From a practical standpoint we need only consider: (1) Filaria bancrofti; the adult of which lives in the lymphatic glands and vessels while the sheathed embryos (which from their appearance in the blood only at night are called Filaria nocturna) obtain access to the peripheral blood vessels.
Fig. 95.—1a, Adult female Guinea worm (Dracunculus medinensis) showing anchoring hook at posterior extremity. 1b, Cross section of female Dracunculus showing uterus filled with embryos. 1c, Striated embryos of the Guinea worm. 1d, Cyclops coronatus, the minute crustacean which serves as the intermediate host of D. medinensis. 2a-2d, Anterior and posterior extremities of L. loa. 2c, Section showing tuberculated cuticle. 2b, Male and female L. loa, natural size. 3a, Bulbous anterior extremity, Filaria bancrofti. 3b, Tail of male. 3c, Tail of female. 3d, Male and female, natural size of F. bancrofti. 4a, Tumor mass of O. volvulus laid open. 5, Mosquito showing filarial embryos in thoracic muscles (a) and in labium (b). The labella which are separated from the labium by Dutton’s membrane are seen at (c). 6(a) Embryo of F. bancrofti. (b) Embryo of L. loa showing filling of tail end with cells. 7, Microfilaria of F. bancrofti in blood. Dotted lines show location of break in cell column and V spot.
Various well-known conditions are caused by this parasite, such as elephantiasis, varicose groin glands, chyluria, etc. This infection was formerly stated to be caused by Filaria sanguinis hominis.
(2) Loa loa, the adult of which wanders about in the subcutaneous tissues, characteristically in the region of the eyes, while the sheathed embryo is found in the blood during the day, hence Filaria diurna.
Calabar swellings, irregular febrile conditions and the disagreeable sensations incident to the wanderings of the worm are clinical features of this infection.
| Adults | Embryos | Remarks | |
| Filaria bancrofti | Male 40 by 0.1 mm. Female 90 by 0.28 mm. Smooth cuticle. Bulbous anterior extremity. Occupy lymphatic glands and vessels. | Sheathed, 300 by 7.5 microns. Distance from head to V spot 90 microns; to break in cells 50 microns. Tail rather straight. Terminal cells do not fill up tail end. Nocturnal periodicity in peripheral circulation. | Transmitted by mosquitoes, Culex fatigans and Stegomyia pseudo-xxx scutellaris. Causes elephantiasis, lymph scrotum, chyluria, etc. |
| Loa loa | Male 27 by 0.3 mm. Female 55 by 0.4 mm. Cuticle tuberculated. Anterior extremity like truncated cone. Wanders in subcutaneous tissues. | Sheathed, 240 × 7 microns. Distance from head to V spot 65 microns; to break in cells 40 microns. Cork-screw tail which is completely filled up with terminal cells. Diurnal periodicity in peripheral circulation. | Transmitted by species of a biting fly—Chrysops. Causes calabar swellings. Worms often visit ocular region. |
| Acanthocheilonema perstans | Male 40 by 0.07 mm. Female 75 by 0.1 mm. Cuticle smooth. Tip of tail shows 2 triangular processes. Found about root of mesentery. | Without sheaths, 200 by 5 microns. Posterior two-thirds tapers to blunt ending. Distance from head to V spot 49 microns; to break in cells 34 microns. Persists in circulation both day and night. | Transmitting agent not surely known. Mosquitoes and ticks suggested. No pathogenicity. |
| Onchocerca volvulus | Male 30 by 0.14 mm. Female usually fragmented. Possibly 75 by 0.36 mm. Cuticle striated. Found coiled up in cyst-like tumors under skin. | Without sheaths, 250 by 7.5 microns. Found in cyst-like spaces of tumors. Not in peripheral circulation. | Method of transmission unknown. Causes small cystic tumors, under skin of thorax especially. |
| Dracunculus medinensis | Male from Leiper’s monkey 22 mm. Female 80 to 90 cm. long by 1.6 mm. wide. Smooth white body. Anchoring hook at tail end. Female lives in subcutaneous tissue of lower extremity. | Without sheaths. 600 × 20 microns. Long slender tail. Cuticle striated. Extruded from break in skin of patient. | Embryos swallowed by Cyclops. Man drinks water containing Cyclops. |
(3) Onchocerca volvulus. The males and females of this parasite are found coiled up in channeled connective tissue tumors of the subcutaneous tissues.
The sheathless embryos have been surely found only within these tumors and not in the blood.