of the Sandwich Islands), Egypt, Algeria, Tunis, Madagascar, Zanzibar, Sudan, etc., the south of the United States of America, Brazil, the Antilles, etc. Whether it is the same species in all cases is questionable.

Filaria demarquayi, Manson, 1895.

Syn.: F. ozzardi, Manson, 1897.

The female only of this species is known. It measures 16 to 20 cm. in length and 0·5 mm. in breadth, and is of a whitish or brownish tint. The cuticle is striated with fine transverse and more marked longitudinal striæ with the exception of a small field surrounding the mouth, which is terminal and has neither papillæ nor lips. The œsophagus measures 0·6 mm. in length. The anus is 3 mm. in front of the rounded posterior extremity, and behind it there are two (glandular?) sacs. The vulva is close behind the oral aperture; the vagina soon divides into two convoluted uteri, which are filled with eggs and embryos. Embryos 350 µ by 5·5 µ.

Filaria (?) conjunctivæ is certainly only an incidental parasite of man; the horse and ass are its normal hosts, but it is not common in these animals, or is frequently confused with Hamularia equi, Gmelin, 1789.

Group. Agamofilaria, Stiles, 1906.

Not a generic but a group name for immature Filariidæ the development of which does not admit of generic determination.

Agamofilaria georgiana.

Adult unknown, length from 32 to 53 mm. Maximum diameter 560 µ to 640 µ. Head no cephalic cone. Mouth small, circular, surrounded by six papillæ (two small latero-median and four sub-median). The larger papillæ are 24 µ from base to tip. Excretory pore about 0·5 mm. from head. Anus 64 µ to 128 µ from tip. Cuticle fine striæ near anus, occasionally elsewhere. Lateral lines clearly marked. Œsophagus 2·5 to 2·9 mm. Rectum 200 µ long.

Habitat.—Superficial sores on the ankle of a negress, Georgia, U.S.A.

Agamofilaria palpebralis, Pace, 1867 (nec Wilson, 1844).

100 by 1·5 mm., removed from a cyst in the left upper eyelid of a boy by Pace, in Palermo.

Agamofilaria oculi humani, v. Nordmann, 1832.

Syn.: Filaria lentis, Diesing, 1851.

The sexless Nematodes observed in the lens of the human eye were termed Filaria oculi humani. Only three cases are known. v. Nordmann observed very small round worms in the lens of a man and woman with cataract, and Gescheidt once found three specimens in the lens of a woman similarly affected.

The demonstration of nematode-like formations in the vitreous remains uncertain even when movements are observed, and when they cannot be extracted and examined microscopically the doubt may occur that one may have mistaken the remains of the hyaloid artery for a worm, which it resembles in form, size and colour; the slightest movement of the eye also causes it to move so that it simulates a living organism.

Agamofilaria labialis, Pane, 1864.

The parasite measures 30 mm. in length; the anterior extremity is pointed; the terminal oral aperture is surrounded by four papillæ; the anus opens 0·5 mm. in front of the posterior extremity; the vulva is 2·5 mm. in front of the anus; the uterus is double; the anterior one passes with convolutions forward to the cephalic end; the posterior one is directed backwards and remains rudimentary.

The position of many of these worms is doubtful, and still more so is that of many other imperfectly described “Filariæ,” which are hardly more than useless and confusing names. These include the following:—

Filaria (?) romanorum-orientalis, Sarcani, 1888.

Observed in the blood of a Roumanian woman; 1 mm. in length, 0·03 mm. in breadth; tail end pointed, a tongue-like appendage on the head. Eggs the size of a red cell with developed embryo, apparently viviparous.

Filaria (?) kilimaræ, Kolb, 1898.

Several female specimens, 10 to 20 cm. long by 0·5 to 1 mm. broad, were once found free in the abdomen of a fallen Kitú warrior; according to Spengel, who examined them, the oral papillæ of these worms were similar to those of Dracunculus medinensis. Moreover, Kolb classifies together Nematodes that probably have no connection with each other.

Filaria (?) sp.?

Cholodkowsky calls attention to Filariæ that are still unknown which cause tumours resembling whitlows on the fingers of peasants of the Twer Government.

Mikrofilaria powelli, Penel, 1905. In Bombay.

Mikrofilaria philippinensis, Ashburn and Craig, 1906. In the Philippines.

Setaria equina, Abildg., 1789.

