Syn.: Filaria volvulus, R. Leuckart, 1893.
The adult male measures 30 to 35 mm. in length by 0·14 mm. in breadth. The body is white, filiform, attenuated at both ends. The head is rounded and has a diameter of 0·048 mm. The cuticle is distinctly transversely striated. The mouth is unarmed. The alimentary canal is straight, the anus opening 0·07 mm. from the tip of the tail. The tail is strongly curved and somewhat flattened on the concave surface. There are three papillæ, one large and two small, on each side of the cloaca and one large and two post-anal small papillæ. Two curved spicules, 0·166 and 0·08 mm. respectively.
The adult female is of uncertain length, but much longer than the male, probably about 10 to 12 cm. The head is rounded and truncated; it measures 0·065 mm. in diameter. The tail is curved. The vulva opens 0·55 mm. from the head. The hand-like cuticular thickenings are well marked. Eggs ovoid with a prolongation at each pole “like an orange wrapped in tissue paper.” The larva measures about 300 µ by 7 µ to 8 µ; 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 V spot.
O. volvulus is found in peculiar subcutaneous 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 they are usually found in the axilla, in the popliteal space, about the elbow, in the sub-occipital region and in the intercostal spaces. The tumours are never adherent to the surrounding structures, and can be easily enucleated. They are formed of a dense connective tissue wall and internally a looser fibrous meshwork. This is traversed by a series of canals in which the worms lie, but they are also partly embedded in the denser wall. The canals apparently dilate into cavities filled with slimy pus-like fluid consisting largely of larvæ. According to Brumpt the posterior extremity of the male, and the anterior extremity of the female with its vaginal opening, are free in one of the spaces for the purpose of copulation and parturition. If a tumour be cut into and placed in salt solution, Rodenwaldt states that the undamaged males wander out into the solution.
The formation of the tumours is elucidated by Labadie-Lagrave and Deguy’s case. The authors found an immature female Onchocerca 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. At any rate, in young tumours the worms appear to lie in a structureless substance permeated by leucocytes in which connective tissue is gradually organized from the periphery, thus isolating the worms.
In cases of infection with O. volvulus larvæ have been found by Ouizilleau, Fülleborn, and Simon in lymph glands, and in the finger blood if considerable pressure is used so as to squeeze lymph out of the tissues. They are sheathless, and the following are the dimensions in ordinary dried films: Length, 274 µ; nerve ring, 23·7 per cent.; G1 cell, 69·6 per cent.; end of last tail cell, 96·3 per cent. The dimensions of larvæ of O. volvulus taken from the uterus and prepared in the same way are: Length, 224·5 µ; nerve ring, 24·3 per cent.; G1 cell, 68·9 per cent.; end of the last tail cell, 95·5 per cent. In all probability the larvæ in the glands and blood are those of O. volvulus.
According to the natives, the tumours may last indefinitely and never ulcerate. Some old patients told Brumpt that their tumours had been present since childhood. Probably Onchocerca volvulus, like some other Filariidæ, may live for many years.
O. volvulus occurs in various parts of West Africa: Gold Coast, Sierra Leone, Dahomey, Lagos, Cameroons. Brumpt, on the banks of the Welle between Dongon and M’Binia (Belgian Congo), found about 5 per cent. of the riverine population affected.
Family. Trichinellidæ, Stiles and Crane, 1910.