Filaria Medinensis (Dracunculus Medinensis, Or Guinea-Worm)

This parasite is of frequent occurrence in tropical lands, where it is met with in the tissues of the foot and leg chiefly. The female is a long thin worm from 12 to 40 inches in length, and it alone is known as a parasite. The male is much smaller. The worm wanders to some extent in the loose subcutaneous connective tissue, and may give rise to considerable irritation. When mature it presents its extremity at the surface, and a small pustule forms from which the extremity projects. The worm may then be removed gradually by rolling it gently round a quill from day to day as it becomes exposed, care being taken not to break it, in which case the part left in may give rise to severe inflammation.

Filaria Sanguinis Hominis. Filaria Bancrofti

This parasite is best known in the embryonic form which inhabits the blood. The adult form rarely comes under observation, but has been found occasionally in the lymphatic system. It has been named Filaria Bancrofti from the first discoverer of the adult.

The adult filaria is a hair-like worm 8 to 10 cm. (3 or 4 inches) in length, and only about 0.35 mm. (1/100 of an inch) in breadth. It sometimes produces considerable irritation in the lymphatics, causing local thickenings. Maitland has excised some of these thickenings and found in one case as many as seven adults in one mass. The adults are believed to live for years in the lymphatics, and the female gives birth to enormous numbers of living embryoes which find their way into the blood.

The living embryo (Fig. 198) is about 1/90 inch in length and 1/3500 inch in thickness; its breadth therefore nearly corresponds with that of a red blood-corpuscle. It is enclosed in a delicate sac, which is rather longer than itself, so -that while moving a portion of the sac extends beyond its extremity. The movements as seen in the blood and lymph are very active and snake-like in character.

This embryo is present in the blood of about 10 per cent, of the natives where it is endemic, and most of these do not appear to suffer in health from it. It is found in many Eastern countries and also in Brazil, the West Indies, etc. According to Manson there are probably several species of filaria sanguinis besides the F. Bancrofti. A very remarkable circumstance is that, during the day, the parasites are, unless in exceptional cases, absent from the blood obtained from the finger or other superficial part, but about six or seven o'clock in the evening they begin to appear, and by twelve o'clock are so numerous that as many as a hundred may be counted in every drop of blood. As morning approaches they diminish in numbers, and by eight or nine o'clock they disappear entirely. This regular rhythm may apparently go on for years. When the periodicity of the bodily functions is interfered with by the person sleeping during the day and doing his work at night, then the parasite is present in the blood in the day time and absent at night.

Fig. 198. - Filaria sanguinis as they appear in the living state in the blood. From a case of cbyluria. x 300. (Lewis).

The periodicity has been variously accounted for. It is either that the animals come to the superficial vessels during the night and remain in the internal organs during the day, or that a fresh brood is produced every evening. As the number in the blood of a single person is estimated at 36-40 millions (Mackenzie) the latter supposition does not seem probable.

Chyluria, chylous diarrhoea, lymph-scrotum, and elephantiasis have been ascribed to the filaria Bancrofti. The embryoes in passing from their parents in the lymphatics to the blood have to traverse the lymphatic glands. In certain cases they seem to stick in the glands, and by filling them up obstruct the passage of lymph. There may thus be virtually a plugging of the lymphatics with a dilatation of the distal parts of the vessels. Rupture of the vessels causes the escape of the chylous contents (see p. 118). According to the situation of the adults the results vary. The rupture may be in the urinary bladder or kidneys, and we then have chyluria. There is usually blood also in the urine from tearing of blood-vessels, and, for a similar reason, the embryoes may be present in the urine. In a similar manner chylous diarrhoea is produced. Lymph-scrotum is a thickening of the scrotum with the presence of dilated lymphatics and vesicles which rupture and discharge fluid. Elephantiasis is not probably a direct effect of the parasite, but the condition of lymph-scrotum may give occasion to elephantiasis (see pp. 320-322).

The mosquito is believed by Manson to be the intermediate host of the filaria, but this view seems to stand in need of confirmation.

In animals many forms of filaria exist. There are several forms in the dog. One of these inhabits the trachea and bronchi, producing bronchitis. It has been named Filaria Oderi, from Prof. Osier who observed it in Canada and regarded it as a strongylus. The filaria immitis inhabits the right cavities of the heart and the pulmonary artery of the dog, and is very common in China and Japan. The adults, which measure 12 to 30 cm. in length, give off embryoes closely resembling the filaria sanguinis hominis, and like it appearing in the peripheral vessels at night. The Spiroptera aanguinolenta (so called from its red colour) is found chiefly in the walls of the stomach and oesophagus of the dog in China and Brazil. It forms considerable cysts, in the interior of which the worms, which measure 3 to 5 cm., are found, a number coiled up together. It also occurs in the walls of the aorta, in the lungs, and in lymphatic glands.

In the horse a frequent parasite is the Filaria papilloma which inhabits the serous membranes, as the peritoneum and pleura. It may be present in enormous numbers in these cavities. It has been found in the tunica vaginalis when a horse was being castrated, having descended from the peritoneum. It measures from 6 to 15 cm. in length.

Literature

Virchow, Die Lehre von den Trichinen, 1866; Lewis, Path, significance of nematode hrematozoa, 1877; Bancroft, Path, trans., 1878, xxix.; Manson, Filaria sang, horn., 1883, also Path, trans., 1881, xxxii.; Mackenzie, Path, trans., 1882, xxxiii., 394; Myers, Observations on Filaria sang, hom., Shanghai, 1881 and 1886; Scheube, in Volkmann's Sammlung, 1883, No, 232; Neumann, transl. by Fleming, 1892; Maitland and Manson, Brit. Med. Jour., 1894, 1., 844.