Syn.: Gordius equinus, Abildg., 1789; Filaria equi, Gmelin, 1789; Hamularia lymphatica, Treutler, 1793; Tentacularia subcompressa, Zedder, 1800; Filaria papillosa, Rud., 1802; Filaria hominis bronchialis, Rud., 1819; Filaria hominis, Dies., 1851; Strongylus bronchialis, Cobb., 1879.

The body is whitish, filiform, pointed posteriorly. The cuticle presents a delicate transverse striation. The mouth is small, round, and surrounded by a chitinous ring, the border of which carries, at the sides, two semilunar lips, and there is on the dorsal as well as on the ventral surface a papilliform process; on the tail, corresponding with each sub-median line, is a conical papilla. The male measures 6 to 8 cm. in length; the posterior extremity ends in a corkscrew spiral; there are on each side four pairs of pre-anal and four or five post-anal papillæ; the spicules are unequal. The female measures 9 to 12 cm. in length and is viviparous; the embryos measure 0·28 mm. in length and 0·007 mm. in breadth.

Treutler, in 1790, found a filaria in the enlarged bronchial lymphatic gland of a patient suffering from phthisis. It measured 26 mm. in length and had two spicules, which Treutler mistook for mouth hooks, hence the name Hamularia. Blanchard mentions another case from Geneva, Brera a third and v. Linstow a fourth. As shown by the synonyms, a few authors consider this form to be a distinct species, which is hardly probable.

Genus. Loa, Stiles, 1905.

Characterized by the possession of cuticular bosses in both sexes (fig. 294).

Loa loa, Guyot, 1778.

Syn.: Filaria oculi, Gerv. et v. Ben., 1859; Dracunculus oculi, Diesing, 1860; Dracunculus loa, Cobbold, 1864; Filaria subconjunctivalis, Guyon, 1864.

The female measures 45 to 63 mm. in length by 0·5 mm. in breadth. It is also beset with irregularly distributed bosses, which in places lie close to each other, and extend to the anterior extremity; posteriorly they become less frequent, but are not entirely absent. The anterior extremity is conical, the posterior one straight, attenuated, rounded off, 0·17 mm. from the anus. The uteri contain eggs in the most various stages of development, as well as hatched-out larvæ, 253 µ to 262 µ in length and 4·7 µ to 5 µ in breadth. The vulva lies about 2 mm. from the head end. The vagina, 9 mm. long, divides into two branches, which at first run posteriorly and parallel to one another for about 18 mm. One then bends forward, runs as far as the œsophagus, bends here again and runs backward to end at the point of its first bending. The other branch at first runs straight backward and then bends forward, but before reaching the point of the first bend of the anterior tube bends backward again, forms again a loop and ends at the level of the anus. The tubes consist in the main of the uterus, then a club-shaped swelling, the receptaculum seminis, then the oviduct 2 mm. long, and finally the ovary.

Unsegmented eggs measure 32 µ by 17 µ, in the morula stage 40 µ by 25 µ, and when containing embryos 50 µ by 25 µ. The vitelline “shell” of the egg is, according to most authors, stretched by the embryo and becomes the sheath of the hatched larva. While still in the vulva, the larva measures 217 µ to 274 µ (average 246 µ) in fresh, 146 to 226 µ (average 192 µ) stained.

Larvæ in Blood.—These from their diurnal periodicity are known as Mikrofilaria diurna. The evidence that these larvæ are the young of the adult worm Loa loa is: (1) They are identical in structure with larvæ taken from the uterus of L. loa; (2) their geographical distribution is the same as that of L. loa; (3) they eventually occur in the blood of patients suffering from Calabar swellings, a condition due to L. loa. Their occurrence in the blood in this latter condition and in L. loa infections we shall consider later.

Periodicity.—Here, as in the case of the larvæ of Filaria bancrofti, the larvæ that appear in the blood are probably the overflow simply of the larvæ which we assume, on analogy, to have their principal site in the lungs. They appear in the blood about the time of getting up, 6 to 8 a.m. (10 in 20 mm.³), at 12 noon there are twenty-four, at 8 p.m. the number has fallen to eighteen, and at midnight to one, while from 2 a.m. to 6 a.m. none, or one only, may be found. This periodicity is, as a rule, a very constant one, but there are exceptions, and in certain cases more have been found at midnight than at 9 a.m. The periodicity is also lost in pathological conditions, e.g., sleeping sickness (vide also under Filaria bancrofti). The possibility of non-periodic Loa loa larvæ should also be considered.

Pathology.—The parasite wanders about the body, and may be seen under the skin in thin parts. Their advance is in some cases at the rate of an inch in two minutes. During their progress they give rise to creeping sensations and to a condition of transient œdematous areas known as Calabar swellings on various parts of the body, e.g., arm. These vary in diameter from 1 to 10 cm., and often shift their position an inch or so a day. They give rise to a certain amount of redness, tension and heat, and their development is promoted by muscular action of the part. They disappear to reappear elsewhere. The condition is associated with a high eosinophilia, 50 per cent. being not uncommon. Patients known to harbour L. loa, e.g., native children, frequently show no larvæ in their blood, but they may do so after years of infection. Again, in patients having an infection of Mikrofilaria diurna, there is frequently at the time no evidence of the presence of Loa loa adults. Here again they may appear later, but the conditions which determine whether persons infected with L. loa show larvæ in the blood, or persons infected with Mikrofilaria diurna also show L. loa, are unknown, though explanations unsupported by facts abound. Likewise also the mode of production of the swellings is unknown.

Not uncommonly Mikrofilaria perstans occurs in the blood together with M. diurna.

Duration of Life.—This is long, as some cases have been observed five to six years after leaving Africa. The incubation period is about a year.

Life-history.—Development of the larvæ takes place in the salivary glands of Chrysops sp. as shown by Leiper.

Geographical Distribution.— West Africa, especially in Congo.

Genus. Acanthocheilonema, Cobbold, 1870.

Cuticle striated longitudinally. Œsophagus divided into two portions. Tail in both sexes with short lateral conical cuticular appendages. Spicules unequal, the larger membranous distally, the smaller hooked. Vulva in œsophageal region.

Acanthocheilonema perstans, Manson, 1891.

Syn.: Filaria perstans, P. Manson, 1891; Filaria sanguinis hominis var. minor, Manson, 1891.

The adult female Ac. perstans measures 70 to 80 mm. in length by 120 µ to 140 µ in breadth. The head is club-shaped and measures 0·07 mm. in diameter. The vulva opens at 0·6 to 1·0 mm. from the head. The tail is curved and presents a cuticular thickening which forms two triangular appendages. The anus opens at the apex of a papilla situated in the concavity of the curve formed by the tail 150 µ from the end. The diameter of the tail just before termination is 0·02 mm.

The adult worms inhabit the connective tissue at the base of the mesentery, especially in the region of the pancreas, abdominal aorta and suprarenals. To find them the mesentery should be removed, placed in a 2 per cent. solution of formalin, and then carefully examined at leisure.

Mikrofilaria perstans.—160 µ to 210 µ by 5 µ to 6 µ broad. Has no sheath. Cuticle transversely striated. Tail rounded off, not pointed. Nerve ring at 34 µ. Excretory pore 49 µ, genital pore 125 µ from head. Smaller larvæ 90 µ to 110 µ by 4 µ broad. A “fang” is also described on the head.

Periodicity.—None.

Life-history.—Unknown.

Geographical Distribution.—Very common in many parts of Africa: Sierra Leone, Dahomey, Northern Nigeria, Southern Nigeria, Cameroons, Ivory Coast, Gold Coast, Old Calabar, Congo, Uganda. Absent from Zululand, Basutoland. On the East Coast of Africa it is not found in the towns of Zanzibar and Mombasa, neither is it found in the country of the Masi, nor amongst the Kavirondo, who dwell along the north-east shores of Lake Victoria.

In South America, Ac. perstans is very common amongst the aboriginal Indians in the interior of British Guiana. However, it is not found in Georgetown and in New Amsterdam, neither is it found in the cultivated strip of coast lying between these two towns, but it is common on the coast farther north near the Venezuelan boundary, where the forests stretch to the sea. The Waran Indians, who live at the mouth of the Waini river, harbour this parasite. It is absent in the West Indies.

Topographically, Ac. perstans is found only in areas covered by dense forest growth and abounding in swamps. In Kavirondo, where the forest disappears and the land is covered with scrub and short grass, it is not found; likewise it is not found on the grassy plains of the highlands of British East Africa. Towns and cultivated areas are free from it.

Genus. Dirofilaria. Railliet and Henry, 1911.

Body very long, thread-like, cuticle transversely striated. Mouth with six papillæ. Male tail spiral with voluminous pre-anal and some large post-anal papillæ; spicules unequal. Vulva near the anterior hundredth of body; viviparous. Parasitic in heart or blood-vessels and subcutaneous tissue.

Dirofilaria magalhãesi, R. Blanchard, 1895.

Syn.: Filaria bancrofti, v. Linstow, 1892; Filaria bancrofti, P. S. de Magalhães, 1892 (nec Cobbold, 1877).